Metals doi: 10.3390/met16080894

Authors: Alejandro Gómez Joan Santiago Cortinez Robinson Aguirre Ocampo Adriana Echavarria José A. Tamayo Andrés F. Vargas Carolina Ramírez Francisco J. Bolívar Alejandro A. Zuleta Esteban Correa Félix Echeverría

Magnesium-based materials are promising candidates for solid-state hydrogen storage due to their high gravimetric capacity; however, their practical application is limited by slow sorption kinetics and high thermal stability. This study investigates the influence of hydride additives on the microstructure and hydrogen desorption performance of ball-milled Mg–Co composites. Flake-like magnesium particles modified with 7 wt.% cobalt were processed by high-energy ball milling and subsequently doped with sodium hydride, potassium hydride, and calcium hydride at concentrations of 0.5 and 5 wt.%. Microstructural, phase, and surface chemical characterization revealed that additive type strongly affects dispersion, interfacial distribution, and the formation of additive-derived surface species within the Mg–Co matrix. Hydrogen sorption measurements conducted at 300–350 °C under different pressure conditions show that alkali hydrides significantly enhance low-temperature hydrogen desorption. In particular, the composite containing 5 wt.% potassium hydride exhibits a marked improvement, releasing approximately 4 wt.% hydrogen at 300 °C, while the unmodified material shows negligible desorption under the same conditions. Thermal analysis confirms that the additives modify the dehydrogenation response, although improved performance is not solely correlated with lower onset temperatures. The results demonstrate a clear asymmetry between hydrogen absorption and desorption, indicating that the primary effect of hydride additives is an enhancement in dehydrogenation kinetics. This behavior is associated with microstructural features, including additive dispersion and interfacial effects induced during processing. These findings provide insight into the design of magnesium-based hydrogen storage materials through microstructure–property relationships.

Metals doi: 10.3390/met16080893

Authors: Tao Wei Haipei Zhang Haoyuan Xu Shuang Shao Shichao Wu Kai Fan Bo Li

A mass action concentration model of FeO-Fe2O3-SiO2-CaO-MgO-Al2O3-ZnO multi-component slag was established to address the problems of high viscosity and high copper content in oxygen-enriched top-blown copper smelting slag. Theoretical calculations, combined with experimental investigations, were performed to evaluate the effects of ZnO additions (0–25 wt.%) on phase transformation, Fe3O4 reduction and copper content in the slag at temperatures ranging from 1200 to 1400 °C. The results indicate that ZnO addition decreases the mass concentrations of Fe2O3, Fe3O4, Fe2SiO4 and SiO2, while increasing the proportions of zinc-bearing structural units and enhancing the reducing capability of the slag. In the copper slag system, Zn2+ substitutes for Fe in Fe3O4 and Fe2SiO4 through isomorphous substitution, forming Fe-Zn spinel and Fe-Zn olivine. As the addition of ZnO gradually increases to 25 wt.%, the liquid slag fraction increases and the slag viscosity decreases, resulting in a reduction in copper content from 5.64 wt.% to 2.04 wt.%. Furthermore, ZnO promotes the transformation of Fe3O4 into zinc–iron spinel, which is more readily reducible by carbothermic reaction than Fe3O4 itself, thereby facilitating the overall reduction of iron oxides in the copper slag. These findings provide a theoretical basis for slag-type regulation and the efficient separation of copper from slag via high-temperature gravity settling of matte.

Metals doi: 10.3390/met16080892

Authors: Atiqur Rahman Sung-Heng Wu Ranjit Joy Frank Liou

Directed energy deposition (DED) of low-alloy steels involves strongly coupled effects among alloy composition, solidification behavior, and post-deposition heat treatment, making mechanical property prediction difficult when target-domain data are limited. This study develops a transfer-learning and continuous optimization framework for predicting heat treatment-dependent yield strength (YS), ultimate tensile strength (UTS), hardness (HV), and as-solidified phase fractions of martensite, ferrite, and austenite in DED-processed low-alloy steels. A CALPHAD-based dataset was generated for 125 low-alloy steel compositions. A multilayer perceptron (MLP) surrogate was first trained as a baseline model, then fine-tuned through transfer learning and progressively updated as staged continuous optimization; the composition pool increased from 72 to 125 compositions using Random, Greedy, and Bayesian upper-confidence-bound acquisition strategies. The heat treatment prediction accuracy improved from an average R2 of 0.757 for the baseline model to 0.929 after transfer learning and to approximately 0.997 after continuous optimization, with a nearly 78% reduction in RMSE relative to transfer learning. For the solidification outputs, the average R2 increased from 0.770 after transfer learning to approximately 0.859 after optimization. Bayesian-UCB provided the most stable and data-efficient improvement by balancing predicted performance with model uncertainty. The optimized prediction system showed low case-study errors for both solidification and heat treatment properties, demonstrating its potential as a rapid screening tool for alloy composition and tempering-condition selection in DED low-alloy steel development.

Metals doi: 10.3390/met16080891

Authors: Yijian Zhang Jianliang Zhang Ping Du Yu Lu Xun Zhou Miao Luo Jianyang Yin

This study aims to investigate the effects of slag chemical composition on the smelting reduction behavior and microstructural evolution of chromite at 1525–1550 °C, thereby providing theoretical guidance for optimizing the smelting reduction process. Through high-temperature melting experiments combined with Scanning Electron Microscope - Energy Dispersive Spectrometer(SEM-EDS) microstructural characterization and thermodynamic calculations, the influences of basicity, MgO content, and Al2O3 content on chromium reduction behavior, slag physicochemical properties, and spinel evolution mechanisms were systematically analyzed. The results indicate that a basicity of 1.2 effectively promotes the dissolution and reduction of chromium spinel, whereas excessively high basicity hinders the reduction process when using graphite as the reducing agent. Although increasing MgO content initially improves slag fluidity and reaction rates, it promotes the formation of a Mg-Al-rich solid product layer during the later stages of the reaction; this restricts the intra-phase diffusion of Cr3+ and causes the reduction process to stall. High Al2O3 content significantly increases system viscosity and impairs mass transfer, thereby reducing the degree of reduction. Under optimized conditions, specifically an Al2O3 content of 14 wt% and a temperature of 1550°C, the degree of reduction approaches 93%. Thermodynamic calculations further reveal that the efficiency of chromite smelting reduction is synergistically controlled by factors such as slag viscosity, liquid-phase behavior, and spinel equilibrium phase mass. The favorable slag composition identified in this study, basicity of 1.2, MgO content of 10 wt%, and Al2O3 content of 14 wt%, provides favorable physicochemical conditions for the efficient smelting reduction of chromite.

Metals doi: 10.3390/met16080890

Authors: Can Chen Ling Ran Ziwang Zeng Jie Li Xi Cao Yubing Wang Bo Han Hongliang Zhang

The side ledge is essential for maintaining thermal stability and protecting the sidewall lining in an aluminum reduction cell. Its shape and temperature distribution strongly influence cell operation and energy efficiency. However, conventional computational fluid dynamics (CFD) methods, while accurate, are computationally intensive and unsuitable for fast evaluation under changing operating conditions. To overcome this limitation, this study develops a CFD-driven machine learning surrogate model for rapid prediction of cross-sectional temperature fields and side ledge morphology in an aluminum reduction cell under magnetohydrodynamic (MHD) conditions. High-fidelity training data are first generated from MHD-CFD simulations. Key physical variables, including heat generation, effective thermal transport properties, and velocity components, are extracted from multiple cross-sections prior to side ledge formation to form the input dataset. Five machine learning methods—Decision Tree, Random Forest, XGBoost, K-Nearest Neighbors, and Support Vector Regression—are then developed to predict the resulting temperature field and side ledge profile after solidification. The performance of each model is systematically compared in terms of accuracy and applicability. Among the tested models, Random Forest demonstrates the best overall performance. Its predicted temperature fields closely match CFD results, with a maximum temperature deviation below 0.23 °C, while the average side ledge thickness error is only 0.0153 m. Moreover, the proposed surrogate model reduces computation time from approximately 168 h to 3 min compared with CFD simulations, while maintaining high predictive accuracy. Overall, the proposed method enables fast and accurate evaluation of thermal states, supports operational optimization, and provides a foundation for digital twin development of aluminum reduction cells.

Metals doi: 10.3390/met16080889

Authors: Farida Kapsalamova Aliya Alimzhanova Akmaral Rakhym Gulnur Kanzhigit Renat Beissenov

A combined CALPHAD-guided thermodynamic and experimental approach was employed to investigate the influence of boron on phase evolution and microstructural development in the Fe–Ni–Cr–Cu–Si–B–C alloy system. Thermodynamic calculations were performed using Thermo-Calc (FE13-2025b) and the TTFe thermodynamic database. Vertical phase-diagram sections and response surface analysis were used to evaluate phase stability over the temperature range of 400–1500 °C and to identify temperature–composition domains favorable for the formation of strengthening phases. The calculations predicted complex multiphase equilibrium behavior involving boride-, carbide-, and silicide-containing phases. Within the investigated composition range, approximately 4 wt.% B provided a favorable balance between the metallic matrix and strengthening phases, while 638 °C corresponded to a thermodynamically favorable equilibrium phase constitution. Response surface analysis further demonstrated that temperature governs phase evolution, whereas boron primarily controls phase redistribution. The optimized alloy composition was characterized experimentally using scanning electron microscopy (SEM), wavelength dispersion spectroscopy (WDS), elemental mapping, and X-ray diffraction (XRD). The experimentally observed heterogeneous multiphase microstructure showed good agreement with the CALPHAD-predicted phase evolution at a qualitative level, demonstrating the usefulness of thermodynamic modeling for guiding alloy design. The proposed CALPHAD-guided workflow integrates thermodynamic modeling with targeted experimental characterization and provides a transferable framework for the accelerated design and optimization of complex Fe-based multicomponent alloys.

Metals doi: 10.3390/met16080888

Authors: Zhengqi Guo Xing Chen Deqing Zhu Jian Pan Congcong Yang Siwei Li

Vanadium–titanium magnetite is a polymetallic resource in which the low reactivity and complex phase constitution of Ti-bearing smelting slag restrict the coordinated recovery of Fe, V, and Ti. In this study, a coupled route involving laboratory-scale induction-furnace smelting separation, magnetic separation, NaOH activation roasting, and staged leaching was investigated for upgrading ground vanadium–titanium magnetite metallized pellets. At 1690 °C for 20 min with 2.5 wt% coke under natural slag basicity, a vanadium-bearing metallic product containing 92.07 wt% Fe and 1.27 wt% V was obtained, while Ti was concentrated in a slag containing 47.83 wt% TiO2. Increasing slag basicity improved vanadium partitioning into the metallic phase but decreased the TiO2 content and subsequent upgrading performance of the slag. Following magnetic separation and NaOH-activated roasting at 900 °C for 90 min with 40 wt% NaOH, staged leaching yielded a rutile-rich product containing 90.70 wt% TiO2, with a Ti recovery of 88.75%. These results demonstrate that controlling the phase constitution of smelting-derived Ti-bearing slag is important for its subsequent alkali-activation upgrading and Ti enrichment.

Metals doi: 10.3390/met16080887

Authors: Guang Ji Xiaming Chen

The corrosion performance of Al-Mg-Si-Cu laser–arc hybrid welded joints modified by 1.8 wt.% Ni remains poorly clarified. In this study, the corrosion behavior was examined via electrochemical measurements combined with SEM, EDS, and SKPFM. Nickel alloying increased the corrosion potential of the α-Al matrix above that of eutectic Si, thereby suppressing the cathodic role of eutectic Si. Nevertheless, the pronounced potential difference and extensive interfacial area between the Al3Ni phase and the α-Al matrix promoted localized galvanic corrosion, resulting in chain-like pits along the Al3Ni phase. This intense galvanic coupling considerably damaged the compactness of the passive film and reduced its resistance. Consequently, the corrosion current density of the welded joint increased significantly from 0.83 μA/cm2 to 1.85 μA/cm2. These findings suggest that Ni alloying is suitable for welding Al-Mg-Si-Cu alloys in applications where high mechanical performance is essential and corrosion resistance is of secondary importance, such as in body-in-white or chassis load-bearing components.

Metals doi: 10.3390/met16080886

Authors: Weiran Zhang Zhenbang Wei Yong Zhang Jin Li

In this study, the influence of precipitated Laves particles on the metastable pitting of VCrFeTa0.1W0.1 and VCrFeTa0.2W0.2 refractory high-entropy alloys (HEAs) in 3.5 wt.% NaCl solution was investigated. Microstructures and corrosion behaviors were characterized by XRD, SEM, TEM, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS), and the underlying mechanisms were elucidated. The PDP test results demonstrate that the precipitated Laves particles reduce the pitting resistance of HEAs. The corrosion current densities of VCrFeTa0.1W0.1 and VCrFeTa0.2W0.2 HEAs are 0.066 and 1.361 μA/cm2, respectively, and the pitting potentials are 1.058 and 0.881 V, respectively; that is, reducing the Laves-particle content lowers the corrosion current density by a factor of approximately 20 and raises the pitting potential by approximately 180 mV. The corrosion current density and pitting potential of VCrFeTa0.1W0.1 are competitive with those of reported HEAs and traditional alloys.

Metals doi: 10.3390/met16080885

Authors: Xueqin Zhang Xiaolan Wu Peihao Zhao Xiangyuan Xiong Zhi Zheng Gaoteng Zhang Shanglong Ao Guishan Shi Kunyuan Gao Wu Wei Shengping Wen Hui Huang Li Rong Zuoren Nie

The role of the Zn/Mg ratio in regulating microstructure, precipitation evolution and coarsening resistance in Al–Zn–Mg-based alloys was investigated by microhardness testing, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) during isothermal aging at 150 °C. Three alloy compositions were designed with Zn/Mg ratios of 1.6, 2.4, and 3.9, whereas the combined Zn and Mg level was fixed at 6.0 wt%. All alloys exhibited a typical age-hardening response, whereas the maximum peak hardness was obtained at an intermediate Zn/Mg level rather than at the two extremes. The optimal composition (Zn/Mg = 2.4) reached 137 HV, which is attributable to the formation of the finest precipitates (~3 nm) and the highest number density. Moreover, this alloy exhibited the smallest hardness loss (ΔH = 19 HV) after prolonged aging (192 h). TEM analysis indicated that this alloy exhibited the lowest coarsening rate constant, Kr = 0.43 at 192 h. Furthermore, the variation in Zn/Mg ratio affected grain boundary precipitation, leading to a minimized PFZ width at Zn/Mg = 2.4 while maintaining a similar discontinuous distribution of grain boundary precipitates among the alloys. Overall, tailoring the Zn/Mg balance offers an effective strategy to achieve refined precipitates, improved coarsening resistance, and enhanced mechanical performance with superior thermal stability.

Metals doi: 10.3390/met16080884

Authors: Florentina Niculescu Mariana-Mirela Stănescu Gheorghe Iacob Adrian Emanuel Onici Lenuta Zidaru

A multicomponent Ni54Cr28Mo8Nb5Ta5 nickel-based superalloy was produced by vacuum induction melting followed by homogenization, hot forging, solution treatment, and aging to investigate its microstructural and mechanical behavior. The X Ray Fluorescence (XRF) analysis confirmed excellent agreement between the nominal and experimental chemical compositions. The X Ray Diffraction(XRD) combined with Rietveld refinement revealed a microstructure dominated by three closely related to face-centered cubic (FCC) (A1) solid-solution regions with slightly different lattice parameters, indicating local compositional variations. The Scanning Electron Microscopy(SEM)/Energy Dispersive Spectroscopy (EDS) observations showed a generally homogeneous elemental distribution, while optical and electron microscopy identified a dendritic microstructure with elongated interdendritic constituents enriched in refractory elements. Mechanical characterization yielded an average hardness of 497 HV0.5, a compressive strength of approximately 1950 MPa, and room-temperature yield and ultimate tensile strengths of 1050 MPa and 1320 MPa, respectively. Tensile strength gradually decreased with increasing temperature up to 900 °C, while ductility increased from 16% to 25% total elongation. The results indicate that the alloy develops a stable FCC matrix primarily strengthened by solid-solution hardening, with the measured mechanical performance suggesting an additional contribution from precipitation hardening. This study provides an experimental baseline for the development and optimization of conventionally processed Ni–Cr–Mo–Nb–Ta superalloys for high-temperature applications.

Metals doi: 10.3390/met16080883

Authors: Guoqi Zhao Yufeng Wen Yanlin Yu Wen Pan

In this work, first-principles calculations based on density functional theory were employed to investigate the structural, elastic, half-metallic, magnetic, and thermal properties of two novel quaternary Heusler alloys, FeMnLiSi and FeMnLiGe. The results revealed that ferrimagnetic FeMnLiSi and FeMnLiGe with type III structures were energetically the most stable, and possessed thermodynamic, dynamic, and mechanical stabilities. Their equilibrium lattice constants were 5.6104 Å and 5.7479 Å. At equilibrium, FeMnLiSi and FeMnLiGe exhibited brittleness, elastic anisotropy, and half-metallic ferrimagnetism, with half-metallic band gaps of 0.7935 eV and 1.0805 eV, respectively. The total magnetic moments per unit cell of FeMnLiSi and FeMnLiGe were both 2.0000 µB, which conforms to the Slater-Pauling rule. Their half-metallic ferrimagnetism remained robust over a broad range of uniform lattice strains. FeMnLiSi exhibited a higher stability, melting point, and Debye temperature, as well as a narrower half-metallic gap, than FeMnLiGe. This work systematically predicted the intrinsic structural, mechanical, magnetic, and thermal properties of FeMnLiSi and FeMnLiGe, and delivered theoretical insights for designing new Heusler-type half-metallic candidates.

Metals doi: 10.3390/met16080882

Authors: Shenggang Wang Jiao Shi Chang Yu Haitao Xu

High-quality WC-Co composite powder is the prerequisite for achieving cemented carbides with superior mechanical properties. However, achieving homogeneous Co distribution on WC particles remains challenging due to the limited surface activity of WC and the high cost associated with noble-metal activation methods. Therefore, this study employed an electroless plating method based on non-noble-metal activation to prepare Co- coated WC composite powders and to clarify the effects of plating parameters on coating behavior, microstructure evolution, and mechanical properties of WC-Co cemented carbides. Results indicate that when plated with a lower reducing-agent concentration (15 g/L) or a lower temperature (70 °C), insufficient Co coating causes poor fracture toughness of the cemented carbides. Increasing the reducing-agent concentration to 25 g/L or the plating temperature to 80 °C promotes a more uniform Co distribution on WC particles, which suppresses WC grain coalescence during sintering. Under the optimized reducing-agent concentration of 25 g/L, the obtained WC-Co cemented carbide exhibits a homogeneous microstructure with an average WC grain size of 0.91 μm, a Vickers hardness of 2054.5 HV30, and a fracture toughness of 11.39 MPa·m1/2. Excessive reducing-agent concentration or plating temperature deteriorates the Co coating uniformity, promoting Co aggregation and grain coarsening of the cemented carbides. This work demonstrates that precise control of electroless plating parameters enables the fabrication of high-quality WC-Co composite powders, providing a practical route for tailoring microstructure and optimizing mechanical performance of the cemented carbides.

Metals doi: 10.3390/met16080881

Authors: Hui Chen Jun Sun Li Shang Chao Jia

Tool steel TD salt-bath vanadizing generally relies on expensive analytical-grade raw materials, yet systematic investigations into low-cost industrial borax-based vanadizing of 9SiCr steel remain insufficient. This work intends to optimize the industrial salt-bath vanadizing process and clarify the growth mechanism of vanadium carbide coatings. TD thermal diffusion vanadizing was performed on 9SiCr steel using a molten borax salt bath containing industrial-grade borax and V2O5. Metallurgical microscopy, XRD, SEM-EDS and microhardness testing were adopted to systematically explore the effects of treatment temperature and holding time on coating thickness, microstructure and hardness. Continuous, dense VC coatings with favorable metallurgical bonding were fabricated. Coating thickness increased linearly with temperature and followed a parabolic growth law with respect to holding time. The optimized parameter was identified as 970 °C for 4 h, yielding a 8.3 μm thick coating with an average microhardness of ~2500 HV and an 8 μm thick diffusion transition layer. Comparative chromizing experiments indicated that the chromium carbide coating (16.7 μm) was approximately twice the thickness of the VC coating under identical conditions, demonstrating that VC coating growth is restricted by the diffusion supply of active carbon from the substrate. This research provides experimental data and theoretical guidance for the industrialized optimization of TD salt-bath vanadizing for 9SiCr steel.

Metals doi: 10.3390/met16080875

Authors: Guotian Cao Miao Chen Huan Yu Jixue Zhou Jinzhe Jiang Qian Su Peng Zhang Junpeng Duan Kaiming Cheng Dongqing Zhao Xuansheng Feng Yuansheng Yang

A rare-earth (RE)-segregation-assisted route combining mechanical alloying and hot extrusion was used to produce a WE43 alloy with an in situ network-like bimodal structure. Mechanical alloying fragmented and partially dissolved RE-containing phases produced a supersaturated Mg-RE solid solution, and dispersed oxygen-bearing surface films. During the pre-sintering stage before hot extrusion, defect-rich prior powder-particle boundaries (PPBs) acted as preferential sinks for RE solutes, establishing RE-enriched regions before extrusion, while some oxygen-bearing species remained near PPBs and grain boundaries. During subsequent hot extrusion, RE solute drag and pinning by RE-containing precipitates and retained oxides restricted grain-boundary migration near PPBs, whereas rotation-assisted grain coalescence and growth occurred within particle interiors. In the 350—extruded alloy, the relatively coarse and fine grains averaged 299 and 144 nm and occupied 71 and 29 vol.%, while the precipitates averaged 97.1 and 9.2 nm. The 400—extruded alloy achieved a yield strength of 396 MPa, an ultimate tensile strength of 432 MPa, and an elongation of 7.9%. For the 350—extruded alloy, Orowan-type, solid-solution, grain-boundary, and dislocation strengthening contributed approximately 118.5, 116.8, 84, and 67 MPa, respectively, leaving an unresolved residual difference of 63.7 MPa. Coupled RE redistribution and oxide dispersion therefore provide a route to a favorable strength–ductility balance in powder-metallurgy Mg alloys.

Metals doi: 10.3390/met16080880

Authors: Peter Mulidrán Emil Spišák Miroslav Tomáš Janka Majerníková

The main objective of this paper is to present a comparative analysis between the finite element method (FEM) and artificial neural networks (ANNs) for predicting sheet metal springback, while addressing the “black-box” nature of machine learning through explainable AI (XAI). To achieve this novelty, a multi-layer perceptron (MLP) architecture was implemented and evaluated against numerical simulations during the bending of a hat-shaped profile. The experimental framework utilized dual-phase HCT600X steel (0.8 mm thickness), supplemented by deep-drawing DC06 and high-strength RAK40/70 steels to ensure dataset diversity and robust generalization capability. A key contribution of this work is the integration of local SHAP (Shapley additive explanations) analysis to interpret the ANN outputs, allowing for a precise quantification and rank ordering of how individual material, design, and process parameters govern the resulting springback angle. The developed MLP model (comprising two hidden layers with five neurons each) achieved high predictive fidelity, yielding an overall correlation coefficient R = 0.99074 alongside robust error metrics (RMSE and MAE).

Metals doi: 10.3390/met16080879

Authors: Monika Keutmann Kirill Saushkin Bernd Friedrich

This study investigated how acid concentration affects leaching from pyrolyzed LIBs’ (lithium-ion batteries’) black mass (BM) by stepwise acidification with eight acids at 70 °C under identical starting conditions. A citric-acid control without BM matched the calculated pH, whereas BM buffered solutions to ∼pH 9.5 and increased the measured pH. Stabilized pH provided a consistent reference within each experiment, but similar pH values across acids produced very different leaching efficiencies. At pH ≈ 3, lithium leaching was ∼pH 85% for formic acid and ∼pH 60% for citric acid. The maximum lithium leaching ranged from 49% (ascorbic acid) to 92% (sulfuric acid), while organic acids often showed limited cobalt and nickel dissolution. For formic acid, speciation and metal-formate solubility calculations showed that higher acid concentration does not necessarily increase transition-metal leaching and may suppress cobalt and nickel. Thus, pH is stable within each acid system but not transferable across acids, and high solid loading (250 g L−1) further requires acid-specific evaluation. The results indicate that acid-dependent speciation and complexation, rather than proton concentration alone, control extraction and can decouple acid dosage from leaching performance.

Metals doi: 10.3390/met16080878

Authors: Chenhao Li Long Meng Zhengjie Chen Zhihui Yu Yu Wang Jue Chen Xiaolan Wang Lijuan Sun Qiqiang Wang Wendi Zhang Otgonjargal Enkhtur Zhiwei Bian Jingkui Qu Shaoyuan Li

Lithium extraction from ores is the main source of lithium salts in China, and the development of green and efficient extraction technologies is an inevitable trend in the country’s lithium industry. Due to the limited availability of domestic lithium ore resources, the efficient utilization of low-grade ores and the development of extraction processes from non-traditional lithium resources will be essential for reducing costs and improving efficiency. This review summarizes the resource characteristics and mineral structures of typical lithium-bearing ores, examines recent advances in extraction processes for representative lithium deposits (spodumene, lepidolite) and discusses strategies for the efficient utilization of low-grade lithium ores (zinnwaldite, petalite, amblygonite, clay-type lithium ore, and jadarite). Finally, the research gap in life cycle assessment of lithium extraction processes from multiple types of lithium ores is addressed by providing a useful reference framework for the development and optimization of lithium extraction technologies from ores.

Metals doi: 10.3390/met16080877

Authors: Yaojun Miao Chongmin She Zhou Feng Kezhen Li Taian Chen Jiafen Cao Jianqiang Zhang Haiyan Gao Haiyang Jiang Baode Sun Jian Wang Yufei Wang

Based on the rotary bending loading principle, an experimental investigation into the fatigue properties of 6201 aluminum alloy individual wires is presented. Considering the long design service life, high-cycle fatigue (HCF) behavior, and slender geometry (high length-to-diameter ratio) of these wires, a high-speed rotary bending fatigue test platform is custom-designed and constructed. The design mechanically maximizes the probability of fracture at the midpoint of the constant-cross-section specimen, even when considering clamping damage at the ends. Through mechanical derivation for the test platform, based on the beam bending theory and the finite element method, a quantitative relationship is established between the bending stress amplitude and the deflection angle at the clamped end. Using this platform, the fatigue lives of 6201 aluminum alloy individual wires under various bending stress amplitudes are tested, and the stress–life (S-N) curve is obtained. The developed experimental method and the reported fatigue data in this study provide essential experimental and material data for fatigue life prediction and engineering design of 6201 aluminum alloy individual wires.

Metals doi: 10.3390/met16080876

Authors: Toshio Haga Hirofumi Sakaue

The high-speed, low-load twin-roll casting of Al-Si alloys with a Si content of approximately 1 at% is needed to prevent the occurrence of cracks. In twin-roll casting, however, the roll load reaches the lower limit required for the sufficient solidification of the aluminum alloy. In this study, a single-roll caster equipped with a scraper was used to cast strips without cracks. The semi-solid forming of the free-solidified surface of an Al-1%Si strip during casting using a single-roll caster was attempted with a scraper under a very small load at a high roll speed of 30 m/min. The effects of the scraper angle and the scraper load on the condition of the scraped surface were investigated. The roll-contact surface and scraped surface of the strips cast under the appropriate conditions were compared by bending and deep drawing tests. After cold-rolling and annealing, no differences were observed between the roll-contact surface and the scraped surface. A sound Al-1%Si strip without cracks can be cast using a single-roll caster equipped with a scraper at a speed of 30 m/min.

Metals doi: 10.3390/met16080874

Authors: Xiao Liu Lipu Xu Tao Wang Zhongkai Ren Hong Xiao Jiang Ji

The growing demand for high-precision thickness control in cold rolling of metal strips calls for continuous improvement in rolling force prediction models. Classical thin-strip rolling theories, notably the Stone model, are based on the assumption of a circular roll arc profile within the contact deformation zone. In practice, however, this assumption often becomes invalid owing to the emergence of a neutral zone under specific rolling conditions, which introduces considerable errors in force calculation and compromises model applicability. To address this issue, the present study develops a numerical analysis framework for thin-strip rolling processes across a range of initial thicknesses and reductions. The proposed method quantitatively captures the effects of single-pass reduction on roll shape evolution and contact pressure distribution along the deformation arc. In addition, a limiting producible thickness model is proposed by incorporating the deformation efficiency of the strip material. This approach enables the precise delineation of a neutral-zone-free deformation regime and establishes a criterion for determining the optimal single-pass reduction based on the ratio of initial thickness to Stone minimum rolling thickness. For given initial thickness and process parameters, a critical single-pass reduction exists that eliminates the neutral zone, yielding a characteristic curve that divides the rolling regimes: above it, the neutral zone vanishes, the Stone model applies, and efficiency is high; below it, a finite neutral zone persists, partially dissipating rolling force in elastic deformation, though rolling remains viable within limits. These findings provide a robust basis for improving rolling force accuracy and pass optimization, ultimately enhancing product quality and forming efficiency in precision strip manufacturing.

Metals doi: 10.3390/met16080873

Authors: Yaowu Zhou Yang Liu Zhaozhi Wu

The advanced manufacturing of metal micro-holes is of great significance in various fields of industrial production, including aerospace, automotive, electronics, and healthcare. New technologies are constantly emerging, including various multi-energy field manufacturing technologies, and the knowledge system is complex and intricate. The present article summarizes recent advancements in metal micro-hole manufacturing technologies, drawing parallels with existing laser processing and electrochemical processing technologies. The present systematic review has been conducted with the objective of providing a comprehensive overview of the latest methodologies. The present review paper is of particular significance in that it encompasses not only the fundamental principles and innovative process methods, but also the most recent research progress and current problems. Furthermore, a synopsis of the developmental trajectory of advanced sustainable manufacturing technology for micro-holes was furnished.

Metals doi: 10.3390/met16080872

Authors: Mohammad Dadgar Martina Müller Max Meerkamp Tim Herrig Stefan Gräfe Thomas Bergs

Additive manufacturing (AM) enables rapid, near-net-shape fabrication with high material efficiency, but the resulting components often exhibit surface roughness, microstructural heterogeneity, and tensile residual stresses that reduce their performance. Machine hammer peening (MHP) is a mechanical surface treatment capable of modifying the surface integrity of AM components. It can be applied either as a conventional post-processing step after fabrication or as a hybrid interlayer treatment integrated into the build process. In this study, the effects of MHP process parameters and treatment strategies on wire-based laser metal deposition (LMD-w) Inconel 718 components were investigated, including the implementation of hybrid interlayer MHP. Surface topography, hardness, microstructure, and residual stresses were examined experimentally, while numerical simulations were developed to support the measurements and to characterize local contact conditions and plastic strain evolution during peening. The results show that MHP significantly reduces surface waviness and roughness, increases near-surface hardness, refines the microstructure, and introduces deep compressive residual stresses. Furthermore, hybrid interlayer MHP enhances the depth and uniformity of the modified layer by influencing the evolving microstructure during deposition. Standard forged Inconel 718 samples were also treated with MHP as a reference, showing comparable characteristics between the forged and AM components. These findings demonstrate that MHP is a versatile and effective modification technique for improving the performance and reliability of AM components, particularly when implemented as a hybrid interlayer treatment during the AM process.

Metals doi: 10.3390/met16080871

Authors: Michael Isakhani Zakaria Janne Sundelin

Metal additive manufacturing (AM) plays an increasingly important role in sustainable production owing to its material efficiency, design freedom, and compatibility with circular economy (CE) strategies. Yet the high cost and environmental burden of producing virgin metallic powders remain major barriers to large-scale adoption. This review synthesizes current and emerging approaches for recycling metallic powder feedstocks within AM, organizing them into four pathways: reusing, reconditioning, repurposing, and resourcing. Reusing preserves powders within the AM loop through controlled handling and qualification strategies, whereas reconditioning applies mechanical, thermal or chemical treatments to restore powder properties. Repurposing redirects powder to alternative value-added routes, including wire feedstock, metal–polymer composites, extrusion materials, and elemental or oxide recovery. Resourcing generates new powder from end-of-life powder, printing scrap, and waste through mechanical size reduction, atomization-based processes, or solid-state conversion routes. Across these pathways, the review highlights technological advances, process limitations, and cross-cutting challenges related to oxidation, morphology deterioration, contamination, and scalability, and identifies underexplored methodologies with potential for AM-specific recycling. By integrating insights across the field, this work outlines the expanding landscape of metallic powder circularity and demonstrates how diversified recycling strategies can reduce environmental impact, lower material costs, and support a more sustainable AM ecosystem.

Metals doi: 10.3390/met16080870

Authors: Qiang Zhou Jiamin Yao Yongsheng Gao Botao Hu Tong Feng Chao Zhang

This study investigates the effects of air cooling and water mist cooling on the microstructure and mechanical properties of friction stir additive manufactured Al-Cu-Li alloy. The results show that under air cooling, coarse grains (average 15.37 μm) form, accompanied by coarse θ phase (Al2Cu), S phase (Al2CuMg), and Fe-containing brittle intermetallic compounds. A strong texture is observed (P_max = 6.45), and the tensile fracture surface exhibits a mixed ductile–brittle fracture mode with the coexistence of cleavage facets and dimples. The tensile strength, yield strength, and elongation are 325 MPa, 165 MPa, and 21%, respectively. Water mist cooling significantly refines the grain size (average 5.15 μm), weakens the texture (P_max = 5.41), suppresses the formation of detrimental Fe-containing phases, and promotes the precipitation of fine, dispersed θ phase and T1 phase (Al2CuLi) (~200 nm). The fracture surface transforms into a uniformly dimpled ductile fracture. Mechanical properties are simultaneously improved: tensile strength reaches 348 MPa (+7%), yield strength 182 MPa (+10%), and elongation 24.5% (+17%). Rapid cooling achieves a synergistic optimization of strength and ductility through grain refinement strengthening, precipitation strengthening, and elimination of harmful phases.

Metals doi: 10.3390/met16080869

Authors: Jie Peng Yichen Qian David Cereceda

In the original publication [...]

Metals doi: 10.3390/met16080868

Authors: Yeong-Jun An Jun-Pyo Hong Hyeon-Seung Jin Min-Guk Kim Sun-Ho Shin Jong-Hun Kang

Large slewing bearings for wind turbines require sufficient hardening depth due to high contact stresses and cyclic loads. In this study, we combined electromagnetic–thermal–phase-transition coupled finite element analysis (FEA) with a surrogate model to predict the induction hardening depth of a dual-inductor system equipped with a magnetic flux concentrator. The air gap and the currents applied to the two inductors were used as input variables, and the hardening depth at five locations was calculated using FEA. Position 4 was identified as the critical location where the minimum hardening depth occurs. Since predictions based on limited FEA data may lead to overfitting and validation uncertainty, DNN, RSM, GPR, and SVR were compared, and LOOCV was applied to the comparison models. DNN predictions were adopted for the selection of candidate process conditions. When A1 and A2 were 8200 A and 8600 A, respectively, the predicted hardening depth was 6.17 mm. Under these conditions, additional FEA results showed a depth of 6.38 mm, while prototype measurements indicated 6.20 mm, representing a difference of 2.90%. This approach can be utilized to select candidate induction hardening conditions within the reviewed process range.

Metals doi: 10.3390/met16080867

Authors: Bin Zhao Kuanjun Zhu Bin Liu Jinshan Wang Junhui Li Jian Gu

In this work, the microstructural evolution and comprehensive performances (mechanical, wear, and corrosion resistance) of LDED-fabricated 2205 DSS subjected to heat treatment at 1000 °C for different holding durations (5 min, 10 min, 30 min, and 60 min) were systematically investigated. The results indicate that the austenite content gradually increases with the extension of heat treatment time, reaching a peak value of 51% at 30 min. Meanwhile, the austenite morphology transforms from dendritic grains to equiaxed grains, accompanied by the massive precipitation of intragranular austenite (IGA) and obvious elemental enrichment behavior. In terms of mechanical and functional performances, the microhardness decreases slightly with prolonged heat treatment, with a total reduction of only 7%. The elongation increases continuously, while the yield strength and tensile strength remain relatively stable. Additionally, the wear coefficient and wear rate present a trend of first decreasing and then increasing. The minimum wear rate of 48.32 × 10−6 mm3/(N·m) is obtained at the heat treatment duration of 30 min, which is 83.4% lower than that of the untreated sample. Moreover, the optimal corrosion resistance is achieved after 30 min of heat treatment, with the corrosion current density decreasing by 45.8% relative to the as-built specimen. These results demonstrate that heat treatment at 1000 °C for 30 min is an optimal processing parameter to significantly optimize the microstructure and comprehensive performances of LDED-2205 DSS.

Metals doi: 10.3390/met16080866

Authors: Alma Terlikbaeva Nazigul Zhumakynbai Nazira Seidakhmetova Feruza A. Berdikulova Abdurassul Zharmenov Galymzhan Maldybayev Rustam Sharipov Makpal Satybayeva

The development of efficient technologies for processing secondary technogenic raw materials represents a promising approach to replenishing vanadium resources. This study investigates the processes of sulfuric acid reductive leaching of vanadium from spent vanadium catalysts using oxalic acid and metallic iron as reducing agents. It was established that oxalic acid provides vanadium extraction of up to 95.2%, whereas the use of metallic iron (2–3 wt.% of the catalyst mass) enables a vanadium recovery rate of 91–92% at a solid-to-liquid ratio of 1:7 and pH 1.3–1.5, offering a more cost-effective alternative. Thermodynamic modeling of the V–Fe–P–SO4–C2O4–H2O system was performed using the Medusa software package over a pH range of 0–3. The results showed that vanadium(IV) predominantly exists as the VOSO4 complex in sulfuric acid solutions, whereas the formation of oxalate and phosphate complexes is thermodynamically insignificant. Iron(III) was found to exhibit a strong affinity toward phosphate ions, promoting their selective precipitation as an iron phosphate phase while maintaining vanadium in solution. The obtained results provide a scientific basis for the efficient preliminary separation of iron and vanadium and for improving the selectivity of subsequent vanadium sorption.

Metals doi: 10.3390/met16080864

Authors: Xinrui Zhang Zhuohang Li Teng Liu Zhisheng Nong Hongliang Zhang

AlCoCrFeNi-based high-entropy alloys have garnered significant attention for high-end applications in aerospace, marine engineering, and the nuclear industry due to their exceptional comprehensive properties, including high strength and good corrosion resistance. However, their widespread application is critically hindered by a fatal disadvantage: poor ductility. Optimizing the ductility of this alloy system has therefore become a key research priority. Optimizing their ductility has emerged as a key research priority in recent literature. This review systematically examined the influences of diverse fabrication techniques on the mechanical properties, particularly ductility, of these alloys. Melting routes (vacuum arc melting and vacuum induction melting), powder consolidation (spark plasma sintering and hot pressing), and additive manufacturing (selective laser melting, laser melting deposition, electron beam melting, and wire arc additive manufacturing) were covered in this review. This review underscores that while each fabrication route offers distinct advantages, future breakthroughs require multi-process hybridization, data-driven optimization, and precise control of precipitation kinetics to overcome the strength–ductility trade-off and enable large-scale applications of AlCoCrFeNi-based HEAs.

Metals doi: 10.3390/met16080865

Authors: Shunqi Mei Zekui Hu Mikhail Guryev Sergey Ivanov Alexey Guryev Sergey Zemlyakov Guojun Fu Quan Zheng

Contactless gas-phase boriding is suitable for strengthening the surface of precision steel components because it avoids direct contact between the workpiece and the boriding medium, thereby helping to maintain dimensional accuracy and surface roughness. To address the toxicity, corrosiveness, flammability, and strict gas-handling requirements associated with externally supplied boron-containing gaseous precursors in conventional gas-phase boriding, this study proposes a novel sealed-container structure for contactless gas-phase boriding, in which powder-filled pockets are distributed along the inner wall of the sealed container, and conducts experimental investigations on gas-phase boriding. Compared with the conventional structure, the modified container places the powder charge in wall-mounted pockets close to the heated container wall, thereby accelerating powder heating. This arrangement also reduced the powder-heating time from approximately 1.1 h to 0.85 h and promoted the earlier generation of an active boron-containing atmosphere, shortening the boriding holding time from 3 h to 1.5 h. Meanwhile, the average boride-layer thickness increased from approximately 54 μm to 117 μm, and the maximum surface microhardness reached 3500 HV. These results indicate that improving the sealed-container structure and optimizing the arrangement of the powder boron source can effectively intensify the contactless gas-phase boriding process. A thick boride diffusion layer can be rapidly formed while maintaining limited dimensional change and acceptable surface roughness.

Metals doi: 10.3390/met16080863

Authors: Shuwan Cui Dao’ai Zhou Zuojin Qin Xingui Ma Guiyou Zhou Mingqian Gao Fuyuan Tian

As piston rods for excavator boom hydraulic cylinders shift from integral forging to welded assemblies of separately manufactured rod bodies and rod heads, joint reliability becomes critical to load-bearing performance. In this study, 60 mm diameter quenched-and-tempered/as-rolled 1045 steel joints were fabricated by continuous-drive friction welding under three coupled secondary-friction pressure–time conditions. Joints made with two quenched-and-tempered base metals were compared under the same high-pressure/short-time condition. Optical microscopy, electron backscatter diffraction, microhardness testing, tensile testing, and scanning electron microscopy were used to characterize microstructure and failure behavior. Fine, multi-oriented reconstructed microstructures formed in all weld zones, while a hardness valley developed in the heat-affected zone on the quenched-and-tempered side. As the machine-displayed secondary-friction pressure increased from 1.43 to 2.14 MPa, the actual secondary-friction time decreased from 57.3 to 37.5 s. Under the corresponding high-pressure/short-time condition, heat-affected-zone softening was slightly mitigated and tensile strength increased from 743.37 to 755.78 MPa. Different elongations were observed between the two joint types. All specimens fractured in the softened heat-affected zone on the quenched-and-tempered side and exhibited dimple-dominated fracture surfaces. Under the present tensile-testing conditions, the weld zone was not the fracture-controlling region.

Metals doi: 10.3390/met16080861

Authors: Ebubekir Atan Mustafa Rasheed Mustafa Öncül Orhan Akyüz Mücahit Sütçü

This study investigates the effect of equal channel angular pressing (ECAP) temperature and pass number on the microstructural evolution and hardness response of a CuAg0.1 alloy. ECAP was performed by using route Bc at room temperature and 100 °C for up to six passes. X-ray diffraction results showed that no additional crystalline phase was detected after ECAP, while peak broadening and relative intensity changes indicated deformation-induced lattice distortion, defect accumulation, and a tendency toward preferred orientation. Optical microscopy revealed progressive microstructural subdivision with increasing pass number, particularly under room-temperature processing. Vickers microhardness increased sharply after the first ECAP pass and approached a saturation-like regime after approximately four passes. Room-temperature ECAP produced higher hardness and hardness-derived estimated strength values than processing at 100 °C, indicating more effective defect storage and suppressed recovery. In contrast, the lower hardening response at 100 °C is attributed mainly to thermally assisted recovery and dislocation rearrangement. The section-dependent hardness response suggests ECAP-induced anisotropy was associated with the imposed shear deformation and preferred crystallographic orientation. Within the investigated processing, four-pass room-temperature ECAP provided the most effective hardness-based strengthening response.

Metals doi: 10.3390/met16080862

Authors: Tengshi Liu Gangsheng Xie Han Yi Di Zhang Zhouyan Cai Yulin Xia Han Dong

The history of steel rail manufacturing at the Hanyang Iron Works in China is briefly summarized first in this paper. The chemical composition, microstructure, inclusions, and mechanical properties of the manufactured rails were then systematically analyzed. The progress of manufacturing process evolution and the enhancement of product quality are elucidated through this study. The chemical composition of steel rails produced by Hanyang Iron Works in its initial stage (before 1904) was characterized by low carbon content (0.13–0.22 wt.%) and high phosphorus levels (P ≥ 0.15 wt.%). Inclusions were primarily identified as sulfides (MnS) and composite inclusions of sulfides and silicates (MnS·SiO2). The microstructure consisted of a large amount of ferrite and pearlite. Following the technical transformation from 1905 to 1908, dephosphorization was achieved and the composition control of the steel rails was optimized. The carbon content of the rails was increased to above 0.48 wt.%, while the phosphorus content was significantly reduced (P ≤ 0.10 wt.%). The inclusions were identified as sulfides (MnS) and composite inclusions consisting of sulfides and aluminum oxides (MnS·Al2O3). The microstructure was transformed into a combination of a small amount of proeutectoid network ferrite and pearlite. The mechanical performance of the steel rails was substantially improved via the implementation of technological upgrades at the Hanyang Iron Works. A tensile strength of 800 MPa grade was achieved in some rails, which constitutes a 200 MPa increment over the strength of rails from the early production period. A transition in the fracture morphology of tensile specimens was observed, shifting from large and shallow dimples with a small amount of cleavage fracture to small, shallow dimples combined with predominant cleavage fracture.

Metals doi: 10.3390/met16080860

Authors: Iosu Mutilva Pedro Imízcoz José Antonio García Carmelo J. Luis-Pérez

The characterization of high-temperature plastic deformation behavior in centrifugally cast alloys has historically been based on curve fitting of experimentally obtained creep data. Although this approach provides acceptable results within the range of experimental conditions used for curve fitting, performance predictions under conditions outside conventional tests—typically derived from constant temperature and stress—remain insufficiently accurate for petrochemical engineering applications. In this study, constant-load creep tests were performed across a stress range of 5–33 MPa at 950–1100 °C. The minimum creep rate was calculated from the creep curves and used to fit Norton-law parameters by log–log regression. A global Norton-law fit was first carried out for each temperature, and an additional segmented fit was then performed by separating the low- and high-stress domains. The results reveal a systematic variation in the apparent Norton stress exponent (n) with the stress range considered. This variation suggests that the creep response changes from one apparent stress domain to another, contradicting the assumption of a single-valued Norton exponent inherent in standard curve-fitting procedures. Although the experimental database was obtained from conventional constant-load and constant-temperature creep tests, the results are discussed in terms of their implications for creep modeling under non-stationary operating conditions, where local stress and temperature fields may evolve during service. Parameters fitted over a broad stress range may produce systematic local errors when applied to stress domains with different apparent sensitivities. Furthermore, it is well known that classical steady-state creep models may be insufficient when their fitted parameters are transferred to non-stationary loading conditions, where thermal transients during start-up and shutdown generate differential thermal strains and high local stress levels. Geometric constraints, combined with these peak stresses, may lead to values exceeding the yield strength, a condition under which classical methods fail to adequately describe material behavior and stress relaxation mechanisms. This manuscript directly addresses this limitation through the analysis of three heats of the same centrifugally cast alloy.

Metals doi: 10.3390/met16080858

Authors: Piotr Kowalik Edyta Wróbel

This article describes the use of NiP alloy-based layers for the production of conductive and resistive layers. The authors demonstrate the potential of this technology for the production of electrodes in photovoltaic structures, among other applications. To facilitate this use of NiP alloy metallization, a selective metallization process was developed. This process is our own proprietary concept and is not reported elsewhere in the literature. To simplify the process, process modeling was performed, enabling the rapid selection of chemical metallization process parameters. We used ultrasound support to ensure that the electroless metallization process with NiP alloys could be applied to all types of substrates used in electronics (including flexible substrates). The use of ultrasound-assisted electroless metallization technology shortens the production time of silicon electrodes made for photovoltaic cells. Furthermore, we proved that it is possible to produce a metallic layer on flexible substrates. The developed technology enables the production of electrodes used in, for example, flexible photovoltaic cells. This type of metallization is advantageous due to its low cost and simplicity, and its ability to produce both the top and bottom electrodes in a single process, offering a wide range of industrial applications. Our previous work demonstrated the feasibility of applying this process to ceramic and silicon substrates exclusively. This research aligns with current research trends focusing on reducing the production costs of photovoltaic cells and, consequently, minimizing the associated carbon footprint.

Metals doi: 10.3390/met16080859

Authors: Shaopeng Wu Geng Cao Dongxin Wang Junyi Li Jiankang Zhang Shuhui Cui Hailong Pang Mingda Han Yiqun Yang

This study examines the microstructural evolution and tensile response of a cold-rolled C17200 Cu–Be–Co alloy strip after short-time annealing at 550 and 610 °C. X-ray diffraction (XRD), electron backscatter diffraction (EBSD), kernel average misorientation (KAM) analysis, transmission electron microscopy (TEM), and room-temperature tensile testing were used to compare phase constitution, grain-boundary character, recrystallization behavior, texture evolution, dislocation substructure, and tensile properties. The results show that both annealed samples mainly consisted of an α-Cu matrix and a small amount of BeCu-related precipitates. After annealing at 550 °C, the alloy retained a recovery-dominated partially recrystallized microstructure, with an average grain size of 1.47 μm, a low-angle grain boundary fraction of 8.4%, a recrystallized fraction of 18.06%, and evident residual dislocation substructures. This condition exhibited a yield strength of 365.5 MPa. After annealing at 610 °C, recrystallization was substantially promoted, the average grain size increased to 1.92 μm, the high-angle grain boundary fraction increased to 97.5%, and the recrystallized fraction reached 82.76%. Meanwhile, the yield strength decreased to 276.6 MPa because of the reduced contribution from dislocation strengthening. These results indicate that, under the two investigated short-time annealing conditions, the strength difference in the alloy is mainly associated with the transition of microstructural evolution from recovery-dominated partial recrystallization to a recrystallization-dominated microstructure.

Metals doi: 10.3390/met16080857

Authors: Xin Wang Yuyong Chen Jingxi Wu Yu Zhang

A large-size ingot (Φ200 mm × 800 mm) with the nominal composition Ti-46Al-8Nb-2.5V (in at.%) was fabricated via triple vacuum consumable electrode arc remelting in this study. XRD, SEM-EDS, TEM, tensile testing, and chemical analysis were employed to examine phase composition, microstructure, mechanical properties, and impurity contents across the height direction of the large-size ingot. Phase composition differences across different positions arose from the solidification path and elemental distributions. The redistribution of major elements during solid–liquid, allotropic and eutectoid transformations contributed to three types of segregation—namely S-segregation, β-segregation, and α-segregation. The maximum deviations in Al, Nb and V content along the height direction of the ingot were 2.05 at.%, 2.24 at.%, and 0.36 at.%, respectively. The bottom position of the ingot exhibited superior tensile properties at both room and elevated temperatures. The average oxygen and nitrogen contents in the ingot were 717 wt. ppm and 183 wt. ppm, respectively.

Metals doi: 10.3390/met16080856

Authors: Feng Chen Renyi Han Yufeng Guo Mingxing Zhu Shuai Wang Mengtu Li Lingzhi Yang Hongzhi Heng

Lump ore reduction generates fines that can induce furnace hanging or slipping. Reducing this degradation is key to maintaining stable operation. To address the degradation problem of lump ores during direct reduction in hydrogen-based shaft furnaces, this study systematically investigated the effects of reduction temperature and reduction time on the degradation behavior of three lump ores with distinct crystal structures under HYL atmosphere. The phase evolution, thermal decomposition characteristics and microstructural damage mechanisms during reduction were elucidated. The results showed that all three lump ores exhibited the most severe degradation after 60 min of reduction at 700 °C, with reduction degradation index values below 3.15 mm (RDI−3.15mm) of 32.50%, 15.17%, and 22.42% for Lump Ore 1, Lump Ore 2, and Lump Ore 3, respectively. During isothermal reduction at 500 °C, pronounced degradation occurred in all three ores at around 20 min (RDI−3.15mm: 33.09%, 18.09%, and 8.85% for Lump Ore 1, Lump Ore 2, and Lump Ore 3, respectively). Microscopic mechanism analysis revealed that dehydration of lump ores with high crystal water content caused structural damage, which was coupled with phase transformation stresses during reduction and led to severe degradation. In porous lump ore, stress was more readily dissipated and crack propagation was effectively buffered. In contrast, dense lump ore was prone to stress accumulation caused by locally nonuniform reduction, ultimately resulting in penetrating cracks. This study clarifies the degradation behavior of the three lump ores under different reduction regimes and reveals the evolution of phases and microstructures during reduction, providing a theoretical basis for stable operation of hydrogen-based shaft furnaces.

Metals doi: 10.3390/met16080855

Authors: Shouzhen Cao Yiyong Jin Guangqing Xu Fuqiang Wang Yao Wang Hongfeng Wang

Aluminum-clad steel wires are widely used in ultra-high-voltage (UHV) transmission lines due to their excellent beneficial properties. To address the inadequate strength–ductility balance of aluminum-clad steel wires for UHV applications, this study investigates the effects of cold drawing and low-temperature annealing (200~330 °C) on the microstructure, aluminum/steel interface, and mechanical properties of 20SA (20.3% IACS) aluminum-clad steel wires. The results indicate that the cold-drawn steel core exhibits high strength due to its high dislocation density and strong <110> fiber texture. Low-temperature annealing promotes overall recovery and partial recrystallization of the microstructure. Specifically, annealing at 240~280 °C significantly enhances ductility while maintaining high strength, achieving optimal strength–ductility synergy; however, higher annealing temperatures result in an unacceptably low ultimate strength, rendering them impractical for application. Interfacial characterization reveals that the as-clad and cold-drawn processes, as well as annealing below 250 °C for 10 min, maintain stable metallurgical bonding at the aluminum/steel interface, whereas annealing at 300 °C for 10 min induces the formation of brittle Fe-Al intermetallic compounds, thereby compromising service reliability. Furthermore, the precipitation of cementite (Fe3C) with increasing temperature partially compensates for the strength loss caused by overall recovery. This study identifies the optimal heat treatment window, providing a theoretical basis for the strength–ductility design and reliable service of UHV transmission lines.

Metals doi: 10.3390/met16080854

Authors: Pierre Heugue Philippe Nugues René Billardon Romain Bergeron Paul Martin Loïc Ferrage Emmanuel Loubère Thomas Perrin Arthur Desprès

Additive manufacturing (AM) is increasingly being considered to produce large aluminum components for aeronautical applications. Larger parts lead to longer build durations, numerous lasers and may result in prolonged exposure to high temperatures if heat dissipation is insufficient, causing in situ ageing during manufacturing and a consequent reduction in the mechanical properties of as-built aluminum alloys. This study investigates the relationship between process parameters, heat dissipation, and resulting mechanical properties in large-scale A357-AlSi7Mg0.6 aluminum alloy manufactured by laser powder bed fusion (LPBF). In the context of developing geometrically complex casings or components using LPBF equipment with multiple lasers (up to 12), mechanical testing of first prototypes revealed up to a 30% reduction in mechanical properties in certain regions, attributed to insufficient heat dissipation during the build. Thermal modelling and in situ experimental measurements have shown that the high thermal mass and extended build times of large components lead to non-uniform temperature distributions, promoting undesired microstructural evolution and advanced over-ageing, effects that are generally less pronounced in smaller specimens reported in the literature. Hardness mapping on samples subjected to monitored ageing ranges, as well as on additively manufactured rods with deliberate geometries for heat accumulation, confirmed that areas with insufficiently optimized support show significant decreases in hardness due to inefficient heat dissipation. A numerical model was developed to link the hardness evolutions to both ageing time and temperature, enabling improved predictions of microstructure and properties as a function of build and heat-removal strategies. These findings emphasize the critical importance of support structure optimization for both mechanical support and thermal management during LPBF, as well as the need for tailored process and post-process heat treatments to achieve consistent and reliable mechanical properties in large, additively manufactured aluminum alloy components.

Metals doi: 10.3390/met16080853

Authors: Halil Ahmet Gören

This study investigates the effect of adding silicon (Si) and cadmium (Cd) elements to AM60 (Mg) magnesium alloy on its corrosion and tribocorrosion (abrasive wear) properties at pH 2.4. Optical Microscopy (OM), X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), SEM mapping, and SEM line methods were applied to the alloys. Additionally, the effect of Cd addition on the alloys was investigated using potentiodynamic polarization corrosion in a medium containing CH3COOH (vinegar) at pH 2.4 (acetic acid) and 20 N and 40 N reciprocal abrasive wear tests in the same medium. The hardness of alloy A1 was determined to be 58.6 HV. Hardness increased by 0.92% in alloy A2, 4.18% in alloy A3, and 10.66% in alloy A4, with the hardness increase occurring as Cd content increased. In potentiodynamic corrosion tests, the corrosion rate (CR) increased with increasing Cd content. In abrasive wear tests, Cd addition increased the abrasive wear rate, and the alloys were ranked in order of increasing wear as follows: A1 < A3 < A2 < A4. These results will contribute to the automotive, aerospace, agricultural, construction, and machinery industries operating in acidic environments, as well as to the scientific literature.

Metals doi: 10.3390/met16080852

Authors: Li-Juan Li Xin-Yu Liu Kai-Chuang Li Yi-Long Zhang Qi-Jie Zhai

The Pulse Magneto Oscillation (PMO) solidification homogenization technique has been successfully applied in the continuous casting production of GCr15 bearing steel. To further investigate the effects of PMO technology on the precipitation mechanisms of primary carbides in GCr15 bearing steel, a series of directional solidification experiments were conducted under the influence of PMO. Characterization and analysis of the area proportion, number density, particle-size distribution, elemental distribution, and types of primary carbides in the as-cast bearing steel under various PMO parameters were conducted using Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Electron Probe Microanalysis (EPMA), and Electron Backscatter Diffraction (EBSD). The findings reveal that the predominant carbide species precipitated in GCr15 bearing steel is M3C type, characterized by a higher Cr content. As the PMO peak current and pulse frequency increase, there is a significant reduction in both the area proportion and number density of primary carbides. Compared to non-PMO conditions, the application of PMO results in a maximum decrease in carbide area proportion by up to 75.6% and a reduction in number density by up to 58.4%, leading to a more dispersed and uniform carbide distribution. Moreover, under the influence of PMO, the local solidification duration of the solution shortens, leading to an increase in the quantity of inclusions such as MnS, which undergo refinement. This facilitates the refinement of primary carbides that utilize inclusions as heterogeneous nucleation sites. Additionally, the reduction in dendritic arm spacing within the solidification structure and the enhancement of solute distribution near the solid–liquid interface, induced by PMO, also create favorable conditions for the reduction in size and quantity of primary carbides. Based on the distinctive characteristics of primary carbides under varying PMO parameters, an innovative dynamic model for the formation of primary carbides during the solidification process of GCr15 bearing steel has been proposed.

Metals doi: 10.3390/met16080851

Authors: Nazerke Serikkyzy Zarina Aringozhina Bauyrzhan Rakhadilov Malgorzata Rutkowska-Gorczyca Meruyert Adilkanova Nurtoleu Magazov

The influence of hydrogenation, mechanical milling, and dehydrogenation parameters on the structure and properties of titanium powders produced from titanium sponge via the hydride–dehydride (HDH) process was investigated. The aim of the study was to compare representative HDH processing routes and identify the processing route that provided the most favorable structural characteristics for subsequent mechanical alloying and powder metallurgy applications. Commercially pure Grade 0 titanium sponge was used as the starting material and was subjected to hydrogenation at temperatures ranging from 350 to 650 °C, short-duration mechanical milling in an argon atmosphere, and vacuum dehydrogenation at temperatures between 750 and 950 °C. The resulting powders were characterized using laser particle size analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The results showed that increasing the hydrogenation temperature promoted the formation of the TiH2 hydride phase and enhanced powder fragmentation during subsequent mechanical milling. XRD analysis demonstrated effective dehydrogenation, as evidenced by the disappearance of detectable TiH2 reflections and the restoration of the α-titanium phase within the detection limits of the technique. Qualitative SEM observations indicated that the investigated HDH processing routes influenced particle morphology and agglomeration behavior, whereas EDS analysis demonstrated a relatively uniform distribution of the detected elements without revealing detectable contamination within the analyzed regions. Mechanical alloying of the selected powders with aluminum and vanadium showed that, among the investigated processing routes, the H2–M2–D2 condition provided the most favorable combination of particle size distribution, phase composition, morphology, and elemental distribution for the production of a mechanically alloyed Ti–Al–V powder mixture.

Metals doi: 10.3390/met16080850

Authors: Ester Villanueva Viteri Iban Vicario Gómez Ignacio Crespo Camino Iñaki Hurtado Hurtado Joseba Albizuri Irigoyen

This study develops novel multicomponent Al–Mg–Si–Zr–Cu-based alloys for high-pressure die casting (HPDC) with improved mechanical properties and thermal stability. Four compositions were designed through Zn and Cr additions, supported by thermodynamic modelling. XRD and SEM/EDS analysed phase formation and microstructure, while density, electrical conductivity, hardness, and mechanical behaviour under tensile and compressive loading at room temperature and 200 °C were evaluated. Hardness increased from 166 to 214 HV3 with Zn and Cr due to the formation of complex intermetallic phases. The Al–Mg–Si–Zr–Cu alloy showed the best balance of strength and ductility under tensile loading, whereas Zn and Cr additions reduced tensile performance. In compression, Zn significantly improved strength, reaching the ultimate compressive strength of 697 MPa. Compared with the reference AlSi9Cu3 alloy, the new alloys achieved up to 30% higher yield strength, 13% higher ultimate tensile strength, and improved thermal stability. Among the studied compositions, Al72Mg10Si5Zr3Cu10 showed the best overall performance, while Al67Mg10Si5Zr3Cu10Zn10 was optimal for compression-dominated applications.

Metals doi: 10.3390/met16080849

Authors: Liangyu Zhang Fengsheng Qi Zhongqiu Liu Sherman C. P. Cheung Baokuan Li

Slag splashing protection is the dominant technology for extending refractory lining service life and enhancing production efficiency in basic oxygen furnace (BOF) steelmaking. However, the intrinsic mechanism of gas-slag-steel multiphase coupled splashing remains poorly understood, and existing numerical methods suffer from prohibitive computational costs and inaccurate characterization of interfacial momentum transfer and multiphase interactions. This study establishes a fully coupled three-dimensional numerical model integrating Volume of Fluid (VOF)–Discrete Particle Method (DPM) bidirectional phase transition, adaptive mesh refinement (AMR), and Eulerian Wall Film Model (EWFM), and the multiphase flow simulation in this study adopts constant thermophysical parameters of molten steel and slag at the industrial splashing temperature of 1650 °C. Taking the Blowing Number (NB) as the core similarity criterion, a 1:10 scaled geometric model of a 50-ton industrial BOF is employed to systematically investigate the regulatory effects of top-blowing flow rate, lance height, and NB on droplet splashing behavior and wall liquid film evolution. The model is validated against mercury-glycerol cold model experimental data, with a relative error of less than 3% in total splashing mass prediction. Results demonstrate that increasing NB significantly enhances splashing intensity. Under optimal conditions (200 mm lance height, 11.76 Nm3/h flow rate, NB = 9.30), the wall liquid film fully covers the middle-upper furnace wall with a uniform thickness of 0.8–1.2 mm. NB dominates jet momentum distribution: high NB forms a deep-penetrating four-lobed impact cavity, remarkably improving droplet axial momentum and residence time. Molten steel droplets concentrate at 3–4 mm, while slag droplets shift to 2–4 mm at high flow rates of 11.76 Nm3/h, with maximum slag droplet production at NB = 6.99. This work provides reliable theoretical support for industrial BOF slag-splashing process optimization.

Metals doi: 10.3390/met16080848

Authors: Gnanesh Talur Chandrashekar Josip Vinčić Stefan Rotzsche Massimo Zampato Christian Finotto Alessandro Salmi Alberta Aversa Paolo Fino

Laser-directed energy deposition (L-DED) was used to manufacture samples of the newly developed W360 hot-work tool steel from voestalpine Böhler Edelstahl. Various heat-treatment processes, including austenitising followed by air or water-quenching and tempering, as well as direct tempering, were applied. The as-built and heat-treated conditions were characterised by optical microscopy (OM), scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM-EDS), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD), while the microstructural evolution during austenitisation was investigated using a high-temperature microscope (HTM). Hardness measurements were performed to determine the material response. The as-built condition exhibited a hardness of 628 ± 12 HV with no manufacturing cracks. The highest hardness (666 ± 13 HV) was obtained after air-quenching, whereas water-quenching produced 651 ± 14 HV. The rapid cooling of water-quenching, however, led to the formation of macroscopic cracks. The lattice distortion differences identified by XRD and the kernel average misorientation values obtained from EBSD indicated differences between the air and water-quenched conditions. High hardness (622–628 HV) was retained after low-temperature direct tempering, whereas high-temperature tempering resulted in significant softening (487 ± 12 HV). These results suggest that low-temperature direct tempering is a promising post-processing treatment for L-DED W360 tool steel, although additional mechanical testing is required to confirm industrial applicability.

Metals doi: 10.3390/met16080847

Authors: Ivan Jovanović Ana Kostov Violeta Nikolić Hadi Waisi Novica Staletović

This study analyzed the content of polluting and toxic elements (Cr, Ni, Cu, Zn, As, Cd and Pb) in the cadastral municipalities immediately surrounding the mining and metallurgical complex Bor in Serbia. The soil is exposed to hazardous substances due to historical pollution. Soil pollution at different locations was assessed based on the measured concentration of metals and the contamination factor (Cf). The increased content of the toxic metals was determined mostly for copper and arsenic. Three types of different plants were used in order to reduce the content of toxic metals in the contaminated mining and metallurgical land. The results showed that these plants (barley Hordeum sativum, sugar grazer Sorghum bicolor, and hybrid BMR 333 Sudan grass) were capable of growing and accumulating metals in plants at copper-mined and metallurgical sites.

Metals doi: 10.3390/met16080846

Authors: Yerlan Zhumagaliyev Yerbol Shabanov Zhadra Shilmagambetova Victor Semenikhin Aliya Mazhit Karlyga Almuratova Svetlana Semenikhina Bauyrrzhan Orynbayev Saltanat Zhumagaliyeva Kanat Kuanyshev Akylbek Shairzhanov

Chromo-magnesian ore materials constitute a complex resource base for producing both metallurgical and chemical products, yet existing research remains fragmented across beneficiation, smelting, chemical extraction, waste valorization, and refractory applications. This systematic review, conducted according to PRISMA 2020 using Scopus, Web of Science Core Collection, and SpringerLink, evaluates processing routes based on feedstock type and product orientation. Of 625 identified records, 19 studies met the final inclusion criteria. The reviewed technologies were classified into four groups: chemical processing, metallurgical reduction and smelting, integrated beneficiation–chemical–metallurgical routes, and refractory/materials production. Primary chromite ores and concentrates are predominantly used for ferrochrome and stainless-steel alloy production, whereas tailings, slimes, overburden, and serpentine-bearing materials are mainly processed into chromium oxide, magnesium compounds, and silica-rich products. Integrated routes show the greatest potential for low-grade and technogenic materials through multi-product recovery and improved resource efficiency. However, route selection depends on feedstock quality, mineralogy, target products, and process intensity. Major research gaps include limited comparative studies, insufficient mineralogy-driven process design, and inadequate techno-economic and environmental evaluation. Overall, future development should focus on integrated, feed-specific processing strategies that maximize resource utilization.

Metals doi: 10.3390/met16080845

Authors: Tingting Zhang Wenbin Zhang Feng Ji Hongli Li Zhenyi Huang Mingzhen Ma

The current internationally largest-diameter and thickest-wall oil and gas transmission line pipe of X80 grade (API Spec 5L) manufactured by longitudinal submerged arc welding (LSAW) is the X80 OD 1422 mm × 32.1 mm straight-seam LSAW pipe, which approaches the limit of manufacturing equipment capability. To overcome the 29-pass limitation of the conventional JCO (J-forming, C-forming, O-forming) forming process for steel pipes, this study conducts a three-dimensional finite element numerical simulation analysis based on ABAQUS 2022/Explicit (explicit dynamic finite element solver within the commercial finite element software Abaqus) to investigate the JCO forming process of this extreme-specification pipe. An innovative involute lower die is designed, enabling a reduction in the forming process to 25 passes. The residual stress and plastic strain distributions in the formed pipes from both the 25-pass and 29-pass processes exhibit consistent patterns, characterized by higher values at the surface layers and lower values in the core region, with the inner surface showing higher stress and strain levels than the outer surface. The maximum residual stress (231.7 MPa) and maximum plastic strain (0.03787) of the 25-pass pipe are slightly lower than those of the 29-pass pipe (231.9 MPa and 0.03859, respectively). In terms of geometric accuracy, the 25-pass process yields an opening gap of 118.8 mm, marginally better than the 118.98 mm of the 29-pass process, and produces a smoother outer circumference profile after forming. These results demonstrate the superiority of the 25-pass process with the novel involute die configuration. The subsequent engineering application validates that the established finite element model possesses high predictive accuracy and practical guidance value. This study provides a breakthrough solution to the technical challenge of excessive forming passes in the JCO forming of the extreme-specification X80 OD 1422 mm × 32.1 mm pipe, achieving a reduction in forming passes while maintaining forming quality, significantly improving efficiency, and reducing manufacturing costs.

Metals doi: 10.3390/met16080844

Authors: Zeynep Üçerler-Çamur Feridun Boylu Kudret Tahsin Perek Murat Olgaç Kangal

This study presents an efficient and environmentally friendly approach for lithium recovery from biotite-rich wastes generated during nepheline syenite processing by combining mechanical activation with sulfuric acid leaching. Mechanical activation was applied as a pretreatment to enhance extraction of lithium and minimize acid consumption. After optimizing the process parameters, lithium extraction efficiencies of up to approximately 91% were achieved. The results clearly demonstrated that mechanical activation substantially reduced sulfuric acid demand up to 85.7%, allowing lithium recoveries comparable to those obtained with 1.75 mol L−1 acid in direct leaching to be achieved using only 0.25 mol L−1 acid. Structural and morphological analyses (XRD, SEM, FTIR, and particle size analysis) confirmed progressive amorphization of biotite, accompanied by the weakening of -OH and siloxane (Si-O-Si) bonds. Needle-like and layered biotite particles transformed into rounded and agglomerated morphologies with increasing activation time, leading to an initial decrease in particle size followed by agglomeration-dominated growth. Although crystallinity continuously decreased with activation time, partially reversible behavior was observed beyond 120 min. Overall, mechanical activation enabled a low-acid, and effective process design for lithium recovery from biotite-rich nepheline syenite wastes.

Metals doi: 10.3390/met16080843

Authors: Yuanjun Ma Zhou Chen Yubi Gao Xueping Song

In this paper, solution-treated Inconel 625 alloy was selected as the research object. Combined with the low-energy characteristic of annealing twin boundaries and the synergistic strengthening effect of gradient structures, the alloy microstructure was tailored without altering its chemical composition. The evolution mechanism of grain size and twin boundary fraction, as well as their influence on corrosion resistance, were investigated. On this basis, the synergistic strengthening effect of gradient structure and interface regulation on the corrosion and mechanical performance of the alloy was further explored. The results show that a gradient-structured Inconel 625 alloy with abundant annealing twins and high-density grain boundaries can be fabricated by surface nanocrystallization combined with high-temperature short-time annealing. The variation in annealing twin fraction with grain size in interface-modified Inconel 625 complies with the Pande model. In terms of corrosion resistance, the microstructure consisting of fine grains and a high fraction of annealing twins exhibits superior performance compared to coarse grains with identical twin content. Its corrosion potential is tripled, while the corrosion current density is reduced by 11 times, delivering outstanding anti-corrosion capability in NaCl solution. Benefiting from the integrated merits of gradient architecture, annealing twins and fine grains, the interface-tailored Inconel 625 alloy achieves excellent comprehensive performance, with a yield strength of 925 MPa, elongation of 26%, and corrosion current density of 3.02 × 10−8 A/cm2, realizing the integration of high strength, good ductility and superior corrosion resistance for Inconel 625 alloy.

Metals doi: 10.3390/met16080842

Authors: Qingyong Zheng Huixue Jiang Yuxing Tian Guanmei Niu Mingchao Yu Xiaobin Guo Zhihao Zhao Gaowu Qin Hutian Li

Room-temperature storage after solution treatment and quenching is often unavoidable during the industrial processing of Al-Mg-Si-Cu alloys, but its interaction with pre-aging and the subsequent artificial aging response remains insufficiently quantified. Here, we demonstrate a pre-aging-assisted delayed artificial aging strategy to regulate β″/L precipitation and improve the strengthening response of an Al-Mg-Si-Cu alloy after short-term room-temperature storage. After solution treatment and quenching, the alloy was stored at room temperature for 6–48 h with or without prior pre-aging at 120 °C, followed by artificial aging at 170 °C. It is found that both the delayed artificial aging (DA) and pre-aging-assisted delayed artificial aging (PDA) routes show limited sensitivity to room-temperature storage time within 6–48 h, whereas PDA consistently increases the yield strength and ultimate tensile strength by approximately 10 MPa compared with the corresponding DA route, with a slight reduction in elongation. Based on Avrami–Johnson–Mehl analysis, the activation energy for β″ precipitation decreases from 102.74 kJ/mol in the DA-pre state and 107.13 kJ/mol in the solution-treated state to 70.63 kJ/mol in the PDA-pre state, indicating that pre-aging modifies the initial microstructural state in a manner that facilitates subsequent β″ precipitation. Quantitative TEM characterization reveals that PDA has little influence on the average sizes of β″ and L precipitates but increases their number densities. In particular, the number density of β″ precipitates increases by approximately 15% relative to the corresponding DA samples. Strengthening-model calculations further show that β″ precipitates make the dominant contribution to precipitation strengthening, and that the strength improvement under the PDA route mainly originates from the increased β″ number density rather than changes in precipitate size. These results establish a quantitative link between pre-aging, precipitation kinetics, β″/L precipitate population, and strengthening response, providing guidance for optimizing heat-treatment schedules of Al-Mg-Si-Cu extrusion alloys that experience unavoidable room-temperature storage before final artificial aging.

Metals doi: 10.3390/met16080841

Authors: Maricruz Hernández-Hernández Adriana Gallegos-Melgar

The growth of electric vehicles has increased the need for reliable, low-resistance Al–Cu battery interconnects. Laser welding provides localized heat input, high productivity, and automation potential, but Al–Cu joining remains limited by thermophysical mismatch, unstable energy coupling, and brittle intermetallic compound formation, which can lead to visible defects, hidden discontinuities, and performance variability. This review focuses on artificial intelligence (AI)-enabled post-process surface inspection of laser-welded Al–Cu battery interconnects. Process–structure–property relationships, defect mechanisms, process enablers, and in-process monitoring are discussed as supporting context to distinguish surface-visible evidence from attributes requiring complementary validation. The review critically examines controlled imaging, illumination and reflectivity effects, defect taxonomy, annotation, dataset design, AI task selection, and risk-based quality decisions. Classification, detection, segmentation, and anomaly detection are compared in terms of annotation requirements, traceability, metrics, and limitations. The main contribution is a post-process inspection framework that links controlled image acquisition, defect taxonomy, weld-level datasets, AI inference, benchmarking, and accept–review–reject decision logic with functional validation. The framework supports reproducible, risk-sensitive, and functionally validated quality assurance for Al–Cu battery welds while preserving expert review for uncertain cases and for the acceptance of welding technologies, process windows, and critical quality decisions.

Metals doi: 10.3390/met16080840

Authors: Qingnan Zhang Yuxin Tian De Liu Han Zhang Junyi Chen Zhen Zhao Qiuyuan Feng Wei Gao Qi Wang Hongying Yu Dongbai Sun

This study investigated microbiologically influenced corrosion (MIC) and passive-film degradation of a Ti-15Mo-3Al-2.7Nb-0.25Si β titanium alloy exposed to Pseudomonas aeruginosa. The alloy comprised a continuous β-Ti matrix with dispersed α-Ti precipitates, and this α/β dual-phase microstructure provided a potential microstructural basis for spatial variations in passivation behavior among different microregions. During immersion, P. aeruginosa formed a heterogeneous biofilm of bacterial cells and extracellular polymeric substances, altering interfacial mass transfer, oxygen distribution, and local chemistry. Relative to the sterile control, the inoculated group showed increases in maximum pit depth from 2.4 to 4.1 μm and corrosion current density from 8.72 to 17.2 nA cm−2, while the charge-transfer resistance decreased to 4.32 MΩ cm2 after 14 d, confirming enhanced localized corrosion. Mott-Schottky and XPS analyses showed that the donor density increased from 1.07 × 1019 to 1.29 × 1019 cm−3 and the Ti4+ fraction decreased from 72.29% to 66.74% and the relative Ti0 fraction increased from 7.01% to 17.59%, reflecting increased defect accumulation within the film, impaired passive-film integrity, and reduced local protective capability. P. aeruginosa therefore increases the MIC susceptibility of this β titanium alloy by biofilm-induced interfacial microenvironmental heterogeneity. These findings support MIC assessment and integrated antifouling-anticorrosion surface design for marine β titanium alloys.

Metals doi: 10.3390/met16080839

Authors: Hongwen Deng Aiwen Li Chenkai Zhou Lingyi Cao Jun Du Xu Cheng

Heat treatment significantly improves the ductility of additively manufactured Zr–2.5Nb alloy, but the mechanisms responsible for this improvement remain poorly understood. In this study, the effects of heat treatment on the microstructure and room-temperature tensile behavior of Zr–2.5Nb fabricated by laser powder bed fusion (LPBF) were investigated by comparing as-built (AB) and heat-treated (HT) specimens. The HT specimens were held at 800 °C for 2 h and subsequently air-cooled. A microstructure-based crystal plasticity fast Fourier transform (CPFFT) model was constructed directly from two-dimensional electron backscatter diffraction (EBSD) orientation and phase maps to quantify the local stress, strain, and slip responses of the α and β phases in the HT microstructure. Heat treatment caused the acicular α′ martensite to decompose, producing a coarser lamellar α + β microstructure. In a representative EBSD field of the HT specimen, β-Zr accounted for 6.0% of the analyzed area and was distributed predominantly between the α lamellae. Compared with the AB condition, heat treatment reduced the mean 0.2% proof stress and ultimate tensile strength from 840 and 1033 MPa to 792 and 881 MPa, respectively, while increasing the mean uniform strain from 4.02% to 6.94%. At an applied axial strain of 3.2%, the β/α ratios of phase-averaged equivalent strain and accumulated absolute slip were 1.59 and 2.51, respectively, whereas the corresponding ratios for von Mises stress and axial stress were 0.57 and 0.81. These results reveal pronounced stress–strain partitioning between the phases: β-Zr accommodated greater equivalent strain and more extensive slip, whereas α-Zr carried higher stresses. This interphase partitioning helps explain the increased uniform strain of the HT specimens, while the reduction in strength is primarily associated with α′-martensite decomposition and α-lamella coarsening.

Metals doi: 10.3390/met16080838

Authors: Lan Thi Ngo Chi Van Phung Son The Le

Porous nickel (Ni) coatings were fabricated by wet powder metallurgy using urea and ammonium bicarbonate (NH4HCO3) as low-temperature pore-forming additives. Ni powder was mixed with 3 wt.% carboxymethyl cellulose (CMC), coated onto Ni mesh substrates, and sintered in a hydrogen atmosphere at temperatures of 550–900 °C for 30–120 min. The microstructural evolution, phase composition, elemental distribution, and pore characteristics were systematically characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) analyses. The results demonstrate that sintering temperature governs the evolution of the porous structure more strongly than the investigated space holders. With increasing temperature, progressive neck growth, grain coarsening, and densification were observed, consistent with the transition from initial particle contact to the intermediate stage of solid-state sintering. An interconnected porous framework formed at 700 °C, identified as the selected condition due to its balance between interparticle bonding and pore preservation. XRD confirmed a single face-centered cubic (FCC) Ni phase after sintering, while BET analysis showed minor differences in specific surface area but noticeable variations in pore volume and pore-size characteristics. The limited influence of urea and NH4HCO3 is attributed to their decomposition at temperatures well below the effective sintering range of Ni. Consequently, the generated gases are likely to escape before a continuous metallic framework is established, resulting in only modest changes in the final pore architecture. These findings indicate that the porous structure is governed predominantly by diffusion-controlled solid-state sintering rather than by the direct pore-forming action of the investigated additives. This study highlights the importance of thermal compatibility between space holders and the sintering window of the metal matrix, providing new insight into the rational design of porous Ni materials prepared by wet powder metallurgy.

Metals doi: 10.3390/met16080837

Authors: Martina Laubertová Michaela Ružičková Martin Sisol Cinta Barba Brioso Joaquín Delgado Rodríguez

This study investigates the hydrometallurgical recovery of valuable metals from copper shaft furnace dust (SFD), a complex industrial waste containing approximately 40 wt.% Zn, 16 wt.% Pb, and 1 wt.% Cu. In contrast to conventional inorganic leaching processes that rely on aggressive acids and bases, this research explores the use of deep eutectic solvents (DESs) as eco-friendly and selective lixiviants. Deep eutectic solvents based on choline chloride combined with citric acid and lactic acid were evaluated as leaching media for metal recovery from SFD. The effects of temperature, leaching time, stirring intensity, and the DES:SFD ratio on metal extraction were systematically investigated. Analytical characterization of the raw material, leaching residues, and pregnant leach solutions was performed using Atomic Absorption Spectroscopy (AAS), X-ray Fluorescence Spectrometry (XRF), and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM–EDS). The experimental results demonstrated efficient recovery of Zn, Pb, Cu, and Sn under mild leaching conditions. For the citric acid–choline chloride system, the highest extraction efficiency was obtained at 60 °C using a DES:SFD ratio of 30, whereas increasing the temperature to 70–80 °C did not significantly improve metal extraction. The lactic acid–choline chloride system exhibited different leaching behaviour, with the highest recoveries achieved after short leaching times. These findings indicate that DES-based systems represent a promising, sustainable alternative for the selective leaching of heavy metals such as Zn, Pb, Cu, and Sn, from metallurgical secondary raw materials, contributing to the development of greener circular economy practices.

Metals doi: 10.3390/met16080835

Authors: Gunter Kullmer Sven Krome Deborah Weiß Britta Schramm Richard Ostwald

Investigating crack growth in sheet metal originating from clinched joints is a major part of predicting the service life of mechanically joined structures. Clinching allows different materials to be joined together. A key task in this context is to perform crack growth simulations in the vicinity of clinched joints considering different load and environmental conditions. This requires formulaic descriptions of the fatigue crack growth rate curves for the materials used. For this purpose, fatigue crack growth rate curves for different R-ratios and temperatures are determined experimentally. Generally, these fatigue crack growth rate curves can be described very well using a novel two-part exponential approach for the formulaic description of fatigue crack growth rate curves developed at Applied Mechanics of Paderborn University (FAM). In this case, three parameters are sufficient to describe the fatigue crack growth rate curves. For the material HCT590X, which is frequently used in clinched joints, it is shown as an example how the parameters vary with the R-ratio and the temperature. In addition, at high crack growth rates, a significant rise in the fatigue crack growth rate curve sometimes occurs at both low and high temperatures. To account for this feature, the two-part exponential approach can be expanded to include a third part.

Metals doi: 10.3390/met16080836

Authors: Ahmed Nabil Elalem Husam Alrehaili Xin Wu

AA6061-T6 undergoes work hardening, dynamic recovery, and progressive flow softening during hot torsion, yet a systematic single-campaign dataset with quantified experimental uncertainty is absent from the literature. Gleeble hot torsion tests were conducted at eleven conditions from 250 to 450 °C and 0.91 to 9.07 s−1. With the stress multiplier fixed a priori at α = 0.045 MPa−1 from compression literature on this alloy, a two-stage calibration determined the remaining Garofalo–Arrhenius constants: the temperature-slope stage anchors Q = 151.1 kJ mol−1 (consistent with Al lattice self-diffusion), and a global Zener–Hollomon regression conditional on Q yields n = 1.371 and A = 3.51 × 1010 s−1; a fully simultaneous three-parameter fit is shown to be practically unidentifiable on the three-level matrix. Training AARE = 15.5% (R = 0.908); leave-one-out cross-validation gives AARE = 23.0%, bounding the predictive uncertainty. The Prasad instability map identifies 400–450 °C at 0.91–2.72 s−1 as the optimal hot-forming window; flow instability is predicted at 350 °C (outright at 2.72 and 9.07 s−1, with the 0.91 s−1 condition at the map boundary), and macroscopic fracture was observed in all three specimens tested there. Optical microscopy in specimen T1 (εeq = 3.69) shows elongated subgrains at the gauge center and fine-grained zones near the fracture surface consistent with localized geometric dynamic recrystallization. The activation energy, smooth post-peak softening, and subgrain wall morphology identify dynamic recovery as the likely dominant restoration mechanism. Adiabatic heating and a 24% peak-stress repeatability scatter at the single repeated condition (450 °C, 9.07 s−1) are quantified and propagated into the constitutive model uncertainty bounds. Because the training-to-cross-validation error gap (15.5% versus 23.0% AARE) reflects the limited three-level strain-rate matrix, the calibrated equation is recommended for interpolation within the tested window of 300 to 450 °C and 0.91 to 9.07 s−1 (noting that 300 °C was tested only at 0.91 s−1, so higher-rate predictions at that temperature are extrapolations) and for forming-window identification, not for extrapolation beyond this domain without additional validation data.

Metals doi: 10.3390/met16080834

Authors: Bowen Cheng Lv Li Dexin Ma Jianhui Wei Yunxing Zhao Yangpi Deng Fuze Xu

The impact of the oxide film in the remelted zone of a seed on the epitaxial solidification of single-crystal superalloys was investigated, with a specific focus on clarifying the hindrance mechanism of complex compositional oxide films during the epitaxial growth process. Experimental findings indicated that the oxide film was composed of multiple constituents, such as WO3 and Al2O3, and displayed no remarkable texture in its crystal orientation. The formation mechanism of coherent oxides during the alloy oxidation process and their potential as nucleation sites for solidification were analyzed. Owing to disparities in symmetry along the growth direction, the γ phase formed through oxide nucleation that deviated from its original orientation. Moreover, the existence of polycrystalline oxide films impeded the effective transfer of single-crystal seed orientation information, leading the epitaxial growth to mainly rely on the mechanism where dendrites penetrate through the damaged areas of the oxide film to reach the upper region. Significantly, aluminum oxide within the oxide film could act as new nucleation sites, potentially triggering the formation of stray grains in the central region of the casting.

Metals doi: 10.3390/met16080833

Authors: Tomas Frydl Nguyen Hong Vu

Two alternative first-stage routes for selective molybdenum recovery from a pretreated spent Co-Mo/Al2O3 hydrodesulfurization catalyst were investigated and compared using the same feedstock: direct sulfuric-acid leaching and oxidative volatilization. The study combined single-factor process tests with XRD, SEM-EDS, XRF, ICP-OES, and particle-size analyses to relate extraction behavior to the distribution of Mo and Co within the catalyst. Direct leaching achieved 98.1% Mo extraction in 2 mol/L H2SO4 at 90 °C for 2 h, while approximately 95% extraction was obtained at only 0.1 mol/L H2SO4 and 40 °C. Co co-extraction remained at approximately 12%, and Al extraction was generally 0.6–0.9%, demonstrating a selective first-stage separation. Water leaching provided an extraction of 51.3% Mo because readily accessible MoO3 forms hydrated aqueous Mo(VI) species. Oxidative roasting removed 92.2% Mo from the coarsely ground material at 1400 °C for 1 h, while fine grinding increased Mo volatilization to 97.8%, whereas no measurable Co volatilization was observed. The two routes therefore offer different advantages: mild leaching lowers thermal demand and produces a Mo-bearing solution, whereas roasting avoids liquid reagents and produces a Mo-bearing vapor that can be collected by controlled condensation. The residual Mo fraction was associated with MoO2 and Mo-bearing regions enclosed by the stable CoAl2O4-Al2O3 matrix. The results establish a comparative basis for selecting an appropriate first-stage Mo-removal route before separate recovery of Co and possible valorization of the alumina-rich residue.

Metals doi: 10.3390/met16080832

Authors: Changming Fang Zhongping Que Zhongyun Fan

Commercial aluminum (Al) metals contain unavoidable impurities, such as iron (Fe) and silicon (Si). Due to its low solubility and high chemical affinity to Al, Fe exists in the form of Fe-containing intermetallic compounds (Fe-IMCs), which are crucial in solidification processes, determining the micro-structure and consequently the mechanical performance of the cast parts. Meanwhile, Si, as an impurity or addition, may join the binary Fe-IMCs. Here, we investigate the Si stabilization effects on the frequently observed Al-rich Fe-IMCs in a comprehensive and systematic way using a first-principles density-functional theory (DFT) approach. The study reveals different Si stabilization effects on the cubic α- and hexagonal α’-phase, as well as other binaries: Al12Fe, η-Al6Fe, τ4-, β-, and θ-phases. The enhancement of stability for the α-phase is moderate, while it is strong for the α’-phase. For the stability series (from higher to lower) is θ-Al13Fe4 > η-Al6Fe > α-Al4.75Fe in the binary system, while it becomes τ4-(Al,Si)5Fe > β-Al4.5SiFe > α’-(Al,Si)4.174Fe for the ternary Fe-IMCs. The information obtained here helps understand the formation of Fe-IMCs particles during casting of Al-Si alloys, and the design of novel Al alloys of fine micro-structures and desired mechanical performances of the products from the primary Al and the scraps and wastes.

Metals doi: 10.3390/met16080831

Authors: Guanyong Sun Zhisheng Shi Hui Ma Wenlong Xu Shaoqi Han

Vanadium–titanium-bearing direct reduced iron (V-Ti DRI) is a promising feedstock for the full-value utilization of V-Ti magnetite. Selective partition of V and Cr into the metal phase, with Ti retained in the slag, requires quantitative thermodynamic guidance. We investigate this slag–metal distribution using the ion and molecule coexistence theory (IMCT). An eight-component slag model with 33 complex-molecule equilibria is coupled to reduction thermodynamics through an iterative mass-balance procedure; the metal-phaseWagner activity is temperature-scaled by Chipman’s rule, and the dissolved oxygen concentration is closed through the C-CO-O equilibrium. The equilibrium V and Cr recovery ceilings (metal side) rise from 89%/96% at 1400 °C to approximately 99.4% at 1500 °C and exceed 99.8% at 1550 °C. Ti-in-slag retention (slag side) drops steadily from 99.998% at 1400 °C to 99.4% at 1700 °C, giving a V/Ti separation factor above 104. Fe recovery to the metal phase exceeds 97% at 1600 °C and above, driven by the strong reduction of FeO, which constitutes approximately 32 wt.% of the initial slag. Carbon activity exerts a cubic power-law effect: at 1450 °C, the V recovery ceiling collapses from 97.4% at aC = 1 to 6.5% at aC = 0.05, identifying imperfect carbon saturation as a primary thermodynamic mechanism behind the ceiling-to-pilot gap. Once temperature and oxygen closure are enforced, the ceilings are only weakly sensitive to metallization, basicity, coke ratio, and TiO2 content. Comparison with pilot data shows the ceilings exceed reported yields by 16–29 percentage points (pp), quantifying the kinetic/mass-transfer deficit and providing a benchmark for scale-up.

Metals doi: 10.3390/met16080830

Authors: Bin Zhang Qing Yin Shouxun Peng Zeyu Zhao Meiyu Shi Xiwen Li Zheng Li Bin Xiao Xiuquan Gu Mingjia Zhi Eugene Chubenko Vitaly Bondarenko Hanna Bandarenka Yanwei Sui

Low-temperature operation of lithium-ion batteries (LIBs) is severely limited by sluggish Li+ transport, aggravated interfacial polarization, and structural degradation of layered oxide cathodes. Herein, a multifunctional Li2O-B2O3-Li2SO4 composite coating, denoted as LBLS, was constructed on LiNi0.6Co0.2Mn0.2O2 (NCM622) through a simple wet-mixing/calcination strategy. Structural and surface characterizations confirm that the LBLS-derived layer is successfully introduced onto NCM622 while the layered α-NaFeO2 framework is well preserved. Benefiting from the regulated surface chemistry and improved interfacial kinetics, NCM622@LBLS exhibits significantly enhanced electrochemical performance, especially under subzero conditions. At −20 °C, the charge-transfer resistance decreases from 160 Ω for pristine NCM622 to 110 Ω after LBLS modification. Moreover, after 500 cycles at −20 °C, NCM622@LBLS maintains 101.57 mAh g−1 with a capacity retention of 80.60%, which compares favorably with representative coated NCM622 cathodes evaluated under comparable subzero conditions. In situ XRD reveals suppressed lattice breathing, while ex situ EIS, DRT and GITT confirm reduced interfacial polarization and faster Li+ diffusion. Depth-profiling XPS further demonstrates that LBLS promotes an inorganic-reinforced CEI containing Li–O, B–O/B–F, and SOx-containing species, thereby stabilizing the cathode/electrolyte interface during low-temperature cycling.

Metals doi: 10.3390/met16080829

Authors: Martin Négyesi Oldřich Guřan Milan Kwaczek Petr Haušild

Post-welding vibratory stress relief (VSR) has been studied extensively for its capability of decreasing welding residual stresses (RS). This study examines the effectiveness of VSR applied on butt-welded thick sheets of high-strength low-alloy steel. The effect of thermal stress relief (TSR) was examined simultaneously. X-ray diffractometry (XRD), hole drilling method (HDM), and instrumented indentation technique (IIT) were employed for evaluating RS distribution. Global mechanical properties of the weld joint were assessed using tensile tests, bending tests, and Charpy impact tests. Hardness was employed to assess local variation in mechanical properties. The microstructure was observed through light optical microscopy (LOM) and electron back-scatter diffraction (EBSD). It was found that RS redistributed after VSR. The overall decrease in RS could be seen after VSR; however, the scatter in RS increased. TSR, on the other hand, resulted in the decrease in both magnitude and scatter of RS. Peak values of the post-welding RS were evaluated in the range of −200 to 200 MPa; meanwhile, the mean RS was within the range of −100 to 100 MPa. After TSR, RS was mostly within the range of −50 to 50 MPa. After VSR, RS was found to lie mostly within the range of −100 to 200 MPa with peak values being close to the yield strength. VSR had no adverse effect on the structural integrity of the weld joint. No significant differences in the microstructure were seen among as-welded, TSR, and VSR conditions.

Metals doi: 10.3390/met16080828

Authors: Nayem Ahmed Ramadan Ahmed Samin Rhythm Catalin Teodoriu

This study investigates hydrogen-assisted fatigue crack growth (FCG) in vintage pipeline steels to quantify grade-dependent degradation under hydrogen–natural gas blending conditions. Fatigue behavior was evaluated using compact-tension specimens extracted from API X52 and X70 pipeline steels and tested in natural gas–hydrogen mixtures at a total pressure of 6.9 MPa and ambient temperature. Hydrogen concentration was systematically varied from 0% to 100% H2 to assess its influence on crack-length evolution, fatigue crack growth rate, and fracture morphology. Crack propagation was characterized as a function of the stress-intensity-factor range, and scanning electron microscopy was used to examine hydrogen-induced changes in fracture mechanisms. The results demonstrate that FCG accelerates as hydrogen concentration increases, with a strong dependence on steel grade. X70 exhibited substantially greater hydrogen-induced FCG acceleration than X52, despite showing better fatigue resistance under hydrogen-free conditions. Fatigue life reductions approached 60% for X70 at 100% hydrogen, compared with approximately 30% for X52 under the same conditions. Significant early-life sensitivity was observed in X70 even at low hydrogen concentrations, whereas X52 showed more pronounced acceleration during later stages of crack growth. The influence of hydrogen was nonlinear and tended to stabilize at elevated blend fractions, indicating a saturation-type response once hydrogen-assisted crack growth became dominant. Fractographic analyses revealed a transition from ductile tearing in natural gas environments to terrace- and facet-controlled crack propagation in hydrogen-rich environments, accompanied by secondary cracking and river-pattern features. These findings demonstrate that hydrogen–natural gas blending can significantly alter fatigue crack growth behavior and relative material performance in pipeline steels, highlighting the need for grade-specific integrity assessment of existing pipeline infrastructure.

Metals doi: 10.3390/met16080827

Authors: Feng Jiang Yang Li Shuai He Wei Sun Hong-Hu Tang

The selective flotation separation of chalcopyrite from pyrite under low-alkalinity conditions remains a challenge due to their similar surface properties. In this study, a sulfonated dextrin (SD) was synthesized via chemical modification and evaluated as a selective depressant for pyrite in the chalcopyrite–pyrite flotation system. Micro-flotation experiments demonstrated that SD exhibited significantly superior selective depression for pyrite compared to unmodified dextrin. At pH 8.0, SD achieved over 95% depression of pyrite with negligible impact on chalcopyrite flotation. In mixed-mineral flotation, SD reduced pyrite recovery from 75.01% to 27.08% at a dosage of 100 mg/L, while chalcopyrite recovery increased from 80.56% to 87.65%. Contact angle measurements revealed that SD markedly enhanced the hydrophilicity of pyrite surfaces, whereas chalcopyrite surfaces retained strong hydrophobicity in the presence of SBX. Zeta potential and FTIR analyses indicated that SD strongly adsorbed onto pyrite surfaces through the introduced sulfonic groups (−SO3−), effectively hindering subsequent SBX adsorption. XPS analysis further suggested chemical interactions between SD and oxidized iron species on pyrite surfaces, forming a stable organic–inorganic composite adsorption layer. These findings demonstrate SD to be a promising environmentally friendly depressant for selective copper–sulfur separation under low-alkalinity conditions, offering a viable alternative to conventional lime-based processes.

Metals doi: 10.3390/met16080826

Authors: Jian Xu Chaohua Zhang Denggao Liu Xianfeng Xiao Jingyi Xue Xiaojun Ye Yanshu Fu

Laser beam oscillation has been recognized as an effective means to modify temperature gradients and relieve stress concentration in welded joints, yet its role in dissimilar titanium alloy bottom-locking configurations—where asymmetric thermo-mechanical responses arise from both material mismatch and structural constraints—remains unclear. This study investigates the influence of circular oscillation amplitude (0, 0.5, 1.0, and 1.5 mm) on residual stress distribution in laser-welded TC4/TA18 bottom-locking tube joints at a constant power of 1000 W. Unlike the monotonic effect of laser power, oscillation amplitude redistributes the heat source spatially. A three-dimensional thermo-elastic–plastic finite element model incorporating a moving oscillating Gaussian conical heat source was developed in ABAQUS and validated against weld macrographs, thermal cycles, and blind-hole residual stress measurements. The results reveal a non-monotonic dependence of residual stress on oscillation amplitude: as amplitude increases from 0 to 0.5 mm, the peak hoop residual stress rises, but further increasing amplitude to 1.5 mm substantially reduces both hoop and axial residual stresses while promoting a more uniform stress field. At 1.5 mm, the molten pool covers the entire bottom-locking step geometry, the region of high hoop tensile stress (>700 MPa) is minimized, and the peak axial tensile stress at the bottom-locking gap end (BLG End) is reduced by 41% (from 415 MPa to 243 MPa) compared with non-oscillation welding. An amplitude of 1.5 mm is therefore recommended as the optimal parameter for residual stress control of these joints at 1000 W within the investigated parameter range. This finding provides a practical guideline for mitigating residual stress-induced failure risks in aerospace hydraulic and fuel delivery systems.

Metals doi: 10.3390/met16080825

Authors: Peter Futas Jozef Petrik Miroslav Pástor Alena Pribulova Peter Blasko Mariusz Łucarz

The manuscript aims to analyze the properties of gray cast iron EN GJL-250 as a function of the charge composition with an emphasis on microhardness and indentation size effect (ISE). Three compositions of cast iron were used: cast iron A as traditionally produced cast iron, B and C as inoculated and overheated cast iron micro-alloyed with FeTi70. The authors used the cutting method to assess residual stresses in castings with a stress grid designed according to Sipp. The specimens from thick and thin bars of the grid, after determination of residual stresses, were used for uniaxial tensile tests, measurement of the hardness (HBW, HV, and Vickers microhardness), metallographic, and fractographic analysis. Results of microhardness were used for the determination of ISE indices, and “true hardness” was calculated. The effect of composition has a statistically significant effect (single ANOVA; specimens from thick and thin bars are considered together) only for Meyer index n, and in the case of thick bars, also for HBW and HV.

Metals doi: 10.3390/met16080824

Authors: Nebojša D. Nikolić Jelena D. Lović Milica Ožegović Evica R. Ivanović Kristina Mojsilović Predrag M. Živković

Electrodeposition of bismuth from an acidic nitrate solution on copper electrodes by use of the potentiostatic mode of electrodeposition has been investigated with the aim to define conditions for obtaining dendritic forms. Morphology and structure of Bi deposits produced at the different cathodic potentials were featured by techniques of scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS) and X-ray diffraction (XRD), and correlated with the polarization features. The Bi dendrites were formed starting from the plateau of the limiting diffusion current density, while granules were formed at the cathodic potential which preceded the plateau. The shape of dendrites changed from very compact, formed at the plateau, to highly branched, formed at cathodic potentials beyond the plateau of the limiting diffusion current density, where the current density continuously grew with the increase in the cathodic potential. Both granules and dendrites showed the forceful preferred orientation in the basal (003) crystal plane with the lowest surface energy. The performed morphological and structural analysis classified Bi into a group of so-called normal metals, characterized by high values of both the exchange current density and overpotential for hydrogen evolution reaction and by low melting points.

Metals doi: 10.3390/met16080823

Authors: Victor Velho de Castro Cristiano Ev Leandro Câmara Noronha Matheus Bullmann Louise Etcheverry Leonardo Moreira dos Santos Rafael Marquetto Vargas Silvana Mattedi Roberto Moreira Schroeder Célia de Fraga Malfatti

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Metals doi: 10.3390/met16080822

Authors: Abdus-Samad Shaik Nicolas Ayers Yongho Sohn

Triply periodic minimal surface (TPMS) lattices are an emerging class of cellular architectures whose smooth, mathematically defined surfaces enable highly tailorable mechanical performance. This study quantifies the compressive elastic response of three sheet-based TPMS topologies, i.e., Diamond, Gyroid, and Lidinoid, through finite element (FE) analysis and experimental validation. For each topology, the effective Young’s modulus was computed by single-cell finite element analysis under uniaxial compression boundary conditions on a 2 mm unit cell across five wall thicknesses (0.35, 0.45, 0.65, 0.95, and 1.30 mm), corresponding to relative densities from approximately 25% to 95%. Experimentally, cylindrical specimens of 316L stainless steel at 70% relative density were fabricated by laser powder bed fusion (LPBF) and tested in uniaxial compression with a strain rate of 10−3 s−1 per ISO 13314:2011 (i.e., 0.02 mm/s). The Diamond topology exhibited the highest effective modulus across the full density range, followed by Lidinoid and Gyroid. FE predictions agreed with experimental moduli within 4.7% for Diamond (100.2 GPa vs. 95.5 ± 3.9 GPa), 0.04% for Gyroid (79.8 GPa vs. 79.8 ± 0.88 GPa), and 1.5% for Lidinoid (85.6 GPa vs. 86.9 ± 3.5 GPa). Moreover, the Gibson–Ashby exponents determined span the range from stretching- to bending-dominated deformation with n = 1.69 for Diamond, 1.74 for Lidinoid, and 2.08 for Gyroid. Single-cell FE analysis accurately captured the effective elastic response of LPBF 316L stainless steel TPMS lattices examined.

Metals doi: 10.3390/met16070821

Authors: Xiaohui Li Hao Tan Mingjia Wu Lijie Chen Lianhao Liu Youxiao Chen Zhexu Zhang

Laser shock peening (LSP) is an advanced surface modification technique that significantly enhances the fatigue resistance of metallic components through the synergistic implantation of deep compressive residual stresses (CRSs) and gradient microstructural refinement. Existing investigations have shown that LSP can generate strengthening layers extending from several hundred micrometers to approximately 1 mm in depth, with affected zones reaching 5–6 times the depth typically achieved by conventional shot peening in representative titanium alloys. In specific cases, LSP has increased the fatigue limit from 483.2 MPa to 593.6 MPa, corresponding to an improvement of approximately 22.8%, while optimized treatment of Ti-17 compressor blades has extended fatigue life by more than two orders of magnitude. This review systematically elucidates the anti-fatigue strengthening mechanisms of LSP across a range of metallic systems, with emphasis on three key aspects: (i) the mechanistic retardation of fatigue crack initiation and propagation, mediated by CRS-induced reductions in the stress intensity factor and enhanced crack closure effects; (ii) the parametric sensitivity of surface integrity and stress field homogeneity to laser energy density, spot overlap ratio, and multiple-impact sequencing; and (iii) the process-specific characteristics of emerging LSP variants, including laser peening without coating, warm laser shock peening, and cryogenic laser shock peening. Furthermore, we critically evaluate the role of multiscale numerical simulations—encompassing macroscopic finite element analysis, mesoscopic crystal plasticity modeling, and molecular dynamics—in optimizing process parameters and predicting fatigue life. By integrating experimental, computational, and theoretical perspectives, this review establishes a coherent process–structure–property framework to guide the rational design of LSP protocols for targeted fatigue performance enhancement.

Metals doi: 10.3390/met16070820

Authors: Matthew Scott Rashiga Walallawita Matthew C. Hinchliff Dimitry Sediako

Hydrogen diffusion plays a central role in the susceptibility of steels to hydrogen embrittlement, yet reported diffusivity values often exhibit significant variability due to differences in experimental methodology. Gaseous hydrogen permeation experiments, while more representative of service conditions, are highly sensitive to surface boundary conditions and trapping effects, which can bias the diffusivity obtained from analysis. In this work, a gaseous hydrogen permeation methodology was developed at the High-Performance Powertrain Materials Laboratory (HPPM) at the University of British Columbia, Okanagan. A dedicated gas management system (GMS) was implemented to enable controlled pressure step transients, allowing partial permeation transients to be collected under gaseous charging conditions. This approach was applied to commercially pure iron and API 5L X60 pipeline steel to evaluate diffusion and trapping behaviour across materials with differing microstructural complexity. The results demonstrate that diffusivity obtained from transients spanning the full charging–discharging range (0–2 MPa) reflects an effective parameter influenced by reversible hydrogen trapping, whereas transients measured over incremental pressure steps (1–2 MPa) provide a more consistent estimate of lattice-controlled diffusion. The application of palladium coatings to the charging surface was found to promote hydrogen entry, reducing surface impedance effects and further improving agreement with Fickian diffusion behaviour.

Metals doi: 10.3390/met16070819

Authors: Xinyi Zhao Shanguang Liu Tao Gu Yang Sun Hong Qin Dan Wang Peizhong Feng

Diffusion solidification is an effective method to produce non-dendritic microstructures and reduce casting defects in magnesium alloys. However, the influence of precursor alloy superheat on the solidification behavior and the resulting microstructure remains insufficiently understood. In this study, pure magnesium was used as the high thermal mass (HTM) alloy and three Mg-Al-Zn alloys with different aluminum and zinc contents were used as the low thermal mass (LTM) alloys. The effects of superheat on grain morphology, solute diffusion, and constitutional supercooling were investigated through a combination of experimental casting and numerical simulation using Ansys Fluent and Matlab. The results show that the solidified interface consists of five distinct regions, including two base metals, two transition zones, and a central controlled diffusion solidification zone. A higher superheat of the HTM alloy relative to the LTM alloy promotes a wider transition zone and finer globular grains, whereas equal or lower superheat leads to columnar or rosette structures. The Mg-30 wt.%Al-3.5 wt.%Zn alloy with moderate aluminum content produces fine globular grains due to a thinner constitutional supercooling layer and a higher degree of supercooling, which suppresses grain growth and increases nucleation rate. In contrast, the Mg-55 wt.%Al-6.5 wt.%Zn alloy with high aluminum content forms coarse rosette and columnar grains. Among the conditions investigated, the combination of 10 °C HTM and 5 °C LTM superheats tends to promote the formation of fine equiaxed grains. Increasing superheat above this range reduces supercooling and coarsens grains, while decreasing superheat inhibits interface diffusion and promotes solute segregation. The findings provide a theoretical basis for designing precursor alloy compositions and superheat parameters in controlled diffusion solidification of magnesium alloys.

Metals doi: 10.3390/met16070818

Authors: Zhenxiang Li Shipin Wu Junlin Dai Yan Wang Zhiwei Gao

Hydrogen serves as a fundamental energy carrier essential for achieving global carbon neutrality, with long-distance pipeline transportation recognized as the most efficient approach for large-scale hydrogen delivery. Nevertheless, hydrogen embrittlement (HE) in pipeline steels constitutes a significant safety challenge for this infrastructure. This review presents a comprehensive and systematic analysis of HE in hydrogen pipeline steels, emphasizing the microstructural fracture mechanisms under hydrogen exposure, the microstructural regulation of hydrogen diffusion and trapping, the interplay of multiple influencing factors, strategies for HE mitigation, and numerical prediction methodologies. Critical factors including microstructural features, hydrogen transport dynamics, and the coupling effects between stress and hydrogen are examined in detail. The review systematically summarizes advanced HE mitigation techniques and strategies, encompassing microstructural engineering, surface modification, alloy composition optimization, finite element modeling, and machine learning applications. Additionally, several principal challenges confronting the field are identified: the ambiguous mechanisms underlying multi-field coupling effects, the limited translation of laboratory-scale findings to practical engineering contexts, especially with regard to multi-scale mitigation of hydrogen-induced fracture, and the incomplete advancement of artificial intelligence-based pipeline integrity assessment tools. To address these issues, the review proposes key research directions and recommendations for future investigations into HE in hydrogen pipeline steels.

Metals doi: 10.3390/met16070817

Authors: Iuliana Stan Constantin Stelian Stan Denisa Elena Anca Eduard Stefan Mihai Chisamera Iulian Riposan

The present paper reviews original data obtained by the authors from recent separate publications with additional unpublished data, specifically concerning the specific graphite morphology in Si/SiMo alloyed ductile irons (2.5–5.5% Si, 0.01–2.3% Mo) with alloying grade, cooling rate, and inoculation as influencing factors. Different formulas used for nodularity evaluation, including different forms of graphite participating in different proportion and two graphite shape factors: Roundness (RSF, involving maximum Ferret) and Sphericity (SSF, involving real perimeter). Slightly irregular spheroidal graphite morphology (Form V, ISO 945) characterized by RSF = 0.59–0.75 was found to be typical for Si and SiMo ductile irons in all of the test conditions, such as Si level (4.2–5.25% Si), Si–Mo system (4.1–4.8% Si + 1.6–2.3% Mo), mould type (green sand, resin sand, metal mould, external metallic chill), un-inoculation and inoculation, and inoculating element type. Increasing Si content negatively affects the compactness degree of spheroidal graphite particles (transition from VI to V form) and nodularity. Metal mould versus sand mould solidification of 4.5% Si ductile iron increases nodule count, graphite shape factors (RSF = 0.68–0.7 versus 0.59–0.64) and nodularity (67% to 76%). An external metallic chill in a resin sand mould promoted directional solidification and showed a nodularity decrease for increasing Si, for all the nodularity formulas and for the cooling rate range. Inoculating elements influenced the shape factors in thin wall castings, where Ca–Ba was better than simple Ca and Ca–RE could promote graphite at higher real perimeter and with lower shape factors. The correlation of the aspect of structure, graphite parameters and nodularity led to the conclusion that the nodularity formula according to ISO/WD 945-4-2015 (100% total area of Form VI and 90% of Form V), with SSF instead of RSF, appears to be better in High-Si/SiMo DI (especially for more than 4% Si), because it takes into account the presence of slightly irregular spheroidal graphite (with high real perimeter) at a high rate.

Metals doi: 10.3390/met16070816

Authors: Boyu Zheng Yufeng Wang Xiaorui Wan Wuhao Zhuang

Aiming at the technical challenges in the Multi-DoF forming of 20CrMnTi high-ribbed ring-groove components, including complex metal flow behavior that easily causes under-filling defects and complicated die stress states prone to die failure, this paper proposes an optimal design method for the Multi-DoF forming process of high-ribbed ring-groove components. The influence mechanism of different blank sizes on metal flow and component filling effect is systematically investigated, and three typical metal flow modes are identified. Furthermore, a die stress optimization method for Multi-DoF forming is proposed. Research results show that, compared with the outward-to-inward and inward-to-outward metal flow modes, the metal flow under the symmetric inward–outward flow metal flow mode is more balanced, ensuring that the two high ribs can be fully formed. Additionally, changing the blank size can balance the forces on both sides of the die boss, thus significantly reducing the risk of die cracking caused by stress concentration. On the basis of the above research results, experimental tests are conducted, and the high-ribbed ring-groove components achieve full forming quality without die failure, which verifies the feasibility and effectiveness of the process optimization design method proposed in this paper.

Metals doi: 10.3390/met16070815

Authors: Fatemeh Khalatbari Joseph R. McDermid

Direct hot press forming (DHPF) of Zn-coated press-hardening steel (PHS) has not been widely adopted by industry due to liquid metal embrittlement (LME), which occurs when coated steel is hot stamped above the Fe-Zn peritectic temperature (~782 °C). In the present study, low-temperature hot stamping was performed on a 2.0 wt% Mn PHS to avoid LME by preventing liquid zinc formation during plastic deformation while achieving target mechanical properties (yield strength (YS) ≥ 1100 MPa and ultimate tensile strength (UTS) ≥ 1500 MPa) and preserving corrosion performance. The enhanced hardenability, indicated by a critical cooling rate (CCR) of 10 °C/s, enabled a predominantly martensitic microstructure following DHPF at 550–700 °C. Tensile testing of samples extracted from U-shaped panels yielded similar results for uncoated and Zn-coated samples, with a YS of ~1170 MPa, a UTS of ~1600 MPa, a uniform elongation (UE) of 0.05, and a total elongation (TE) of 0.09, demonstrating the preservation of baseline mechanical properties in the coated samples. Microstructural analysis confirmed the absence of LME-induced substrate cracking. Additionally, XRD, SEM-BSE, and EDS analyses confirmed Γ-Fe3Zn10 formation in DHPF galvanized coatings, with volume fractions averaging ~0.6, well above the critical value of 0.15, irrespective of the DHPF temperature, demonstrating the formation of a cathodically protective coating microstructure.

Metals doi: 10.3390/met16070814

Authors: Qi Zhang Yamei Jin Sai Tang Jiankai Ma

Heterogeneous nucleation is almost invariably responsible for the solidification of metals in practice, and this process governs the fabrication techniques for numerous advanced materials. Hence, a profound understanding of the physical essence of heterogeneous nucleation at the atomic scale is urgently required. In this study, we systematically investigate the substrate orientation dependence of liquid ordering and crystal nucleation in Al melts using molecular dynamics simulations (MD). Results show that the ability of nanoparticles to promote crystal nucleation originates from their capacity to facilitate the formation of crystal-like structures at the melt–substrate interface. Regarding the influence of substrate orientations on the ordered layers at the Al liquid–solid interface, the following trends are observed: the (111) plane has the strongest induction ability, followed by the (110) and then the (100) planes. For in-plane ordering, the (100) plane exhibits the highest order, followed by the (111) plane, with the (110) plane being the weakest. Notably, despite its highest atomic density in the first-ordered layer, the (111) substrate suffers from lower atomic mobility than the (100) and (110) substrates, hindering rapid rearrangement into the FCC structure. The synergy of the layer-by-layer growth mode, strong templating efficiency, and high atomic mobility leads to the fastest crystal growth for the (100) orientation.

Metals doi: 10.3390/met16070813

Authors: Shuicong Lu Dehong Lu Yongkun Li Yongtai Chen

To simultaneously suppress shrinkage-related defects and refine the solidification microstructure of Mn70Ni25Cr5 alloy ingots, ProCAST simulation was combined with Box–Behnken response surface methodology to optimize pouring temperature, filling time, and mold temperature. Porosity in the ingot body and secondary dendrite arm spacing (SDAS) were selected as the response variables, and quadratic regression models were established for both responses. The optimized casting parameters were determined using analysis of variance, response surface analysis, and the desirability function approach. The porosity and SDAS models were both statistically significant, with non-significant lack-of-fit terms and R2 values of 0.9906 and 0.9901, respectively. The optimal parameters were a pouring temperature of 1220.74 °C, a filling time of 6.34 s, and a mold temperature of 294.47 °C, corresponding to a predicted porosity of 0.426% and a predicted SDAS of 47.51 μm. A supplementary simulation and a validation casting experiment were then performed using practical process settings derived from the optimized solution. The supplementary simulation indicated that shrinkage-related defects were concentrated mainly in the riser, while metallographic examination revealed no large continuous shrinkage-porosity region in the examined ingot-body sections. The overall measured SDAS across the center, half-radius, and edge positions was 48.54 μm, differing from the response-surface prediction by approximately 2.2%. These results support the applicability of the combined ProCAST–RSM approach for simulation-assisted optimization of Mn70Ni25Cr5 alloy casting parameters within the investigated process range.

Metals doi: 10.3390/met16070811

Authors: Kaisheng Chen Yan Chen Kuoli Zhai

To overcome the welding-induced residual tensile stress of Q235B welded joints, a sequential thermal-mechanical welding and DEM-FEM dynamic shot peening coupled model is established. The Goldak double-ellipsoidal heat source model is adopted to simulate welding temperature evolution, and the discrete element method fully considers random shot ejection and shot–shot collision energy attenuation, which addresses the simplification defect of traditional single-shot finite element models. The effects of shot diameter d, incident angle θ, initial shot velocity v and mass flow rate rm on the residual compressive stress layer are systematically analyzed. Results reveal that larger shot diameter and initial shot velocity deepen the residual compressive stress layer. Meanwhile, the maximum residual compressive stress first increases and then decreases with the increase in rm and θ. The optimal parameter combination is determined as d = 1 mm, θ = 60°, v = 60 m/s, rm = 9 kg/min. Under these parameters, the maximum residual compressive stresses reach −306 MPa (σx) and −310 MPa (σz), with the depths of the residual compressive stress layer being up to 0.78 mm for σx and up to 0.66 mm for σz, respectively. Different from previous simplified simulations, this study quantifies the collision energy attenuation caused by shot trajectory overlap. This proposed model can provide guidance for post-weld surface strengthening of low-carbon steel engineering structures.

Metals doi: 10.3390/met16070812

Authors: Xiang Guo Yongyi Yang Wei Liu Dexing Huang Tianhao Lin Huang Feng

Existing BIM-based workflows for complex spatial steel bridges often support 3D visualization and documentation, but they still lack a formal requirement-to-function traceability mechanism and a reliable automated link from special-shaped surface modeling to fabrication-oriented data. To address this gap, this study develops and validates a Model-Based Systems Engineering (MBSE)-oriented design–fabrication integration workflow for special-shaped steel bridges. The workflow combines requirement decomposition, functional architecture modeling, ENOVIA-based collaborative data management, skeleton-driven parametric modeling, User-Defined Feature (UDF) templates, Engineering Knowledge Language (EKL) batch instantiation, an IFC-based manufacturing information extension, ProNest nesting, and model-driven NC-code generation. The method was implemented for the Q7 North Pedestrian Bridge, a spatially twisted special-shaped steel landscape bridge. In the case study, the proposed workflow reduced typical repetitive component modeling time by 70.8%, shortened drawing generation time by 80.0%, increased nesting material utilization from 84.6% to 91.8%, and controlled the maximum coordinate-transformation deviation of formwork points within 1.42 mm. Field validation showed a mean fabrication deviation of 1.6 mm and a maximum site assembly closure deviation of 4.5 mm. The results indicate that the proposed MBSE-oriented digital thread improves design consistency, reduces manual data re-entry, and strengthens traceability from requirements to manufacturing and assembly. The study provides a reproducible case-study framework for model-driven steel bridge design–fabrication integration and identifies the limitations of UDF-library construction cost, software-specific learning requirements, and single-project validation.

Metals doi: 10.3390/met16070810

Authors: Valeriy Volodin Sergey Trebukhov Alina Nitsenko Arailym Mukangaliyeva Xeniya Linnik Nurila Burabayeva

In this study, the partial pressure values of magnesium over Mg–Ag system alloys were determined by the boiling point method and are presented as a temperature–concentration dependence. A similar dependence for the partial vapor pressure of silver was obtained with the numerical integration of the Gibbs–Duhem equation. The boundaries of the vapor–liquid equilibrium fields were calculated at atmospheric pressure (101.3 kPa) and under vacuum (1.33 kPa). A complete phase diagram was constructed, including the boundaries of the liquid–vapor phase transition at the specified pressures. It was shown that the composition of the equilibrium vapor phase is represented almost entirely by magnesium over nearly the entire range of component concentrations. Thus, when the melt contains 1 wt. % in the melt and exhibits a boiling temperature of 1187 °C (1460 K), the vapor phase contains 94.67 wt. % magnesium, with silver accounting for the remainder. Therefore, the separation of liquid magnesium–silver alloys presents no significant technological difficulties. Based on the thermodynamic activities of the components, the partial and integral mixing functions, namely, entropy and enthalpy, were determined. The thermodynamic functions of formation and evaporation of Mg–Ag system alloys may be used for energy calculations of distillation processes and will supplement the physicochemical database.

Metals doi: 10.3390/met16070808

Authors: Rongsheng Shi Ming Zhan Hao Wang Yuntao Wang

Spherical shells are a commonly used structural form in submarine pressure-resistant structures. This study employed machine learning to predict the ultimate strength statistical properties of spherical shells considering inevitable multi-source uncertain imperfections. Thirty nominally identical spherical shells were fabricated, the thickness distribution and geometric imperfections were measured, and the ultimate strength of these shells were obtained by hydrostatic experiments. Then, the measured imperfections were reconstructed and mapped into the finite element model, and the buckling performance of the spherical shells were numerically investigated. Subsequently, two XGBoost models with considerable accuracy were trained to predict the ultimate strength statistical properties. The pole-smoothing double Fourier series expansion was adopted to reconstruct the geometric imperfections with accuracies exceeding 0.985 on all tested shells. The experimental ultimate strength of the spherical shells was consistent with the numerical predictions with an error of 0.81%. The evaluation metrics R2 of the XGBoost models for the mean and standard deviation of spherical shell ultimate strength were 0.9977 and 0.9246, respectively. At a confidence level of 99.74%, the margin of the upper bound prediction was 0.018 MPa, and the margin of the lower bound prediction was 0.624 MPa. The findings of this study propose an innovative method to predict the ultimate strength bounds of spherical shells, offering a generalizable workflow that can potentially inform the design of submarine pressure hulls when extended to application-specific geometric dimensions and materials.

Metals doi: 10.3390/met16070809

Authors: Shaowen Deng Guangyao Chen Hang Guo Kunjie Peng Hui Xu Enhui Wang Xinmei Hou Chonghe Li

Induction melting with a crucible was a commonly employed method for the preparation of Ni-based superalloys. However, it inevitably introduced contamination to the superalloy during the melting process. In this study, the effect of Ca addition was investigated on the interaction between the Al2O3 crucible and the superalloy melts. The variations in impurity elements and inclusion contamination for the alloys were studied. The results revealed that the interaction between the melt and the Al2O3 crucible led to the dissolution of Al2O3, introducing oxygen contamination and promoting the formation of inclusions. After adding Ca, the dissolved oxygen readily reacted with Ca to form CaO, which further reacted with the Al2O3 matrix and inclusions to form CaO-Al2O3 oxides. The total O content in the alloy was reduced from 0.0141 ± 0.0005 wt.% to 0.0030 ± 0.0003 wt.%, and the S content decreased from 1.60 ± 0.17 × 10−4 wt.% to 0.82 ± 0.05 × 10−4 wt.%. Meanwhile, the detected area-to-mass ratio of floated inclusion contamination in the alloys decreased from 0.36 cm2/kg to 0.05 cm2/kg. This process reduced both oxygen-related impurities and inclusion-derived contaminants, thereby providing an effective approach for preparing high-purity alloys.

Metals doi: 10.3390/met16070807

Authors: Paula C. Cintrón-Núñez Karina Suárez-Alcántara Ignacio A. Figueroa-Vargas Juan R. Tena-García Joaquín E. González-Hernández Jorge M. Cubero-Sesin Yoshikazu Todaka Daniel Bahena-Uribe Armando Salinas-Rodríguez José G. Cabañas-Moreno

Hydrogen storage represents a key technological challenge to the widespread use of hydrogen as a fuel and energy carrier. For this purpose, the hydrogen storage properties of medium-entropy and high-entropy alloys are under extensive investigation, including the study of the effects of compositional variations, nanostructuring, and catalyst additions. The present work characterizes the hydrogen storage behavior of a medium-entropy, near equiatomic Ti-V-Cr-Mn alloy, both in the as-cast condition and after nanostructuring by severe plastic deformation. The alloy consists of a matrix of BCC solid solution and a dispersed C14 Laves phase. Processing by high-pressure torsion results in the refinement of the crystallite size of the BCC phase down to about 30 nm. The absorption capacity of the alloy at 45 °C and 2.5 MPa is 1.6 wt%. Regardless of its initial condition, the first hydrogenation of the Ti-V-Cr-Mn alloy at room temperature and 2.5 MPa occurs without any pre-activation treatment. On the other hand, hydrogen is partially released at room temperature, while full dehydrogenation requires a temperature of 300 °C. Severe plastic deformation considerably reduces the susceptibility of the alloy to become deactivated for hydrogen absorption. These results highlight the potential of plastic straining to tailor the hydrogen storage properties of metallic BCC alloys.

Metals doi: 10.3390/met16070806

Authors: Zeyu Liu Kaijiao Kang Dequan Shi

Two-dimensional metallography cannot be used to determine how graphite volume is partitioned among three-dimensional connected structures in compacted graphite iron (CGI), even when the conventional graphite fractions are similar. This study therefore uses archived micro-CT data to determine whether 75FeSi additions in thermal analysis specimens alter the three-dimensional distribution of graphite volume. Three spherical specimens were cast from an industrial CGI melt with 0, 0.15, and 0.30 wt.% 75FeSi placed at the bottom of the specimen cavity. Center coupons were examined using a ZEISS Xradia 620 Versa X-ray microscope, and the retained reconstructed volumes had 3.0 µm isotropic voxels. We decoded the archived Dragonfly volumetric datasets, removed inactive historical labels, and calculated number-weighted and volume-weighted size, concentration, and shape descriptors. Graphite volume fraction remained within 8.56–8.83%, whereas connected object number density changed from 9764 mm−3 without additional 75FeSi to 5739 and 6854 mm−3 at 0.15 and 0.30 wt.%, respectively. Number-weighted median diameter remained near 13 µm, but volume-weighted D90 increased from 185.0 to 454.7 and 501.9 µm. The largest connected object contained 3.42%, 20.30%, and 31.39% of graphite volume, respectively. The main contribution is a specimen-level three-dimensional graphite volume-partitioning signature that separates graphite amount from graphite connectivity and upper-tail concentration. The results show that similar total graphite fractions can correspond to different internal graphite architectures, which conventional planar measurements cannot resolve.

Metals doi: 10.3390/met16070805

Authors: Bao Yang Xiaoyong Tang Wenming Xiong Zhuang Li Minglin Wang Hui Zhang

The anisotropic permeability tensor governs interdendritic fluid flow and solute transport during the directional solidification of metallic alloys, fundamentally influencing crystal growth kinetics and microstructural evolution. Traditional scalar models, notably the Kozeny–Carman equation, are fundamentally limited by isotropic assumptions that contradict the inherent anisotropy of dendritic microstructures and preclude description of microstructure–transport coupling. Recent advances in multiscale computational crystal growth modeling, integrating phase-field simulations of dendritic morphology, lattice Boltzmann calculations of interdendritic flow, and synchrotron X-ray tomography for in situ microstructural characterization, have enabled tensor-resolved quantification of permeability evolution, yet the dynamic feedback between solid skeleton deformation and permeability remains poorly understood. This work establishes a critically assessed mechanistic framework coupling dendritic microstructure evolution, anisotropic permeability tensor dynamics, and solidification transport phenomena. By explicitly addressing the hitherto unresolved dynamic feedback between solid skeleton deformation and permeability, this review provides a theoretical foundation and a conceptual framework for future predictive modeling for solidification microstructure control, offering fundamental insights into the physics of crystal growth and interdendritic transport in metallic systems.

Metals doi: 10.3390/met16070804

Authors: Tianwei Qiu Muhammed Nafis Bin Osman Zahid

Aluminum/magnesium (Al/Mg) hybrid structures are promising candidates for lightweight engineering, but reliable joining is still limited by brittle intermetallic compounds (IMCs), oxide films, pores, cracks, and corrosion-related degradation. This review summarizes recent advances in Al/Mg dissimilar-metal joining, including solid-state welding, fusion welding, brazing, resistance-based joining, and mechanical joining. Emphasis is placed on process characteristics, interfacial reactions, defect formation, mechanical properties, service reliability, and simulation-assisted process understanding. The reviewed studies indicate that joint reliability cannot be interpreted solely from IMC thickness; phase type, continuity, spatial distribution, interfacial morphology, and involvement in the fracture path are also critical. Solid-state and high-speed impact processes can restrict continuous Al–Mg reaction layers by reducing thermal exposure and promoting plastic contact, whereas fusion-based processes provide greater manufacturing flexibility but require stricter control of molten-pool behavior, Mg evaporation, porosity, and interlayer stability. Recent numerical simulations and data-driven studies are further discussed as tools for mechanism-guided parameter design. This review provides an integrated comparison of joining routes and highlights future needs for standardized testing, fatigue and corrosion evaluation, thermal-cycling assessment, coupled service-performance analysis, and process selection for engineering applications.

Metals doi: 10.3390/met16070803

Authors: Zhiyuan Zhang Junchao An Junfang Shen Yi Liu Yan Gao

The current progressive forming process for large-scale longitudinally submerged arc-welded (LSAW) pipes is continuously losing competitiveness in terms of manufacturing quality and production efficiency. Based on the asymmetric four-point bending (AFB) mechanical model and classical elastic–plastic bending theory, in this paper, we investigate sheet bending behavior during the four-point bending stage. Analytical expressions are derived for the main influencing factors during the forming and springback process. Finite element simulation and experimental research into the mechanical model are conducted to analyze the effects of various process parameters on the forming results. On this basis, an AFB progressive forming process parameter formulation strategy is established and programmed. Experiments and simulations were conducted using the process parameters formulated by this strategy. The results showed that pipes could complete the progressive forming process in fewer passes, thereby improving production efficiency. The ovality of most experimental pipes was less than 1.5% and consistently below 0.7% in simulations—significantly lower than the engineering requirement of 2%. These results demonstrate the feasibility and reliability of the strategy, highlight the significant improvement in pipe quality achieved through the AFB process, and lay a solid foundation for the development and intelligentization of future progressive forming processes for LSAW pipes.

Metals doi: 10.3390/met16070802

Authors: Xiangqian Bai Zize Zhang Xingzhong Zhang

Internal cracks during slab bending and straightening are continuous-casting defects. Existing caster curves rely on plastic deformation, while curvature variation is concentrated within short sections, causing excessive strain rates and increasing the risk of internal straightening cracks. This study proposes a novel method for slab straightening through creep deformation and develops a curve for an R9300 caster by connecting cubic transition curves with cycloidal main segments. High-temperature tensile and constant-stress creep tests of Q345C steel were combined with transient thermal simulation and geometric strain-rate calculations. Under constraints on caster height, minimum curvature radius, and steady-state creep rate, the optimized parameters were a = 2600 mm and t = 3.6 rad. The curve eliminates the circular-arc section and ensures continuous position, tangent, and curvature. Its bending and straightening sections are each 9379 mm long, increases of 8349 and 7859 mm, respectively, while caster height increases by only 0.47 m. At the internal 1200 °C isotherm, the maximum strain rates are 6.75×10−5 s−1 and 5.19×10−5 s−1, reductions of 82.2% and 81.1% relative to the conventional caster. Both remain below the steady-state creep rate of 7.45×10−5 s−1 under ±10% secondary-cooling and ±10 °C casting-temperature fluctuations. The curve alleviates deformation concentration and enables the slab region at 1200 °C and above to bend and straighten through creep deformation.

Metals doi: 10.3390/met16070801

Authors: Jiaxiang Zheng Chengwei Fei Tian Xie Chuangliang Wu Xi Gao Wei Jiang

Fe-Mn-Al-C lightweight high-strength steels are promising for aerospace and defense applications, but selective laser melting (SLM) introduces steep thermal gradients and rapid solidification, causing directional grain growth, crystallographic texture, and the non-uniform precipitation of κ-carbides and B2 phase at grain boundaries. This results in pronounced mechanical anisotropy between XY and YZ planes, limiting engineering use. To eliminate this anisotropy, we investigate the post-SLM solution treatment of an SLM-fabricated Fe-Mn-Al-C steel at 1050–1150 °C for 0.5–1.5 h followed by oil quenching, and characterize microstructures and tensile properties on both planes. At 1050 °C, the XY plane remained equiaxed γ-austenite, while the YZ plane transformed to α and became equiaxed over time, causing strength–ductility anisotropy. At 1100 °C for 1 h, anisotropy was effectively removed: XY and YZ planes exhibited tensile strengths of ~1159 and 1154 MPa and elongations of ~40% and 41%. TEM revealed that uniform fine κ-carbides and coarsened B2 at grain boundaries suppressed direction-dependent strain. At 1150 °C, dissolved boundary phases and diffuse intragranular κ-carbides severely reduced ductility. The optimal treatment is 1100 °C for 1 h, yielding a homogeneous microstructure and excellent isotropic properties.

Metals doi: 10.3390/met16070799

Authors: Hanzheng Zhang Guobao Li Yongjie Yang Fang Zhang Yuhui Sha

Grain-oriented silicon steel is a key soft magnetic material for transformer cores, and femtosecond laser scribing provides a potential approach for achieving high-precision magnetic-domain refinement while reducing thermal damage. However, the near-surface electronic response and charge-imbalance behavior of grain-oriented silicon steel during femtosecond laser irradiation are still not well understood. In this study, a two-temperature model coupled with an electron transport model was employed to investigate the evolution of electron temperature and net charge density under different laser fluences and pulse durations. The results showed that laser fluence and pulse duration jointly affected the near-surface electron-temperature response, electron-emission process, and net charge-density evolution in grain-oriented silicon steel. Increasing laser fluence enhanced electron excitation and the degree of charge-distribution imbalance. Meanwhile, increasing pulse duration promoted the extension of the net charge distribution along the depth direction, which indicated that there was a pulse-duration range that can simultaneously promote charge accumulation at the surface and in the near-surface region. These results provided comprehensive insight into the near-surface charge-imbalance behavior during femtosecond laser etching of grain-oriented silicon steel.

Metals doi: 10.3390/met16070800

Authors: Eulyong Ha Myungsu Yi Younghyun Kim Jaewoong Kim

As the demand for eco-friendly energy increases, offshore wind power structures are gradually becoming larger to increase power generation capacity, which in turn requires the use of thick TMCP steels and the securing of structural integrity. In this study, multi-pass FCAW was applied to 40 mm thick S355ML and S420ML steels in 2G and 3G welding positions, and the welding conditions for each experiment were designed to simulate actual industrial site construction conditions. After the experiments, tensile, low-temperature impact, and hardness tests were performed on the welded joints, and a comparative analysis was conducted on whether the relevant standards were satisfied and their major characteristics. As a result of the tensile test, tensile strengths exceeding the standard requirements were measured under all conditions, and base metal fracture occurred. In addition, the low-temperature impact test conducted at −50 °C exceeded the standard requirement of 27 J, ensuring sufficient low-temperature toughness, and the Vickers hardness test results were measured to be less than the reference value of 380 HV10. Through this study, the structural integrity and mechanical reliability of multi-pass FCAW welded joints for thick TMCP steel plates were secured.

Metals doi: 10.3390/met16070798

Authors: Liqiang Ma Dongdong Zhang

High-strength Mg alloys always contain heavy RE solutes, which leads to the high cost of Mg alloys preventing commercial use. In this work, we developed a new high-performance Mg–3Nd–1Yb–0.6Zn–0.4Zr alloy with low RE content and investigated the effects of heat treatment on the microstructure and mechanical properties. The results show that the main secondary phase in the as-cast alloy is the eutectic Mg12RE phase at grain boundaries. The average grain size is measured to be 24.6 μm. After solution treatment, the grain-boundary eutectic Mg12RE phase is completely dissolved into the matrix, without obvious grain growth. The alloy exhibits an obvious age-hardening effect during aging at 200 °C, and its hardness reaches a peak at 15 h, with a hardness increment of ~31 HV. A high-density prismatic β′ phase is formed in the matrix after peak aging. The peak-aged alloy presents optimal mechanical properties, with ultimate tensile strength, yield strength and elongation of 282 MPa, 202 MPa and 6.8%, respectively, which are remarkably superior to those of typical alloys such as EV31A and WE43. Quantitative calculation of strengthening mechanisms indicates that age hardening is the dominant strengthening mechanism of the peak-aged alloy, and the precipitation strengthening contribution of prismatic β′ phase is 158 MPa, accounting for approximately 78% of the yield strength.

Metals doi: 10.3390/met16070797

Authors: Xinying Zhang Chunmao Jiang Fengsheng Lu Lei Zhang Minghuang Bi Hao Jin Xudong Lu Guanglin Zhu Cean Guo Jian Zhang

The self-lubricating MoS2 coating is highly susceptible to degradation in marine environments due to oxidative corrosion. To expand its application in high-humidity and high-salt-fog conditions, this study mixed W with MoS2 and prepared W-MoS2 self-lubricating coatings on the surface of CrNi3MoVA steel by electrospark deposition technology. The electrochemical corrosion behaviors of these coatings, with varying W/MoS2 mass ratios, were examined using an electrochemical workstation in a 3.5 wt.% NaCl solution. The findings indicated that as the MoS2 content increased, the low-frequency impedance modulus (LIMs) of the W-MoS2 coating initially rose and then declined. At a MoS2 content of 20 wt.%, the coating exhibited the highest LIM and the greatest corrosion resistance. In comparison to the CrNi3MoVA steel substrate, the corrosion current density was reduced by 67.4%, a result attributed to the coating’s dense microstructure and improved charge transfer resistance, thereby demonstrating its optimal protective performance. These results provide a laboratory electrochemical basis for designing corrosion-resistant self-lubricating ESD coatings for steel components exposed to chloride-containing environments; however, long-term immersion, cyclic salt-spray, field-exposure, and quantitative adhesion tests are still required before direct long-term marine-service durability can be confirmed.

Metals doi: 10.3390/met16070796

Authors: Zhenliang Zhang Can Guo Shengkai Cao Zhangle Xie Jiankai Ma Yiming Hao Junhao Zhu Wanli Cao Daniel Safranchik Chunjie Xu

As a typical class of high-strength and high-conductivity materials, particle-reinforced copper matrix composites show great promise for application in critical conductive components. However, when such composites are prepared via melting methods, challenges such as the agglomeration of reinforcing particles and difficulty controlling their spatial distribution often arise, limiting the application of these composites in conductive parts. In this study, a phase-field method is employed with order parameters introduced to characterize the interaction between solid–liquid interfaces and reinforcing phases. By reconstructing the free-energy functional of the multi-phase-field model, the effects of undercooling and solid–liquid interface properties on particle–interface interactions are investigated. Simulations are conducted for solidification for different particle sizes and in different particle aggregation states, dynamically illustrating the evolution behavior of nanoparticles at the solid–liquid interface. The results indicate that particle migration velocity and distance rise with increased particle mobility due to reduced melt flow resistance. Higher undercooling accelerates solidification front propagation but curtails particle pushing distance, while the interface gradient coefficient (ε2) only inhibits particle migration distance with negligible influence on peak migration velocity. In single-crystal matrices, agglomerate morphology, orientation angle, and aggregation degree jointly affect migration behavior: irregular agglomerates undergo obvious morphological deformation, and migration distance increases when the orientation angle ranges from 0° to 90° and decreases with higher aggregation degrees. Fine particles are repelled to grain boundaries for agglomeration, whereas large particles are engulfed inside grains. Powders were fabricated via gas atomization, and the results of scanning electron microscopy characterization experiments confirm the simulation reliability. The results provide valuable insights for the controlled distribution of nanoparticles within composite materials.

Metals doi: 10.3390/met16070795

Authors: Muhammad Bilal Jan Zengchao Wu Mengyu Chai

Accurate prediction of creep rupture life is essential for ensuring the long-term reliability of high-temperature components in power generation and petrochemical industries. Selecting appropriate data-driven models for limited and heterogeneous creep datasets remains a critical challenge, as conventional accuracy-based comparisons do not fully capture model behavior under varying service conditions. This study presents a unified evaluation framework for systematically comparing multiple machine learning and deep learning models for creep rupture life prediction of 2.25Cr–1Mo steel. The framework integrates predictive accuracy, prediction reliability, regime-specific error analysis, and computational efficiency, enabling a comprehensive assessment beyond global error metrics. The input feature space is reduced from seventeen to eight physically meaningful variables without loss of predictive performance. To further assess model robustness, prediction errors are analyzed across four distinct rupture life regimes, revealing significant variations in model behavior that are not reflected in aggregate metrics. Results indicate that support vector regression (SVR) provides the most consistent overall performance across all regimes and offers a strong balance between accuracy and computational efficiency. Among deep learning models, a Bayesian neural network (BNN) achieves competitive predictive performance while additionally enabling uncertainty estimation. These findings demonstrate that, for small tabular creep datasets, appropriately regularized models outperform complex neural network architectures, highlighting the importance of matching model complexity to dataset characteristics. This study is limited to a single steel grade, moderate dataset size, and extrapolation beyond trained stress and temperature ranges, which are key directions for future work.