Metals

19 pages, 7270 KB

Open AccessArticle

Evaluation of Microstructure and Tensile Properties of Al-12Si-4Cu-2Ni-0.5Mg Alloy Modified with Ca/P and TCB Complex

by Yuan Sun, Xiaoming Ren, Xueting Li, Hong Duan, Weiyi Wang, Mengxia Han, Guiliang Liu, Sida Liu and Xiangfa Liu

Metals 2025, 15(11), 1276; https://doi.org/10.3390/met15111276 - 20 Nov 2025

Viewed by 658

Abstract

The room-temperature and high-temperature microstructural characteristics and tensile properties of an Al-12Si-4Cu-2Ni-0.5Mg piston alloy modified with calcium (Ca; denoted as AC sample) or phosphorus (P; denoted as AP sample) under different heat treatment conditions were systematically analyzed. Under Ca modification, the second-phase network [...] Read more.

The room-temperature and high-temperature microstructural characteristics and tensile properties of an Al-12Si-4Cu-2Ni-0.5Mg piston alloy modified with calcium (Ca; denoted as AC sample) or phosphorus (P; denoted as AP sample) under different heat treatment conditions were systematically analyzed. Under Ca modification, the second-phase network structure of the alloy was adjusted and strengthened by an Al-TCB master alloy. Eutectic silicon (Si) particles in the AC sample possessed a fibrous structure, whereas the AP sample contained elongated eutectic Si particles, and Ca modification was found to be a potential method for simultaneously enhancing the strength and plasticity of the alloy to a matching degree at high temperatures. The T6 treatment noticeably increased the density of nanoscale precipitates; however, it also disrupted the growth of the second-phase network structure. Micron and submicron C-TiB₂ and Al₄C₃ particles formed by the in-situ reaction of TCB particles acted as bridging phases within the second-phase network structure and enhanced the strength of the piston alloy. The ultimate tensile strength of the alloy at 350 °C increased from 74 to 101 MPa, representing a 36.5% enhancement. A comprehensive analysis revealed that Orowan strengthening was the main strengthening mechanism of the alloy at room temperature, whereas load transfer and network structure strengthening were the dominant strengthening mechanisms at high temperatures. Full article

(This article belongs to the Special Issue Microstructure, Crystallography, and Mechanical Properties of Metallic Materials)

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19 pages, 3042 KB

Open AccessArticle

Selective Oxidation Control for Synchronous Vanadium Extraction and Chromium Retention from Vanadium- and Chromium-Bearing Hot Metal

by Xin-Yu Wang, Hai-Quan Zhao, Lu-Feng Wang, Qiao-Chu Liu, Ding-Liu Yan, Feng Wang and Yuan-Hong Qi

Metals 2025, 15(11), 1275; https://doi.org/10.3390/met15111275 - 20 Nov 2025

Viewed by 584

Abstract

To address the technical challenges involved in the resource utilization of hot metal containing high levels of vanadium (V: 2–5%) and chromium (Cr: 1–5%), this study proposes a novel method based on pyrometallurgical selective oxidation for simultaneously extracting vanadium and retaining chromium. Through [...] Read more.

To address the technical challenges involved in the resource utilization of hot metal containing high levels of vanadium (V: 2–5%) and chromium (Cr: 1–5%), this study proposes a novel method based on pyrometallurgical selective oxidation for simultaneously extracting vanadium and retaining chromium. Through thermodynamic analysis and high-temperature smelting experiments, the competitive oxidation behaviors of carbon, vanadium, and chromium were revealed, and the synergistic control mechanism of temperature and oxygen partial pressure was clarified. The results indicate that within a temperature range of 1693–1753 K, adjusted over 1 h, vanadium preferentially oxidizes over carbon and chromium, while carbon effectively suppresses chromium oxidation. By optimizing ω(FeO) (10.0–15.7%), we achieved a vanadium oxidation efficiency (η_V) of 72.5–82.2% and maintained a chromium retention efficiency (100−η_Cr) exceeding 57.1%. Compared to traditional methods, which rely on high-oxygen blowing (oxygen supply: 43–195 kg/tFe), multi-stage roasting, and hydrometallurgical refining, this approach eliminates roasting and hydrometallurgical steps (such as sodium/calcium roasting and the associated leaching–precipitation units), shortens the process chain, reduces oxygen consumption (>80 kg/tFe), and lowers environmental risks (Cr oxidation reduced > 40%). This study establishes a theoretical framework for achieving sustainable V/Cr separation, enhancing resource efficiency and minimizing pollution (e.g., Cr(VI)-containing wastewater, high-salinity NH₄⁺/Na⁺ wastewater). Full article

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14 pages, 5951 KB

Open AccessArticle

The Low-Cycle Fatigue Performance of Emerging Titanium Alloys for Aeroengine Applications

by Peter Davies, Sean John, Helen Davies, Martin Bache, Kate Fox, Christopher Collins, Nigel Martin and Rebecca Sandala

Metals 2025, 15(11), 1274; https://doi.org/10.3390/met15111274 - 20 Nov 2025

Cited by 1 | Viewed by 960

Abstract

The low-cycle fatigue behavior of three titanium alloys (including two wrought alloys that are commercially available and one under development via a powder sintering technique) is described in order to assess the relative capabilities of a fourth, novel proprietary alloy, designated as RR11. [...] Read more.

The low-cycle fatigue behavior of three titanium alloys (including two wrought alloys that are commercially available and one under development via a powder sintering technique) is described in order to assess the relative capabilities of a fourth, novel proprietary alloy, designated as RR11. Despite relatively increased levels of beta stabilization, each alloy remains within the general alpha–beta microstructural category and could be considered as an engineering alternative to the well-established Ti-6Al-4V. The relationships between fatigue behavior, microstructure, grain morphology, micro-texture, and alloy chemistry are explored. Emphasis is placed upon the potential cold dwell fatigue sensitivity of the four alternative alloys, which is particularly pertinent since it was recognized that Ti-6Al-4V can suffer from cold dwell-related behavior subject to selected thermo-mechanical processing. Full article

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20 pages, 5665 KB

Open AccessArticle

The Impact of Electron Beam Melting on the Purification of Recycled Zirconium

by Katia Vutova, Vladislava Stefanova, Evgeniy Manoilov, Irena Mihailova, Maria Naplatanova and Peter Iliev

Metals 2025, 15(11), 1273; https://doi.org/10.3390/met15111273 - 20 Nov 2025

Viewed by 761

Abstract

Zirconium belongs to the group of critical rare metals and is primarily used in industry. Its most important application, as the basis for specialized alloys, is in nuclear reactors, owing to its exceptionally very low thermal neutron absorption cross-section. Based on theoretical and [...] Read more.

Zirconium belongs to the group of critical rare metals and is primarily used in industry. Its most important application, as the basis for specialized alloys, is in nuclear reactors, owing to its exceptionally very low thermal neutron absorption cross-section. Based on theoretical and experimental investigation, the potential for removing metallic (Al, Ti, Hf, V, Fe, Cr, Cu, Ni) and non-metallic (O, C) impurities from technogenic zirconium during electron beam melting (EBM) was assessed. The influence of temperature (ranging from 2350 K to 2750 K) and refining duration (10, 15, and 20 min) under vacuum conditions (1 × 10⁻³ Pa) was investigated concerning the degree of impurity removal, the microstructure, and the micro-hardness of the resulting ingots. It was established that under optimal EBM conditions for technogenic zirconium (T = 2750 K, τ = 20 min), the total refining efficiency reached approximately 87%, and the achieved Zr purity was 99.756%. Among the impurities present in the technogenic zirconium, the lowest removal efficiencies were recorded for Al (54.90%) and Cr (88.89%), with the lower refining efficiency for Al influencing the microstructure and micro-hardness of the ingots produced after EBM. Full article

(This article belongs to the Special Issue Metal Extraction and Smelting Technology)

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19 pages, 5594 KB

Open AccessArticle

Multimodal Analysis Unveils the Correlation Between Graphite Anode Characteristics and Operational Longevity in Pr/Nd Rare Earth Metals Electrolysis

by Baoling Jia, Yangtao Xu, Zhenxu Zhu, Lihong Xu, Wei Sun, Feng Liang and Boming Chen

Metals 2025, 15(11), 1272; https://doi.org/10.3390/met15111272 - 20 Nov 2025

Viewed by 1022

Abstract

The service life of graphite anodes—key consumables in the Pr/Nd fluoride molten salt electrolysis process—directly governs production continuity, cost-efficiency, and supply chain stability. This study systematically evaluated five industrial-grade anodes produced from different raw materials and processes. Multimodal characterization—combining macroscopic and microscopic morphology, [...] Read more.

The service life of graphite anodes—key consumables in the Pr/Nd fluoride molten salt electrolysis process—directly governs production continuity, cost-efficiency, and supply chain stability. This study systematically evaluated five industrial-grade anodes produced from different raw materials and processes. Multimodal characterization—combining macroscopic and microscopic morphology, SEM/EDS, XRD, Raman, and physical property analysis—was employed to correlate initial anode properties with corrosion-induced morphological and mass changes during electrolysis. The results show that the raw material quality and preparation methods synergistically regulate both the crystal structure and microstructure, thereby governing the corrosion behaviour and mass loss. Anodes #2 and #3, which were fabricated from high-quality petroleum coke and subjected to full densification and graphitization, exhibited high graphitization (93.7–94.5%), large crystallites (59.6–64.5 nm), minimal defects (low I_D/I_G), and suppressed microporosity, leading to the lowest mass loss (10.2 ± 0.8 kg and 10.6 ±0.9 kg). In contrast, anodes #1, #4, and #5, made from recycled graphite without graphitization, contained abundant structural defects and large pores and led to greater morphological changes and quality losses. Moreover, for recycled graphite anodes, the presence of large pores and cracks is one of the important reasons for their failure. This work clarifies the “process–microstructure–mass loss” relationship in graphite anodes for Pr/Nd electrolysis, offering key insights for designing high-performance anodes and advancing sustainable rare earth production. Full article

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16 pages, 4085 KB

Open AccessArticle

Vacuum Distillation-Assisted Hydrometallurgical Route for Industrial Production of 99.999% Pure Gold from Au–Ag Alloys Feedstocks

by Weihuang Wu and Guozheng Zha

Metals 2025, 15(11), 1271; https://doi.org/10.3390/met15111271 - 20 Nov 2025

Viewed by 1031

Abstract

In response to the growing industrial demand for ultra-high-purity gold, a vacuum distillation-assisted hydrometallurgical process is developed in this study for the industrial-scale production of 99.999% pure (5N) gold from crude Au–Ag alloy feedstocks. This integrated approach combines vacuum distillation, aqua regia dissolution, [...] Read more.

In response to the growing industrial demand for ultra-high-purity gold, a vacuum distillation-assisted hydrometallurgical process is developed in this study for the industrial-scale production of 99.999% pure (5N) gold from crude Au–Ag alloy feedstocks. This integrated approach combines vacuum distillation, aqua regia dissolution, solvent extraction, and in situ reduction. An alloy containing approximately 56.47 wt% Au and 43.06 wt% Ag was first vacuum distilled, yielding a pre-enriched alloy with 94.76 wt% Au and less than 5.17 wt% Ag. The enriched Au alloy was subjected to aqua regia dissolution, solvent extraction, and Na₂SO₃-assisted reduction. The influence of the liquid-to-solid ratio, settling time, phase ratio, extraction time, and centrifugation speed on gold purity and recovery was systematically investigated. Under optimized conditions, the process achieved 99.999% purity and over 99.5% overall recovery, meeting the GB/T 25933-2010 standard. The use of Na₂SO₃ as a combined reducing and stripping agent simplified the operation, lowered reagent consumption, and improved environmental compatibility. This method provides a scalable, cost-effective, and environmentally friendly alternative to conventional refining techniques and is suitable for advanced manufacturing applications. Full article

(This article belongs to the Special Issue Green Technologies in Metal Recovery)

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15 pages, 12859 KB

Open AccessArticle

Effect of Nitrogen Content on the Cavitation Erosion Resistance of 316LN Stainless Steel

by Yong Wang, Wei Wang, Qingrui Xiao, Jinxu Yu, Yingping Ji and Kewei Deng

Metals 2025, 15(11), 1270; https://doi.org/10.3390/met15111270 - 20 Nov 2025

Cited by 1 | Viewed by 1007

Abstract

Cavitation erosion is a predominant failure mode of austenitic stainless steels in corrosive fluid environments, severely limiting their durability in nuclear piping and hydraulic components. In this study, five 316LN steels with 0.008–0.34 wt.% nitrogen content were fabricated, and both short-term (2 h) [...] Read more.

Cavitation erosion is a predominant failure mode of austenitic stainless steels in corrosive fluid environments, severely limiting their durability in nuclear piping and hydraulic components. In this study, five 316LN steels with 0.008–0.34 wt.% nitrogen content were fabricated, and both short-term (2 h) and long-term (24 h) cavitation tests were performed to elucidate the effect and mechanism of nitrogen. Increasing nitrogen markedly enhanced cavitation resistance: after 24 h, the cumulative mass loss decreased by 36%, 52%, 60%, and 71% for 09N, 17N, 22N, and 34N relative to 00N, accompanied by lower surface roughness, shallower pit depth, and a prolonged incubation stage. SEM revealed a progressive damage process from twin/high-angle grain boundaries to intragranular deformation bands and finally to spalling at slip intersections, whereas high-N steels exhibited only slight local detachment. TEM demonstrated that nitrogen transformed dislocations from random networks into dense slip bands and planar arrays with stacking faults, raising hardness from ~140 HV to ~260 HV. EBSD further confirmed strain-induced martensite transformation under severe deformation, providing additional strengthening. These results reveal that nitrogen improves cavitation resistance by tailoring dislocation structures and enhancing strength–plasticity compatibility, offering guidance for the design of high-performance austenitic stainless steels in cavitation environments. Full article

(This article belongs to the Special Issue Erosion–Corrosion Behaviour and Mechanisms of Metallic Materials)

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15 pages, 11821 KB

Open AccessArticle

High-Magnification In Situ Observation of Welding Solidification

by Tamaki Ito, Shaowei Yang, Keita Marumoto, Kenji Shinozaki and Motomichi Yamamoto

Metals 2025, 15(11), 1269; https://doi.org/10.3390/met15111269 - 20 Nov 2025

Viewed by 617

Abstract

In welding solidification, the morphology of residual liquid in the solid–liquid coexistence region affects the susceptibility to solidification cracking because this cracking is due to localized shrinkage strain in the residual liquid. Therefore, it is important to observe the residual liquid state during [...] Read more.

In welding solidification, the morphology of residual liquid in the solid–liquid coexistence region affects the susceptibility to solidification cracking because this cracking is due to localized shrinkage strain in the residual liquid. Therefore, it is important to observe the residual liquid state during solidification in detail to elucidate the occurrence of solidification cracking. In this study, a high-magnification in situ observation system was developed by combining an optical microscope and a high-speed camera. This system enables continuous, high-magnification, and high-resolution observation of welding solidification, because the objective lens of a microscope is attached to a high-speed camera. Laser welding solidification of stainless steel sheets was observed using this system and the morphology of residual liquid was visualized with higher magnification and higher definition than previous observation methods. Compared with a high-magnification image and quenched solidification microstructure, the residual state of the liquid phase during solidification could be observed in detail and dynamically. Additionally, the difference in solidification between two types of stainless sheets could be observed with high magnification in situ at one point. Finally, the combination of the observation results from this system and a high-temperature ductility curve revealed the relationship between the morphology of residual liquid and solidification cracking susceptibility. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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15 pages, 7149 KB

Open AccessArticle

CAFE Simulation of Solidification Microstructure of Cast WE54 Alloy: Influences of Simulation Parameters and Experimental Verification

by Jilin Li, Ruohan Zhao and Junning Feng

Metals 2025, 15(11), 1268; https://doi.org/10.3390/met15111268 - 20 Nov 2025

Cited by 2 | Viewed by 717

Abstract

The simulation of solidification microstructures of cast alloys is crucial to the integrated “process–microstructure–property” numerical simulation. In order to verify the accuracy of the solidification microstructure simulation results, the solidification microstructures of WE54 alloy under both metal mold casting (MMC) and sand mold [...] Read more.

The simulation of solidification microstructures of cast alloys is crucial to the integrated “process–microstructure–property” numerical simulation. In order to verify the accuracy of the solidification microstructure simulation results, the solidification microstructures of WE54 alloy under both metal mold casting (MMC) and sand mold casting (SMC) conditions were simulated using the CAFE (Cellular Automaton–Finite Element) method, and the simulation results were validated experimentally. First, the effects of microstructure simulation parameters on the results were investigated, including nucleation density (n), nucleation undercooling (ΔT), and dendrite tip growth kinetics parameters (a₂, a₃). The results showed that, with the maximum surface nucleation undercooling (ΔT_s,max) kept constant, increasing the maximum volume nucleation undercooling (ΔT_v,max) significantly increases the proportion of columnar grains in the ingot structure. Moreover, when nucleation parameters remain constant, increasing a₂ and a₃ leads to expansion of the columnar grain zone. Secondly, numerical simulations of the solidification microstructure of WE54 alloy under different solidification conditions were carried out. The results indicated that as the cooling rate increases, the grain structure of the ingot becomes significantly refined, and the proportion of columnar grains decreases notably. Based on these findings, the simulation parameters suitable for simulating the solidification process and microstructure of MMC and SMC WE54 alloy were determined. Simulations of the temperature field and solidification microstructure were performed and compared with experimental results. Full article

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13 pages, 6025 KB

Open AccessArticle

The Magnetocaloric Properties and Critical Behavior of (Gd₄Co₃)_100−xGe_x Rapidly Quenched Alloys

by Xichun Zhong, Yaxiang Wu, Haongya Yu and Zhongwu Liu

Metals 2025, 15(11), 1267; https://doi.org/10.3390/met15111267 - 19 Nov 2025

Cited by 1 | Viewed by 894

Abstract

Gd₄Co₃ is a promising magnetocaloric material with a high magnetic entropy value. However, it undergoes a first-order magnetic transition, which hinders practical applications. Hence, (Gd₄Co₃)_100−xGe_x (x = 5, 10, 15) were studied to [...] Read more.

Gd₄Co₃ is a promising magnetocaloric material with a high magnetic entropy value. However, it undergoes a first-order magnetic transition, which hinders practical applications. Hence, (Gd₄Co₃)_100−xGe_x (x = 5, 10, 15) were studied to obtain high magnetic entropy values and a second-order magnetic transition. To investigate the effects of Ge addition on the thermal stability, magnetocaloric properties, and critical behavior of Gd₄Co₃-based alloys, (Gd₄Co₃)_100−xGe_x (x = 5, 10, 15) melt spun ribbons were prepared. Phase analysis showed these alloys are mainly amorphous, with a minority nanocrystalline phase. All alloys undergo a second-order ferromagnetic-to-paramagnetic transition. The Curie temperature (T_C) increases linearly from 211 K (x = 5) to 217 K (x = 15) with increasing Ge content. Under a magnetic field variation of 5 T, the alloys with x = 5, 10, and 15 exhibit peak magnetic entropy change (−ΔS_M) values of 7.15, 6.83, and 6.71 J/(kg·K), respectively, along with considerable refrigerant capacity (RC) in the range of 435–458 J/kg. These excellent magnetocaloric properties collectively demonstrate their great potential for magnetic refrigeration applications. Critical behavior analysis revealed critical exponents broadly consistent with mean-field theory (MFT, β = 0.5, γ = 1.0, δ = 3.0), indicating nanocrystals in the amorphous matrix induce long-range magnetic interactions. Full article

(This article belongs to the Special Issue Metallic Magnetic Materials: Manufacture, Properties and Applications)

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13 pages, 1543 KB

Open AccessArticle

Investigation of Weld Quality Grades for Aluminum Alloys Based on Fatigue Life

by Zhibiao Zhao, Gangyi Cai, Yufeng Ye and Yuebing Li

Metals 2025, 15(11), 1266; https://doi.org/10.3390/met15111266 - 19 Nov 2025

Viewed by 915

Abstract

In the design and manufacturing of pressure vessels, the quality of welded joints and their operational safety are critical considerations. Weld quality classification is closely linked to its impact on fatigue performance. In this study, aluminum alloy welds with varying levels of porosity [...] Read more.

In the design and manufacturing of pressure vessels, the quality of welded joints and their operational safety are critical considerations. Weld quality classification is closely linked to its impact on fatigue performance. In this study, aluminum alloy welds with varying levels of porosity were produced by adjusting welding parameters, and X-ray inspection was used to assess porosity levels. Representative welds corresponding to different quality grades were selected to fabricate fatigue specimens, and their fatigue lives were determined. The influence of quality grades on the residual fatigue life of aluminum alloy welded sheets was systematically analyzed. The results indicate that, under identical loading conditions, the fatigue life of specimens with defects is significantly reduced compared to defect-free specimens. This reduction becomes more pronounced as the quality grade decreases—corresponding to an increase in circular hole defects. Specifically, for 5083 aluminum alloy, transitioning from Grade I to Grade III results in fatigue life reductions of approximately 25%, 35%, and 50%, respectively. Full article

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19 pages, 2205 KB

Open AccessArticle

Prediction Modeling and Parameter Optimization for Robotic Belt Grinding 42CrMo Steel Using Response Surface Methodology and Grey Relational Analysis

by Dequan Shi, Wuyang Zhang, Jiahao Wang, Guili Gao and Huajun Zhang

Metals 2025, 15(11), 1265; https://doi.org/10.3390/met15111265 - 19 Nov 2025

Viewed by 714

Abstract

To address high-precision robotic abrasive belt grinding of 42CrMo steel, this study adopted the orthogonal central composite design with grinding force, feed rate, and rotational speed as key parameters, establishing and verifying regression models for material removal depth (MRD) and surface roughness (Ra). [...] Read more.

To address high-precision robotic abrasive belt grinding of 42CrMo steel, this study adopted the orthogonal central composite design with grinding force, feed rate, and rotational speed as key parameters, establishing and verifying regression models for material removal depth (MRD) and surface roughness (Ra). Results showed that the models’ relative errors are within 6% (MRD) and 10% (Ra). Grinding force and feed rate exert a strong coupling effect on MRD, while feed rate–rotational speed and grinding force–feed rate interactions significantly influence Ra, with “saddle-shaped” response surfaces. Grey relational analysis determined the optimal parameters: 75 N grinding force, 22.4 mm·s⁻¹ feed rate, and 3261 rpm rotational speed, achieving a maximum MRD of 1.975 mm and a minimum Ra of 3.506 μm. The tolerance range of the optimal parameters is F = 70–80 N, v_f = 20–24 mm·s⁻¹, and ω = 3000–3500 rpm. This research provides robust support for process parameter prediction and optimization in high-precision robotic abrasive belt grinding of 42CrMo steel. Full article

(This article belongs to the Special Issue Metals Machining—Analysis of Metal Cutting Processes)

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16 pages, 4111 KB

Open AccessArticle

Mechanism of Grain Structure Formation in Pure Copper Wire During Directional Heat Treatment

by Hao Xu, Xin Dong, Huihui Ruan, Gong Zheng and Guang Chen

Metals 2025, 15(11), 1264; https://doi.org/10.3390/met15111264 - 19 Nov 2025

Cited by 1 | Viewed by 3146

Abstract

Directional heat treatment reduces the number of transverse grain boundaries in pure copper wires at suitable temperatures, thereby promoting the formation of columnar or even single-crystal structures. This process significantly enhances the electrical conductivity of the wires and has become a research focus. [...] Read more.

Directional heat treatment reduces the number of transverse grain boundaries in pure copper wires at suitable temperatures, thereby promoting the formation of columnar or even single-crystal structures. This process significantly enhances the electrical conductivity of the wires and has become a research focus. Fundamentally, directional heat treatment is a secondary recrystallization process, involving key microstructural evolutions such as grain growth and grain boundary migration. Investigating its mechanism in pure copper wires is essential for optimizing their conductive performance. In this study, pure copper wires were subjected to directional heat treatment and systematically characterized using electron backscatter diffraction (EBSD). The effects of treatment on grain growth and boundary migration were analyzed, clarifying the evolution of grain boundary structures and crystallographic textures during columnar grain development. It was revealed that grains with a <112> orientation preferentially develop into columnar structures, with most inter-columnar grain boundaries being low-energy ∑ 3 and ∑ 9 types. The novelty of this work lies in revealing the mechanism of directional grain boundary migration in pure copper wires and elucidating the formation mechanism of island grains after directional heat treatment. Full article

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23 pages, 3088 KB

Open AccessArticle

Influence of Perforation on Elastic Modulus and Shear Modulus of Lightweight Thin-Walled Cylindrical Shells

by Inga Lasenko, Viktors Mironovs, Pavel Akishin, Marija Osipova, Anastasija Sirotkina and Andris Skromulis

Metals 2025, 15(11), 1263; https://doi.org/10.3390/met15111263 - 19 Nov 2025

Viewed by 812

Abstract

Perforated cylindrical shaped metal plates are used with high efficiency in the manufacture of deflectors, components of cooling systems, wind tunnels, climatic chambers, filters, and cylindrical implants. This is particularly important for lightweight cylindrical structures, where even minor changes in stiffness can affect [...] Read more.

Perforated cylindrical shaped metal plates are used with high efficiency in the manufacture of deflectors, components of cooling systems, wind tunnels, climatic chambers, filters, and cylindrical implants. This is particularly important for lightweight cylindrical structures, where even minor changes in stiffness can affect structural strength. One of the most important parameters determining the mechanical behavior of such structures is the effective elastic modulus of the perforated element which characterizes its resistance to deformation. The research involves plates made of stainless steel 304 alloy, where perforations were created using the laser-cutting method. The cylindrical shape of the samples with height 50 mm, thickness 1 mm, and diameter 48 mm of each specimen was obtained using metal rolling and welding techniques. To determine the effective elastic modulus, a non-destructive material property evaluation method was applied by solving an inverse problem. In this research, resonance frequencies were determined using a laser vibrometer and a full factorial experimental plan was developed. Physical samples were digitized into 3D models using 3D scanning technology. To evaluate the accuracy of the applied finite element numerical model, its convergence analysis was performed. Numerical results were approximated using the least-squares method, while the effective elastic modulus was calculated by formulating and minimizing the error functional between experimental and numerical eigenfrequencies. The results indicate that increasing the relative perforation area from 0% to 50.24% leads to a decrease in the effective elastic modulus from 184.76 GPa to 50.69 GPa, confirming that increasing the perforation area in a stainless steel 304 cylinder reduces its elastic properties. The observed reduction in resonance frequencies and elastic properties is primarily due to the stiffness decrease caused by the higher perforation volume. Full article

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14 pages, 2656 KB

Open AccessEditor’s ChoiceArticle

Evaluation of Filter Cake Washing Processes in Hydrometallurgical Battery Recycling of Lithium-Ion Batteries to Optimize Recoveries

by Dominic Dittmer, Maya Andary, Fabian Diaz and Bernd Friedrich

Metals 2025, 15(11), 1262; https://doi.org/10.3390/met15111262 - 19 Nov 2025

Cited by 1 | Viewed by 1290

Abstract

Due to climate change, electromobility and thus lithium-ion batteries are attracting increased interest. With a simultaneous increase in demand for raw materials like Li, Ni, Co, and Mn, their hydrometallurgical recycling is also gaining attention. The associated recoveries must be improved due to [...] Read more.

Due to climate change, electromobility and thus lithium-ion batteries are attracting increased interest. With a simultaneous increase in demand for raw materials like Li, Ni, Co, and Mn, their hydrometallurgical recycling is also gaining attention. The associated recoveries must be improved due to EU regulations. In a lab scale, metals are lost to the wrong filter cakes after leaching, cementation, and precipitations. Therefore, this work investigates the question of how many wash steps are suitable after each process step to optimize the recoveries and purity of filter cakes by comparing a reference process and a process with extended washing. The comparison showed that it is possible to recover up to 3.5% of Ni, Co, and Mn by extended washing at each step and in total nearly 100% of Li if wash water is recirculated. An investigation of the substeps of washing demonstrated that single wash steps are able to recover from 0.5% to 3.5% of Ni, Co, and Mn and from 1.6% to 8.7% of Li. The impact of extended washing on purity is shown by the analysis of filter cakes, where the purity of Fe and Al could be improved by 43.0% and for Ni, Co, and Mn by 48.0%. The paper closes with recommendations on how many wash steps are suitable after each process step. Full article

(This article belongs to the Special Issue New Science-Based Concepts for Enhancing Efficiency in Battery Recycling)

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18 pages, 5646 KB

Open AccessArticle

Microstructure, Compression Properties and Wear Performance of Compacted Al10SiMg Alloy Powders Processed Through Suction Casting

by Mila Christy de Oliveira, Marcella Gaute Cavalcante Xavier, Danusa Araújo de Moura and José Eduardo Spinelli

Metals 2025, 15(11), 1261; https://doi.org/10.3390/met15111261 - 18 Nov 2025

Viewed by 625

Abstract

Surplus out-of-spec Al powders, typically discarded, remain an underused resource. Their reuse via alternative consolidation routes is a sustainable path for AlSi10Mg alloy recycling, but studies on the feasibility of such routes remain scarce. This study proposes a novel route combining powder compaction [...] Read more.

Surplus out-of-spec Al powders, typically discarded, remain an underused resource. Their reuse via alternative consolidation routes is a sustainable path for AlSi10Mg alloy recycling, but studies on the feasibility of such routes remain scarce. This study proposes a novel route combining powder compaction (under 50 kN and 80 kN loads) and remelting/solidification via suction casting to assess the feasibility of producing dense parts with enhanced properties. Microstructure, mechanical properties (compression and Vickers microhardness), and tribological performance (ball-crater wear under dry and abrasive conditions) were evaluated. The proposed route produced dense AlSi10Mg parts with low porosity levels (≤0.2%) and refined dendritic microstructures (spacing between 2.4 and 4.6 µm). Increased cooling rates promoted microstructural refinement, while higher compaction loads improved densification. The refined microstructure samples achieved compressive strengths above 500 MPa. Remarkably, microstructural refinement led to significantly increased hardness, with values reaching ≥100 HV. The samples compacted at 50 kN and subjected to the highest cooling rate exhibited the lowest dry wear rate (2.3 × 10⁻⁴ mm³/N·m), comparable to additively manufactured AlSi10Mg (AM) samples, confirming the efficiency of this recycling route. The dry wear rates ranged from 2.3 to 3.9 × 10⁻⁴ mm³/N·m, reinforcing the inverse correlation between hardness and dry wear performance. Although abrasive wear resulted in a material loss approximately 3 times higher than dry wear, it preserved the same microstructural dependence: finer, harder, and denser samples exhibited better wear resistance. Full article

(This article belongs to the Section Metal Casting, Forming and Heat Treatment)

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12 pages, 7113 KB

Open AccessArticle

The Microstructural Observation in Precipitations of Peak-Aged Al–Zn–Mg Alloys with Various Zn/Mg Ratios

by Wanlalak Sanphiboon, Seungwon Lee, Taiki Tsuchiya, Abrar Ahmed, Susumu Ikeno, Tomoo Yoshida and Kenji Matsuda

Metals 2025, 15(11), 1260; https://doi.org/10.3390/met15111260 - 18 Nov 2025

Cited by 3 | Viewed by 878

Abstract

The precipitation behavior of peak-aged Al–Zn–Mg alloys with various Zn/Mg ratios was investigated to clarify the relationship between aging microstructure and mechanical response using (scanning) transmission electron microscopy (STEM/TEM). The results revealed that both aging temperature and Zn/Mg ratio significantly influence the type, [...] Read more.

The precipitation behavior of peak-aged Al–Zn–Mg alloys with various Zn/Mg ratios was investigated to clarify the relationship between aging microstructure and mechanical response using (scanning) transmission electron microscopy (STEM/TEM). The results revealed that both aging temperature and Zn/Mg ratio significantly influence the type, size, and density of precipitates, thereby determining the alloy hardness. At higher temperatures, coarser and lower-density precipitates led to reduced hardness, while finer and denser precipitates formed at lower temperatures enhanced hardening. For alloys with Zn/Mg < 1.0, the T′/T phases dominate strengthening, whereas η′/η phases are predominant for Zn/Mg > 2.0. Moreover, this study identifies a novel type of precipitate aligned along [110] Al in high-Mg alloys aged at 120 °C, which has not been reported previously and may contribute additional strengthening. These findings provide new insight into the compositional and thermal control of precipitation mechanisms in Al–Zn–Mg alloys. Full article

(This article belongs to the Section Metal Casting, Forming and Heat Treatment)

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13 pages, 5693 KB

Open AccessArticle

Effect of a Single-Sided Magnetic Field on Microstructure and Properties of Resistance Spot Weld Nuggets in H1000/DP590 Dissimilar Steels

by Qiaobo Feng, Jiale Li, Detian Xie and Yongbing Li

Metals 2025, 15(11), 1259; https://doi.org/10.3390/met15111259 - 18 Nov 2025

Cited by 1 | Viewed by 656

Abstract

H1000 stainless steel is defined as a nickel-saving austenitic stainless steel, characterized by high strength and high elongation. DP590 steel is widely used in the manufacturing of vehicle bodies. DP590 dual-phase steel is classified as a high-strength low-alloy steel, known for its high [...] Read more.

H1000 stainless steel is defined as a nickel-saving austenitic stainless steel, characterized by high strength and high elongation. DP590 steel is widely used in the manufacturing of vehicle bodies. DP590 dual-phase steel is classified as a high-strength low-alloy steel, known for its high strength and good formability. To address issues such as nugget deviation, inhomogeneous mixing of the internal nugget microstructure, and interfacial fracture during tensile-shear testing in resistance spot-welded joints of these dissimilar materials, a unilateral magnetic-assisted resistance spot-welding process was proposed. The influence of the external magnetic field on various properties of the joint was systematically investigated. The results indicate that the application of an external magnetic field significantly enhances the strength of H1000/DP590 dissimilar spot-welded joints, with joint strength increasing by approximately 14% and energy absorption capacity improving by about 30%. These improvements are attributed to the electromagnetic stirring effect induced by the magnetic field, through which the effective nugget diameter was enlarged, the microstructure was homogenized, and the macroscopic morphology of the nugget was modified. As a result, the bonding area between the nugget and the base metal is expanded, and the fracture mode of the joint is shifted from interfacial failure to partial button failure, thereby enhancing the mechanical properties of the joint. Full article

(This article belongs to the Special Issue Welding and Joining Technology of Dissimilar Metal Materials)

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33 pages, 11997 KB

Open AccessArticle

The Effects of Knife Milling and Ball Milling on Hydrogen Decrepitated Sm₂TM₁₇ Sintered Magnet Powder for Short-Loop Recycling

by James Thomas Griffiths, Oliver Peter Brooks, Viktoria Kozak, Alexis Lambourne, Alexander Campbell and Richard Stuart Sheridan

Metals 2025, 15(11), 1258; https://doi.org/10.3390/met15111258 - 18 Nov 2025

Cited by 3 | Viewed by 1099

Abstract

Sm₂TM₁₇ sintered magnets (TM = Co, Fe, Cu, Zr) are utilised in high-temperature rotor applications due to their stable magnetic properties at elevated temperatures of 200–350 °C. However, Sm and Co are critical elements, and the reliance on virgin material [...] Read more.

Sm₂TM₁₇ sintered magnets (TM = Co, Fe, Cu, Zr) are utilised in high-temperature rotor applications due to their stable magnetic properties at elevated temperatures of 200–350 °C. However, Sm and Co are critical elements, and the reliance on virgin material supply chains must be reduced. Hydrogen decrepitation (HD) could facilitate magnet-to-magnet recycling of scrap material, but the milling characteristics of the powders generated by HD requires investigation. Sm₂TM₁₇ sintered magnets were exposed to 18 bar and 2 bar hydrogen pressure at 100 °C for 72 h and then knife-milled, roller ball-milled, and planetary ball-milled for varying milling times utilising a variety of surfactants. The particle size and morphology of the powders were investigated, and sintered magnets manufactured from chosen powders were characterised in terms of composition, density, microstructure, and magnetic properties. Knife milling for two minutes showed major particle size reductions of 70 and 82% in D50 for 18 bar and 2 bar samples respectively. Roller ball milling trials showed that a cyclohexane and oleic acid mixture was the most effective at reducing particle size, reducing D10, 50, and 90 by 92, 91, and 80% respectively. Knife milling HD powder for two minutes and then planetary ball milling this powder in a cyclohexane and 1 wt.% oleic acid mixture generated a particle size distribution of 1.3–6.8 µm. This powder formed a sintered compact with a density 0.08 g/cm³ lower than the as-received material. Sm losses due to oxidation and sublimation in addition to carbon impurities from surfactant usage caused the precipitation of an α-Fe/Co phase and formed ZrC phases respectively. Sm-hydride additions of 2–3 wt.% mitigated the formation of the α-Fe/Co phase, but ZrC phases remained and likely prevented cell structure formation and inhibited domain wall pinning in recycled magnets. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metallic Materials by Powder Metallurgy)

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1 pages, 121 KB

Open AccessCorrection

Correction: Qiao et al. Effect of Solution Treatment on Mechanical Properties and Wear Resistance of Alloyed High-Manganese Steel. Metals 2025, 15, 937

by Xiya Qiao, Boyong Li, Xiao Han, Xiangyun Zhang and Xin Yang

Metals 2025, 15(11), 1257; https://doi.org/10.3390/met15111257 - 18 Nov 2025

Viewed by 372

Abstract

In the published article [...] Full article

17 pages, 4599 KB

Open AccessArticle

Reproducible Thermo-Fluid–Solid-Coupled Modeling of Wet Milling of Al6061: Parametric Influence and Surface Integrity Assessment

by Yanping Xiao, Xuanzhong Wu, Xin Tong, Enqing Chen and Cheng Zhang

Metals 2025, 15(11), 1256; https://doi.org/10.3390/met15111256 - 17 Nov 2025

Viewed by 610

Abstract

Wet milling of aluminum alloys involves complex interactions among thermal, fluid, and mechanical fields that strongly affect cutting temperature, stress distribution, and surface integrity. To achieve reproducible and physics-based predictions of these coupled phenomena, this study develops a three-dimensional thermo–fluid–solid-coupled Eulerian–Lagrangian (CEL) framework [...] Read more.

Wet milling of aluminum alloys involves complex interactions among thermal, fluid, and mechanical fields that strongly affect cutting temperature, stress distribution, and surface integrity. To achieve reproducible and physics-based predictions of these coupled phenomena, this study develops a three-dimensional thermo–fluid–solid-coupled Eulerian–Lagrangian (CEL) framework for the wet milling of Al6061. The model system in this study evaluated the effects of milling cutter feed rate and spindle speed, feed per tooth of the milling cutter, axial cutting depth, and coolant flow rate on equivalent stress and peak milling temperature., as well as their correlation with surface roughness metrics (Ra, Sa). Simulation results reveal that higher feed rates significantly raise T_peak (+12.9%) while reducing σ_eq (−22.7%) and deteriorating surface quality (Ra +104.2%, Sa +29.9%). Increasing spindle speed lowers both T_peak (−2.2%) and σ_eq (−8.5%) and improves surface finish (Ra −39.3%, Sa −16.6%). A greater depth of cut amplifies mechanical and thermal loads, increasing T_peak (+10.3%) and σ_eq (+17%). Enhanced coolant flow reduces T_peak (−23.5%) and σ_eq (−6.1%) and markedly improves surface quality (Ra −88.8%, Sa −51.3%). Research findings indicate that coolant coverage is the dominant factor determining surface integrity. Although experimental data for T_peak and σeq were not directly validated, this framework clearly articulates modeling assumptions, quantifies parameter sensitivities, and provides a reproducible methodology for future experimental-numerical verification. Full article

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25 pages, 15526 KB

Open AccessArticle

Quasi-Static Compression and Tensile Behavior of Additively Manufactured Al-Mg-Sc-Zr Alloy Lattices: The Role of Cell Topology

by Jingwen Li, Zhiwei Luo, Yanwu Guo, Zhenyu Yan and Yangwei Wang

Metals 2025, 15(11), 1255; https://doi.org/10.3390/met15111255 - 17 Nov 2025

Viewed by 968

Abstract

To achieve lightweight objectives in the aerospace sector, this paper systematically investigates the influence of unit cell topology on the quasi-static mechanical properties of Al-Mg-Sc-Zr alloy lattice structures fabricated by Selective Laser Melting (SLM). A comparative analysis of the mechanical response and failure [...] Read more.

To achieve lightweight objectives in the aerospace sector, this paper systematically investigates the influence of unit cell topology on the quasi-static mechanical properties of Al-Mg-Sc-Zr alloy lattice structures fabricated by Selective Laser Melting (SLM). A comparative analysis of the mechanical response and failure mechanisms of eight distinct unit cell topologies was conducted through a combination of quasi-static compression and tensile experiments, finite element (FE) simulation, and fractography via Scanning Electron Microscopy (SEM). The results demonstrate that the mechanical performance is highly dependent on the unit cell topology. Under compression, the structures exhibited a layer-by-layer collapse, whereas under tension, they failed through sequential fracture of multiple struts initiated by stress concentration. Finite element simulations effectively predicted the general trends of the mechanical behavior; however, the actual strength and ductility of the SLM-fabricated specimens were lower than the simulated values due to intrinsic process-induced defects such as pores and lack of fusion. Analysis using the Maxwell index revealed that stretching-dominated structures possess superior specific modulus and specific strength compared to bending-dominated ones. Furthermore, among structures with similar Maxwell indices, those incorporating vertical struts demonstrated higher load-bearing efficiency. This study provides significant experimental and theoretical foundations for the design and application of high-performance lattice materials in lightweight structures. Full article

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17 pages, 3419 KB

Open AccessArticle

Effect of (NH₄)₂SO₄ Solution Concentration on Bound Water Content in Ion Adsorption Rare-Earth Raw Ore

by Yuehua Liang, Jie Wang, Zhikui Fei, Chenliang Peng, Hourui An and Zhanfeng Fan

Metals 2025, 15(11), 1254; https://doi.org/10.3390/met15111254 - 17 Nov 2025

Cited by 4 | Viewed by 679

Abstract

Ion adsorption rare-earth (IARE) ores, a strategic metal resource, are extracted by leaching with ammonium sulfate [(NH4)₂SO₄] solution, our samples have ∑REO grades of 0.032–0.079% wt%. IARE sandstone, mudstone, clay, and strongly weathered rock were selected as test materials. [...] Read more.

Ion adsorption rare-earth (IARE) ores, a strategic metal resource, are extracted by leaching with ammonium sulfate [(NH4)₂SO₄] solution, our samples have ∑REO grades of 0.032–0.079% wt%. IARE sandstone, mudstone, clay, and strongly weathered rock were selected as test materials. Surface-related physicochemical parameters were determined, and bound water was determined by volumetric flask pycnometry. For each IARE lithology, we also obtained particle size distributions and evaluated bound water variation in (NH₄)₂SO₄ solutions at 0, 1, 2, and 3 wt%. Based on the Gouy–Chapman theory, the relationship between the surface bound water and solution concentration, as well as the surface charge of IARE samples, and other influencing factors was explored. The experimental results show the following: ① The surface charge per unit area of four types of IARE samples, namely mudstone, sandstone, clay, and strongly weathered rock, are 0.7072 × 10⁻² mmol/m², 1.9620 × 10⁻² mmol/m², 1.5418 × 10⁻² mmol/m², and 2.1003 × 10⁻² mmol/m², respectively, with strongly weathered rock having the highest and mudstone having the lowest. ② As the concentration of aqueous (NH₄)₂SO₄ increases (0, 1, 2, 3 wt%), the total volume reduction in free water ∆V in the system increases, and the mass of adsorbed bound water per unit mass of IARE sample also increases. ③ As the concentration of the solution increases, the thickness of the diffusion double layer on the surface of the IARE sample is compressed, the total amount of adsorbed anions and cations on the surface increases, and the density of the surface water film also increases, leading to a corresponding increase in the quality of adsorbed bound water. ④ Under the same solution concentration, the variation trend of adsorbed bound water mass per unit area of IARE samples is strongly weathered rock > sandstone > clay > mudstone, which is consistent with the trend of surface charge per unit area of IARE samples. A higher lixiviant concentration increases bound water, shrinks the effective pore throats of the ore body, reduces hydraulic conductivity, and consequently diminishes leaching efficiency. Full article

(This article belongs to the Special Issue Advances in Recycling of Valuable Metals—2nd Edition)

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20 pages, 3814 KB

Open AccessArticle

The Time–Frequency Analysis and Prediction of Mold Level Fluctuations in the Continuous Casting Process

by Mohan Cai, Meixia Fu, Wei Li, Qu Wang, Na Chen, Zhangchao Ma, Lei Sun, Ronghui Zhang, Hongbin Wang and Jianquan Wang

Metals 2025, 15(11), 1253; https://doi.org/10.3390/met15111253 - 17 Nov 2025

Cited by 1 | Viewed by 1053

Abstract

Mold level fluctuation significantly affects the stability and quality of the slab during the continuous casting process. However, traditional mechanism models are insufficient for providing accurate time-series predictions under complex and multivariable operating conditions. Additionally, the dynamic interdependencies between process variables and transient [...] Read more.

Mold level fluctuation significantly affects the stability and quality of the slab during the continuous casting process. However, traditional mechanism models are insufficient for providing accurate time-series predictions under complex and multivariable operating conditions. Additionally, the dynamic interdependencies between process variables and transient abnormal fluctuation events have been largely overlooked in existing studies. To address these limitations, we propose an integrated time–frequency characterization and prediction framework that combines multi-domain feature extraction with a long-sequence Informer model. First, the preprocessing pipeline transforms heterogeneous sensor data into standardized time series through normalization and standardization, thereby establishing a robust foundation for subsequent feature extraction and predictive modeling. Second, the time–domain and frequency–domain feature extraction methods are integrated to capture essential patterns in casting signals with improved resolution and interpretability. Third, the fusion features are embedded into a time-series prediction model, which performs robust forecasting of mold level behavior and enhances the identification of root causes behind fluctuation anomalies. Compared with conventional LSTM and Transformer models, the proposed framework achieves over 90% reduction in prediction error and provides interpretable insights into the correlations between casting parameters and mold level variations. Finally, real industrial experimental results demonstrate the performance of the proposed framework in enhancing prediction reliability and providing insight into fluctuations with scalable implementation. Full article

(This article belongs to the Section Metal Casting, Forming and Heat Treatment)

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17 pages, 9226 KB

Open AccessArticle

Determination of Density and Surface Tension of CaO–Al₂O₃ Molten Slag Using Pendant Drop Method

by Jian Chen and Yunming Gao

Metals 2025, 15(11), 1252; https://doi.org/10.3390/met15111252 - 16 Nov 2025

Viewed by 960

Abstract

The pendant drop method is often used to determine the surface tension of liquids. However, in the process of calculating surface tension, corresponding density data are required, which brings a series of problems to the determination of the surface tension of high-temperature slag, [...] Read more.

The pendant drop method is often used to determine the surface tension of liquids. However, in the process of calculating surface tension, corresponding density data are required, which brings a series of problems to the determination of the surface tension of high-temperature slag, especially. So far, there have been few reports on determining the two properties of density and surface tension by the pendant drop method in a single experiment. In this work, CaO–50% Al₂O₃ slag was taken as the research object, a novel ring-shaped-pendant drop-forming device constructed with Pt–10% Ir alloy was employed, and the outer diameter of the alloy ring at experimental temperatures was determined as a reference scale by pixel analyses of images. The density and surface tension of the slag within the range of 1450 to 1650 °C were simultaneously determined under heating and cooling modes, respectively, and the effect of slag mass on measurement results was also investigated. The results show that the measurement mode (heating or cooling) has little effect under experimental conditions, whereas the slag mass has a certain effect when it is small. The average density and surface tension values obtained both decrease with increasing temperature, and the temperature coefficients are −3.406 × 10⁻⁴ g/(cm³⋅°C) and −4.2 × 10⁻² mN/(m⋅°C), respectively. The density and surface tension of the slag at 1550 °C are 2.836 g/cm³ and 624 mN/m, respectively. In addition, the combined standard uncertainties of the measured density and surface tension are 0.01 g/cm³ and 4 mN/m, respectively. The density and surface tension values are basically consistent with literature data. This work can provide an experimental basis for the development of a pendant drop method used to determine the density and surface tension properties of molten slag. Full article

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21 pages, 2911 KB

Open AccessReview

Elastic Origins of Hardness in Quenchable High-Pressure Metal Nitrides: A Unified Structure-Elasticity Baseline

by Shoufeng Zhang, Yuhao Liu, Zhaoqing Wang, Jinming Zhu, Jiaman Wu and Kuo Bao

Metals 2025, 15(11), 1251; https://doi.org/10.3390/met15111251 - 16 Nov 2025

Viewed by 748

Abstract

We review bulk transition-metal nitrides synthesized at high pressure–high temperature and recoverable at ambient conditions. We establish an elasticity-anchored framework that links crystal structure and bonding to elastic descriptors and hardness at the phase-resolved level, enabling fair cross-study comparison. Overall, hardness shows a [...] Read more.

We review bulk transition-metal nitrides synthesized at high pressure–high temperature and recoverable at ambient conditions. We establish an elasticity-anchored framework that links crystal structure and bonding to elastic descriptors and hardness at the phase-resolved level, enabling fair cross-study comparison. Overall, hardness shows a robust association with the shear modulus G, while the Pugh ratio k = G/B modulates relative rankings across phases. When metallic bonding or non-stoichiometry/defects are pronounced, systematic deviations arise; accordingly, elasticity-based models are best used for cross-phase trends and qualitative guidance rather than absolute predictions, especially for metallic or defect-rich phases. Building on this baseline, we outline application pathways and future research directions, and we propose a minimal reporting checklist to improve reproducibility and cross-study comparability. Full article

(This article belongs to the Special Issue Recent Insights into Mechanical Properties of Metallic Alloys)

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23 pages, 6053 KB

Open AccessArticle

Investigation of the Possibility of Obtaining Metallized Titanomagnetite Briquettes Suitable for Utilization in the Steelmaking Process

by Andrey N. Dmitriev, Galina Yu. Vitkina, Elena A. Vyaznikova, Roman V. Alektorov, Vladimir V. Kataev, Larisa A. Marshuk and Yulia E. Burova

Metals 2025, 15(11), 1250; https://doi.org/10.3390/met15111250 - 16 Nov 2025

Cited by 1 | Viewed by 731

Abstract

The present study explores the production of metallized titanomagnetite briquettes, with a view to addressing two key issues. Firstly, it seeks to address the growing shortage of high-quality iron-bearing raw materials. Secondly, it looks at how to meet the increasingly stringent environmental constraints. [...] Read more.

The present study explores the production of metallized titanomagnetite briquettes, with a view to addressing two key issues. Firstly, it seeks to address the growing shortage of high-quality iron-bearing raw materials. Secondly, it looks at how to meet the increasingly stringent environmental constraints. The conventional blast-furnace treatment of titanomagnetite is hindered by the formation of refractory Ti-rich slags. It is hereby proposed that a single-cycle briquetting process in conjunction with a thermal reduction route should be utilized. This approach enables precise regulation of the Fe/flux ratio. Experiments were conducted on a low-grade titanomagnetite concentrate (68.5% Fe) from the Pervouralsk deposit (Russia). Cylindrical briquettes (D 15–20 mm, h 8–10 mm) were subjected to a pressure of 300 MPa during the pressing process, with the utilization of diverse binders comprising rubber cement, CaO, graphite + water, and basic oxygen-furnace (BOF) slag + sodium silicate. Following an oxidative pre-heating process at 1300 °C for two hours, followed by a gas-based reduction process at 1050 °C for three hours, with a CO/N₂ ratio of 90/10, the products demonstrated an oxidation rate of 85–95% and a cold compression strength of 16–80 MPa. The highest observed strength (80 MPa) was obtained with a binder comprising CaO·MgO·2SiO₂ (diopside/merwinite), which forms a low-viscosity melt, fills 90% of pores and crystallizes as acicular Mg-SFCA-I during cooling. Conversely, the CaO·TiO₂ and FeO·TiO₂ + Fe₃C associations yield brittle structures and a maximum strength of 16 MPa. The optimum briquette (0.55% CaO, D/H = 20/10 mm) exhibited a 95.7% metallization degree, a compressive strength of 48.9 MPa, and dimensional changes within acceptable limits, thus fulfilling the requirements for electric arc furnace feedstock. Further research is required in the form of a full Life Cycle Assessment and pilot-scale testing. However, the results obtained thus far confirm that titanomagnetite briquettes with a binder consisting of CaO, MgO and SiO₂ are a promising alternative to pellets for low-carbon steelmaking. Full article

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16 pages, 5351 KB

Open AccessArticle

Effect of Aluminum Content on the Corrosion Behavior of Fe-Mn-Al-C Structural Steels in Marine Environments

by Suotao Wang, Zhidong Sun, Dongjie Li, Qiang Yu and Qingfeng Wang

Metals 2025, 15(11), 1249; https://doi.org/10.3390/met15111249 - 15 Nov 2025

Cited by 2 | Viewed by 868

Abstract

Fe-Mn-Al-C lightweight steel is an alternative to traditional low-alloy structural steels. It is lightweight and can be used to reduce the weight of structures without increasing their density. However, in the marine environment, traditional low-alloy structural steels can be damaged by chloride ions, [...] Read more.

Fe-Mn-Al-C lightweight steel is an alternative to traditional low-alloy structural steels. It is lightweight and can be used to reduce the weight of structures without increasing their density. However, in the marine environment, traditional low-alloy structural steels can be damaged by chloride ions, which shortens their service life. We do not yet understand how aluminum, an important alloying element in lightweight steel, affects the process of corrosion. In this study, we examined Fe-Mn-Al-C lightweight steels with different amounts of aluminum. We used full-immersion simulated marine corrosion tests and multi-dimensional characterization techniques, such as microstructure observation and electrochemical measurements, to explore the relationship between aluminum content and the steel’s corrosion rate, corrosion product structure, and corrosion resistance. The results showed that, compared with CS, the weight loss and rate of corrosion of steels that contain aluminum were a lot lower. While the corrosion rate of CS is approximately 0.068 g·h⁻¹·m⁻², that of 7Al steel is reduced to 0.050 g·h⁻¹·m⁻². The stable phases α-FeOOH and FeAl₂O₄ are formed in the corrosion products when Al is added. As the Al content increases, so does the relative content of these phases. Furthermore, FeAl₂O₄ acts as a nucleation site that refines corrosion product grains, reduces pores and cracks, and significantly improves the compactness of corrosion products. It also forms a dense inner rust layer that blocks the penetration of corrosive ions such as Cl⁻. This study confirmed that aluminum improves the corrosion resistance of steel synergistically by regulating the structure of the corrosion products, optimizing the phase composition, and improving the electrochemical properties. The optimal aluminum content for lightweight steel in marine environments is 7%, within a range of 5–9%. Full article

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17 pages, 5230 KB

Open AccessArticle

Scalable Advanced Dual-Engineered Superhydrophobic Aluminum Surfaces for Industrial-Grade Corrosion Protection

by N. Rahul, Ho-Eon Sung, Sang Won Lee and Min-Suk Oh

Metals 2025, 15(11), 1248; https://doi.org/10.3390/met15111248 - 15 Nov 2025

Cited by 2 | Viewed by 782

Abstract

Superhydrophobic coatings on aluminum play a crucial role in enhancing corrosion resistance in harsh marine and chloride-rich environments. This study introduces a scalable fabrication method for superhydrophobic aluminum surfaces exhibiting outstanding corrosion resistance. The process involves a two-step technique combining chemical etching with [...] Read more.

Superhydrophobic coatings on aluminum play a crucial role in enhancing corrosion resistance in harsh marine and chloride-rich environments. This study introduces a scalable fabrication method for superhydrophobic aluminum surfaces exhibiting outstanding corrosion resistance. The process involves a two-step technique combining chemical etching with atmospheric pressure chemical vapor deposition (AP-CVD) of perfluorooctyltriethoxysilane (PFOTES). Hierarchical micro- and nanostructures were created by HCl etching, followed by conformal PFOTES functionalization to impart low surface energy. The fabricated surfaces demonstrated water contact angles reaching as high as 175°, coupled with very-low-contact-angle hysteresis, indicative of the Cassie–Baxter wetting state. Electrochemical analyses in saline environments demonstrated a substantial increase in charge transfer resistance and a reduction in corrosion rates by more than an order of magnitude compared to uncoated aluminum, with inhibition efficiencies exceeding 98%. Extended salt spray testing corroborated the durability and efficacy of the dual-modified surfaces. This facile and cost-effective method offers promising prospects for multifunctional aluminum components in marine, infrastructure, and aerospace applications where long-term protection against aggressive environments is required. Full article

(This article belongs to the Section Corrosion and Protection)

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18 pages, 6604 KB

Open AccessArticle

Effect of H₃PO₄ Coating, Polyimide Binder, and MoS₂/Graphite Lubricants on the Formability and Electromagnetic Properties of Fe-5.0 wt.%Si SMC Toroidal Cores

by Seongsu Kang and Seonbong Lee

Metals 2025, 15(11), 1247; https://doi.org/10.3390/met15111247 - 14 Nov 2025

Viewed by 798

Abstract

This study examined the effects of phosphoric acid (H₃PO₄), polyimide (PI), and lubricants (MoS₂, graphite) on the phase stability, microstructure, and magnetic performance of Fe-5.0 wt.%Si soft magnetic composites (SMCs). Warm compaction (≤550 °C) and annealing at [...] Read more.

This study examined the effects of phosphoric acid (H₃PO₄), polyimide (PI), and lubricants (MoS₂, graphite) on the phase stability, microstructure, and magnetic performance of Fe-5.0 wt.%Si soft magnetic composites (SMCs). Warm compaction (≤550 °C) and annealing at 700 °C were applied to samples prepared under a full factorial design. X-ray diffraction confirmed stable α-Fe(Si) phases without secondary phases. SEM and TEM–EDS revealed interfacial insulating layers mainly composed of Si-O, with localized phosphorus and carbon. Additive composition strongly influenced magnetic and physical properties. Increasing H₃PO₄ and PI reduced the density from 7.50 to 7.27 g/cm³ and lowered the permeability (from 189 at 1 kHz to 156), due to thicker interparticle layers that restricted metallic contact and domain wall motion. In contrast, Q-values rose significantly with frequency: for H₃PO₄ 0.25 wt.% + PI 0.25 wt.% + graphite 0.3 wt.%, Q increased from 0.39 (1 kHz) to 2.91 (10 kHz), reflecting effective eddy current suppression. Lubricant type further influenced performance: graphite consistently outperformed MoS₂, with 0.3 wt.% graphite providing the best balance of high density, permeability, and a frequency-stable Q-value. Overall, Fe-5.0 wt.%Si performance is governed not by bulk phase changes but by the trade-off between densification and insulation at particle interfaces. The optimal combination of low H₃PO₄ and PI with 0.3 wt.% graphite offers practical guidelines for designing high-frequency, high-efficiency motor materials. Full article

(This article belongs to the Special Issue Metallic Magnetic Materials: Manufacture, Properties and Applications)

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