Metals doi: 10.3390/met16090994

Authors: Ke Zhou Zhaoqiang Li Yongkun Li

7xxx series aluminum alloys exhibit high strength and low density; however, their high degree of alloying results in a pronounced hot-cracking tendency, making direct casting forming challenging. In this study, a rheo-squeeze-cast AA7075 alloy was investigated. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and room-temperature tensile testing were employed to systematically examine the effects of the solution treatment window on the microstructure and mechanical properties of the castings. The distinctive contribution of this work is the quantitative correlation of solution-time-dependent second-phase evolution and porosity with the tensile behavior of ECSC-assisted rheo-squeeze-cast AA7075. The results show that, with increasing solution treatment time, the intergranular eutectic phases gradually dissolved, and their morphology evolved from lamellar structures into fine rod-like features. When the solution treatment time was extended to 12 h, a small number of pore defects appeared in the microstructure. Under the conditions of solution treatment at 470 °C for 8 h followed by aging at 120 °C for 24 h, uniformly distributed Zn–Mg-rich aging precipitates were observed in the matrix, resulting in the best comprehensive mechanical properties, with an ultimate tensile strength, yield strength, and elongation of 498.1 MPa, 413.7 MPa, and 8.2%, respectively. The optimized heat-treatment condition provides a practical route for achieving a favorable strength–ductility balance in rheo-squeeze-cast AA7075 components.

Metals doi: 10.3390/met16090993

Authors: Yueyue Yang Yufeng Chen Haoran Hong Hongliang Zhang Teng Liu Zhisheng Nong

Mg alloys are among the lightest metallic structural materials used in engineering applications, possessing a range of favorable properties and holding broad application prospects. However, the corrosion resistance of Mg alloys is relatively poor compared to other metallic structural materials, which limits their use in various working environments. The addition of rare earth elements is one approach to improving the corrosion resistance of Mg alloys; nevertheless, the corrosion resistance of Mg-rare earth alloys still falls short of industrial application requirements. This paper aims to introduce the corrosion resistance of Mg-rare earth alloys and their applied protective coatings. Through coating characterization techniques, the protective effects of coatings on Mg-rare earth alloys are analyzed and elucidated. Finally, a summary and outlook on the corrosion resistance of Mg-rare earth alloys and coating protection technologies are provided.

Metals doi: 10.3390/met16090992

Authors: Seung Cheol Shin Yong Kim Hye Chan Park Hyun Jin Woo

Cold-roll-bonded (CRB) Fe–Al clad sheets, which incorporate an internal steel layer within the clad structure, are candidate materials for dissimilar joining in lightweight structural applications, yet systematic comparisons of their weldability across multiple joining processes remain limited. This study evaluates the process-dependent weldability of CRB Fe–Al clad sheets using three joining processes: laser lap welding, DC resistance spot welding, and cold metal transfer-pulse (CMT-P) arc welding. Weld appearance, cross-sectional morphology, tensile shear behavior, and fracture characteristics were assessed for multiple sheet configurations and clad-layer thicknesses. Across all three processes, configurations that placed the clad sheet directly toward the heat source were prone to cracking or strength degradation when the internal steel layer melted extensively, whereas limiting steel-layer involvement produced more stable joints. Among the three processes, resistance spot welding provided the widest workable process window, while laser and CMT-P arc welding achieved peak strengths only within a narrow heat-input range. These findings indicate that the role of the internal steel layer is process-dependent and provide practical guidance for sheet configuration and parameter selection when joining CRB Fe–Al clad sheets to steel or aluminum components.

Metals doi: 10.3390/met16090991

Authors: Xian Meng Hao Xu Hui Zhang Jinwen Cao Ying Zhang Jinyue Geng Cong Yan Heji Huang

Molybdenum (Mo), owing to its excellent high-temperature resistance and low sputtering yield, is widely used in advanced equipment such as extreme ultraviolet (EUV) lithography systems. To meet the demand for regulating the surface wettability of Mo, this study employs micromilling to fabricate microgroove arrays on Mo surfaces to enhance their hydrophobicity. First, comparative micromilling experiments are conducted under flood cooling and minimum quantity cooling lubrication (MQCL) conditions. The effects of process parameters, including axial depth of cut (ap), spindle speed (n), and feed per tooth (fz), on burr height (H) are investigated under the two cooling/lubrication conditions. The results show that the burr heights obtained under flood cooling are generally lower than those obtained under MQCL. Subsequently, the machining parameters under flood cooling are evaluated using an orthogonal experimental design. A mathematical model relating the microgroove array geometry to the contact angle is then established based on Gibbs free energy to guide the design of surface microgroove structures. Finally, microgroove arrays are fabricated on Mo surfaces using the preferred machining parameters. The results demonstrate that the microgroove arrays effectively enhance the water hydrophobicity of the Mo surface. The static water contact angle increases from 62.45 ± 0.25° for the untreated Mo surface to a maximum of 128.50 ± 0.12°, thereby achieving a transition from hydrophilic to hydrophobic behavior.

Metals doi: 10.3390/met16090990

Authors: Yunfei Wu Jianxiang Wang Kaiwen Li Jiaheng Wang Nan Lyu Zhiyong Bao Wenjuan Chen Yong Zhang Yucheng Wu

1D hollow Ni/C microtubes with tunable carbon shell coating were fabricated through a three-step method with carbon fiber templating, polydopamine coating and carbothermal reduction. The competitive behavior between NiO reduction and Ni-catalyzed graphitization dominates the evolution of carbon structure and interface state. Adjusting dopamine content achieves the dielectric polarization mode evolution from NiO/Ni Schottky junction to Ni/C interfacial and intrinsic dipole polarization, realizing band-tunable microwave absorption. With favorable modulation of the carbon shell, the absorber thickness required for efficient absorption declines substantially, while the absorbing bands shift from the X-Ku boundary toward high-frequency Ku and low-frequency S-C band. NC-3 with the thickest carbon coating delivers the strongest absorption of −49.58 dB at merely 1 mm, and its absorbing band can also be tuned to the S band at 6.6 mm. This work offers a concise interfacial strategy for lightweight and band-tunable microwave absorbers.

Metals doi: 10.3390/met16090989

Authors: Jinhua Zhao Ziyang Li Yali Hou Zongyan Zou Wenli Hu Fei Ji Wenwu He

Industrial pure copper sheets as a crucial electronic material have currently attracted extensive attention from scholars due to the rapid development of the information technology industry. However, past investigations into the regulation discipline of the microstructure and mechanical properties of pure copper have not paid sufficient attention due to the inevitably low strength induced by the lack of alloying elements. In this study, a typical T2 copper sheet was fabricated by a severe cold-rolling process with a deformation amount of 83% followed by different annealing temperatures ranging from 200 to 500 °C, and the influence of annealing temperature on the evolution of microstructure, mechanical and physical properties and crystallographic orientation (CRO) was investigated systematically. The microstructure features and micro-texture of the studied T2 copper sheet were characterized by optical microscopy (OM) and scanning electron microscopy equipped with electron back-scattered diffraction (EBSD) techniques throughout the entire process from the initial state to the deformed state and annealed state, and the tensile property and electrical conductivity were tested by utilizing a universal testing machine and a digital micro-ohmmeter. Results indicate that the yield strength and tensile strength of the studied T2 copper sheet are both decreased with increasing annealing temperature, accompanied by an increase in electrical conductivity, and the maximum conductivity of up to 98.2% IACS can be reached at the annealing temperature of 500 °C. With the increase in annealing temperature, the degree of recrystallization becomes increasingly sufficient, and the volume fraction of recrystallized grains is increased from ~17.8% to ~35.7% with the annealing temperature increased from 200 to 500 °C. The texture component of the studied T2 copper sheet processed by severe cold rolling with a deformation amount of 83% is characterized by a deformation texture composed of copper texture and S texture, and is then transformed into a texture that predominantly consists of Cube texture under the application of annealing treatment, and the maximum intensity value of Cube texture is enhanced with the increase in annealing temperature.

Metals doi: 10.3390/met16090988

Authors: Haochang Tang Muhua Chang Lin Lu

Zn-Al-Mg (ZAM) coatings have attracted significant attention in the field of corrosion protection owing to their combination of excellent corrosion resistance and cost-effectiveness. However, the corrosion behavior of ZAM coatings was governed by the synergistic coupling effects of multiple factors, including alloy composition, coating thickness, corrosive medium, and multiphase microstructure, making it challenging for traditional empirical analysis to systematically reveal the underlying mechanisms. To address this challenge, we constructed a multidimensional corrosion dataset comprising alloy composition, corrosive medium, coating thickness, and phase composition, based on literature data from the past three decades combined with self-measured potentiodynamic polarization experimental results. After data normalization and correlation analysis, we introduced phase structure features—including the Al-rich phase, MgZn2 phase, Mg2Si phase, and eutectic microstructures—to enhance the model’s capability in representing microstructural factors. On this basis, we established random forest (RF), support vector regression (SVR), and artificial neural network (ANN) models to predict the corrosion current density, and subsequently conducted an interpretability analysis using the SHapley Additive exPlanations (SHAP) method. The results demonstrated that the expanded feature set significantly improved the prediction performance of the models. Among them, the RF model exhibited the best performance, achieving a determination coefficient (R2) of 0.7363 on the test set, which represented a substantial improvement over the baseline dataset. Feature importance analysis revealed that coating thickness, Mg content, NaCl concentration, and Zn content were the primary factors influencing the corrosion current density. Further SHAP analysis showed that the marginal contribution of the eutectic phase was more prominent in local samples. Meanwhile, the Mg element exhibited distinct non-linear regulation characteristics, exerting varying impacts on the corrosion behavior across different concentration ranges. This study demonstrated that the interpretable machine learning models constructed via feature engineering not only improved the prediction accuracy of the corrosion performance of ZAM coatings, but also provided a novel data-driven approach to revealing the intrinsic correlations among alloy composition, phase structure, and corrosion response.

Metals doi: 10.3390/met16090985

Authors: Gürkan Soy Hasan Öktem Sıtkı Akıncıoğlu İlyas Uygur

The tribological performance of copper-matrix sintered brake pads for high-speed rail applications is strongly influenced by ceramic reinforcement type. However, a systematic comparison of SiC, ZrO2, and SiO2 within Cu and Cu–Bronze (Cu–Br) matrix systems remains limited. In this study, six powder metallurgy composites were produced by cold pressing and sintering at 900 °C, with each matrix reinforced with 2 wt.% SiC, ZrO2, or SiO2 and containing graphite and MoS2 as solid lubricants. Tribological tests were performed at 25, 100, and 400 °C under an 18 N normal load. Microstructural and thermal characteristics were evaluated using optical microscopy, SEM/EDS, and DTA/TGA. The coefficient of friction (COF) ranged from 0.163 to 0.364 across all formulations and temperatures. The Cu–Br-based composites exhibited a narrower reinforcement-dependent COF range than the Cu-based composites, particularly at elevated temperatures. Cu–SiO2 showed the highest COF within the Cu-based at all test temperatures, whereas Cu–Br–SiC composite exhibited the highest COF among the Cu–Br-based composites at 400 °C. The lowest specific wear rates were obtained for Cu–SiO2 at 25 °C and Cu–SiC at 400 °C. SiC-reinforced composites exhibited the highest hardness within both matrix systems.

Metals doi: 10.3390/met16090987

Authors: Alexander Kim Alexander Akberdin Ruslan Sultangaziyev Kalamkas Titosheva

This paper presents the results of a study on the utilization of chromium-containing waste in the production of mineral wool based on natural basalt. It was shown that a mixture of low-dolomite chromate sludge and low-carbon ferrochrome slag in a 1:1 ratio is compositionally close to dolomite. When dolomite is equivalently replaced in the mineral wool batch, the physicochemical characteristics of the melt remain suitable for mineral wool production. The complete reduction of iron and chromium oxides is achieved in the presence of carbon, resulting in their transfer to the metallic phase, where iron and chromium cations are present in the form of carbides. Due to the cost difference between chromium waste and dolomite, implementing the proposed technology makes it possible to significantly improve the efficiency of chromium waste utilization by reducing the production cost of mineral wool. The Aktobe region has all the prerequisites for implementing the developed technology, with active sources of chromium-containing waste pollution (ACCP, AFP) and basalt deposits, as well as the operational experience of the mineral-wool-manufacturing enterprise Basalt-A LLP.

Metals doi: 10.3390/met16090986

Authors: Fang Zhang Yan Xie Zhanyi Xu Hanzheng Zhang Yuhui Sha

Quasi in situ observations of the early stage of secondary recrystallization in Fe-3.25 wt.% Si high-permeability grain-oriented silicon steel indicate that large matrix grains locally impede the migration of secondary recrystallized grain boundaries. A critical grain-size criterion for identifying potential pinning grains is proposed, and a kinetic model incorporating the matrix grain-size distribution is developed. For the abnormal grain tracked at 1000 °C, the measured grain-size increment over 100 s was approximately 60 μm; the proposed pinning model predicted 47 μm, whereas the weighted-average model predicted 171 μm. Model calculations further suggest that matrix grain-size dispersion, pinning force, grain size, and relative grain-boundary energy jointly affect the early-stage growth of Goss grains. These results provide a framework for interpreting early secondary-recrystallization kinetics, while broader experimental validation is still required before the predicted parameter combinations can be used for process control.

Metals doi: 10.3390/met16090984

Authors: Leon Proud Ian Cook Pete Crawforth Chris M. Taylor

As manufacturers seek to improve cutting process sustainability, alternative metalworking fluid (MWF) strategies are increasingly being explored. For the first time, this study characterises tool wear when shoulder milling both Grade 5 titanium (Ti-6Al-4V) and Grade 2 commercially pure titanium (CP-Ti) with a novel through-spindle Aurion Machining Technologies ionised air (IA) MWF setup. Preliminary results show that during CP-Ti milling trials, the IA strategy led to a tool life of between 85% and 91% of that which was achieved with soluble oil emulsion MWF, whilst during Ti-6Al-4V milling the observed tool life with IA was between 158% and 278% greater than with emulsion coolant at analogous cutting conditions (2.58 and 3.78 times respectively). In addition, IA generated a 26.2% reduction in surface roughness after Ti-6Al-4V milling, potentially indicating a change in tool–surface interaction behaviour. These benefits are compounded as IA returns to its original condition rapidly after utilisation, meaning low environmental and health impact with no waste MWF liquids/gases/mist, clean metal cuttings and low delivery power. Beyond these promising results, cooled and dried but non-ionised air was also shown to perform strongly (regarding tool wear in Ti-6Al-4V milling), relative to emulsion MWF, such that at 190 m/min cutting speed it generated 90% of the tool life which was achieved by the IA strategy. Whilst these preliminary findings require confirmation through repeat testing, IA remains of clear interest for further experimental investigation across a range of subtractive processes. Moreover, this work highlights the potential benefits, niches and configurations for air-based MWFs in general, with further mechanistic and tribological exploration warranted.

Metals doi: 10.3390/met16090983

Authors: Shuai Zhang Bingbing Li Zhaofeng Wang Jiawei Han Qiang Shi

Additive manufacturing offers a novel technical route for the fabrication of complex lightweight aluminum alloy components in the aerospace field. However, high-strength aluminum alloys still suffer from defects such as hot cracking, porosity and microstructural inhomogeneity during the forming process. Particle reinforcement is a critical strategy to enhance the properties of additively manufactured aluminum matrix composites. Focusing on three mainstream processes, namely powder bed fusion–laser beam (PBF-LB), directed energy deposition–arc (DED-Arc) and directed energy deposition–laser beam (DED-LB), this paper elaborates on the roles of typical reinforcement particles including TiB2, TiC, SiC and CaB6 in microstructure tailoring, defect suppression and property enhancement. It further compares the three processes in terms of forming characteristics, microstructure evolution and aerospace applications. Finally, key challenges including particle dispersion, interfacial stability, process consistency and engineering application are summarized, and corresponding future development prospects are discussed.

Metals doi: 10.3390/met16090982

Authors: Prakarsh Pandey Shiva Rudraraju

Nanocrystalline (NC) alloys hold significant promise as structural alloys due to their superior mechanical properties over the traditional coarser grained microcrystalline alloys. Often, there is an optimal range of mean grain size for most metals about which maximum material strength can be realized. In the context of NC alloys, stabilization of the grain size in this optimal range is one of the primary synthesis challenges. A large volume fraction of NC alloy microstructure is occupied by grain boundaries (GBs). Since GBs increase the internal surface energy of the system, during solidification and grain growth phases, there is a tendency to minimize GBs through grain coarsening. However, in NC alloys, phenomena like GB–solute segregation and solute precipitation are active and mitigate grain growth and thus stabilize the desired small grains. Numerically modeling these phenomena of GB–solute interactions, and the evolution of these stabilized GBs under mechanical load, is of immense interest to the NC alloy community. To enrich the numerical modeling formulations available in this space, we present here a phase-field-method-based numerical framework to model GB segregation, solute precipitation and effect of external loading on NC alloys. While some of these effects have been modeled in isolation, a unified treatment of the solute–GB segregation-related effects and its coupling with mechanics has not be considered in the literature. We present a three-dimensional, finite element method (FEM)-based, finite-strain phase-field formulation for modeling grain evolution and microstructure stabilization in NC alloys. Beyond the formulation and its computational implementation, various case studies demonstrate the applicability of this framework. Further, thermodynamic and kinetic arguments are provided based on the evolution of GB energy to explain the effects of solute drag, GB pinning and mechanical deformation.

Metals doi: 10.3390/met16090981

Authors: Lianjie Li Hongqiang Liu Xindong Wang Haibo Xie Hongwei Cao Teng Li Xu Liu Tianwu Liu Kai Chen Chuanbao Zheng Haobin Tian Li Sun Zhengyi Jiang

The strip width in ultra-wide-strip tandem cold rolling changes not only the total rolling load, but also the transverse span over which the work roll (WR) is loaded. This study quantifies the isolated width effect on strip crown at 40 mm from the edge (C40), flatness and WR elastic deformation in a 2180 mm CVC-6 tandem cold mill. A three-dimensional multi-stand elastic–plastic finite element (EPFE) model was established for five representative widths of 900, 1200, 1500, 1800 and 2100 mm, corresponding to contact-span ratios of 0.413–0.963. The results show that the strip width increased from 900 mm to 2100 mm, C40 decreased from 20~80 μm to −50~−280 μm, and 1800 mm was the transition point from the positive crown to the negative crown. At the same time, the quadratic flatness component increased toward a center-wave mode, whereas the quartic component decreased toward an edge–center coupled-wave mode. Mechanistically, the relative WR axis deflection at the strip edge increased much faster than the local WR flattening compensation, producing an edge-open loaded roll gap. The findings indicate that strip width should be treated as an independent preset variable for WR bending, intermediate-roll bending and intermediate-roll shifting in ultra-wide cold rolling.

Metals doi: 10.3390/met16090980

Authors: Bohan Zhang Ze Sun Wei Liu Kaiming Wang Yulong Zheng Hanguang Fu

Continuous laser cladding of Ni-based composite coatings commonly suffers from coarse microstructures, high residual stress, severe cracking susceptibility, and limited wear performance. Although substrate preheating is an effective strategy for crack suppression, it inevitably induces microstructural coarsening and deteriorates mechanical and tribological properties, while the independent and coupled effects of pulsed laser modulation and preheating on (Ti, V)C/Ni coating performance remain insufficiently quantified and clarified. To address these technical gaps, this work fabricates (Ti, V)C/Ni composite coatings on Cr12MoV die steel via pulsed laser cladding. An L16 orthogonal experiment is employed to systematically investigate the influences of average power, duty cycle, and pulse frequency on coating hardness, and the optimal pulsed laser parameters are determined as 1750 W average power, 65% duty cycle, and 10 Hz pulse frequency. Under optimized parameters, the pulsed-laser-clad coating achieves a maximum hardness of 898.6 HV0.2, exhibiting 10.2% higher hardness and 41.4% better wear resistance than its continuous laser-clad counterpart, owing to the refined microstructure and enhanced grain-strengthening effect induced by rapid pulsed thermal cycling. Further comparative experiments demonstrate that substrate preheating combined with pulsed laser cladding effectively eliminates coating cracks and reduces residual stress by alleviating concentrated thermal strain. Nevertheless, preheating-induced microstructure coarsening slightly reduces the hardness and wear resistance of the composite coating compared with the purely pulsed laser-processed coating. In summary, pure pulsed laser processing dominates the improvement in wear resistance, whereas preheating mainly contributes to defect suppression and stress relief, enabling reliable engineering application of laser-clad coatings.

Metals doi: 10.3390/met16090979

Authors: Mingyuan Xiong Changshi Huang Guowei Wang Xiaocheng Zhou Dan Song

Chloride-induced steel corrosion is one of the major causes of durability degradation in reinforced concrete (RC) structures. Conventional inhibitors have inherent drawbacks in environmental safety, long-term stability, and cement compatibility. Plant extracts, featuring renewability, biodegradability, and abundant bioactive components, have emerged as promising green corrosion inhibitors. This review summarizes the categories, inhibition mechanisms, and evaluation methods of plant-based inhibitors, and discusses multi-scale characterization and computational techniques for mechanism research. A conceptual Ginkgo biloba extract (EGb)-LDH strategy is discussed as a possible future route for plant-based inhibitor delivery, but its chloride-responsive release and corrosion-protection performance remain to be experimentally verified.

Metals doi: 10.3390/met16090978

Authors: Xinyu Zhou Zhiqiang Xia Qiang Wen Zhen Pang Baisen Hou Yunxia Shi Hu Sun Junpeng Li Zhuo Qian Xianglei Yu Guoyou Gan

Micron-sized spherical gold powders possessing high dispersibility and favorable sintering performance are critical for high-performance thick-film gold conductor pastes. Herein, monodisperse micron-sized spherical gold powders were fabricated through an environmentally benign chemical reduction route, where L-ascorbic acid served as the reductant and gum arabic acted as the dispersant. The influences of solution pH, reaction temperature, stirring speed and reaction time on particle morphology and size distribution were systematically explored. With the mass ratio of gold precursor to reductant maintained at 1:1, the optimal synthetic conditions were determined as pH 3, 20 °C, 550 rpm and 20 min. Under such optimized conditions, spherical gold particles with an average diameter of 0.88 μm were harvested, featuring narrow particle-size distribution, high sphericity, good dispersibility and low organic residue of 0.70 wt%. The as-prepared powder delivered high crystallinity and appropriate sintering activity. Quantitative porosity characterization demonstrated that the thick film derived from this micron-scale gold powder achieved the minimum residual porosity in comparison with the other two counterparts, verifying its outstanding densification behavior. Benefiting from the well-developed dense conductive network, the resultant thick film achieved a low sheet resistance of 1.73 mΩ/sq, a superior adhesion strength of 3.65 N/mm2, as well as reliable multi-firing stability. This work offers a feasible approach for large-scale manufacturing of high-quality gold powders toward thick-film electronic devices.

Metals doi: 10.3390/met16090977

Authors: Xinchan Nie Caijiao Sun Lukuo Hong Shuai Tong Meijie Zhou

Controlling carbon removal while limiting surface oxidation is essential for constructing composition gradients in high-carbon medium-Mn steel. In this study, solid-state decarburization of Fe-12 wt%Mn-2.7 wt%C alloy sheets was investigated in H2O-H2 and CO2-CO atmospheres by combining thermodynamic calculations with XRD, SEM, OM, EBSD, and GDOES characterization. Thermodynamic analysis showed that, above 1190 K, the critical gas partial-pressure ratio for Fe oxidation is lower in CO2-CO than in H2O-H2, while the competitive-oxidation analysis further indicated a wider selective-oxidation window in the H2O-H2 atmosphere. Experimentally, H2O-H2 produced a relatively uniform oxide layer with a clear interface, whereas PCO2/PCO ≥ 0.29 promoted finger-like MnO growth along grain boundaries in CO2-CO. In both atmospheres, increasing temperature accelerated carbon removal. At 1363 K and 50 min, increasing PH2O/PH2 from 0.47 to 0.51 and further to 0.56 progressively reduced the carbon concentration at a depth of approximately 450 μm from approximately 0.50 to 0.45 and finally to 0.30 at%, demonstrating effective regulation of the through-thickness carbon gradient. EBSD of the specimen treated at 1323 K for 50 min with PH2O/PH2 = 0.47 revealed a near-surface α + γ microstructure and a γ-dominated near-center region, with the number-weighted mean grain size increasing from approximately 14.5 to 59.5 μm. These results establish a processing-microstructure relationship among atmosphere-dependent selective oxidation, carbon removal, and carbon-gradient microstructure formation in medium-Mn steel.

Metals doi: 10.3390/met16090976

Authors: Quan Xiao Haoran Zhang Xianglei Dong Hui Xing Shuya Zhang Yuheng Fan Junhua Hu Hongliang Zhao

Magnetic field-assisted casting technologies have received extensive research attention. Applying a transverse magnetic field during directional solidification offers an effective, non-contact approach to control the microstructure of Cu-Ag alloys by modulating melt convection. However, a comprehensive quantitative understanding of its mesoscopic influence on solute-driven dendritic growth and the columnar-to-equiaxed transition (CET) is still lacking. In this study, a coupled phase-field and lattice Boltzmann (PF-LBM) model is employed to systematically investigate the effect of a transverse magnetic field on columnar dendrite evolution and CET kinetics during the directional solidification of Cu-Ag alloys. Results show that the field-induced Lorentz force disrupts the symmetry of the solute field ahead of the dendrite tip, driving tilted dendritic growth that intensifies with decreasing initial primary spacing. During the CET process, the magnetic field overrides the randomness of grain nucleation by selecting specific crystallographic orientations. More importantly, it effectively mitigates the thermodynamic suppression of equiaxed nucleation typically caused by high temperature gradients. Furthermore, an increased magnetic field intensity not only accelerates the occurrence of CET but also significantly diminishes the inhibitory effect of high nucleation barriers on the transition. Ultimately, this work provides fundamental insights into external field-induced orientation selection mechanisms of as-cast grains and establishes a theoretical framework for quantitatively controlling texture evolution during the subsequent processing of high-flexure Cu-Ag alloys.

Metals doi: 10.3390/met16090974

Authors: Đorđe Ogrizović Predrag Škobalj Dušan Topalović Ivana Jelić Aleksandar Krstić Maja Đolić Marija Šljivić-Ivanović

This study investigates trace element concentrations in surface waters of Lake Međuvršje and evaluates their environmental relevance within Serbian and EU regulatory frameworks. Seventy-five samples were analyzed for B, Ba, Cu, Mn, Ni, Pb, and Zn. Multivariate analyses (Pearson correlation, PCA, and hierarchical clustering) revealed distinct geochemical groupings, indicating both natural lithogenic influences and potential anthropogenic inputs. Censored data analysis showed that Ni, Pb, Zn, and B were dominated by values below the analytical detection limit, rendering conventional geostatistical interpolation inappropriate. These elements were therefore assessed using detection-based spatial analyses, whereas Cu, Mn, and Ba exhibited sufficient variability for quantitative spatial interpolation. This study highlights the importance of integrating regulatory assessment, multivariate statistics, and censoring-aware spatial analysis to ensure reliable interpretation of freshwater trace element distributions.

Metals doi: 10.3390/met16090975

Authors: Qi Shao Binghai Lyu Luguang Guo Jiahuan Wang Xiaofeng Lin Dabin Zhang Ping Zhao Julong Yuan

The increasing demand for ultra-precision components with complex surface geometries has stimulated the development of advanced deterministic polishing technologies. This investigation explores the impact of external vibration on the rheological properties of polishing slurry and the material removal performance during the vibration-assisted force rheological polishing (VFRP) process. The mechanical response of the vibrating workpiece surface under various vibration conditions was numerically analyzed using ANSYS Fluent 14.5. The results demonstrated a strong correlation between the surface pressure imposed on the workpiece and the applied vibration amplitude as well as vibration frequency. Experimental results validate that the introduction of vibration promotes a reversible rheological transition of the slurry from a fluid-predominant state to a solid-resembling structure, which facilitates abrasive particle confinement and subsequently enhances polishing capability. The reliance of stainless-steel sheet polishing performance on vibration parameters was evaluated. With the optimized combination of polishing speed (40 rpm), vibration frequency (80 Hz), and amplitude (0.35 mm), the 30 min polishing process yielded a material removal rate of 68.1 nm/min and reduced the average surface roughness (Sa) from 80 nm to 7.1 nm. The acquired results provide constructive direction for optimizing the VFRP process and promoting its application in high-efficiency, ultra-precision surface polishing.

Metals doi: 10.3390/met16090973

Authors: Weichen Qiu Hongyu Liu Qian Yao Weilong Wang Shibing Liu Kun Shi Jiashuo Zhang

With the rapid development of the nuclear power industry, the requirement for nuclear structural materials is continuously growing. Eu-Ni intermetallic alloys are promising structural candidates for nuclear applications, while relevant fundamental investigations and underlying mechanisms remain insufficient worldwide. In this work, four Eu-Ni alloys with Eu mass fractions from 30 wt.% to 75 wt.% were fabricated via vacuum electromagnetic levitation melting. Thermodynamic calculations were performed to analyze high-temperature evaporation behaviors of Eu and Ni, and desired compositions were accurately achieved by evaporation loss compensation. XRD, SEM-EDS, TEM-SAED and hardness measurements were used to characterize phase constituents, microstructure and mechanical properties. The maximum evaporation rates of Eu and Ni increase with rising respective elemental contents. As Eu content increases, the dominant phase evolves from hexagonal EuNi5 to EuNi2 and finally FCC Eu-rich Eu0.56Ni0.44. The average grain size decreases from 127.82 μm to 67.59 μm, and intergranular spacing increases from 9.09 μm to 17.72 μm. Grain-boundary segregation of Eu softens the matrix, leading to a gradual hardness reduction from 529.2 kg/mm2 to 247.4 kg/mm2. This study clarifies composition-dependent evolution rules and provides fundamental data for industrial preparation and nuclear application of Eu-Ni alloys.

Metals doi: 10.3390/met16090972

Authors: Zilong Zhao Yuhao Wang Qinfang An Jiang Wen Dong Yan

To address the key problems of the dual-phase magnesium–lithium alloy LAZ931, such as easy corrosion, flammability and low strength, an AA6061 protective coating was fabricated on LAZ931 alloy via cold spraying to form an Al6061/LAZ931/Al6061 sandwich structure. The strengthening mechanism of the coating on interfacial microstructure, mechanical properties, creep behavior and corrosion resistance was systematically investigated. The results show that the cold-sprayed AA6061 coating is compact and uniform with a low porosity of 0.3% and surface roughness of 37.02 μm, which significantly improves the combustion resistance and corrosion resistance of the alloy. The coating/substrate interface exhibits jagged and tight bonding without obvious cracks or delamination. Abundant dislocations and Al–Mg–Li composite precipitates form at the interface, which effectively strengthen the interfacial bonding and enhance the tensile and yield strengths. Room-temperature creep tests reveal that the creep behavior of the composite is dominated by the LAZ931 matrix, and the coating remains intact and well-bonded throughout creep deformation without compromising the creep resistance. Electrochemical impedance spectroscopy shows that the coating increases the low-frequency impedance by more than two orders of magnitude, greatly elevating corrosion resistance. This study confirms that a cold-sprayed AA6061 protective layer can comprehensively enhance LAZ931 alloy through interfacial bonding, microstructural strengthening and protective barrier effects, providing a new strategy for protection and toughening of ultra-light Mg-Li alloys.

Metals doi: 10.3390/met16090971

Authors: Qian Zhang Patrick S. Chepaitis Mark Wilson Marilyn S. Black

Material extrusion 3D printing has been widely used in industrial, educational and residential environments. However, the associated emissions and exposure health impacts need to be evaluated, especially for the new and emerging filament materials. This study characterized particle and chemical emissions from 3D printing using five different metal composite filaments, which contain over 90% (by weight) of metal powder blended with polymer binders. The emission characterization was conducted using an exposure chamber following a standard testing method. Real-time particle measurements showed that particle emission rates ranged from 8 × 109 to 2 × 1011 particles/h for particle number and 200 to 1400 µg/h for particle mass. Over 98% of the emitted particles were smaller than 1 µm, which poses an inhalation hazard. Inductively coupled plasma–mass spectrometry analysis detected manganese, copper, zinc, and selenium in emitted particles from all filaments. However, metal powder in raw filaments tended not to be transferred into particle emissions, resulting in the total metals (and metalloids) accounting for 0.07% to 0.95% of emitted particle mass. Sorbent tube sampling and analytical analyses showed various volatile organic compounds emitted during printing, including hydrocarbons, alcohols, aldehydes, and aromatic compounds. Overall, metal composite filaments generated lower levels of volatile organic compounds (VOCs) compared to thermoplastic polymer filaments; in addition, the emitted VOC compositions differed. Organic chemicals associated with metal composite filament emissions included formaldehyde, benzaldehyde, acetaldehyde, naphthalene, and trimethylbenzene, exposure to which may cause irritations or other adverse health impacts. This study estimated personal exposure to hazardous components assuming a person is close to the printer with low ventilation to represent an acute worst-case exposure scenario. Modeled personal exposure to emissions showed potential exceedances of exposure to fine (PM2.5) and coarse (PM10) particulate matter, arsenic, manganese, formaldehyde, caprolactam, acetaldehyde, and naphthalene compared to reference levels. A modeled office room with ventilation showed reduced exposure levels by up to two orders of magnitude, assuming the same emission source. Users can avoid close proximity to an operating printer and increase dilution through larger room volumes and higher air change rates to reduce potential inhalation exposures at given printing conditions.

Metals doi: 10.3390/met16090970

Authors: Tianxiang Jiao Junye Li Xuelin Wang Ping Hu Wenbin Ding Zhenjia Xie Chengjia Shang

This study comparatively investigates the coarse-grained heat-affected zone (CGHAZ) responses of two industrial X65 seamless pipeline steels with distinct composition–microstructure characteristics under simulated girth-welding thermal cycles. One steel exhibits a predominantly bainitic initial microstructure, whereas the other consists of a ferrite–bainite dual-phase microstructure. Low-temperature Charpy impact testing, microhardness measurements, scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), prior-austenite grain reconstruction, and JMatPro 13.0-based continuous cooling transformation (CCT) calculations were employed to evaluate their heat-input sensitivity and microstructural evolution. At heat inputs of 7–10 kJ/cm, both steels maintained high impact toughness at −20 °C, with average absorbed energies of approximately 250 J. A pronounced difference emerged at 15 kJ/cm the bainite-dominated steel retained relatively high impact toughness and higher crack-initiation and -propagation energies, whereas the ferrite–bainite steel exhibited a marked toughness reduction. At higher heat inputs of 20–30 kJ/cm, both steels showed substantial toughness deterioration associated with severe prior-austenite grain growth and coarsening of the bainitic transformation products. Microstructural and crystallographic analyses showed that the bainite-dominated steel generally retained finer prior-austenite grains and more refined crystallographic features under the investigated thermal cycles. Detailed characterization at 15 kJ/cm further revealed finer prior-austenite grain, packet, and block structures, together with more tortuous crack-propagation paths. JMatPro calculations predicted a lower bainitic transformation temperature for this steel, which is consistent with the experimentally observed tendency toward finer bainitic transformation products. The superior CGHAZ toughness retained by the bainite-dominated steel is therefore associated with the combined effects of alloy composition, initial metallurgical state, transformation behavior, and hierarchical crystallographic refinement rather than the initial microstructure alone. The results highlight the importance of coupled composition–transformation–microstructure effects in determining the welding heat-input tolerance of industrial X65 seamless pipeline steels.

Metals doi: 10.3390/met16090969

Authors: Jan Bartolj Ana Trajkovski Franc Majdič

Metal additive manufacturing (AM) enables compact hydraulic manifolds with curved internal channels, reduced part count and integrated functionality. However, these benefits also create major inspection challenges, especially in thick metallic sections containing closely spaced and intersecting passages. This study examines the practical use of X-ray computed tomography (CT) for an industrial hydraulic manifold manufactured from maraging steel MS1 by laser powder bed fusion (LPBF). Selected cross-sections from the reconstructed CT volume were compared with the nominal computer-aided design (CAD) geometry and evaluated using a qualitative interpretability classification supported by comparative image contrast-to-noise ratio (CNR) analysis and approximate projected steel thicknesses. Clearly interpretable regions showed higher and more consistent CNR, whereas geometrically congested regions generally exhibited lower and more variable local contrast. However, projected material thickness alone did not determine interpretability, indicating an additional influence of geometric overlap, orientation and reconstruction artefacts. Particular attention was given to a channel wall adjacent to a locally collapsed external support structure. No spatially persistent through-wall discontinuity was identified, although smaller defects, local wall thinning and metallurgical changes could not be excluded. A pneumatic immersion test at 0.8 MPa showed no visible bubble formation or observable pressure decrease. This pressure exceeded the expected operating pressure of the affected relief or tank channel but was substantially below the 35 MPa maximum intended pressure of the pressure-side circuits and therefore did not constitute structural qualification. The study demonstrates that whole-component CT can provide useful local inspection information for complex LPBF manifolds, but its reliability depends strongly on local geometry and acquisition conditions. Quantitative image assessment and complementary functional testing may therefore be required when CT results are insufficient for complete qualification.

Metals doi: 10.3390/met16090968

Authors: David Gonzalez-Nino Gary S. Prinz

Additive manufacturing (AM) technologies, such as laser powder bed fusion (LPBF), allow for rapid fabrication of geometrically complex components that would be difficult to create using traditional casting or subtractive fabrication processes; however, research into AM metals has shown that fabrication defects resulting from LPBF processes (i.e., voids, un-melted particles, etc.) can have deleterious effects on mechanical behavior. Material testing using traditional macro (coupon-scale) volumes may not accurately capture scalable material behavior in LPBF metals, as the distribution of fabrication defects is volume-dependent. To understand fundamental material behavior at scales independent of geometrical fabrication defects (including print-induced material arrangements), in situ micro-mechanical testing of AM LPBF 17-4 PH stainless steel materials is conducted, opening possibilities for future bottom-up material simulation scaling. In this study, the tensile and compressive behavior of LPBF-fabricated 17-4PH stainless steel is characterized at the micron scale to aid future efforts in the predictive upscaling of structural components, while eliminating void effects and micro-scale print-induced material arrangements in any characterizations. Not surprisingly, behavior comparisons between multiple length scales (micro and macro scales) indicate strength reductions in larger bulk volumes. Micro-tensile measurements resulted in ultimate tensile strength (1359 MPa ± 99.9 MPa standard deviation) and strain before failure (0.31 ± 0.063 μm/μm) values that exceeded those of the macro-tensile specimens (1025 MPa tensile strength and 0.190 μm/μm strain at fracture, respectively).

Metals doi: 10.3390/met16090967

Authors: Arun K. Chattopadhyay Jonathan Pegues Sandy Awad Eric Bono Tuncay Simsek Animesh Bose

This paper investigates the Electrode Induction Gas Atomization (EIGA) of a Class 4 tungsten heavy alloy (WHA-4) containing 97.8 wt.% W, with the balance comprising Ni and Fe. Compared with conventional tungsten heavy alloys containing less than 95 wt.% W, the high tungsten content reduces the liquid-phase fraction and melt fluidity, making stable processing significantly more challenging. Powder-metallurgy-fabricated electrodes were atomized under varying resonant induction conditions to evaluate the effects of capacitance, frequency, and input power on melt stability. The results show that stable processing can be achieved through an optimum combination of capacitance and resonant frequency, providing sufficient energy to maintain a steady melt stream and uninterrupted atomization. Under optimized conditions, predominantly spherical powders with minimal defects were successfully produced. Microstructural characterization revealed that the Ni–Fe binder phase remained localized along tungsten grain boundaries and in isolated pockets between tungsten grains. X-ray diffraction and chemical analyses confirmed that the phase constitution and alloy composition of the electrode were preserved during atomization. Under non-optimum conditions, process instability was associated with incomplete melting, beard formation, unstable melt flow, and nozzle blockage. These findings provide new insights into the atomization behavior of high-tungsten heavy alloys and establish practical processing procedures for producing high-quality WHA-4 powders for advanced manufacturing applications.

Metals doi: 10.3390/met16090966

Authors: Yiming Xu Yaxu Jin Yong Hu Meihua Wang Chao Shi Fei Ning

A quaternary electrolyte system consisting of sulfuric acid, boric acid, citric acid, and aluminum sulfate was developed to regulate oxide film growth and improve the corrosion resistance of hard anodic oxide films on 2A12 aluminum alloy. The electrolyte composition and anodizing parameters were systematically optimized using single-factor experiments and orthogonal design. The optimized oxide film exhibits a thickness of 55.43 μm and a microhardness of 278 HV, exhibiting a compact and continuous microstructure with fewer structural defects. SEM, EDS, XRD, and XPS analyses reveal that the optimized coating mainly consists of amorphous or poorly crystalline alumina. Electrochemical measurements demonstrate that the corrosion current density decreases from 5.32 × 10−5 A/cm2 for the substrate to 2.14 × 10−8 A/cm2, corresponding to a corrosion inhibition efficiency of 99.96%. The quaternary electrolyte system promoted the formation of a thicker and more compact oxide layer with fewer structural defects, thereby significantly enhancing the corrosion resistance and providing insights into the design of multicomponent electrolytes for the hard anodizing of high-copper aluminum alloys.

Metals doi: 10.3390/met16090965

Authors: Yuan Deng Tao Deng Yongguang Wang Yi Huangfu Xin Zhao Long Luo

For hydrogen refueling stations, metal hydride compressors offer a safe and efficient alternative to mechanical systems. This work systematically investigates Ti0.94Zr0.08Cr1.0Mn0.6−xFe0.4+x (x = 0, 0.1, 0.2, 0.3, 0.4) alloys for primary hydrogen compression targeting 25 MPa. All alloys crystallize as a single C14 Laves phase, with Fe substitution causing negligible lattice changes but leading to linearly increased particle size due to solid-solution strengthening. In the testing temperature range of −80 to −50 °C, the hydrogen storage capacity decreases with increasing Fe, whereas the effective desorption capacity improves. Pressure–composition isotherms exhibit single plateaus with elevated plateau pressures at higher Fe/Mn ratios. In the range of x = 0–0.4, the enthalpy of desorption decreases in magnitude with Fe content. Using Van’t Hoff extrapolations to 30 °C absorption and 80 °C desorption, the compression factor shows a non-monotonic trend, reaching a maximum of 1.99 at x = 0.2. This composition provides nearly a two-fold pressure boost, demonstrating promise for low-grade heat driven hydrogen compression in refueling infrastructure.

Metals doi: 10.3390/met16090964

Authors: Zhengping Lu Yinxi Ding Nachuan Ju Jianneng Zheng Lianlong Li Bin Qiu Jie Zeng Tao Liu Haomin Wu

X2CrNiMo18.12 (nitrogen-controlled) stainless steel is prone to slag-shell erosion during electroslag remelting (ESR), which may lead to steel breakout and mold leakage. To investigate the evolution behavior of the slag shell and molten pool, a transient multiphysics model coupling electromagnetic, flow, and thermal fields was developed based on the volume of fluid (VOF) method and dynamic mesh technique. The distributions of the coupled physical fields and the effects of electrical parameters and cooling intensity on slag-shell stability and molten-pool morphology were systematically analyzed. The results show that a pronounced edge effect exists at the lower electrode corner, resulting in concentrated current density, Joule heating, and Lorentz force. Under the combined effects of electromagnetic force and thermal buoyancy, a dominant circulation vortex is formed in the slag pool, which governs heat transfer and slag-shell evolution. The slag-shell thickness is determined by the competition among vortex-induced erosion near the mold wall, erosion by molten steel at the slag–metal interface, and mold cooling. Among these factors, erosion by molten steel is the primary cause of steel breakout and mold leakage. Increasing the current from 2.5 to 3.5 kA significantly increases the melt superheat, transforms the molten pool from a shallow U-shape to a deep V-shape, and reduces the slag-shell thickness to approximately 0.95 mm, leading to leakage failure. In contrast, a moderate current of 2.5–3.0 kA combined with a cooling intensity above 2400 W·m−2·K−1 maintains the slag-shell thickness at approximately 2 mm and effectively suppresses steel breakout and mold leakage. These findings provide guidance for process optimization and operational safety in the ESR of X2CrNiMo18.12 steel.

Metals doi: 10.3390/met16090963

Authors: Lei Zhang Shifu Chen Hong Lei Haoyu Ling

The Rheinstahl–Heraeus with ladle bottom-blowing (LBB-RH) vacuum refining process has been developed to enhance circulation flow and decarburization efficiency for ultra-low carbon steel production. However, current numerical models rely on the steady-state assumption for Ar-molten steel flow, neglecting the transient evolution of CO bubbles generated by decarburization in LBB-RH. Thus, a transient coupled model integrating unsteady CO-Ar-molten steel flow with decarburization kinetics is established in this paper. The transient distributions of CO gas, flow velocity, circulation flow rate, and carbon mass concentration are systematically investigated. The results show that LBB-RH achieves higher velocity on the main longitudinal section but lower velocity at the vacuum chamber free surface. The circulation flow rate of LBB-RH reaches 1.58 times that of conventional RH at the 25th minute. Under identical argon flow rates, the carbon mass concentration in LBB-RH is less than that in conventional RH, but the difference diminishes to 4 × 10−6 at the 25th minute as the decarburization rate decays significantly. At the 4th minute, the average carbon mass concentration in LBB-RH is only 73.26% of that in conventional RH. The proposed transient coupled model quantitatively elucidates the transfer mechanism in LBB-RH, and offers a theoretical foundation for the industrial production of ultra-low carbon steel with enhanced overall performance.

Metals doi: 10.3390/met16090961

Authors: Qinghong Deng Fei You Xiaodong Liu

Post-weld cold rolling and subsequent annealing were applied to friction-stir-welded Al/Cu joints to examine their interfacial evolution, tensile behavior, and local cupping response. Multi-pass cold rolling reduced the sheet thickness from 3.0 to 0.4 mm and transformed the initially inclined Al/Cu interface into a near-horizontal laminated structure with an average inclination of 3.97° relative to the sheet plane. Rolling fragmented and thinned the interfacial reaction layer (narrow nanoscale reaction-product layer) and increased the average tensile strength from 99 to 370 MPa, whereas the elongation remained low at approximately 0.6%. Annealing at 300 °C for 30 min promoted recovery and recrystallization, reduced the hardness difference across the joint, and increased the elongation to 8.8%, with an average tensile strength of 182 MPa. The macroscopic tensile fracture path changed from the Al/Cu interfacial region (broad transition zone) in the as-welded joint to the laminated region (rolled interfacial region characterized by alternating Al-rich/Cu-rich lamellae) after rolling and annealing. In contrast, interface-centered cupping specimens exhibited a lower load-carrying capacity and cracking along the interfacial region. These results show that post-weld rolling and annealing improve the uniaxial tensile response through interface flattening and microstructural homogenization, while the interfacial region remains susceptible to cracking during combined stretching and bending deformation.

Metals doi: 10.3390/met16090962

Authors: Hang Zhang Mingyuan Xiong Changshi Huang Guowei Wang Shuguang Zhang Tengbin Liu Dan Song

The initiation of electrochemical corrosion on steel surfaces begins with water molecule aggregation, though the atomic-scale mechanisms from adsorption and wetting to corrosive microdroplet formation remain unclear. Using molecular dynamics simulations, this work investigates the formation of corrosive aqueous micro-environments on iron-based surfaces during early condensation. It focuses on the regulatory effects of surface roughness and local hydrophilic sites on condensation nucleation, droplet growth, and wetting. Results show a linear correlation between droplet contact angle and solid–liquid interaction energy, with temperature dependence controlled by the substrate’s intrinsic wettability. For fence-type rough surfaces, we clarify the transition from a critical to a mixed (Cassie–Wenzel) wetting state, confirming that roughness enhances intrinsic wettability. Condensation analysis reveals that stronger solid–liquid interaction promotes water adsorption and induces a shift from dropwise to filmwise condensation, with interphase temperature difference driving heat transfer. On hydrophobic surfaces with local hydrophilic sites, these sites serve as preferential nucleation points. Their size effect can pin the three-phase contact line, leading to droplet growth in a high-contact-angle mode. This study offers an atomic-scale view of how condensation creates the initial aqueous environment required for electrochemical corrosion, providing theoretical insight into phase-change heat transfer and interfacial behaviour on complex surfaces. The findings guide the design of surfaces resistant to condensation-induced corrosion.

Metals doi: 10.3390/met16090959

Authors: Mehran Saddat Zainab Nasrullah Frank Agyemang Richard LaDouceur

Rare earth elements (REE) are critical to 21st-century technology, from electronics and defense applications to renewables and beyond. The processing of REE is primarily based on minerals (bastnasite, monazite, and xenotime), but alternative resources (coal ash, E-waste, and permanent magnets) are also gaining increasing interest. Adsorption remains one of the most efficient, environmentally friendly extraction methods despite its lengthy mixing time. In the present research article, a hemp biochar prepared by vacuum pyrolysis at 700 °C was examined for its applicability in the adsorption of selected REE (La3+, Nd3+, Dy3+) from synthetic solutions. An innovative technique, Resonant Vibratory Mixing (RVM), was applied to improve adsorption kinetics, with factors including time (5–30 min) and intensity (30–70%) at room temperature. Using the Thermo Scientific 4000 M shaker for mixing, the maximum adsorption capacities were 77.56 mg/g for Dy3+, 75.85 mg/g for La3+, and 72.65 mg/g for Nd3+ using 100 mg of hemp biochar and 10 mL solutions (1000 mg/L). The adsorption capacity of 100 mg hemp biochar was 79.79 mg/g for Dy3+, followed by 77.61 mg/g for La3+ and 75.75 mg/g for Nd3+, using RVM for only 40 min at 70% intensity. RVM increased the adsorption capacities of all REE in only 40 min. Surface and structural analyses were carried out using Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller analysis (BET), Zeta Potential, and Carbon/Hydrogen/Nitrogen (CHN) methods. The adsorption recoveries of all REE in the single-element system were higher than 98.5%. However, in a multi-element system, the adsorption recoveries of La3+, Nd3+, and Dy3+ were 83.7%, 96.2%, and 99.2%, respectively, demonstrating that hemp biochar has low selectivity for Dy3+ and Nd3+. The adsorption process could be well described by the Langmuir isotherm and the pseudo-second-order kinetic model, indicating monolayer adsorption and chemical process involvement. Based on the characterization analysis of hemp biochar, electrostatic interaction was the dominant mechanism in this study. REE desorption using 0.5 M nitric acid was the most efficient, with >80% of REE recovered. The combination of hemp biochar as an adsorbent and RVM as a mixing technique demonstrated excellent performance in synthetic solutions; the reusability and application of hemp biochar to natural solutions require further study.

Metals doi: 10.3390/met16090960

Authors: Li Zheng Qirong Wang Zhenghong Zhu Xuexia Li Hongfei Zhang Jiale Zhao Bo Liu

Laser powder bed fusion enables the fabrication of complex Inconel 718 components, but rapid solidification produces pronounced microsegregation that complicates subsequent phase evolution. In this study, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy were combined with JMatPro calculations to examine as-built microsegregation and phase behavior in laser powder bed-fused Inconel 718. The as-built alloy exhibited a continuous cellular and dendritic substructure, a high dislocation density, and interdendritic constituents with pronounced Nb enrichment and weaker local Mo enrichment. Equilibrium calculations based on the measured powder composition predicted γ formation at approximately 1350 °C and a liquid plus γ region between 1195 and 1350 °C. The calculated stability ranges of MC, δ, η, γ′, σ, M23C6, Laves, and μ phases were also identified. Comparison with the experimental observations showed that calculations using the nominal composition cannot directly represent the strongly segregated interdendritic regions formed during rapid solidification. The TTT and CCT calculations indicated that δ phase precipitation is most sensitive at approximately 900 to 1000 °C. The results clarify the distinction between local nonequilibrium phase formation and bulk phase stability and highlight the role of Nb redistribution among interdendritic constituents, the δ phase, and γ″ and γ′ precipitates. The calculated results should be regarded as a qualitative reference. Further local composition-based calculations and experimental validation are required before they can be applied to heat treatment design.

Metals doi: 10.3390/met16090958

Authors: Dongsheng Wang Qing’e Zhao Jianbo Zhang Yanqing Hou Bo Xiao

The “high-temperature carbonization and low-temperature chlorination process” can recover titanium from high-titanium blast furnace slag containing 20–25% TiO2 at 1450–1700 °C and 500–600 °C. The carbonization process was carried out in an industrial three-phase AC electric furnace with a rated power of 9000 kVA. Through Factsage calculations, XRD, SEM-EDS, and industrial data collection, the mechanism of carbonization and the impact of smelting parameters were illustrated. The results indicated that Ti primarily existed as titanaugite or perovskite in the slag, and the reduction reaction of TiO2 began at 1301 °C. But to complete perovskite transformation, a temperature exceeding 1550 °C was necessary. When the reaction began, the reaction rate of TiO2 to Ti2O3 was faster than that of Ti2O3 to TiC, and TiC grains appeared as small island-shaped particles (0–3 μm) and larger aggregates (0–10 μm) surrounding Fe. Furthermore, as the molten pool was agitated, the TiC particles detached from the surface of the carbon and it became very difficult for them to grow. In the final reaction stage, most of the TiC contained a certain amount of oxygen and was dispersed, with a particle size of 0–5 μm and a settling tendency. In terms of industrial production, the results indicate that employing coke with a particle size of 0.074–1 mm, maintaining a bath temperature ≥1550 °C, and implementing stage-specific power supply protocols (particularly for the high-conductivity final stage) are crucial for achieving a ≥88% industrial carbonization rate.

Metals doi: 10.3390/met16090957

Authors: Fengli Yue Zhaohui Liu Yu Xiao Songwei Wang Hongwu Song

In this study, an “oxide layer” was formed on the surface of Cu-0.97Cr-0.11Zr alloy sheets by introducing oxygen via a non-vacuum solid solution treatment, followed by vacuum solid solution and aging treatments to obtain a layered composite microstructure. The macro- and microstructures were characterized using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Furthermore, the properties of the alloy were evaluated through electrical conductivity and hardness measurements. The results indicate that during the non-vacuum solid solution process, oxygen atoms diffused into the copper alloy matrix and underwent an in situ oxidation reaction with the solute Cr. As the temperature increased from 800 °C to 900 °C, the thickness of the oxide layer grew from 23.2 μm to 77.8 μm. The formation of Cr2O3 nanophases within the oxide layer increased the alloy hardness from 87.3 HV to 101.8 HV and the electrical conductivity from 68.75% IACS to 78.85% IACS. Following subsequent vacuum solid solution and aging treatments, both hardness and electrical conductivity were significantly enhanced, reaching an edge hardness of 114.6 HV, a core hardness of 125.1 HV, and a conductivity of 80.32% IACS. Through this method, a layered composite structure of the Cu-0.97Cr-0.11Zr alloy, characterized by a highly conductive surface and a high-hardness core, can be successfully obtained.

Metals doi: 10.3390/met16090956

Authors: Xi Lan Lidong Xing Anjun Shi Xiang Li

Super-gravity technology was applied during the solidification of high-conductivity No. 2 oxygen-free copper (TU2) to achieve synergistic optimization of its electrical and mechanical properties. Theoretically, super-gravity promoted grain refinement by increasing the nucleation rate (via dendrite fragmentation and enhanced heterogeneous nucleation) and reducing the grain growth rate (due to increased melt viscosity). Experimentally, applying the super-gravity field specifically during solidification proved essential for effective microstructural modification. As the gravity coefficient (G) increased from 1 to 1000, grain size was significantly refined, especially when G > 500. Consequently, Vickers hardness increased from 59 to 95 kg/mm2 and ultimate tensile strength rose from 112.2 to 124.7 MPa, while electrical conductivity remained nearly unchanged (from 106.92% to 106.38% IACS). The slight initial increase in conductivity was attributed to reduced porosity, followed by a minor decrease due to enhanced grain boundary scattering. This study demonstrated that super-gravity solidification was an effective strategy for fabricating high-conductivity metallic materials with simultaneously improved strength and hardness.

Metals doi: 10.3390/met16090955

Authors: Lin Wu Yi Lu Songge Li Youcong Liu Peifan Zhang Yiwa Luo

Porous Ti6Al4V scaffolds with tailored architectures are promising candidates for orthopedic implants due to their potential to mitigate stress shielding and enhance osseointegration. In this study, porous Ti6Al4V scaffolds with different unit cell geometries and porosities were fabricated via laser powder bed fusion (LPBF). The effects of pore structure and porosity on mechanical and biological properties were systematically investigated. The results show that both elastic modulus and compressive strength decrease with increasing porosity, and a critical porosity of 70% is identified for uniform structures, beyond which their load-bearing capacity becomes insufficient; however, a radial gradient design can overcome this limitation. Alkali heat treatment generates a uniform sodium titanate nanowire coating, which significantly improves wear resistance and promotes apatite deposition, thereby enhancing bioactivity. Among all samples, the hexagonal diamond structure with 70% porosity exhibits the highest cell viability. To overcome the trade-off between mechanical strength and biological performance inherent in uniform porous structures, a radial gradient porous scaffold with an average porosity of 72.5% was designed. The gradient structure demonstrates improved mechanical strength while maintaining high bioactivity, indicating its potential for optimized orthopedic implant applications.

Metals doi: 10.3390/met16090954

Authors: Di Wang Jia-Nan Dong Jiang-Tao Li Yi-Fan Che Yang Zhang Ming-Xia Liu Zhi-Fu Yin Cong-Ying Jia Pan-Pan Ren Yan-Xia Su Yu-Na Xue

CrN coatings prepared by physical vapor deposition may fail prematurely in localized regions during machining due to stress and high temperature. To address this problem, three groups of CrN coatings with different bias voltages were deposited on cemented carbide tools using cathodic arc ion plating. The influence of coating microstructure on cutting performance was investigated. The surface and cross-sectional morphologies of the coatings were observed using scanning electron microscopy. The crystal structures of the coatings were characterized using X-ray diffraction. The nanohardness values and elastic moduli of the coatings were measured using nanoindentation, and the coating–substrate adhesion was evaluated using a scratch tester. The residual stresses of the coatings were determined using the substrate bending method. The cutting performance of the coated tool was tested using a Computer Numerical Control (CNC) machine tool. The cutting process using coated tools was simulated using ABAQUS 6.14 software. The results indicated that, as the bias voltage increased, the droplets on the surface of the CrN coating became smaller and the structure became denser, but the thickness gradually decreased. The hardness increased from 18.59 GPa at 100 V to 24.57 GPa at 200 V, the bonding force increased from 72.6 N to 78.5 N, and the residual stress also increased to −2.22 GPa. Cutting tests showed that the cutting performance of the 200V-CrN coating was nearly twice that of the 100V-CrN coating. According to the microstructure and finite element simulation results after cutting, the 200V-CrN coating with a dense structure and higher residual compressive stress exhibited better stress-absorption capacity and was less susceptible to wear or fracture during the cutting process, thereby extending tool life.

Metals doi: 10.3390/met16090953

Authors: Xin Zhao Shujing Dong Rui Guo Yuanbo Chu Dongzhe Song Zhibin Yang

Laser–arc hybrid multi-layer multi-pass welding is adopted to fabricate high-quality joints in 25 mm thick A710 steel, and the microstructure and mechanical properties of the welded joints are systematically studied. The results indicate that the weld is well-formed and free of obvious defects. The weld zone microstructure consists of acicular ferrite, bainitic ferrite, and polygonal ferrite, while the heat-affected zone consists of polygonal ferrite and bainitic ferrite. The inter-layer of the weld is composed of coarse ferrite blocks formed by the recrystallization of acicular ferrite. Moreover, the weld zone consists of fine-grained columnar structures with a high density of high-angle grain boundaries. The grains in the heat-affected zone are coarse, with numerous low-angle grain boundaries. The average ultimate tensile strength of the welded joints is 696 MPa, the average yield strength is 619 MPa, and the average elongation is 32%. All tensile specimens fracture within the weld zone and exhibit ductile fracture characteristics. The average microhardness value of the upper heat-affected zone (291 HV) is higher than that of the weld zone (228 HV). In comparison, the average microhardness value of the lower weld zone (267 HV) is higher than that of the heat-affected zone (255 HV). The average impact toughness at −40 °C is 111 J for the weld zone and 91 J for the heat-affected zone. The fibrous region in the weld zone fracture occupies a larger area than that in the heat-affected zone, and is characterized by larger dimples.

Metals doi: 10.3390/met16090952

Authors: Lei Shi Zhongxia Liu Aiyun Jiang Bin Cai Bo Ren

To address the prevalent defects in industrially cast 8021 aluminum alloy for battery foil, including coarse iron-rich phases that sever the matrix and hard-to-remove micrometer-scale inclusions, alloys with different chemical compositions were manufactured on a 100-ton integrated industrial melting and holding production line. The regulatory principles and underlying mechanisms of Fe–Ce composite microalloying on solidification thermal behavior, melt purification efficiency, as-cast microstructure, mechanical properties, and corrosion resistance of the alloy were systematically investigated. The results show that when the mass fractions of Fe and Ce are 1.7% and 0.3%, respectively, the mean intercept length of the α-Al grains of the alloy is reduced by 29% compared with the reference alloy. The acicular iron-rich phases are modified into dispersively distributed short rod-like and granular particles, and the filtration removal efficiency of micro-inclusions in the melt is significantly improved. The ultimate tensile strength of the alloy reaches 94.0 MPa, and the elongation is increased to 44.2%. The corrosion current density in 3.5 wt.% NaCl solution is only 20% of that of the Ce-free reference alloy. Through multi-stage effects including melt purification, grain refinement and second-phase modification induced by joint Fe and Ce additions, the combined addition of Fe and Ce simultaneously improves the metallurgical quality and service performance of the alloy. This work provides theoretical support and engineering references for the stable industrial production of high-performance aluminum foil for lithium-ion battery packaging.

Metals doi: 10.3390/met16090951

Authors: Fatemeh Asadi Ulises Martin Olivia Esmacher Rebecca Crow Mahmodul Hasan Maheen Marcelo Paredes Homero Castaneda

This study examines the corrosion behavior of nitinol (NiTi) across its transformation range (10–60 °C) using a multimodal approach combining electrochemical testing with advanced surface and compositional characterization. The results reveal a distinct phase-dependent corrosion response. At 10 °C, fully martensitic NiTi exhibited the lowest corrosion current density and the most stable passive film, confirmed by electrochemical impedance analysis showing high film ideality and low pseudo-capacitance. At 20 °C, a mixed martensite–austenite structure led to degraded corrosion performance, reflected by increased current density and reduced passive film stability. Despite this, at 10 °C, the fully martensitic surface exhibited no measurable pit damage (0% surface coverage), while the mixed structure at 20 °C maintained minimal damage at 0.14% surface coverage. Corrosion susceptibility increased at 40 °C due to the higher phase mismatch combined with enhanced chloride activity, resulting in reduced electrochemical performance and substantial pit damage, increasing the surface coverage to 15%. At 60 °C, the fully austenitic structure partially restored corrosion resistance and reduced pitting severity. These results establish a direct link between NiTi’s thermo-mechanical phase state and its corrosion behavior, highlighting the critical role of phase coexistence and microstructural heterogeneity. The findings provide guidance for designing corrosion-resistant NiTi components for harsh environments such as marine and energy applications.

Metals doi: 10.3390/met16090950

Authors: Anoop Kumar Maurya Jong-Taek Yeom Jae H. Kim Junha Yang Chan Hee Park Jae-Keun Hong Nagireddy Gari Subba Reddy

Wire and arc additive manufacturing (WAAM) is a cost-efficient technology for large-scale production; however, the high cost of Ti-6Al-4V filler wire, primarily associated with conventional billet-based thermomechanical processing, remains a critical limitation. This study proposes a direct and cost-effective manufacturing route for Ti-6Al-4V filler wire from an as-cast ingot, enabled by processing map-guided thermomechanical design. Hot deformation behavior was systematically investigated for the as-cast ingot, the β-forged billet, and the α + β-forged billet over 700–1200 °C and strain rates of 0.01–10 s−1. An artificial neural network (ANN)-assisted correction was employed to compensate for adiabatic heating, enabling reliable construction of processing maps and identification of stable deformation domains associated with dynamic recrystallization (DRX). The optimized deformation conditions derived from the processing maps were directly applied to hot-rolling, followed by room-temperature wire drawing. As a result, high-quality Ti-6Al-4V filler wire with a diameter of 1.7 mm was successfully fabricated. Microstructural analysis revealed deformation-induced refinement and alignment of the α phase, with variations depending on the initial state. Despite relatively coarser features, the wire fabricated from the as-cast ingot exhibited a tensile strength of 1408 MPa and elongation of 6.7%, demonstrating tensile properties comparable to those of the wires fabricated from the forged billets. These results provide direct experimental validation that processing map-guided design enables the direct conversion of as-cast Ti-6Al-4V ingots into high-quality filler wire. The proposed approach offers a simplified and economically competitive alternative to conventional billet-based processing routes for WAAM applications.

Metals doi: 10.3390/met16090949

Authors: Peng Yang Zhe Ni Jie Yan En Zhang Jin Zhang

Aluminum and its alloys feature low weight and high strength. They are widely applied in aerospace, automobile manufacturing, and marine engineering. However, they are highly susceptible to localized corrosion. Such defects can severely restrict the service life of the substrate materials. Pristine graphene exhibits atomic-level compact impermeability, stable chemical inertness, and excellent mechanical properties. It is a promising candidate material for the protection of aluminum substrates. Nevertheless, an electrically insulating interlayer is generally required between pristine graphene and aluminum to achieve reliable protection. This measure avoids the risk of galvanic corrosion. This paper systematically reviews the latest research progress of graphene-based coatings on aluminum, focusing on pristine graphene, graphene oxide (GO), reduced graphene oxide (rGO), and graphene-polymer composite coatings. It focuses on the preparation methods and corrosion protection performance of the materials. This study compares various mainstream preparation technologies in detail. The technologies include chemical vapor deposition, electrochemical deposition, mechanical exfoliation, solution coating, laser induction, and thermal spraying. The corrosion protection mechanism is discussed from three dimensions. The dimensions include physical barrier effect, tortuous path mechanism, and electrochemical protection. Key influencing factors, such as coating defects and environmental conditions, are also investigated. This paper summarizes the application potential of graphene-based coated aluminum in high-end manufacturing fields. It points out the major existing challenges of the material. The challenges involve coating uniformity, adhesion strength, long-term stability, and industrial production. Finally, future research directions are proposed in this work. These directions include the development of innovative coating technologies, the construction of composite protection systems, the design of intelligent self-healing functions, and the exploration of environmentally friendly preparation processes.

Metals doi: 10.3390/met16090948

Authors: Melih Canlıdinç

Laser powder bed fusion (L-PBF)-fabricated Inconel 718 lattice structures offer considerable potential for lightweight load-bearing applications, but their mechanical integrity depends on architecture, geometric scale, manufacturing defects, and post-processing condition. This study examined the combined effects of Diamond, Gyroid, and Octet architectures, nominal feature sizes of 1.0, 1.25, and 1.5 mm, and four heat-treatment conditions on tensile behavior and fracture characteristics. The specimens were evaluated using explicit-dynamics finite element analysis, room-temperature quasi-static tensile testing, and SEM fractography. A feature-size-dependent reversal in architecture ranking was observed: Gyroid exhibited the highest mean apparent tensile strength among the 1.0 mm lattices across the investigated heat-treatment conditions, whereas Diamond exhibited the highest mean apparent tensile strength among the 1.5 mm lattices across the same conditions. HT-C shifted the tensile response toward higher apparent strength and lower apparent deformation capacity, whereas selected HT-B-treated specimens exhibited more ductile fracture morphologies. These findings show that architecture, nominal feature size, and post-processing condition must be considered jointly when designing L-PBF Inconel 718 lattice components within the investigated design range.

Metals doi: 10.3390/met16090947

Authors: Xinyu Song Fucong Guo Lizhi Gao Xiaojie Yang Peng Zhao Shanwen Dong Jiangmin Xu Mingxiao Shi Zhidong Yang

This review systematically investigates the developmental trajectory of Gas Metal Arc Welding (GMAW), beginning with its fundamental forms: Metal Inert Gas (MIG) and Metal Active Gas (MAG) welding. In the analysis of high-efficiency GMAW processes, a comparative evaluation was conducted across five major categories of efficiency enhancement strategies: single-wire high-efficiency welding, dual-wire high-efficiency welding, hybrid high-efficiency welding, Narrow-Gap Gas Metal Arc Welding, and Deep Penetration Gas Metal Arc Welding, accompanied by a detailed elaboration on auxiliary high-efficiency measures. This article systematically reviews the arc behavior, droplet transfer behavior, and the influence of residual stress distribution on weld formation and mechanical properties in high-efficiency gas-shielded welding processes utilizing various advanced welding methods. The mechanisms behind typical defects, such as pores, undercutting, and cracks, are elucidated, and corresponding mitigation strategies are summarized. The existing high-efficiency melting electrode gas-shielded welding technology has been widely applied in fields such as automobile manufacturing, shipbuilding, and pipeline welding, resulting in significant economic benefits. In response to the evolving demands of intelligent manufacturing, future research should prioritize the development of real-time monitoring, adaptive control systems, and cost-effective automation solutions for high-efficiency GMAW processes. By constructing high-precision process models, the advancement of efficient welding technology can progress towards greater intelligence and reliability, thereby providing more competitive solutions for industrial manufacturing.

Metals doi: 10.3390/met16090946

Authors: Yu Guo Mingyuan Xiong Changshi Huang Jingjing Li Shaoming Liu Dan Song

The coarse-grained heat-affected zone (CGHAZ) is a critical brittle region in welded reactor pressure vessel steels, and phosphorus segregation at prior-austenite grain boundaries can further impair its low-temperature toughness during long-term service. Although phosphorus-induced embrittlement has been established for SA508-4N base metal, the quantitative relationship between grain-boundary phosphorus segregation and the ductile-to-brittle transition temperature (DBTT) in the CGHAZ—and the role of its distinct bainitic microstructure relative to the base metal—remains insufficiently understood. Here, a CGHAZ was simulated in P-doped SA508-4N steel and thermally aged at 500, 530, and 560 °C to establish different equilibrium segregation levels. Optical metallography, Vickers hardness testing, Charpy impact testing, and Auger electron spectroscopy were used to correlate microstructure, hardness, DBTT, and grain-boundary phosphorus concentration. As the aging temperature increased from 500 to 560 °C, the grain-boundary phosphorus concentration decreased from 21.40 to 18.46 at. %, while the DBTT decreased from −53 to −91 °C. The nearly unchanged hardness excludes hardening as the principal cause, demonstrating that the toughness variation is governed predominantly by non-hardening embrittlement associated with phosphorus segregation. The DBTT exhibited a strong positive linear correlation with the equilibrium grain-boundary phosphorus concentration. Moreover, at a comparable prior-austenite grain size, hardness, and phosphorus segregation level, the CGHAZ showed a higher DBTT than the base metal, which is attributed to the lower crack-deflection capability of tempered bainite compared with tempered martensite. These results fill the quantitative gap linking phosphorus segregation to CGHAZ embrittlement and provide a basis for assessing the long-term integrity of SA508-4N welded joints.

Metals doi: 10.3390/met16090945

Authors: Wei Xiong Yong Jiang Fatang Tan

A large amount of germanium-containing waste is generated during optical fiber preform production, representing a critical secondary germanium resource. To address recovery challenges from low germanium content, high silicon content and complex occurrence states in optical fiber solid waste, this study proposes a short-flow clean hydrometallurgical process based on low-modulus alkaline leaching coupled with direct adsorption using customized meglumine resin. Results show that under low-modulus (M = 1) strong alkaline conditions, the system achieved a maximum germanium release concentration of 331.25 mg/L and exhibited excellent anti-gelation stability. The self-synthesized alkali-resistant NMG resin was applied for direct adsorption in raw M = 1 leachate without pH adjustment. The adsorption process follows pseudo-second-order kinetics and the Langmuir isotherm, with a maximum theoretical adsorption capacity of 3.529 mg/g. Spectral analysis indicates that the ortho-cis-diol groups of the resin can specifically chelate with germanate, overcoming competitive interference from strong alkali and high silicon. This process provides a theoretical basis for the green recycling of high-silicon germanium-containing secondary resources.

Metals doi: 10.3390/met16090944

Authors: Ziqi He Yufei Pan Penghui Guo Jiale Song Xuhui Lin Ke Ma Donghui Wei Xiangdong Xing Shan Ren

Vanadium slag is an important secondary vanadium resource. Although microwave-assisted calcification roasting improves the leachability of vanadium-bearing phases, further extraction can still be limited during acid leaching, making optimization of the leaching process essential for efficient vanadium recovery. Using this slag, leaching was evaluated at different temperatures, times, liquid-to-solid ratios (L/S), sulfuric acid concentrations, and agitation speeds. A Box–Behnken design (BBD) was used to optimize leaching parameters within the selected ranges. Residue phase composition and microstructure were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). Leaching efficiency increased with temperature, L/S, and acid concentration, but plateaued above 60 °C, 6 mL·g−1, and 14 wt.%, respectively; increases beyond 50 min or 200 rpm gave marginal improvements. Analysis of variance (ANOVA) of the BBD model ranked the statistical effects of the four linear terms within the investigated BBD range as sulfuric acid concentration > L/S > leaching time > temperature. Within the selected BBD parameter ranges, optimization yielded 64.95 °C, 55.21 min, 6.56 mL·g−1, and 15.17 wt.% sulfuric acid, with agitation fixed at 200 rpm. Validation gave an average leaching efficiency of 92.92%, with a relative error of 0.205% compared with the model prediction. After leaching, Mn2V2O7 was undetected. The residue mainly contained irregular particles, 10–30 μm acicular or plate-like CaSO4·2H2O crystals, and minor residual vanadium-bearing CrVO3 and CaVH2Si4O12 phases. Surface CaSO4·2H2O deposition and refractory-phase encapsulation of vanadium-bearing constituents increased mass-transfer resistance and limited further leaching. This study clarified the relative effects of the investigated leaching conditions on vanadium leaching efficiency within the design range and the interactions among these conditions, and provided microstructural evidence related to the factors limiting further vanadium leaching, thereby providing theoretical guidance for the efficient extraction of vanadium from vanadium slag.

Metals doi: 10.3390/met16090943

Authors: Rethinam Vignesh Shivraj Gahir Abhishek Agarwal Uthappan Karthick Jose Immanuel

Magnesium alloys are attractive for temporary orthopaedic applications because of their biodegradability and favourable mechanical properties; however, their relatively rapid degradation under physiological conditions remains a challenge. In this study, the microstructural evolution, residual stress and electrochemical corrosion behaviour of WE43, a rare earth-containing magnesium alloy with yttrium, neodymium and zirconium as alloying elements, coated with titanium, were investigated as functions of deposition time using direct-current magnetron sputtering. Titanium coatings were deposited for 1, 1.5, 2 and 3 h, producing coating thicknesses of approximately 500, 650, 1000 and 1400 nm, respectively. Field-emission scanning electron microscopy, atomic force microscopy and grazing-incidence X-ray diffraction revealed progressive changes from fine-grained to dense and, subsequently, coarse-grained morphologies with increasing deposition time. The 2 h coating exhibited the largest crystallite size (27.17 ± 3.42 nm) and a moderate compressive residual stress of 605.3 ± 15.11 MPa. Potentiodynamic polarisation measurements showed that the 2 h coating produced the lowest corrosion current density (0.133 ± 0.026 mA/cm2) and calculated corrosion rate (2.93 ± 0.57 mm/year), representing a 67% reduction relative to independently measured, uncoated WE43 (8.87 ± 1.11 mm/year). The 3 h coating exhibited a higher compressive residual stress of 992.4 ± 21.7 MPa and a higher corrosion rate of 4.81 ± 0.74 mm/year, accompanied by localised microcracking after corrosion testing. Contact-angle measurements performed on the uncoated alloy and the 2 h coating showed an increase from 75.0 ± 2.1° to 83.0 ± 1.8°. Overall, the results indicated that corrosion performance was governed by the combined effects of coating morphology, crystallographic development and residual stress, with the 2 h deposition condition providing the most favourable balance under the present experimental conditions.

Metals doi: 10.3390/met16090942

Authors: Chang-Jeong Kim Yeon-Jun Chung Jei-Pil Wang

The increasing use of electric vehicles has led to a growing demand for rare-earth elements, particularly neodymium (Nd), which is a critical component of Nd–Fe–B permanent magnets used in traction motors. End-of-life electric vehicle motors are therefore considered promising secondary resources for Nd recovery. In this study, a pyrometallurgical process using non-ferrous smelting slag as a flux was proposed for recovering Nd from Nd–Fe–B magnets contained in waste electric vehicle motors. Steel and magnet fractions obtained from a dismantled motor were melted at approximately 1600 °C under an air atmosphere, and Fe2O3 was added as an oxidizing agent to promote the selective oxidation of Nd. The oxidized Nd was subsequently partitioned into the slag phase as Nd2O3 through metal–slag separation. The effects of the slag flux addition ratio, Fe2O3 content, slag flux type, and crucible material on Nd recovery behavior were systematically investigated. Increasing the fayalite-based slag flux addition enhanced Nd transfer into the slag phase, and the highest Nd recovery of approximately 80% was obtained at a slag flux addition ratio of 30 wt%. The addition of 2 wt% Fe2O3 was found to be suitable for promoting stable Nd oxidation and efficient slag–metal separation. The non-ferrous smelting slag exhibited chemical and phase characteristics comparable to those of synthetic fayalite slag flux, resulting in similar Nd recovery performance. In addition, the crucible material significantly affected the process stability and Nd recovery behavior. Although a carbon crucible showed relatively high Nd recovery, severe slag foaming and crucible erosion occurred during melting. In contrast, alumina and MgO crucibles provided stable process conditions with comparable Nd recovery behavior, whereas zirconia crucibles caused relatively higher Nd loss. These results demonstrate that non-ferrous smelting slag can be effectively used as a flux for the pyrometallurgical recovery of Nd from end-of-life electric vehicle motors, offering a potential route for sustainable rare-earth recycling.

Metals doi: 10.3390/met16090941

Authors: Guomu Chen Tingfang Xie Botao Gao Runan Jia Lei Gao Xiaolei Ye Shenghui Guo Li Yang

To address the core industrial bottlenecks of conventional batch tannic acid-based germanium precipitation processes—high reagent consumption, long reaction cycles of several hours, severe impurity co-precipitation as well as the common mismatch between single-channel microreactor throughput and industrial production demands. This work combines numerical simulation with experimental validation to investigate microscale two-phase flow regulation, high-throughput microreactor optimization, and tannic acid precipitation intensification. Two-dimensional two-phase flow models are established for straight and zigzag microchannels, with the level set method applied to track interfacial evolution. The regulatory effects of inlet velocity and channel geometry on flow patterns, droplet behavior and mixing performance are clarified. Zigzag channels induce chaotic convection via periodic corners, achieving an order-of-magnitude improvement in mixing efficiency at low Reynolds numbers (Re < 400), which lays a fundamental basis for reaction intensification. Taking zigzag channels as core units, a bidirectional symmetric superposition scale-up strategy is proposed to break the throughput limitation of single-channel systems, and a 3D-printed high-throughput microreactor integrating 78 parallel zigzag channels is designed. 3D simulations reveal a three-stage mixing mechanism and uniform flow distribution among parallel channels, with total throughput two orders of magnitude higher than a single channel. Single-channel experiments with industrial germanium-bearing raffinate yield 91.81% precipitation efficiency under optimal conditions, reducing the reaction residence time from hours in conventional batch processes to the second scale. Staged reagent addition and two-stage serial configuration further raise the efficiency to ~98%, realizing deep germanium recovery with significantly improved reagent utilization and reduced impurity co-precipitation. This process achieves efficient intensification of the chelation precipitation process while balancing throughput and mixing performance, providing a novel and technically feasible approach for efficient low-consumption germanium recovery, and offering solid technical support for the industrial application of microreactors in the hydrometallurgy field.

Metals doi: 10.3390/met16090940

Authors: Alibek Baisanov Nina Vorobkalo Askhat Akuov Yerulan Samuratov Amir Makishev Symbat Sharieva Zhanna Ibrakhimova

The beneficiation of ferruginous manganese ores is limited by the intimate intergrowth of manganese-, iron-, and silicate-bearing phases. This study evaluated coal-based magnetizing roasting followed by dry magnetic separation in an externally heated chamber furnace with a charge capacity of up to 100 kg. A 0–5 mm ore fraction with an initial Mn/Fe ratio of 2.9 was roasted with Shubarkol coal. The best separation was obtained at an actual ore–coal bed temperature of 550–600 °C and an ore-to-coal mass ratio of 1:0.4. Relative to the magnetic-separation feed, 80.0–83.4% of Fe was recovered in the magnetic fraction, while 69.9–72.6% of Mn remained in the non-magnetic product. Its Fe content decreased to 3.2–3.5%, increasing the Mn/Fe ratio to 7.30–7.84. X-ray diffraction showed preferential concentration of magnetite and jacobsite in the magnetic fraction, whereas hausmannite and braunite were concentrated mainly in the non-magnetic fraction together with the gangue phases. Multipoint measurements also demonstrated a substantial difference between the combustion-zone and actual bed temperatures. The results demonstrate that controlled low-temperature roasting can generate sufficient magnetic contrast for selective iron removal from ferruginous manganese ore.

Metals doi: 10.3390/met16090939

Authors: Zhisheng Shi Guanyong Sun Qi Liu

Effective iron removal from highly acidic leachates without neutralizer addition is a long-standing challenge in hydrometallurgy. For Cu-Co-bearing pyrite cinder, we demonstrate that a cyclic leaching process achieves this outcome. Operating entirely without neutralizers, the process consumed 96% of residual acid, enriched Cu and Co 4.76- and 3.88-fold, and removed 48.2% of iron, all while maintaining pH below 1.5 across four closed-loop cycles. Thermodynamic analysis reveals that Fe3+-SO42− complexation suppresses free Fe3+ to approximately 10−8 mol/L, ruling out conventional hydrolytic precipitation and directing precipitation towards schwertmannite-type basic ferric sulfate (Fe8O8(OH)6SO4). The formation of this sulfate-bearing Fe precipitate is consistent with the thermodynamic analysis, the iron mass balance, and a 176% increase in solid-phase sulfur. This neutralizer-free strategy offers a sustainable paradigm for recovering critical metals from iron-rich secondary resources.

Metals doi: 10.3390/met16080938

Authors: Zengwei Ji Lang Guo Liqin Wang Yanni Ma Ren Li Zeduan Pan Xing Zhao

This study investigates the atmospheric corrosion behavior of high-lead bronze alloys within a simulated aggressive environment characterized by high humidity, acidity, chlorides, oxygen, and CO2. The evolution of surface morphology and corrosion products was systematically monitored using colorimetric analysis and micro-Raman spectroscopy. Results indicate that the initial patina primarily comprised cuprite (Cu2O) and cassiterite (SnO2), which are predominantly benign phases. During the early corrosion stage, lead oxidation and carbonation prevailed, generating abundant bright-white cerussite. Subsequently, as copper-driven corrosion became dominant, these white deposits diminished and were progressively replaced by characteristic green “bronze disease”, identified as atacamite (Cu2(OH)3Cl). The findings reveal that preferential lead corrosion is likely to induce localized pitting, thereby accelerating degradation of the copper substrate. Consequently, higher lead content may reduce the overall corrosion resistance of bronze artifacts under these specific conditions. These results offer experimental insights into atmospheric corrosion mechanisms and inform the development of evidence-based conservation strategies for bronze cultural heritage.

Metals doi: 10.3390/met16080937

Authors: Zong Guo Zhenyu Wang Zhixing Qin Tao Li Haibei Wang Yunchuan Ma Yun Li Guang Fu Hao Ma Chaozhen Zheng

Germanium is a critical rare-dispersed metal with irreplaceable applications in infrared optics, fiber-optic communications, and semiconductor industries, making its efficient recovery from secondary resources of great strategic importance. This study investigates the selective recovery of germanium from complex zinc smelting leachates using a novel hydroxamic acid extractant, BGYW, in synergistic combination with P204. The feed solution contained approximately 360 mg/L Ge, 10,790 mg/L Fe2+, and 98,530 mg/L Zn, representing a highly complex matrix. Continuous counter-current extraction was performed in a 30-stage miniature mixer-settler. Under optimized conditions of 10% BGYW + 5% P204 in white oil, an O/A ratio of 1:1, and 8 mol/L NH4F as strippant, the single-stage germanium extraction efficiency reached 99.4%. Over 16 consecutive cycles, the extraction system maintained stable performance with average germanium extraction above 99%. A 3-stage scrubbing section using 50 g/L H2SO4 effectively removed co-extracted Zn, Cu, and Al impurities. Iron co-extraction, a major challenge, was successfully mitigated through a 2–3 stage iron scrubbing step using a chloride-containing scrubbing solution, which reduced the iron concentration in the strip liquor from approximately 600 mg/L to below 4 mg/L, and decreased the Fe/Ge mass ratio from 0.197 to below 0.01. The overall germanium recovery across the entire 30-stage continuous process reached 98.82%, and the dissolution loss of BGYW in the aqueous phase was reduced by over 85% compared to the conventional YW100 extractant. Third-phase formation caused by residual organic flocculants from the leaching step was eliminated through enhanced pre-treatment, while ferric fluoride precipitation in the stripping section was resolved by incorporating the iron scrubbing stage. This study demonstrates that the BGYW-P204 extraction system with the integrated iron scrubbing step offers an efficient, stable, and industrially viable approach for germanium recovery from zinc smelting leachates, providing a practical solution to the long-standing challenge of germanium–iron separation and contributing to the sustainable supply of this critical metal.

Metals doi: 10.3390/met16080936

Authors: Hui Wang Shuxin Bo Chen Yuan Shouwei Xu Guanyu Deng Yu Liu Rui Wang

The grain refinement of high-stacking-fault-energy metals during high-pressure torsion (HPT) is governed by dislocation activity and boundary evolution. However, how local misorientation evolves during different stages of grain refinement remains insufficiently clarified. In this study, AA1050 aluminium was processed by HPT to selected equivalent strains of 0, 0.90, 2.69, 10.76 and 53.78, and electron backscatter diffraction (EBSD) was used to analyse grain morphology, boundary fractions and EBSD-derived misorientation parameters. The results reveal strongly stage-dependent grain refinement during HPT. The average grain size decreases rapidly from 12.63 μm in the initial state to 3.29 μm at ε = 0.90 and 2.19 μm at ε = 2.69, remains nearly unchanged at ε = 10.76, and finally decreases to 0.58 μm at ε = 53.78. The fraction of low-angle grain boundaries increases markedly at ε = 0.90, indicating intensive formation of dislocation substructures, whereas high-angle grain boundaries become dominant at high strain. Grain orientation spread (GOS) and grain reference orientation deviation (GROD) exhibit non-monotonic evolution, whereas the geometrically necessary dislocation (GND) density increases markedly at the early deformation stage and subsequently decreases with further deformation. These results indicate that the stage-dependent grain refinement of AA1050 during HPT is closely associated with dislocation-mediated grain subdivision involving alternating grain elongation and fragmentation.

Metals doi: 10.3390/met16080935

Authors: Xian Meng Hao Xu Haochen Li Jinwen Cao Jinyue Geng Cong Yan Xiang Cheng Heji Huang

Molybdenum (Mo), owing to its excellent properties, is widely used as a plasma-facing material and is recognized as a typical difficult-to-machine material. Achieving high-quality, low-damage machining is essential for ensuring the service reliability of Mo components. However, studies on the milling of Mo remain limited. Therefore, this study investigates a high-quality, low-damage milling technique for Mo based on analyses of milling force, machined surface roughness, and white layer formation. First, the effects of machining parameters, including radial depth of cut (ae), spindle speed (n), and feed per tooth (fz), on the responses, namely milling force (F) and surface roughness (Ra), were investigated. The relationships between milling force, surface roughness, and white layer formation were analyzed. Subsequently, the response surface methodology (RSM) was employed to reveal the influence mechanisms of the machining parameters and their interactions on the response variables. Finally, a Kriging surrogate model integrated with the Non-dominated Sorting Genetic Algorithm II (NSGA-II) was adopted to identify the optimal machining parameter combination for high-quality, low-damage milling. The results indicate that the milling force and white-layer thickness exhibit consistent increasing trends with increasing feed per tooth under the investigated conditions, demonstrating that controlling the milling force is an effective approach for achieving high-quality, low-damage milling of Mo. For the simultaneous minimization of milling force and surface roughness, the optimal machining parameters were determined to be a radial depth of cut of 0.2101 mm, a spindle speed of 10,090.7 rpm, and a feed per tooth of 0.01 mm/z. These findings provide valuable process parameter guidance for the precision machining of Mo components.

Metals doi: 10.3390/met16080934

Authors: Haitao Xie Zhiwei Liang Di Mei Aiyue Zhang Chenchen Jiang Qingshan Du Yang Xiao Shijie Zhu Liguo Wang Chujie Liu Jinxue Liu Shaokang Guan

Mg-Gd-Y-Zr alloys, with strong age-hardening and thermal stability, are ideal for lightweight load-bearing components, yet forming large complex parts is limited by high sensitivity to hot deformation parameters. This work investigates the hot deformation behavior and microstructure evolution of a Mg-9Gd-4Y-0.5Zr (wt.%) alloy via hot compression at 400 to 510 °C and strain rates of 0.001 to 10 s−1. An Arrhenius constitutive equation with an activation energy Q of 158.63 kJ/mol was established, and a hot processing map was constructed. EBSD characterization revealed the dynamic recrystallization, grain size evolution, and texture transition. The results show that flow stress depends strongly on temperature and strain rate. At strain rates of 0.001~1 s−1, a dynamic balance between work hardening and dynamic softening is achieved, and the post-peak flow stress gradually stabilizes. At a high strain rate of 10 s−1, the flow stress continues to decrease because the competition between softening from dynamic recrystallization and work hardening is disrupted by deformation-induced heating. Low strain rates (≤0.01 s−1) and high temperatures (≥470 °C) promote dynamic recrystallization and significant grain refinement. Two optimal processing windows were determined: 400 to 430 °C at 0.001 to 0.01 s−1, giving fully recrystallized fine equiaxed grains, and 440 to 460 °C at 0.01 to 0.1 s−1 with a power dissipation efficiency η of 0.43 to 0.51, balancing processing efficiency and microstructural uniformity. This work provides systematic theoretical and data support for optimizing hot forming parameters of large Mg-Gd-Y-Zr load-bearing components and offers guidance for applying high-strength magnesium alloys in high-end equipment.

Metals doi: 10.3390/met16080932

Authors: Yi Feng Guangjie Huang Kejian Li Wei Li Hongzhou Lu Cansheng Yu Hui Song Jianing Bao Junping Zhang Jie He

To investigate the effect of microalloying on hydrogen embrittlement resistance of hot-stamped steels with strength levels of 1.8 GPa and above, six composition schemes were designed based on conventional 34MnB5 steel, including three routes, namely Nb, V, and Nb–V. U-bend constant-strain bending tests and slow strain rate tensile (SSRT) tests were conducted on quenched specimens for each scheme. Results indicated that the Nb-containing compositions exhibited superior hydrogen embrittlement resistance. The mechanism by which microalloying refines the martensitic microstructure of 34MnB5 in the quenched state and enhances its resistance to hydrogen embrittlement was studied in detail. It was found that Nb exhibits stronger effects than V in refining and homogenizing the martensite structure. The fundamental reasons for Nb’s enhanced ability to pin austenite grain boundaries at high temperatures—leading to better microstructural refinement and homogenization—are its higher temperature range for second-phase precipitation, greater driving force for grain boundary diffusion, lower austenite grain boundary diffusion coefficient, and weaker tendency for high-temperature coarsening of precipitates. The microstructural refinement and homogenization induced by Nb addition are more pronounced than those achieved by combined additions of Nb and V. Furthermore, within the concentration range of 0–0.1%, the amount of Nb is positively correlated with the degree of microstructural refinement and homogenization. By reducing martensite lath size through microalloying, multiple microstructural modifications occur: decreased density of geometrically necessary dislocations (GNDs) in the matrix, significant increase in interface density—especially a higher proportion of high-angle grain boundaries—reduced number of Σ3 special harmful grain boundaries, weakened matrix texture intensity, fewer twin martensites, and smaller twin martensite sizes. These factors collectively contribute significantly to the improved hydrogen embrittlement resistance of Nb-containing steels.

Metals doi: 10.3390/met16080933

Authors: Saurabh Tiwari Hyoju Ahn Jongwon Lee Nokeun Park

Industrial steel property prediction is often constrained by limited labelled data, reducing the effectiveness of conventional machine learning models. This study investigated whether metallurgy-informed feature engineering enhances predictive performance under small-data conditions. A representative set of 300 samples from an industrial low-carbon hot-rolled steel strip dataset (C: 0.02–0.06 wt%; Mn: 0.17–0.38 wt%) was used to derive five physically meaningful descriptors: carbon equivalent (CE), nitrogen-to-aluminum ratio (N/Al), microalloying efficiency index (MEI), thermal processing parameter (TPP), and solid solution strengthening index (SSSI). These descriptors were combined with the original 17 compositional and processing variables to create a 22-feature dataset. Random Forest (RF) and Extreme Gradient Boosting (XGBoost) models were evaluated on an independent 60-sample test set using 5-fold cross-validation. Feature engineering improved the prediction accuracy, with the greatest gain observed for elongation. For XGBoost, the mean percentage error decreased from 3.23% to 3.05%, whereas the test-set R2 increased from 0.4935 to 0.5444, representing a 10.3% improvement in the explained variance. For the yield strength, the Random Forest method increased the R2 from 0.4744 to 0.4861. Permutation importance and partial dependence analyses identified MEI and TPP as the six most influential predictors across all targets, confirming that the engineered descriptors provide complementary metallurgical information. Learning curve analysis showed slightly higher cross-validation R2 values at intermediate training sizes (n = 125–175), indicating modestly improved sample efficiency. These findings establish domain-informed feature engineering as an interpretable and practical strategy for improving machine learning in data-limited steel manufacturing processes.

Metals doi: 10.3390/met16080931

Authors: Olena Shved Vasyl Girzhon Oleksandr Smolyakov Ihor Shtablavyi Philipp Dörflinger Helmut Riedl Andrey Prokofiev Stepan Mudry

The structure, mechanical and electrical properties of Zr-based melt-spun Zr–(Al)–Ni–Cr–Ag alloys were investigated as a function of elemental composition. X-ray diffraction reveals the structural evolution from fully amorphous to nanocrystalline states, with the latter containing Zr2Ni “big-cube” (space group Fd3̄m, cF96), fcc-Zr2Ni, and β-Zr phases depending on the alloying ratio: Cr-rich compositions (≥15 at.%) stabilize β-Zr within the amorphous matrix, whereas Ag-enriched alloys promote “big-cube” phase formation. Ag atoms can replace both Zr and Ni sites in the “big-cube” lattice, yielding a (Zr,Ag)2(Ni,Ag) solid solution and highlighting its role as a structural bridge between the amorphous and crystalline states. Nanoindentation measurements show that hardness increases from 6.5 GPa in fully amorphous ribbons to 10.12 GPa in three-phase nanocrystalline composites, with an H/E ratio of ~0.08 indicating predominantly covalent bonding, and the fracture strength of the amorphous alloys is ~2 GPa, exceeding literature values for related Zr-based systems. Electrical resistivity measurements over the 4–298 K range show that most alloys deviate from Matthiessen’s rule, exhibiting a negative temperature coefficient of resistivity consistent with the Mooij correlation; the presence of the icosahedrally ordered “big-cube” phase further increases resistivity relative to fully amorphous alloys.

Metals doi: 10.3390/met16080930

Authors: Kai Tao Hanbin Chen Fangzi Zhao Shiqi Li Zhiyong Liu

Flexible transparent conductive films with symmetric and asymmetric multilayered structures are studied using the ZnS–TiO2–Ag material system, in order to capitalize on the divergent properties of the two dielectric layers for improved performance. The dielectric/metal/dielectric-structured films were deposited by magnetron sputtering sequentially, with high-purity targets. Multilayered films with various dielectric combinations and metallic layer thicknesses were prepared and analyzed. The surface morphology and phase structure were characterized by atomic force microscopy and scanning electronic microscopy. The optical properties were tested by spectrophotometry and analyzed by numerical simulation approach. The sheet resistance was measured via a four-point probe tester. Among the series of multilayers, asymmetric ZnS/Ag/TiO2 film with 35 nm thickness of dielectric layers and 8.5 nm of metallic layer possesses the optimum comprehensive optoelectronic performance. The average light transmittance reaches 90.72% in the visible spectrum, and the sheet resistance is 7.69 Ω/sq. The good result is ascribed primarily to the combined advantages of superior percolation effect of bottom ZnS layer on ultrathin Ag layer, beneficial impingement effect of top layer deposition on the metallic layer, and excellent surface smoothness of the top dielectric layer.

Metals doi: 10.3390/met16080928

Authors: Samuel Castro-Lopes Ivanilda Ramos de Melo Viviane Drumond Rodrigues José Anselmo da Silva Neto Emanoel Araújo Marcelo Medeiros Severino Leopoldino Urtiga Filho Tiago Felipe de Abreu Santos Cinthia Pederneiras Romildo Berenguer

This research investigates the potential for valorizing submerged arc welding (SAW) slag as a partial substitute for Portland cement in eco-efficient mortars. The research focuses on microstructural characterization, mechanical performance, and, innovatively, resistance to microbial adhesion by Escherichia coli. The residue was processed by grinding and incorporated at substitution levels of 5%, 10%, and 15% by weight. The mechanical results demonstrate that the 5% substitution (AM5%) showed the best performance, reaching 47.55 MPa at 28 days, an increase of approximately 20% compared to the reference sample. This improvement is attributed to the pozzolanic effect with the filling and refinement of the pore structure, in the production of the secondary C-A-S-H phase. In the bioreactor biological assay, the AM5% sample demonstrated a significant reduction in bacterial colonization adhering to the material’s surface, with values of 9.4 × 101 CFU/cm2. Scanning electron microscopy (SEM) analyses revealed that the denser surface, with lower porosity, hindered the anchoring of E. coli and the formation of biofilm. The study concludes that the use of 5% SAW slag not only improves the structural properties of mortars but also increases their durability in environments prone to biological contamination, such as sanitation systems, promoting a sustainable alternative for the management of industrial waste in civil construction.

Metals doi: 10.3390/met16080929

Authors: Vera Tolokonnikova Sailaubai Baisanov Amankeldy Ahmetov Yerbolat Makhambetov Olzhas Kenzhaliyev Alexey Orlov

Carrying out a series of fundamental studies in the field of physicochemical analysis, based on an approach that considers the phase state of alloys and accounts for the regular patterns of interaction of substances in multicomponent ores that are complex in both chemical and phase composition, makes it possible to formulate a number of scientifically substantiated practical recommendations. The aim of this work is to assess the degree of zinc sublimation from a magnesium alloy through the behavior of the Bjerrum–Guggenheim osmotic coefficient and the degree of dissociation of the congruent compound. The paper presents a method for processing phase equilibrium lines in a temperature–composition phase diagram, resulting in mathematical expressions for the liquidus and solidus lines on a unified analytical basis in the form of a semi-empirical dependence derived from the Schröder–Le Chatelier equation. Indirectly, through the Bjerrum–Guggenheim osmotic coefficient, the degree of dissociation of MgZn2 in the Mg–Zn system was determined to range from 17% to 46%. This result is in good agreement with the conclusions of Nikolay Semyonovich Kurnakov regarding the degree of dissociation of congruent compounds inferred from the shape of the maximum on phase diagrams. For MgZn2, this maximum is very smooth, i.e., the composition of the liquid phase changes continuously with deviation from stoichiometry, resulting in a symmetrical rounded peak. An experimental study was carried out using a SEM/EDS analytical complex to confirm the high volatility of zinc. The key zinc-concentrating phases were identified in the investigated processing products (slag, metal, and dust), which is consistent with the theoretical premises and explains the mechanism of zinc behavior during high-temperature processing of zinc-containing slags. The form of zinc occurrence in different phases was established. In the initial slag, the zinc content reaches 51.79%. In the metallic phase, zinc is detected as fine dispersed inclusions. In the collected dust (flue ducts), particles enriched in zinc up to 44.09 wt.% were identified.

Metals doi: 10.3390/met16080927

Authors: Gen Li Deqing Zhu Jian Pan Qingshi Song Wei Liu Ming Wang

Limonitic nickel laterite is difficult to sinter because of its high loss on ignition, high combined-water content, and complex refractory mineral composition, which often result in poor sinter strength and high solid fuel consumption. In this study, a pellet-sintering process was adopted to improve the sintering performance of limonitic nickel laterite. Pot sintering tests were carried out to investigate the effects of key process parameters—including moisture content, solid fuel dosage, return fines dosage, and drying–holding regime—on yield, tumble index, productivity index, and solid fuel consumption. The selected conditions were determined as follows: moisture content of 21%, solid fuel dosage of 5.8%, return fines dosage of 25%, drying at 450 °C for 5 min, and holding at 1000 °C for 10 min, under a fixed basicity of 1.5 and a bed height of 850 mm. Under these conditions, the yield, tumble index, productivity index, and solid fuel consumption reached 70.19%, 57.87%, 1.37 t·m−2·h−1, and 95.86 kg·t−1, respectively. Compared with conventional sintering, pellet sintering increased the yield, tumble index, and productivity index by 24.05%, 35.56%, and 31.73%, respectively, while reducing solid fuel consumption by 22.87%. XRD, OM, quantitative image analysis, and SEM–EDS analyses showed that pellet sintering reduced the average two-dimensional pore area fraction from 33.29% to 18.05% and the large-pore area fraction from 22.25% to 11.61%, while promoting a more continuous bonding structure characterized by a spinel-rich mineral framework, spinel–olivine eutectic-type composite bonding phases, and SFCA-type bonding phases. These results demonstrate that pellet sintering is a feasible route for improving the sintering performance and consolidation behavior of limonitic nickel laterite.

Metals doi: 10.3390/met16080926

Authors: Yiming Li Bihui Hong Wenbin Li

This study presents a systematic investigation into the mechanical responses of two tungsten-based alloys—84W–11.2Ni–4.8Fe and 88W–8.4Ni–3.6Fe—fabricated via selective laser melting (SLM). Quasi-static compression tests using a universal testing machine and dynamic impact experiments employing a split Hopkinson pressure bar (SHPB) were conducted over a temperature range of 298–598 K and strain rates spanning from 1 × 10−3 s−1 to 2.3 × 103 s−1. Both alloys exhibited significant strain-rate hardening and thermal softening effects. Based on the experimental data, a Johnson–Cook (J–C) constitutive model was established. The fidelity of the calibrated model for the 84W alloy was rigorously validated through pulsed X-ray radiography and static armor penetration tests. The SLM-fabricated 84W-shaped charge liner produced a well-collimated jet with a tip velocity of 5101.5 m/s and achieved a penetration depth of 87 mm into rolled homogeneous armor (RHA)-equivalent steel targets. Numerical simulations using the developed J–C model showed close agreement with experimental measurements, with a maximum discrepancy of only 9.19%, thereby confirming the predictive capability of the constitutive model. These results demonstrate that the proposed J–C model can reliably characterize the large-deformation behavior of SLM-processed 84W and 88W liners under the extreme thermomechanical conditions characteristic of shaped charge jet formation—namely high temperature, high pressure, and ultra-high strain rate. Collectively, this work establishes a foundational framework for the application of SLM technology to shaped charge liner design and provides a critical basis for further research into jet formation physics and penetration mechanics of tungsten-based alloys.

Metals doi: 10.3390/met16080924

Authors: Wei Li Liming Zhou

Dissimilar resistance spot welding of Al-Si-coated B1500HS hot-stamped steel to HC340/590DP dual-phase steel suffers from a narrow process window and HAZ temper softening. A sequential orthogonal-central composite design strategy screened factors and constructed local second-order models for nugget diameter and tensile-shear force. Because the complete tensile-shear CCD dataset is unavailable for independent verification, the tensile-shear model is used strictly as an auxiliary local calibration and is not assigned the same validation level as the nugget-diameter model. Within-batch ANOVA showed that electrode force dominated diameter variation and first-pulse current dominated force variation. A model-assisted variance-aware compromise (7.8/8.5 kA, 2.9 kN, 13/17 cycles) was point-wise validated at 6.5065 ± 0.1366 mm and 15.053 ± 0.1899 kN (n = 20, CV 2.10%/1.26%). The measured performance-optimal orthogonal condition remained Run 11; thus, the compromise is interpreted as a stability-oriented choice rather than a global optimum. A joint-specific HAZ screening envelope (width < 0.7 mm; hardness loss < 50%) is proposed as a descriptive screening criterion only; because HAZ width and microhardness were not measured for the n = 20 validation condition, the envelope was not validated on that condition and remains conditional on the single-factor HAZ data. The framework integrates process optimization with transparent statistical qualification and reports its model calibration limits.

Metals doi: 10.3390/met16080925

Authors: Yuguang Fan Ning Li Kaifeng Chen Zhi You Xinguo Liu Lijuan Zhu Chun Feng Kai Zhang Tian Wang Hao Qu

The mechanical behavior of S135 and V150 (Mo-V-Nb microalloyed) drill pipe steels was systematically investigated at room temperature (RT) and elevated temperatures (100–300 °C), alongside the microstructural evolution after long-term thermal exposure at 310 °C (200–500 h). V150 steel exhibits a superior RT yield strength (1099 vs. 1012 MPa) relative to S135, attributed to grain refinement and precipitation strengthening from nanoscale MC precipitates. However, at 200–300 °C, S135 steel displays strength recovery due to dynamic strain aging (DSA) facilitated by the formation of Cottrell atmospheres. Conversely, in V150 steel, V and Nb pin free interstitial atoms, suppressing Cottrell atmosphere formation and DSA. Consequently, V150 cannot gain DSA-induced strengthening, resulting in a steeper yield strength decline (a 17.3% drop at 300 °C versus 11.5% for S135). Long-term thermal exposure further reveals divergent microstructural evolution: S135 steel achieves synchronous improvements in strength and ductility via the transformation of coarse M3C into stable alloy carbides and the precipitation of nanoscale Mo-enriched carbides. In contrast, V150 steel undergoes Ostwald ripening and coherency loss of high-volume-fraction nano-MC precipitates, weakening dislocation pinning and accelerating dislocation annihilation, ultimately leading to the simultaneous degradation of strength and ductility. This study elucidates that while Mo-V-Nb microalloying enhances RT strength, it compromises high-temperature mechanical stability.

Metals doi: 10.3390/met16080923

Authors: Yeongsu Ha Seung Yong Lee Bong Cheon Park Su Hwan Kim Jung Kwan Seo

Laser beam welding (LBW) offers low thermal distortion for thin austenitic stainless steel sheets but is sensitive to butt-joint fit-up and edge quality. This study compared machined and sheared joint edges under selected autogenous and ER308L filler-wire LBW conditions. Bead geometry, defects, microstructure, microhardness, tensile properties, and fracture behavior were characterized using conventional microscopy, EBSD-KAM, and three-dimensional digital image correlation (3D-DIC). The machined-edge autogenous condition (LBW-A-M) produced a stable bead with 0.04 mm top underfill and only a small number of internal discontinuities, while its tensile properties remained close to those of the base metal and fracture occurred in the base metal. In contrast, the sheared-edge autogenous condition (LBW-A-S) exhibited 0.24 mm top underfill, 0.18 mm misalignment, multiple pores, and localized strain near the weld, with tensile strength and elongation of 682.31 MPa and 44.04%, respectively. Under the selected filler-wire conditions, no measurable top underfill was observed, although pores remained. Because the autogenous and filler-wire modes used different process parameters and heat inputs, cross-mode differences are condition-specific rather than isolated filler-wire effects. Overall, joint-edge preparation and fit-up control remained important for thin-sheet LBW.

Metals doi: 10.3390/met16080922

Authors: Guangya Hou Jingnan Wei Jianli Zhang Qiang Chen Yiping Tang

The development of lightweight, low-cost, and high-performance non-precious metal electrocatalytic electrodes is critical to advancing the practical implementation of methanol and urea oxidation reactions (MOR and UOR) in next-generation energy conversion systems. Herein, we reported a facile synthesis of a W-Se co-modified porous Ni/Cu paper electrode (W-NiSe/Cup) via synchronous pulse electrodeposition onto filter paper-derived porous Cu foil. The hierarchical porosity and high specific surface area originated from the paper template, while synergistic electronic modulation among Ni, W, and Se enhanced intrinsic catalytic activity. At 0.8 V, the W-NiSe/Cup electrode delivered current densities of 298 mA·cm−2 (MOR) and 305 mA·cm−2 (UOR) with a lower-mass loading, representing 1.29-fold and 1.34-fold enhancements over the Ni/Cup electrode. Furthermore, the electrode exhibited exceptional durability: under chronopotentiometry operation at 100 mA·cm−2 in a 6-fold-concentrated electrolyte (6 M KOH + 3.0 M CH3OH + 1.98 M CO(NH2)2), the operating potentials retained 95.74% (MOR) and 118.05% (UOR) of their initial values after 9 h. This study offers a novel strategy for designing lightweight non-precious metal catalytic electrodes for portable energy devices and also verifies the broad potential of biomass templates in constructing advanced energy electrocatalytic materials.

Metals doi: 10.3390/met16080921

Authors: Jiawei Chen Yufei Pan Penghui Guo Xinyi Li Zhuogang Pang Zhenghua Shen Shan Ren Donghui Wei Xiangdong Xing

To reveal the effect of vanadium content on the viscous flow behavior of vanadium-containing hot metal, viscosity measurements and molecular dynamics simulations were conducted. The viscosity and melting characteristic temperature were measured. The local structures of Fe, V, and C atoms were analyzed using radial distribution functions, average coordination numbers, mean square displacements, and cluster evolution. Both viscosity and melting characteristic temperature increased with vanadium content. At 1300 °C, the viscosity increased from 11.8 to 19.9 mPa·s as the vanadium content increased from 0.20 to 0.30 wt%. The melting characteristic temperature increased from 1242 to 1323 °C. Structural analysis showed that increasing vanadium content promoted the redistribution of C atoms. The average coordination number of V–C increased from 7.780 to 8.218. In contrast, the coordination numbers of C–Fe and Fe–C decreased. The mean square displacements of Fe and C atoms also decreased, indicating that atomic diffusion was suppressed. Cluster evolution further showed that V–C structures could dissociate and recombine with Fe–C and Fe–V units. Therefore, increasing vanadium content reduced the fluidity of hot metal by increasing the melting characteristic temperature, strengthening V–C local coordination, and promoting complex cluster formation.

Metals doi: 10.3390/met16080920

Authors: Zixuan Liu Xin Chen Chengduo Wang Hao Shi Yanghan Li Jiaqiang Yang Ning Luo Qingkui Li Benshuang Sun Jilin He

Hot pressing is a promising technique for fabricating high-density molybdenum (Mo) alloys; however, obtaining low oxygen content remains a significant challenge. In this study, Mo10Cr alloy billets were prepared by hot pressing with nanocarbon addition and a two-step pressurization strategy to reduce the oxygen content. Results show that the relative density of the Mo10Cr alloy increases with hot-pressing temperature and eventually remains above 98%, accompanied by grain growth and an increased degree of solid solution. The incorporation of nanocarbon facilitates in situ oxygen reduction during hot pressing under one-step pressurization, but this deoxygenation process is impeded by the applied pressure. In contrast, the two-step pressurization method effectively reduces the oxygen content of the nanocarbon-added Mo10Cr alloy to 169 ppm while maintaining a low residual carbon level. Furthermore, this approach significantly improves the compositional uniformity of the alloy. It is also observed that increasing the applied pressure promotes densification alongside grain growth. Consequently, the combination of two-step pressurization and in situ nanocarbon deoxygenation presents an effective pathway for fabricating dense, low-oxygen Mo alloys.

Metals doi: 10.3390/met16080919

Authors: Chengyi Wang Libin Yang Wei Wu Guangheng Ji Yuxiang Dai Guoqiang Wei Zhouhua Jiang

Smelting with a high scrap ratio in converters holds significant importance for carbon reduction and emission reduction in the iron and steel industry. Under high scrap ratio conditions, the kinetic and thermodynamic conditions of the molten bath change significantly, leading to considerable differences in the elemental reactions and slag formation patterns during the smelting process. To investigate the reaction characteristics and dephosphorization behavior of the molten bath under different scrap ratios, this study conducted thermal simulation experiments of converter smelting with four scrap ratios (20%, 30%, 40%, and 50%) using a 500 kg induction furnace. Scrap preheating and supplemental heating agents were applied as needed. Slag petrographic analysis was carried out using SEM and EDS. The experimental results indicate that with scrap ratios of 20% and 30%, the carbon–oxygen reaction and slag formation efficiency are relatively high. The dephosphorization rate in the early stage of smelting can exceed 50%, and phosphorus is effectively enriched in the CaO–SiO2 matrix phase, with the highest phosphorus distribution ratio observed at a 30% scrap ratio. In contrast, with scrap ratios of 40% and 50%, the carbon–oxygen reaction is slower, and the dephosphorization rate in the early smelting stage is less than 10%. In the 40% scrap ratio experiment, phosphorus began to accumulate significantly in the dicalcium silicate phase during the mid-smelting stage as the basicity increased. At a 50% scrap ratio, the silicate matrix remained the dominant phase throughout all smelting stages, and no distinct phosphorus-rich phase was formed.

Metals doi: 10.3390/met16080918

Authors: Aiala Urbegain Carlos G. San-Gabino Antonio Santiago Berta Antelo Javier Franco Iñigo Braceras

Cathodic protection (CP) is used in the marine industry to prevent corrosion of metal components in seawater but may also promote biofilm formation. When steel and copper alloy components are in contact, the latter is often subjected to higher applied CP voltages than otherwise required when a steel component is not present. In this study, the protection that CP offers in bronze alloys (RG-10 and CC492K) was assessed, both in controlled laboratory conditions and in real marine conditions in the Bay of Biscay (up to 3000 h), with various temperatures and methods: sacrificial anodes and impressed currents under different voltages. After the exposures, visual, scanning electron microscopy (SEM), X-ray diffraction (XRD) and corrosion rate analyses were performed. The results showed faster biofouling deposition on surfaces with a higher CP voltage, exposed to marine seawater, at the early stages. Subsequently, for longer exposure times, intermediate CP voltages offered less biofouling protection. XRD analyses showed the presence of calcareous compounds (calcite and aragonite), among others. Meanwhile, the corrosion observed in the laboratory was mediated by the amounts of deposited salts, with higher corrosion corresponding to higher CP voltages. Changes in temperature for the same CP voltage caused quantitative and qualitative differences in salt deposition. The higher Pb content of the CC492K alloy compared with the higher Cu and Sn contents of GR-10 did not manifest at the biofouling level, but different corrosion rates were measured (GR-10 < CC492K). Thus, the optimal CP protection conditions for marine and laboratory environments are not the same, because of the different conditions involved.

Metals doi: 10.3390/met16080917

Authors: Linghui Kong Lei Zhang Yi Li Hushtarbek Mametimin Xuyang Liu Jiabing Lei

Ni60/WC composite coatings reinforced with various WC contents were fabricated on 45 steels via high-speed laser cladding. First-principles calculations were adopted to investigate the interfacial characteristics between Ni and WC. The microstructures of the coating were analyzed by a scanning electron microscope (SEM). The microhardness and wear resistance of the coatings were evaluated by a Vickers hardness tester and a friction and wear tester. Theoretical calculations indicate that the C-terminated WC (001) crystal plane achieves the most stable bonding with the Ni (111) surface through the hcp site, with an interface energy of 9.57 J·m−2. The interface is mainly provided by Ni-W metal bonds and Ni-C covalent bonds. The microstructure results show that the WC particles have good metallurgical bonding with the Ni matrix. Thus, the good interface ensures efficient load transfer to hard WC particles. The microhardness rose markedly with the increase in WC content, reaching 760 HV0.2 for the 40 wt.% WC, which is 1.8 times that of Ni60 coatings. Tribological experiments showed that appropriate WC content could significantly improve the wear resistance of the coating.

Metals doi: 10.3390/met16080916

Authors: Yini She Zhiqiang Wang Linye Zhang Zhibin Shen Licheng Ruan Yuxuan Song

In ultra-supercritical (USC) power plants, P92 steel welded joints are continuously subjected to creep-fatigue (CF) loading, rendering them susceptible to premature cracking during service. To investigate the CF interaction behavior, CF tests were performed on P92 steel welded joints at 650 °C under various dwell times. The results indicate that prolonged dwell periods progressively shorten the cycle life. Scanning electron microscopy (SEM) observations reveal that with increasing dwell time, the fracture mechanism of the P92 steel gradually transitions from a fatigue-dominated failure mode to one governed by creep-fatigue interaction damage. Subsequently, nanoindentation was employed to evaluate the hardness (H), elastic modulus (E), and creep deformation, based on which the strain rate sensitivity (m) was estimated and the underlying damage mechanisms were thoroughly discussed.

Metals doi: 10.3390/met16080915

Authors: Qian Sun Junzhong Zou Qi Xiang

To further improve the impact toughness of aged 6082 aluminum alloy, electromagnetic shocking treatment (EST) was applied to IHC (solution treatment + unidirectional compression + peak aging) samples. The mechanical properties and impact toughness of the IHC and EST samples were evaluated through room-temperature tensile tests and Charpy impact tests, respectively. The results indicate that, compared to the IHC samples, the EST samples exhibit higher tensile strength (an increase of approximately 9.4%), greater elongation, and significantly higher impact energy (an increase of approximately 26.5%). Microstructural characterization reveals that, compared to the IHC samples, the EST samples possess a lower dislocation density, a larger grain size, and shorter precipitates. Striped grain boundaries were observed in both IHC and EST samples, but they were considerably more pronounced in the EST samples. This indicates that more distinct interface wetting occurred in the EST samples, which promoted grain growth to some extent, a reduction in dislocation density, precipitate dissolution, and the occurrence of interface bridging. This paper primarily investigates the microstructural evolution within the alloy under EST and discusses how these microstructural changes influence the alloy’s performance, thereby providing a novel approach to enhancing the impact toughness of aluminum alloys.

Metals doi: 10.3390/met16080914

Authors: Qing Zhang Jamile Mohammadi Moradian Jiahao Li Sabereh Nazari Haifeng Wang Yanping Zhang

The rapid growth of tennis participation and the widespread use of lithium-ion batteries have led to increasing volumes of rubber waste and spent battery materials, underscoring the need for integrated recycling strategies. In this work, a thermochemical co-pyrolysis process is developed to convert waste tennis ball rubber particles (TBRPs) and spent lithium-ion battery (LIB) cathodes into valuable products. The decomposition of TBRPs generates reactive gaseous and liquid hydrocarbons that function as in situ reductants, enabling the breakdown of high-valence transition metal oxides in the cathode material. Subsequent magnetic separation and mild acid-washing yield nonmagnetic solids enriched in lithium compounds and carbonaceous residues. Structural and chemical analyses (SEM, XRD, TEM, EDS, and XPS) confirm extensive cathode reduction and the formation of Li2CO3 at optimized conditions (650 °C, 1 h, cathode-to-TBRPs mass ratio 1:0.65). The carbonized rubber evolves into a highly porous carbon material with a carbon purity of approximately 95.37 At%. This study demonstrates a low-energy, environmentally friendly pathway for the co-valorization of two challenging waste streams while simultaneously recovering lithium salts, reduced metal oxides, and functional porous carbon.

Metals doi: 10.3390/met16080913

Authors: Mohammad S. Alsoufi

Abrasive Water Jet Machining (AWJM) is increasingly used for post-weld surface modification of dissimilar metallic joints; however, the depth-dependent surface response of welded stainless–carbon steel joints remains insufficiently quantified. In this study, four dissimilar welded systems, TIG 316, TIG 309, ARC 316, and ARC 309, were systematically investigated to elucidate the combined influence of welding technology, filler composition, and jet parameters on surface integrity. Surface roughness was evaluated at multiple jet-penetration depths using amplitude (Ra, Rq, Rt, Rz) and statistical (Rsk, Rku) descriptors. The results reveal three distinct hydrodynamic erosion regimes governing texture evolution. Duplex welds (TIG 309 and ARC 309) exhibited highly stable erosion behavior, with Ra confined to 1.91–2.99 µm, low roughness gradients (ΔRa/Δdepth = 0.012–0.015 µm·mm−1), and near-Gaussian surface statistics (Rsk ≈ 0, Rku ≈ 3–4). In contrast, austenitic welds (TIG 316 and ARC 316) showed pronounced depth-dependent instability, with Ra increasing up to 4.54 µm and the normalized roughness ratio Rz/Ra reaching 5.69 in TIG 316 near the jet exit. Strong inter-parameter correlations in duplex welds (r ≥ 0.94) confirm uniform erosion kinetics, whereas weakened correlations in austenitic systems (r ≈ 0.70–0.83) reflect jet-energy dissipation. These findings establish a mechanistically grounded AWJM performance window for achieving Ra ≤ 3 µm in dissimilar welded steels.

Metals doi: 10.3390/met16080912

Authors: Zhenchao Han Di Wang Qintian Zhu Hao Qiu Heping Liu

During vacuum induction melting (VIM) of superalloys, oxygen and nitrogen control involves interfacial processes at both the melt free surface and the crucible–melt interface, where melt flow is an important factor affecting reaction kinetics. A coupled electromagnetic and fluid flow model with a deformable free surface was developed and validated for a 3 t industrial VIM furnace with two electromagnetic excitation modes. The melt flow under the Heating and Stirring modes is compared, with particular attention to the role of free-surface deformation, and the effects of input power and filling ratio are further examined. The results show that at an input power of 190 kW and a filling ratio of 85%, the Heating mode produces two counter-rotating vortices separated by a low-velocity mid-region, while the Stirring mode generates a dominant upper vortex covering most of the melt volume with a smaller counter-rotating vortex at the bottom. The Stirring mode achieves approximately 1.3 times the surface velocity, 1.7 times the wall friction velocity, and half the mixing time of the Heating mode. Free-surface deformation significantly affects the predicted flow structure, particularly under the Heating mode. Parametric results further show that input power mainly changes the flow intensity without altering the flow structure under either mode. By contrast, the filling ratio strongly affects the flow structure under the Heating mode, while that under the Stirring mode is largely preserved. These findings provide insight into the melt flow conditions relevant to oxygen and nitrogen removal during VIM processing.

Metals doi: 10.3390/met16080911

Authors: Aristotel Issagulov Aibar Myrzagaliyev Saule Sagintayeva Yerbolat Makhambetov Diana Issagulova Kuanysh Ilyassov

This study investigates the possibility of using aluminosilicochrome (ASC) produced from technogenic raw materials as a potential alternative to FSC-48 ferrosilicochrome in refined ferrochrome smelting. Laboratory smelting tests were carried out in an induction furnace using alumina crucibles with a charge mass of 50 g. The two variants were compared based on the material balance, SEM-EDS analysis of the metallic and slag phases, a conditional estimate of chromium transfer to the metal, and the results of thermodynamic modeling in FactSage 8.4. It was established that a Cr–Fe metallic phase is formed when both FSC-48 and ASC are used. The average metal mass was 13.8 g for FSC-48 and 13.3 g for ASC. According to SEM-EDS data, the Cr content in the metallic phase was 70.53 and 68.64 wt. %, respectively. Aluminum introduced with ASC predominantly transfers into the slag, increasing its Al content to 20.81 wt. %. The conditional estimate of total chromium transfer from the charge to the metallic phase was 91.9% for FSC-48 and 91.6% for ASC. FactSage modeling showed higher calculated ore-derived Cr recovery for ASC under equilibrium conditions; however, excessive ASC addition increased the Si content in the metal. The obtained results confirm the fundamental possibility of using ASC as a complex reductant in refined ferrochrome smelting.

Metals doi: 10.3390/met16080910

Authors: Ming Gao Yang Liu Yanling Zhang Yaqiang Li Qiang Liu Lei Cheng

Temperature- and strain-rate-dependent serrated flow, localized plastic instability, and qualitative microcrack evolution in Mn13 Hadfield steel were investigated using stress–strain analysis and in situ tensile observation. Solution treatment at 1050 °C for 1–1.5 h followed by water quenching yielded homogeneous single-phase austenite. Type A and Type B serrations were dominant at room temperature at 1 × 10−3 s−1 and at 100 °C at 1 × 10−2 s−1, whereas the room-temperature specimen tested at 1 × 10−2 s−1 showed delayed serration onset and pronounced Type B stress drops only at high strains. Type C serrations occurred mainly near fracture at 100 °C at 1 × 10−3 s−1, 200 °C at 1 × 10−2 s−1 and 200 °C at 5 × 10−2 s−1. In situ observations further reveal that different serration types correspond to distinct localized deformation modes. During Type A serrations, the tracked feature exhibited unidirectional stepwise migration involving forward motion, arrest, and renewed advance. Type B serrations were associated with discontinuous pulse-like migration characterized by rapid forward motion, brief arrest, local backward motion, and renewed advance. No regular trajectory was observed during Type C stress drops; only local brightness changes and slight positional shifts occurred. These observations link macroscopic serrations to localized deformation in Mn13 steel and provide qualitative in situ evidence for grain-boundary microcrack initiation and evolution during deformation.

Metals doi: 10.3390/met16080909

Authors: Maria Emanuela Palmieri Matteo Villa Giuseppe Macoretta Michele Maria Tedesco Luigi Tricarico

Resistance spot welding (RSW) is the primary joining technology for automotive advanced high-strength steels (AHSSs), where the inherent severe thermal cycles profoundly alter the heat-affected zone (HAZ) microstructure, leading to localized variations in mechanical properties. Characterizing the spatial gradients in microstructure and the resulting mechanical properties remains a major challenge in weld failure analysis due to the small size of the HAZ and its complex thermal history. In this study, the HAZ of two prominent AHSS grades, a first-generation press hardening steel (PHS1500) and a third-generation quenching and partitioning steel (Q&P1180), was physically simulated using a Gleeble® 3180 thermomechanical simulator to achieve precise control over the localized thermal cycles. The investigation first evaluated the role of thermal cycle duration, governed by the welding time parameter (300 ms vs. 800 ms), on the microstructural evolution of the PHS1500 steel. Increasing the weld time from 300 ms to 800 ms reduced the cooling rate under the nominal 1400 °C condition from approximately 3000 K/s to 2500 K/s; however, no marked change was observed in the overall microstructural and hardness trends within the investigated range. Subsequently, using the 300 ms thermal profile as a reference baseline, a comparative metallurgical study was conducted between PHS1500 and Q&P1180. Under the same 300 ms thermal history, the maximum hardness reduction relative to the corresponding base material was approximately 42% for PHS1500 and 12% for Q&P1180. The hardness minima were located within FE-estimated temperature ranges close to the Ac1 region for PHS1500 and around 600 °C for Q&P1180, respectively. This comparison highlighted the distinct microstructural responses of the two generations across the upper-critical (UCHAZ), inter-critical (ICHAZ), and sub-critical (SCHAZ) zones. Moreover, microhardness profiles were correlated with the microstructural findings, establishing a correlation among the simulated thermal history, the observed microstructural evolution, and localized mechanical performance.

Metals doi: 10.3390/met16080908

Authors: Leandro João da Silva Cauê Almeida Stein Anselmo Thiesen Jhonattan Gutjahr Danielle Bond

Metal parts produced by directed energy deposition go through a complex thermal history during the deposition stage, which can result in heterogeneous microstructures and the accumulation of residual stress. While individual post-processing heat treatments are widely used to address these issues, the industrial logistics of manufacturing large components often demand specific sequences of combined treatments (e.g., applying stress relief prior to substrate detachment to prevent distortion, followed by high-temperature solubilization, or vice versa). The microstructural and mechanical consequences of altering this sequence remain underexplored. Therefore, this study aimed to investigate the effects of different post-processing heat treatment sequences on the mechanical properties of AISI 316L deposited through laser-directed energy deposition. Tensile and Charpy impact tests were carried out on the specimens under five conditions: (i) as-built; (ii) stress relief; (iii) solubilization; (iv) stress relief and solubilization; and (v) solubilization and stress relief. A statistical analysis of variance supported a comparison between each treatment’s influence on the mechanical properties under each condition. Furthermore, the typical microstructures were assessed by optical microscopy, scanning electron microscopy (SEM) equipped with electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). The solubilization treatment reduced the ultimate tensile strength (from ~618 MPa to ~576 MPa) and the yield stress (from ~424 MPa to ~299 MPa), while no significant change was observed in elongation (ranging from 27% to 38%) due to high data dispersion. The stress relief, however, did not significantly change these mechanical properties. Considering the heat treatment combinations, the solubilization had a stronger impact on tensile stress than the stress relief, regardless of the treatment order. Impact resistance was not significantly affected by any of the heat treatments, maintaining an average of ~114 J. The solubilization treatment fully recrystallized the microstructure, while the stress relief did not promote any significant changes at an optical microscopy level. Ultimately, this study demonstrates that the microstructural transformations induced by the solubilization step dominate the final mechanical baseline, indicating that the sequence order is not a determining factor. This finding grants critical flexibility for industrial manufacturing logistics, allowing stress relief to be strategically applied when most convenient for dimensional stability without compromising final part performance.

Metals doi: 10.3390/met16080907

Authors: Xubiao Wang Yanhui Wang Dongyun Sun Jun Cheng Lin Wang Wei Liu Cheng Liu Zhinan Yang Fucheng Zhang Wanshuo Sun

This study examines the evolution of microstructure, the metastability of retained austenite (RA), and the corresponding mechanical behavior exhibited by a nanostructured bainitic bearing steel subjected to prolonged austempering within a transformation stasis regime. The results indicate that following the completion of nanostructured bainitic formation at 300 °C for 3 h, a prolonged austempering time does not alter the microstructure, but reduces the dislocation density in BF while increasing the carbon content in RA. For the 4 h and 6 h specimens, a reduction in the overall RA mechanical stability is observed, accompanied by different transformation rates of stress-induced martensite during tensile deformation. This behavior is largely due to the weakened constraint effect of the BF matrix and the evolution of a carbon concentration gradient within the RA. During the transformation stasis, prolonged austempering elevates the yield strength while maintaining an unchanged ultimate tensile strength, albeit with a marginal reduction in microhardness. Relative to the baseline elongation recorded for the 3 h specimen, both the 4 h and 6 h specimens exhibit enhanced ductility, with the 4 h specimen yielding a peak value of 16.8%, which is 1.66 times that of the 3 h specimen. This improvement stems largely from the greater RA volume fraction that transforms into stress-induced martensite in the 4 h specimen, as well as its continuous and stable transformation rate during tensile deformation. Therefore, it can be concluded that an appropriately prolonged austempering time within nanostructured bainitic transformation stasis is essential for optimizing mechanical performance. This study provides a low-cost, energy-saving isothermal heat treatment technical scheme for mass industrial production of high-performance bearing steel.

Metals doi: 10.3390/met16080906

Authors: Yong Wang Sawei Qiu Tuo Ye Qinghang Cui Jiajun Han Pengcheng Guo

A solid solution treatment (SST) followed by single-stage aging (0–30 h, 140 °C) was performed on 7075 aluminum alloy specimens with longitudinal axes oriented at 0°, 45° and 90° to the rolling direction. The mechanical properties and microstructure were analyzed by tensile testing, optical microscope (OM), electron backscatter diffraction (EBSD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the average tensile strengths of the as-received 7075 aluminum alloy in the three directions were 304 MPa (0°), 295 MPa (45°) and 297 MPa (90°), respectively, with an anisotropy index (AI) of 0.97, indicating that the as-received samples exhibited negligible anisotropic mechanical properties. After SST, elongated grains with coarse size were formed, which is primarily attributed to the inheritance of the deformed fiber texture introduced by hot rolling. EBSD analysis of the 30 h aged specimens revealed that, within the same analyzed area, the total grain-boundary length in the 45° direction (16.4 cm) was much larger than that in the 0° (10.4 cm) and 90° (13.5 cm) directions. As the grain morphology showed no significant change between the SST and aged conditions, this grain-boundary distribution was representative of the microstructural state established during SST and persisted throughout the artificial aging process, contributing to the anisotropic mechanical properties. During artificial aging, prolonged aging time significantly facilitated the precipitation, with the 30 h aged sample exhibiting a significantly higher density of precipitates compared to the 6 h aged sample, leading to enhanced mechanical properties. The tensile strengths of the 30 h aged samples increased to 165 MPa, 236 MPa and 196 MPa in the three directions, respectively. Meanwhile, due to the fixed crystallographic orientation relationship between the precipitates and the Al matrix, the precipitates tended to form on specific planes, which enhanced the anisotropic mechanical properties. Consequently, the AI value increased from 0.97 (as-received) to 1.43 (30 h aged) with prolonged aging time.

Metals doi: 10.3390/met16080905

Authors: Shuai Liu Minggui Qu Zhenhua Wang

The ultra-large steam turbine rotor and heavy gas turbine disk are key components of power stations. They are manufactured from very large ingots, and extremely low strain rates are used during forging. In this study, a high-strength CrNiMoV steel, 25Cr1Ni4MoV, was hot-compressed at 1000–1200 °C and strain rates of 0.01–0.0001 s−1, and the resulting deformed microstructures were observed. The peak stress ranged from 17 to 72 MPa. The hot deformation equation was obtained, and the activation energy for deformation was determined to be 329 kJ/mol, which was lower than that reported in previous studies due to the extremely low strain rate. The deformation mechanism is dynamic recrystallization even at a strain rate of 0.0001 s−1. The critical strains for complete dynamic recrystallization were determined. The dynamic recrystallization grain size increased slowly with decreasing ln(Z), where Z is the Zener–Hollomon parameter, within the ln(Z) range of 22–27. However, when ln(Z) was below 21, the dynamic recrystallization grain size increased rapidly. This critical ln(Z) value is a new finding. Strategies for controlling grain size in the production of ultra-large steam turbine rotors and heavy gas turbine disk forgings were provided. Finally, future research directions were discussed.

Metals doi: 10.3390/met16080904

Authors: Renhong Zhu Guangzheng Wang Yang Li Shaozhu Wang Jianze Liu Xianglong Guo

Driven by energy conservation, emission reduction and lightweight manufacturing demands, wrought magnesium alloys feature low density, high specific strength and balanced comprehensive performances, making them promising lightweight materials for aerospace, automobile, electronic and other industries. This paper systematically reviews the rolling fabrication technologies and recent research progress of wrought magnesium alloy sheets. Special attention is paid to deformation characteristics, microstructure evolution mechanisms and property regulation rules of typical rolling processes, including conventional rolling, cross rolling, accumulative roll bonding, equal-channel angular rolling, asymmetric rolling and twin-roll casting. Existing studies confirm that dynamic recrystallization, grain refinement, activation of non-basal slips and basal texture weakening act as core mechanisms to enhance the strength–ductility matching, formability and anisotropy of magnesium alloy sheets. Each rolling technology possesses unique merits in production efficiency, microstructural homogeneity, texture modification and industrial practicability. Nevertheless, several bottlenecks still restrict its large-scale promotion, such as edge cracking, strong basal texture, poor process stability and high manufacturing cost. Future research priorities lie in multi-process compound forming, intelligent parameter control and short-process eco-friendly manufacturing, so as to facilitate mass production and extensive engineering application of high-performance wrought magnesium alloy sheets.

Metals doi: 10.3390/met16080903

Authors: Tatiana E. Litvinova Vladimir O. Golubev Nickolai V. Tuleshov

The industrial testing of the optimal control system for the gibbsite precipitation area revealed the cases where the optimizer finds and exploits vulnerabilities in the predictive data-driven model, recommending erroneous control actions. The present paper considers a more robust alternative, i.e., training of neural network models using a first-principle model, known as physics-informed neural network (PINN). To address the problem, the system of population balance equations (PBE) describing the bulk crystallization process was transformed into a linearized form, and a PINN-PBE model was generated, which represents a set of interconnected neural networks approximating the solution of the equation system under the batch conditions.

Metals doi: 10.3390/met16080902

Authors: Xiaofei Meng Haitao Zhou Xiaoping Zou Yingping Jiang Shengmei Zhang Yanwen Sun Chi Zhang

With the rapid expansion of the global lithium-battery industry, efficient and sustainable lithium recovery from low-grade lithium resources, such as lithium precipitation mother liquor characterized by a high sodium-to-lithium ratio, has become a critical research challenge. Among the emerging technologies, the adsorption method, recognized for its operational simplicity, high selectivity, and process flexibility, has garnered significant attention. This review systematically summarizes recent advancements in two primary categories of adsorbents for selective lithium recovery: organic adsorbents (crown ether-based materials) and inorganic adsorbents (aluminum-based layered double hydroxides (LiAl-LDHs), titanium-based ion sieves (H2TiO3, H4Ti5O12), and manganese-based ion sieves (HMn2O4, H1.6Mn1.6O4, H4Mn5O12). For each class, the synthesis methods, adsorption mechanisms, performance (capacity, selectivity, kinetics, and cycling stability), and key influencing factors are thoroughly discussed and compared. Titanium-based sieves demonstrate high capacity and stability, manganese-based materials show excellent kinetics, aluminum-based adsorbents offer industrial scalability, and crown ether-based materials exhibit superior ion size selectivity. The review also identifies limitations, such as the slow kinetics of H2TiO3, manganese dissolution in manganese-based ion sieves, and the cost of functionalized organics. Finally, future research directions are proposed, focusing on enhancing adsorption kinetics and stability via material design (e.g., morphology control, doping, hybridization), developing scalable and cost-effective synthesis routes, and exploring the integration of adsorption with other separation technologies to create efficient hybrid processes for the sustainable exploitation of low-grade lithium.

Metals doi: 10.3390/met16080901

Authors: Jee-Hwan Bae Yena Kwon Seung-Moon Baek Choong-Do Lee Cheol-Woong Yang

The interfacial reaction between solder and substrate is a critical factor governing joint reliability, making it essential to understand the formation and stability of interfacial reaction layers when developing new high-temperature lead-free solders. This study investigates the interfacial reaction layers formed in Zn-5Al-3Mg solder/Cu substrate joints soldered at 693 K under vacuum. With a binary Zn-Al solder, the Cu substrate is progressively consumed by Zn, and the intermediate phases CuZn4, Cu5Zn8, and CuZn nucleate and grow concurrently at the solder interface. The addition of a minor amount of Mg to the Zn-Al alloy, however, fundamentally alters this reaction sequence. Transmission electron microscopy analyses, including scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy (STEM-EDS), energy-filtered TEM (EF-TEM), and electron diffraction, reveal three distinct interfacial layers: an outer Mg2Zn11 layer, a middle two-phase mixture of CuZn4/Mg2CuZn3, and an inner Cu5Zn8 layer adjacent to the Cu substrate. The biphasic CuZn4/Mg2CuZn3 mixture layer is shown to form via a quasi-peritectic reaction governed by sequential four-phase equilibria in the Zn-Mg-Cu ternary system. These findings demonstrate that minor Mg additions redirect the interfacial reaction pathway between Zn-Al-based solders and Cu substrates, providing new insight for the design of high-temperature Pb-free solder systems.

Metals doi: 10.3390/met16080900

Authors: Yunpeng Zhang Shilong Che Xin Lin Xufei Lu

Laser powder bed fusion (LPBF)-fabricated TA15 titanium alloy commonly exhibits a fine acicular lath morphology, which has frequently been interpreted as martensitic in previous studies and is generally associated with high strength and limited plastic accommodation. In this study, LPBF-TA15 specimens were annealed at 800, 900, and 950 °C for 2 h, followed by furnace cooling, and subsequently subjected to secondary annealing at 550 °C for 4 h. Each sequentially annealed condition was compared with its corresponding single-step condition to distinguish retained microstructural differences from the tensile-property changes associated with the subsequent treatment. Microstructural evolution and monotonic tensile properties at room temperature and 300–600 °C were investigated. Annealing at 800 °C retained a relatively fine lamellar morphology. Increasing the initial annealing temperature to 900 and 950 °C produced progressively larger apparent lath and colony scales, with the most pronounced coarsening observed at 950 °C. Tensile results are reported as mean ± standard deviation. After secondary annealing, A800-S550 exhibited the highest mean room-temperature strength among the three secondary-annealed conditions, with a yield strength of 1045.0 ± 2.6 MPa, an ultimate tensile strength of 1116.7 ± 2.3 MPa, and an elongation of 14.3 ± 0.7%. From 300 to 600 °C, its yield strength decreased from 701.0 ± 3.2 to 493.6 ± 9.8 MPa, while its ultimate tensile strength decreased from 823.5 ± 3.8 to 585.6 ± 7.1 MPa; the elongation at 600 °C was 19.0 ± 1.8%. In this study, microstructural inheritance refers to the persistence, after the common 550 °C treatment, of differences in lath and lamellar-colony scales and EBSD boundary characteristics established during initial annealing. The secondary-annealed conditions retained distinct microstructural scales and exhibited different tensile responses; however, a unique causal relationship between the retained morphology and the magnitude of the property changes was not established. Residual stress, post-heat-treatment oxygen variation, and quantitative texture evolution were not independently evaluated. The conclusions are limited to the heat-treatment schedules and monotonic tensile conditions examined in this study.

Metals doi: 10.3390/met16080899

Authors: Stefan Dikić Hongqiang Liu Dragomir Glišić Jin Pan Yongning Zhou Nenad Radović Cheng Ma

The aim of this work is to investigate the influence of different welding technologies on the mechanical properties and corrosion resistance of welded joints of SGH340D + ZMA steel with a Zn–Mg–Al (ZMA) protective coating. Two different welding technologies were used: the gas metal arc welding(GMAW) process at a welding speed of 0.8 m/min and laser welding at speeds of 2 and 4 m/min. Mechanical properties were determined using tensile testing and hardness testing. Corrosion resistance was estimated using a salt spray test. Residual stresses were determined experimentally using the drill hole method. The highest residual stresses were measured in GMAW-welded joints, while the lowest were measured in laser-welded joints at a speed of 4 m/min. The sample welded by laser at a speed of 4 m/min exhibited hardness values close to the upper acceptable limit, indicating that further increases in welding speed without preheating may lead to excessive hardness. All samples exhibited good corrosion resistance in a salt chamber. According to the results, increased welding speed reduced residual stresses but increased the risk of brittle fracture.

Metals doi: 10.3390/met16080898

Authors: Biao Wang Yongsheng Ren

Aqueous zinc-ion batteries (AZIBs) are promising for scalable energy storage, yet their practical viability is constrained by zinc dendrite propagation, parasitic hydrogen evolution, and interfacial corrosion. Formulating electrolyte additives represents an economically viable strategy to address these long-standing bottlenecks by modulating the bulk solution and double-layer environments. Diverging from traditional composition-based classifications, this review categorizes recent additive strategies according to their underlying physical chemistry mechanisms. Specifically, we evaluate how these additives regulate the primary and secondary Zn2+ solvation sheaths, reconstruct the electric double layer (EDL) for crystallographic facet control, induce sacrificial or mineralized solid electrolyte interphases (SEIs), and establish responsive polymer confinement networks. Furthermore, we critically discuss the operational limitations, trade-offs, and parameter dependencies of these strategies under non-ideal, realistic conditions. Finally, prospective directions are outlined—focusing on descriptor-driven design, operando non-equilibrium characterizations, and performance validation under standard industrial metrics (e.g., low E/C ratios and high depths of discharge)—to provide an objective framework for advancing electrolyte optimization in practical zinc-based energy storage.

Metals doi: 10.3390/met16080897

Authors: Myung-Su Yi Da-Bin Jung Tae-Gu Kang Jung-Goo Park Joo-Shin Park

This study presents a traceable global–local finite element (FE) framework for assessing stern-boss structural integrity under operationally derived loading. Two production-scale MSC Nastran models—a shell-dominant model and an otherwise equivalent global model with a locally solid stern-boss region—were compared under five vessel-specific states generated from trim-and-stability weight, buoyancy, hydrostatic, ballast, and machinery-load distributions. Baseline-to-fine mesh changes were limited to 0.68% for the shell model and 1.07% for the solid model. Both models reproduced the same global deformation mode, while the solid model predicted 5.9–6.3% greater maximum vertical deflection. Within a common stern-boss assessment region, the shell and solid peak von Mises stresses were 42.1–70.9 MPa and 41.5–72.4 MPa, respectively, with differences confined to −1.4% to +2.3%. By contrast, stresses extracted at the stern-tube interface were 17.2–26.8 MPa in the shell model and 29.7–46.6 MPa in the solid model, demonstrating the importance of three-dimensional constraint, transverse shear, and through-thickness response at the local interface. The governing design-draught/APT-full condition produced a solid-model deflection of 46.8 mm and a regional stress of 72.4 MPa. Its nominal SS400 yield-utilization ratio was 0.308, whereas the LR rule-based inverse safety-factor index ranged from 1.3 to 2.1 and identified surrounding panel buckling as the more restrictive limit state. The shell model reduced wall-clock time by 38.6% and is therefore appropriate for global screening, while the solid representation is required for interface-level assessment. The framework constitutes a numerically verified, digital-twin-compatible baseline; independent validation against measured structural or shaft-line data remains necessary.

Metals doi: 10.3390/met16080896

Authors: Kang Ai Zhaoyuan Zhang Jing Guo Bohan Yao Jiahui Xi Luyan Ju

In this study, graphite particles and short-cut carbon fibers were used to prepare a hybrid-reinforced composite with AZ91 magnesium alloy as the matrix via the powder metallurgy process. The effects of different added phase ratios on microstructure, density, compressive strength, and fracture morphology were investigated. The results show that the addition of 5% graphite particles alone reduced the compressive strength by 20.1% compared to pure magnesium, attributed to interfacial delamination and interlaminar peeling in the graphite’s layered structure. The introduction of carbon fibers effectively compensates for this degradation. When the carbon fiber content was increased to 10% (with graphite fixed at 5%), the compressive strength reached a peak of 375 MPa—a 63.0% increase over the graphite-only system—and the fracture strain rose to 16.98%. However, an excessive amount of carbon fibers (15%) led to agglomeration, causing the porosity to rise to 9.1% and resulting in a significant decline in mechanical properties. Microstructural analysis indicates that carbon fibers exert a reinforcing effect by sharing the load and constraining the lateral deformation of the matrix, while graphite particles induce microcracks and pores, resulting in a weakening effect; under appropriate ratios, the two can achieve synergistic reinforcement. This study provides experimental evidence for the component design and performance control of high-strength, rapidly dissolving magnesium-based composites.

Metals doi: 10.3390/met16080895

Authors: Chenghong Liu Tuo Zhao Chunlei Guo Erdou Li Yufang Qin Bo Zhang

NdFeB waste is an important rare earth secondary resource, and the current industrial practice primarily employs a hydrochloric acid preferential dissolution method to recover rare earth elements (REEs). However, approximately 1% of REEs (e.g., cerium oxide, neodymium oxide, praseodymium oxide, and dysprosium oxide) remain in the leaching residue, resulting in low recovery efficiency. This work puts forward mechanochemical leaching (integrating mechanical activation and acid leaching) to replace traditional agitated leaching, which realizes synchronous mechanical activation and acid leaching within a stirred ball mill. A systematic comparison is conducted between these two leaching technologies, and the influences of operational variables on rare earth leaching efficiency are explored. The experimental results reveal that sustained mechanical grinding can pulverize particles down to the submicron level, induce substantial lattice distortion and amorphous transformation, destroy the physical coating of rare earth-bearing phases by iron oxides, and thereby drastically improve the extraction efficiency of REEs. The optimal conditions were determined as follows: stirring speed of 700 r/min, leaching temperature of 85 °C, HCl concentration of 1 mol/L, leaching time of 180 min and solid–liquid ratio of 100 g/L. Furthermore, this study reveals the synchronous evolution mechanism of particle refinement and phase transformation during mechanochemical leaching, providing an alternative and more economical recycling route for NdFeB waste.