Metals

21 pages, 2148 KiB

Open AccessArticle

On the Optimization of T6 Heat Treatment Parameters of a Secondary Al-Si-Cu-Mg Foundry Aluminum Alloy: A Microstructural and Mechanical Characterization

by Mattia Merlin, Lorenzo Antonioli, Federico Bin, Cindy Morales and Chiara Soffritti

Metals 2025, 15(7), 742; https://doi.org/10.3390/met15070742 (registering DOI) - 30 Jun 2025

Abstract

Foundry aluminum-silicon (Al-Si) alloys, especially those containing Cu and/or Mg, are widely used in casting processes for fabricating lightweight parts. This study focuses on the optimization of the solution heat treatment parameters within the T6 heat treatment of an innovative AlSi7Cu0.5Mg0.3 secondary alloy, [...] Read more.

Foundry aluminum-silicon (Al-Si) alloys, especially those containing Cu and/or Mg, are widely used in casting processes for fabricating lightweight parts. This study focuses on the optimization of the solution heat treatment parameters within the T6 heat treatment of an innovative AlSi7Cu0.5Mg0.3 secondary alloy, aiming at achieving energy savings and reducing the environmental impact related to the production of foundry components for the automotive industry. Different combinations of solution times and temperatures lower than those typically adopted in industrial practice were evaluated, and their effects on tensile properties were investigated on samples machined from as-cast and T6-treated castings produced by pouring the alloy into a steel permanent mold. Thermal analysis (TA) and differential thermal analysis (DTA) were performed to monitor the solidification sequence of microstructural phases as well as their dissolution on heating according to the proposed solution heat treatments. Microstructural analysis by light microscopy (LM) and scanning electron microscopy (SEM), together with Brinell hardness testing, was also carried out to assess the effects of heat treatment parameters. The results suggested that a shorter solution heat treatment set at a temperature lower than that currently adopted for the heat treatment of the studied alloy can still ensure the required mechanical properties while improving productivity and reducing energy consumption. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metallic Materials Under Heat Treatment)

18 pages, 4753 KiB

Open AccessArticle

Characterization of Different Types of Screen-Printed Carbon Electrodes Modified Electrochemically by Ceria Coatings

by Reni Andreeva, Aleksandar Tsanev, Georgi Avdeev and Dimitar Stoychev

Metals 2025, 15(7), 741; https://doi.org/10.3390/met15070741 (registering DOI) - 30 Jun 2025

Abstract

Electrochemical formation of ceria (mixed Ce₂O₃ and CeO₂) coatings on different types of screen-printed carbon electrodes (SPCEs) (based on graphite (C110), carbon nanotubes (CNT), single-walled carbon nanotubes (SWCNT), carbon nanofibers (CNF), and mesoporous carbon (MC)) were studied. Their [...] Read more.

Electrochemical formation of ceria (mixed Ce₂O₃ and CeO₂) coatings on different types of screen-printed carbon electrodes (SPCEs) (based on graphite (C110), carbon nanotubes (CNT), single-walled carbon nanotubes (SWCNT), carbon nanofibers (CNF), and mesoporous carbon (MC)) were studied. Their potential applications as catalysts for various redox reactions and electrochemical sensors were investigated. The ceria oxide layers were electrodeposited on SPCEs at various current densities and deposition time. The morphology, structure, and chemical composition in the bulk of the ceria layers were studied by SEM and EDS methods. XRD was used to identify the formed phases. The concentration, chemical composition and chemical state of the elements on the surface of studied samples were characterized by XPS. It was established that the increase of the concentration of CeCl₃ in the solution and the cathode current density strongly affected the surface structure and concentration (relation between Ce³⁺ and Ce⁴⁺, respectively) in the formed ceria layers. At low concentration of CeCl₃ (0.1M) and low values of cathode current density (0.5 mA·cm⁻²), porous samples were obtained, while with their increase, the ceria coatings grew denser. Full article

17 pages, 9323 KiB

Open AccessArticle

Analysis and Chromium Recovery from Ferrochrome Waste (Stockpiled Refined Ferrochrome Slags)

by Otegen Sariyev, Lyazat Tolymbekova, Murat Dossekenov, Bauyrzhan Kelamanov, Dauren Yessengaliyev, Assel Davletova and Assylbek Abdirashit

Metals 2025, 15(7), 740; https://doi.org/10.3390/met15070740 (registering DOI) - 30 Jun 2025

Abstract

This study investigates the effectiveness of various beneficiation methods for recovering chromium from refined ferrochrome slag. Dry magnetic separation at different field intensities (0.45 T and 0.8 T) showed that selective extraction of metallic chromium (Cr_met) is more efficient at 0.45 [...] Read more.

This study investigates the effectiveness of various beneficiation methods for recovering chromium from refined ferrochrome slag. Dry magnetic separation at different field intensities (0.45 T and 0.8 T) showed that selective extraction of metallic chromium (Cr_met) is more efficient at 0.45 T, achieving a recovery rate of up to 90.05%. Pneumatic separation using SEPAIR technology demonstrated promising results, especially for wide particle size fractions (0–20 mm), where chromium recovery reached 40.32% due to density differences between slag particles and metallic inclusions. Enrichment on a shaking table proved to be the most selective method, producing a concentrate with 29.9% Cr and 90.7% recovery, although the yield was low (3.8%). SEM-EDX and SEM-BSE analyses confirmed the heterogeneous phase composition of slag grains, revealing chromium–iron alloys embedded in oxide matrices. Based on laboratory experiments and material characterization, it is concluded that magnetic separation can be used for preliminary concentration, pneumatic classification is effective for processing bulk slag with economic potential, and gravity concentration on shaking tables is suitable for producing high-grade concentrates. The resulting tailings, low in chromium, are suitable for reuse in the production of building materials after carbonation treatment. Full article

15 pages, 1645 KiB

Open AccessArticle

Effect of Oxidative Roasting on Selective Leaching of Lithium from Industrially Shredded Lithium Iron Phosphate Blackmass

by Ayesha Tasawar, Daniel Dotto Munchen, Alexander Birich, Rungsima Yeetsorn and Bernd Friedrich

Metals 2025, 15(7), 739; https://doi.org/10.3390/met15070739 (registering DOI) - 30 Jun 2025

Abstract

The increasing need-based demand for lithium iron phosphate (LFP) batteries in electric vehicles and energy storage systems necessitates the development of efficient and sustainable recycling methods. This study investigates the effect of oxidative roasting on lithium extraction from industrially sourced LiFePO₄ (LFP) [...] Read more.

The increasing need-based demand for lithium iron phosphate (LFP) batteries in electric vehicles and energy storage systems necessitates the development of efficient and sustainable recycling methods. This study investigates the effect of oxidative roasting on lithium extraction from industrially sourced LiFePO₄ (LFP) blackmass containing high graphite content (~46%) and mixed electrode materials. Roasting at 650 °C for one hour converted LiFePO₄ into water-soluble Li₃Fe₂(PO₄)₃ and Fe₂O₃, while reducing carbon and fluorine levels. However, contrary to expectations, mild-acid leaching (pH 2, 40 g/L, 20 °C) of roasted blackmass did not improve lithium recovery compared to unroasted material, yielding approximately 33% extraction efficiency. Strong-acid leaching (pH 0, H₂SO₄/H₂O₂) achieved over 95% lithium recovery but also resulted in significant co-dissolution of iron and other impurities. Our XRD and SEM analyses showed that some lithium-containing phases remained in the residue after water leaching, while acid leaching left mainly iron oxide and graphite. These results suggest that, for complex and graphite-rich industrial blackmass, roasting may not always deliver the expected boost in lithium recovery. Our findings highlight the need to tailor recycling processes to the specific characteristics of battery waste and suggest that direct hydrometallurgical methods could be more effective for complex, impurity-rich LFP blackmass streams. Full article

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

21 pages, 26006 KiB

Open AccessArticle

Molecular Dynamics Simulation of the Effect of B2-NiAl Phase Volume Fractions on Mechanical Properties and Deformation Mechanisms of Dual-Phase FeNiAl Alloys

by Wang Xiang, Yachen Gui, Xingchang Tang, Xuefeng Lu, Jie Sheng, Zhijian Zhang and Junqiang Ren

Metals 2025, 15(7), 738; https://doi.org/10.3390/met15070738 (registering DOI) - 30 Jun 2025

Abstract

In this study, the effects of B2-NiAl phase volume fractions (2–50%) on the mechanical properties and deformation mechanism of dual-phase FeNiAl alloys were systematically investigated by molecular dynamics simulation. A two-phase alloy atomic model with different B2 phase volume fractions was constructed. The [...] Read more.

In this study, the effects of B2-NiAl phase volume fractions (2–50%) on the mechanical properties and deformation mechanism of dual-phase FeNiAl alloys were systematically investigated by molecular dynamics simulation. A two-phase alloy atomic model with different B2 phase volume fractions was constructed. The simulation results show that when the volume fraction of the B2 phase is 3%, the alloy exhibits the best comprehensive mechanical properties. The strengthening is mainly due to the back stress field effect induced by the B2 phase. However, when the content of the B2 phase exceeds 5%, it will cause grain boundary stress concentration, resulting in a sharp decrease in the ductility of the alloy. Atomic-scale simulation analysis further reveals that low B2 content (3%) maintains grain boundary stability by inhibiting grain rotation, regulating superdislocation pairs and inverse boundary slip modes. This study provides a theoretical basis for the design of dual-phase alloys, reveals the cooperation mechanism of B2 and FCC, and has guiding significance for the development of high-strength and toughness Fe-based alloys. Full article

18 pages, 2510 KiB

Open AccessArticle

Life Prediction of Crack Growth for P92 Steel Under Strain-Controlled Creep–Fatigue Conditions Using a Sharp Notched Round Bar Specimen

by A. Toshimitsu Yokobori,Jr, Go Ozeki, Kazutaka Jinnno, Hiroaki Seino, Ryuji Sugiura and Isamu Nonaka

Metals 2025, 15(7), 737; https://doi.org/10.3390/met15070737 (registering DOI) - 30 Jun 2025

Abstract

Testing and the estimation methods for predicting the life of crack initiation and crack growth for P92 steel using a circular sharp notched round bar specimen (CNS) under strain-controlled creep and fatigue conditions have been reported previously. A unique estimation method for the [...] Read more.

Testing and the estimation methods for predicting the life of crack initiation and crack growth for P92 steel using a circular sharp notched round bar specimen (CNS) under strain-controlled creep and fatigue conditions have been reported previously. A unique estimation method for the cycle-sequential characteristics of tensile and compressive peak stresses is proposed; specifically, the nominal stress range

{∆ σ}_{n e t} = {{(σ}_{m a x} - σ_{m i n})}_{n e t}

and the measurement of crack length using the direct current electric potential drop (DCPD) method were adopted. This method was effective in specifying the failure life and crack initiation life by verifying the crack growth length. However, to show the universality of these results, it is important to compare the experimental results obtained under strain-controlled creep and fatigue conditions with those obtained under stress-controlled creep and fatigue conditions and with those for smooth specimens estimated based on the linear and nonlinear damage summation rule. Furthermore, it may also be important to compare these results with those of smooth specimens estimated based on the Manson–Coffin law when the failure life is fatigue-dominant. Considering these aspects, detailed experiments and analyses were systematically conducted for P92 steel in this study, and the above comparisons were conducted. The results aid in achieving a unified understanding of the law of fracture life, including those under stress- and strain-controlled creep and fatigue conditions. Full article

(This article belongs to the Special Issue Creep and Fatigue Behavior of Alloys)

22 pages, 11408 KiB

Open AccessArticle

The Influence of Beryllium Incorporation into an Al-5wt.%Cu-1wt.%Si Alloy on the Solidification Cooling Rate, Microstructural Length Scale, and Corrosion Resistance

by Joyce Ranay Santos, Milena Poletto Araújo, Talita Vida, Fabio Faria Conde, Noé Cheung, Amauri Garcia and Crystopher Brito

Metals 2025, 15(7), 736; https://doi.org/10.3390/met15070736 (registering DOI) - 30 Jun 2025

Abstract

The addition of beryllium (Be) to Al–Cu alloys enhances their mechanical properties and corrosion resistance. This study aims to investigate the effects of solidification cooling rates and the addition of Be on the microstructural refinement and corrosion behavior of an Al–5wt.%Cu–1wt.%Si–0.5wt.%Be alloy. Radial [...] Read more.

The addition of beryllium (Be) to Al–Cu alloys enhances their mechanical properties and corrosion resistance. This study aims to investigate the effects of solidification cooling rates and the addition of Be on the microstructural refinement and corrosion behavior of an Al–5wt.%Cu–1wt.%Si–0.5wt.%Be alloy. Radial solidification under unsteady-state conditions was performed using a stepped brass mold, producing four distinct cooling rates. An experimental growth law, λ₂ = 26

{\dot{T}}^{- 1 / 3}

, was established, confirming the influence of Be and the cooling rate on dendritic size reduction. The final microstructure was characterized by an α-Al dendritic matrix with eutectic compounds (α-Al + θ-Al₂Cu + Si + Fe-rich phase) confined to the interdendritic regions. No Be-containing intermetallic phases were detected, and beryllium remained homogeneously distributed within the eutectic. Notably, Be addition promoted a morphological transformation of the Fe-rich phases from angular or acicular forms into a Chinese-script-like structure, which is associated with reduced local stress concentrations. Tensile tests revealed an ultimate tensile strength of 248.8 ± 11.2 MPa and elongation of approximately 6.4 ± 0.5%, indicating a favorable balance between strength and ductility. Corrosion resistance assessment by EIS and polarization tests in a 0.06 M NaCl solution showed a corrosion rate of 28.9 µm·year⁻¹ and an Epit of −645 mV for the Be-containing alloy, which are lower than those measured for the reference Al–Cu and Al–Cu–Si alloys. Full article

(This article belongs to the Special Issue High-Performance Aluminum Alloy: Design, Strengthening, Manufacturing and Application)

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10 pages, 2749 KiB

Open AccessArticle

The Mechanism of High Electrical Conductivity in Copper–Chromium Alloy

by Jiaoyan Dai and Guoqiang Liu

Metals 2025, 15(7), 735; https://doi.org/10.3390/met15070735 (registering DOI) - 30 Jun 2025

Abstract

Cr alloyed Cu exhibits puzzlingly high electrical conductivity compared with other 3d elements alloying. Here, we present a theoretical understanding based on standard electronic band structure calculations. The influence of local spin-polarization on electrical conductivity was first investigated. It is found that the [...] Read more.

Cr alloyed Cu exhibits puzzlingly high electrical conductivity compared with other 3d elements alloying. Here, we present a theoretical understanding based on standard electronic band structure calculations. The influence of local spin-polarization on electrical conductivity was first investigated. It is found that the non-magnetic calculation produces a high density of states peak at the Fermi level, and then it fails to explain the high electrical conductivity of Cu-Cr alloy. When spin polarization is taken into account, the density of states is significantly reduced, and the results are in good agreement with experimental measurements. Meanwhile, the calculation results can explain the increase in strength and also lead to some interesting deductions. Finally, a computational program is proposed to select a high electrical conductivity Cu alloy based on a simple calculation model. Full article

19 pages, 12177 KiB

Open AccessArticle

Comparison of Microstructure and Hardening Ability of DCI with Different Pearlite Contents by Laser Surface Treatment

by Zile Wang, Xianmin Zhou, Daxin Zeng, Wei Yang, Jianyong Liu and Qiuyue Shi

Metals 2025, 15(7), 734; https://doi.org/10.3390/met15070734 (registering DOI) - 30 Jun 2025

Abstract

Laser surface treatment (LST) has been employed on ductile cast iron (DCI) parts to obtain a good performance and a long service life. There is a need to understand the laser surface-treated microstructure and hardening ability of DCIs with different matrix structures to [...] Read more.

Laser surface treatment (LST) has been employed on ductile cast iron (DCI) parts to obtain a good performance and a long service life. There is a need to understand the laser surface-treated microstructure and hardening ability of DCIs with different matrix structures to facilitate the scientific selection of DCI for specific applications. In this study, a Laserline-LDF3000 fiber-coupled semiconductor laser with a rectangular spot was used to harden the surface of ductile cast irons (DCIs) with different pearlite contents. The hardened surface layer having been solid state transformed (SST) and with or without being melted–solidified (MS) was obtained under various process parameters. The microstructure, hardened layer depth, hardness and hardening ability were analyzed and compared as functions of pearlite contents and laser processing parameters. The results show that the MS layers on the DCIs with varied pearlite contents have similar microstructures consisting of fine transformed ledeburite, martensite and residual austenite. The microstructure of the SST layer includes martensite, residual austenite and ferrite, whose contents vary with the pearlite content of DCI. In the pearlite DCI, martensite and residual austenite are found, while in ferrite DCI, there is only a small amount of martensite around the graphite nodule, with a large amount of unaltered ferrite remaining. There exists no significant difference in the hardness of MS layers among DCIs with different pearlite contents. Within the SST layer, the variation in the hardness value in the pearlite DCI is relatively small, but it gradually decreases along the depth in the ferrite DCI. In the transition region between the SST layer and the base metal (BM), there is a steep decrease in hardness in the pearlite DCI, but it decreases gently in the ferrite DCI. The depth of the hardened layer increases slightly with the increase in the pearlite content in the DCI; however, the effective hardened depth and the hardening ability increase significantly. When the pearlite content of DCI increases from 10% to 95%, its hardening ability increases by 1.1 times. Full article

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25 pages, 5297 KiB

Open AccessArticle

Composition Design and Property Prediction for AlCoCrCuFeNi High-Entropy Alloy Based on Machine Learning

by Cuixia Liu, Meng Meng and Xian Luo

Metals 2025, 15(7), 733; https://doi.org/10.3390/met15070733 (registering DOI) - 30 Jun 2025

Abstract

Based on the innovative mode driven by “data + artificial intelligence”, in this study, three methods, namely Gaussian noise (GAUSS Noise), the Generative Adversarial Network (GAN), and the optimized Generative Adversarial Network (GANPro), are adopted to expand and enhance the collected dataset of [...] Read more.

Based on the innovative mode driven by “data + artificial intelligence”, in this study, three methods, namely Gaussian noise (GAUSS Noise), the Generative Adversarial Network (GAN), and the optimized Generative Adversarial Network (GANPro), are adopted to expand and enhance the collected dataset of element contents and the hardness of the AlCoCrCuFeNi high-entropy alloy. Bayesian optimization with grid search is used to determine the optimal combination of hyperparameters, and two interpretability methods, SHAP and permutation importance, are employed to further explore the relationship between the element features of high-entropy alloys and hardness. The results show that the optimal data augmentation method is Gaussian noise enhancement; its accuracy reaches 97.4% under the addition of medium noise (σ = 0.003), and an optimal performance prediction model based on the existing dataset is finally constructed. Through the interpretability method, it is found that the contributions of Al and Ni are the most prominent. When the Al content exceeds 0.18 mol, it has a positive promoting effect on hardness, while Ni and Cu exhibit a critical effect of promotion–inhibition near 0.175 mol and 0.14 mol, respectively, revealing the nonlinear regulation law of element contents. This study solves the problem of revealing the mutual relationship between the element contents and hardness of high-entropy alloys in the case of a lack of alloy data and provides theoretical guidance for further improving the performance of high-entropy alloys. Full article

(This article belongs to the Special Issue Preparation, Properties, Microstructure and Applications of High Entropy Alloys)

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17 pages, 3910 KiB

Open AccessArticle

Extraction of Valuable Metals from Spent Li-Ion Batteries Combining Reduction Smelting and Chlorination

by Chen Wang, Wei Liu, Congren Yang and Hongbin Ling

Metals 2025, 15(7), 732; https://doi.org/10.3390/met15070732 (registering DOI) - 30 Jun 2025

Abstract

Pyrometallurgical recycling of lithium-ion batteries presents distinct advantages including streamlined processing, simplified pretreatment requirements, and high throughput capacity. However, its industrial implementation faces challenges associated with high energy demands and lithium loss into slag phases. This investigation develops an integrated reduction smelting–chloridizing volatilization [...] Read more.

Pyrometallurgical recycling of lithium-ion batteries presents distinct advantages including streamlined processing, simplified pretreatment requirements, and high throughput capacity. However, its industrial implementation faces challenges associated with high energy demands and lithium loss into slag phases. This investigation develops an integrated reduction smelting–chloridizing volatilization process for the comprehensive recovery of strategic metals (Li, Mn, Cu, Co, Ni) from spent ternary lithium-ion batteries; calcium chloride was selected as the chlorinating agent for this purpose. Thermodynamic analysis was performed to understand the phase evolution during reduction smelting and to design an appropriate slag composition. Preliminary experiments compared carbon and aluminum powder as reducing agents to identify optimal operational parameters: a smelting temperature of 1450 °C, 2.5 times theoretical CaCl₂ dosage, and duration of 120 min. The process achieved effective element partitioning with lithium and manganese volatilizing as chloride species, while transition metals (Cu, Ni, Co) were concentrated into an alloy phase. Process validation in an induction furnace with N₂-O₂ top blowing demonstrated enhanced recovery efficiency through optimized oxygen supplementation (four times the theoretical oxygen requirement). The recovery rates of Li, Mn, Cu, Co, and Ni reached 94.1%, 93.5%, 97.6%, 94.4%, and 96.4%, respectively. This synergistic approach establishes an energy-efficient pathway for simultaneous multi-metal recovery, demonstrating industrial viability for large-scale lithium-ion battery recycling through minimized processing steps and maximized resource utilization. Full article

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

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19 pages, 4240 KiB

Open AccessArticle

Sonication-Assisted Surface Erosion and Its Impact on the Flotation of Ultrafine Smithsonite

by Weiguang Zhou, Weiwei Cao, Haobin Wei, Shulan Shi, Chenwei Li and Liuyang Dong

Metals 2025, 15(7), 731; https://doi.org/10.3390/met15070731 (registering DOI) - 30 Jun 2025

Abstract

Regulating the dissolution and interfacial behavior of minerals via external force fields is considered a promising strategy for enhancing the flotation of soluble minerals. This study explored the potential of ultrasound-assisted pulp conditioning in improving ultrafine smithsonite flotation. Specifically, we systematically evaluated the [...] Read more.

Regulating the dissolution and interfacial behavior of minerals via external force fields is considered a promising strategy for enhancing the flotation of soluble minerals. This study explored the potential of ultrasound-assisted pulp conditioning in improving ultrafine smithsonite flotation. Specifically, we systematically evaluated the effects of ultrasonic pretreatment (UP) on the physicochemical properties of smithsonite suspensions (focusing on surface erosion behavior) and assessed subsequent flotation performance using flotation tests and modern analytical techniques. It has been found that UP can significantly modify smithsonite suspension characteristics, including particle morphology, ionic composition, electrokinetic properties, and pulp pH. Flotation results demonstrate that UP yields higher recovery compared to traditional stirring (TS) conditioning, especially at medium-to-high sodium oleate (NaOL) concentrations. Comparative analysis reveals that ultrasonic-assisted dissolution and ion-selective migration are the main factors driving improved flotation performance. Unlike TS, UP promotes greater zinc ion release, facilitates the dissolution–hydrolysis–precipitation equilibrium, generates more and finer nanoparticles in the bulk phase, and induces the deposition of hydrozincite on smithsonite surfaces. These changes increase active zinc sites for more stable NaOL adsorption, thereby enhancing the flotation of ultrafine smithsonite particles. Full article

(This article belongs to the Special Issue State of the Art in Flotation and Separation of Metallic Minerals)

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13 pages, 3443 KiB

Open AccessArticle

Influence of Wear-Induced Turning on the Roll’s Fatigue Life

by Francisko Lukša, Željko Domazet, Đorđe Dobrota and Branko Lalić

Metals 2025, 15(7), 730; https://doi.org/10.3390/met15070730 (registering DOI) - 29 Jun 2025

Abstract

Friction-induced wear during the rolling process needs periodic remachining of caliber roll grooves, which increases operational costs and reduces roll fatigue life. Stress analysis showed that a regular reduction in the initial diameter by up to 3.5% results in a 12.2% increase in [...] Read more.

Friction-induced wear during the rolling process needs periodic remachining of caliber roll grooves, which increases operational costs and reduces roll fatigue life. Stress analysis showed that a regular reduction in the initial diameter by up to 3.5% results in a 12.2% increase in maximum stress amplitude, reducing the estimated fatigue life by a factor of 1.5. Although fatigue life is reduced, the risk of failure under normal operating conditions remains low. Further analysis, considering mill design and roll hardness, demonstrated the feasibility of additional roll diameter reduction, thereby enabling increased production using the same rolls. The findings support further diameter reduction without compromising performance and underscore the importance of integrating such analysis into the roller design process to optimize fatigue life and roll utilization. Full article

(This article belongs to the Special Issue Tribological Property and Failure Analysis of Metallic Materials)

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14 pages, 5034 KiB

Open AccessArticle

Topology Optimization of a Milling Cutter Head for Additive Manufacturing

by Ilídio Brito Costa, Bruno Rafael Cunha, João Marouvo, Daniel Figueiredo, Bruno Miguel Guimarães, Manuel Fernando Vieira and José Manuel Costa

Metals 2025, 15(7), 729; https://doi.org/10.3390/met15070729 (registering DOI) - 29 Jun 2025

Abstract

The rapid growth of the machining market and advancements in additive manufacturing (AM) present new opportunities for innovative tool designs. This preliminary study proposes a design for additive manufacturing (DfAM) approach to redesign a milling cutter head in 17-4 PH stainless steel by [...] Read more.

The rapid growth of the machining market and advancements in additive manufacturing (AM) present new opportunities for innovative tool designs. This preliminary study proposes a design for additive manufacturing (DfAM) approach to redesign a milling cutter head in 17-4 PH stainless steel by integrating topology optimization (TO) and internal coolant channel optimization, enabled by laser powder bed fusion (LPBF). An industrial eight-insert milling cutting tool was reimagined with conformal cooling channels and a lightweight topology-optimized structure. The design process considered LPBF constraints and was iteratively refined using computational fluid dynamics (CFD) and finite element analysis (FEA) to validate fluid flow and structural performance. The optimized milling head achieved approximately 10% weight reduction while improving stiffness (reducing maximum deformation under load from 160 μm to 151 μm) and providing enhanced coolant distribution to the cutting inserts. The results demonstrate that combining TO with internal channel design can yield a high-performance and lightweight milling tool that leverages the freedom of additive manufacturing. As proof of concept, this integrated CFD–FEA validation approach under DfAM guidelines highlights a promising pathway toward superior cutting tool designs for industrial applications. Full article

(This article belongs to the Section Additive Manufacturing)

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20 pages, 8782 KiB

Open AccessArticle

Laser Powder Bed Fusion of a Ti-16Nb-Based Alloy: Processability, Microstructure, and Mechanical Properties

by Azim Gökçe, Vamsi Krishna Balla, Subrata Deb Nath, Arulselvan Arumugham Akilan and Sundar V. Atre

Metals 2025, 15(7), 728; https://doi.org/10.3390/met15070728 (registering DOI) - 29 Jun 2025

Abstract

Titanium alloys, especially Ti6Al4V, are widely used in biomedical implants due to their biocompatibility and mechanical strength. However, their high elastic modulus (>100 GPa), compared to that of human bone (10–30 GPa), often causes stress shielding, reducing implant lifespan. To address this, titanium [...] Read more.

Titanium alloys, especially Ti6Al4V, are widely used in biomedical implants due to their biocompatibility and mechanical strength. However, their high elastic modulus (>100 GPa), compared to that of human bone (10–30 GPa), often causes stress shielding, reducing implant lifespan. To address this, titanium alloys with lower elastic modulus are under development. In this study, Ti-based multi-element alloy with 16 wt.% Nb samples were fabricated using laser powder bed fusion (L-PBF) from a premixed powder blend of Ti6Al4V and Nb-Hf-Ti. Processing high-melting Nb-based alloys via L-PBF poses challenges, which were mitigated through optimized parameters, including a maximum laser power of 100 W. Eleven parameter sets were employed to evaluate printability, microstructure, and mechanical properties. Microstructural analysis revealed Widmanstätten structures composed of α and β phases, along with isolated spherical pores. Reduced hatch spacing and slower laser speed led to increased hardness. The highest hardness (~43 HRC) was observed at the highest energy density (266 J/mm³), while the lowest (~28 HRC) corresponded to 44 J/mm³. Elastic modulus values ranged from 30 to 35 GPa, closely matching that of bone. These results demonstrate the potential of the developed Ti-based alloy containing 16 wt.% Nb as a promising candidate for load-bearing biomedical implants. Full article

(This article belongs to the Section Additive Manufacturing)

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12 pages, 1005 KiB

Open AccessArticle

Density Functional Theory-Based Study of UC₂ and Cr-Doped UO₂

by Barbara Szpunar, Jayangani I. Ranasinghe and Jerzy A. Szpunar

Metals 2025, 15(7), 727; https://doi.org/10.3390/met15070727 (registering DOI) - 29 Jun 2025

Abstract

A density functional theory-based study of UC₂ and Cr-doped UO₂ using the phono3py and VASP computational simulation packages is presented. Furthermore, the temperature-dependent thermal conductivities are compared to the traditional urania fuel. Doping of urania with Cr allows for improved fission [...] Read more.

A density functional theory-based study of UC₂ and Cr-doped UO₂ using the phono3py and VASP computational simulation packages is presented. Furthermore, the temperature-dependent thermal conductivities are compared to the traditional urania fuel. Doping of urania with Cr allows for improved fission gas retention, reducing the fission gas release and lowering the oxidation rate of UO₂. The thermal conductivity calculated using the random alloy method with one U atom replaced by Cr in a supercell (CrU₃₁O₆₄) shows a slight decrease; however, this may be compensated for by larger grain sizes in the presence of Cr. The reduction of thermal conductivity for the 0.61 wt.% Cr substation in urania is presented. Investigated here, the UC₂ metallic high-temperature fcc phase looks promising due to additional electronic contribution to conductivity. Furthermore, we found that the temperature-dependent phonon-assisted thermal conductivities for UC₂ and UO₂ are very similar. The elastic properties of UC₂ were also evaluated and compared with UO₂. The presented analysis provides information for further improvement of the design of nuclear fuels. Full article

(This article belongs to the Special Issue Advances in the Manufacture and Performance of Nuclear Metallic Materials)

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17 pages, 5649 KiB

Open AccessArticle

Heat Treatment Analysis and Mechanical Characterization of a Recycled Gravity Die Cast EN 42000 Alloy

by Cristian Cascioli, Riccardo Arcaleni, Alessandro Morri and Lorella Ceschini

Metals 2025, 15(7), 726; https://doi.org/10.3390/met15070726 (registering DOI) - 29 Jun 2025

Abstract

Recycled aluminum–silicon alloys provide significant environmental benefits by reducing the consumption of raw materials and lowering carbon emissions. However, their industrial application is limited by the presence of iron-based intermetallic compounds and the insufficient investigation in the literature regarding their effects on mechanical [...] Read more.

Recycled aluminum–silicon alloys provide significant environmental benefits by reducing the consumption of raw materials and lowering carbon emissions. However, their industrial application is limited by the presence of iron-based intermetallic compounds and the insufficient investigation in the literature regarding their effects on mechanical behavior. This study focuses on a recycled EN 42000 alloy, comprising 95% recycled aluminum, with a focus on the effect of its elevated iron content (0.447 wt%) on aging behavior and mechanical performance. Laboratory-scale specimens were produced through gravity die casting and subjected to T6 heat treatment, consisting of solution, quenching, and artificial aging from 160 °C to 190 °C for up to 8 h. To investigate overaging, analyses were conducted at 160 °C and 170 °C for durations up to 184 h. Tensile tests were conducted on specimens aged under the most promising conditions. Based on innovative quality indices and predictive modeling, aging at 160 °C for 4.5 h was identified as the optimal condition, providing a well-balanced combination of strength and ductility (YS = 258 MPa, UTS = 313 MPa, and e% = 3.9%). Mechanical behavior was also assessed through microstructural and fractographic analyses, highlighting the capability of EN 42000 to achieve properties suitable for high-performance automotive components. Full article

(This article belongs to the Special Issue Sustainability Approaches in the Recycling of Light Alloys)

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14 pages, 4333 KiB

Open AccessArticle

Hot Deformation Behavior, Processing Maps, and Microstructure Evolution of 7E97 Alloy

by Fangyan He, Xiaolan Wu, Shengping Wen, Liang Hong, Zhizheng Rong, Hanyu Chen, Kunyuan Gao, Wu Wei, Hui Huang and Zuoren Nie

Metals 2025, 15(7), 725; https://doi.org/10.3390/met15070725 (registering DOI) - 28 Jun 2025

Abstract

A hot compression simulation was conducted on the Al-7.62Zn-2.22Mg-0.90Cu-0.30Mn-0.09Er-0.13Zr alloy (7E97) within the temperature range of 300~460 °C and strain rate range of 0.001~10 s⁻¹ using a Gleeble-3500 hot simulator. A flow-stress constitutive equation and hot processing maps were established for the [...] Read more.

A hot compression simulation was conducted on the Al-7.62Zn-2.22Mg-0.90Cu-0.30Mn-0.09Er-0.13Zr alloy (7E97) within the temperature range of 300~460 °C and strain rate range of 0.001~10 s⁻¹ using a Gleeble-3500 hot simulator. A flow-stress constitutive equation and hot processing maps were established for the alloy, and the microstructural evolution of the alloy after hot deformation was investigated. It was found that the dominant dynamic softening mechanism of the alloy was dynamic recovery, accompanied by minor dynamic recrystallization. The optimal hot processing window for the alloy was determined to be in the ranges of 0.001~0.05 s⁻¹ and 350~410 °C. Full article

(This article belongs to the Special Issue Research on Mechanical Properties, Deformation, and Microstructures of Metallic Materials)

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12 pages, 3731 KiB

Open AccessArticle

Research on Corrosion Protection of TETA-Modified Li–Al LDHs for AZ31 Magnesium Alloy in Simulated Seawater

by Sifan Tu, Liyan Wang, Sixu Wang, Haoran Chen, Qian Huang, Ning Hou, Zhiyuan Feng and Guozhe Meng

Metals 2025, 15(7), 724; https://doi.org/10.3390/met15070724 (registering DOI) - 28 Jun 2025

Abstract

Magnesium alloys are lightweight metals but suffer from high corrosion susceptibility due to their chemical reactivity, limiting their large-scale applications. To enhance corrosion resistance, this work combines Li–Al layered double hydroxides (LDHs) with triethylenetetramine (TETA) inhibitors to form an efficient corrosion protection system. [...] Read more.

Magnesium alloys are lightweight metals but suffer from high corrosion susceptibility due to their chemical reactivity, limiting their large-scale applications. To enhance corrosion resistance, this work combines Li–Al layered double hydroxides (LDHs) with triethylenetetramine (TETA) inhibitors to form an efficient corrosion protection system. Electrochemical tests, SEM, FT-IR, XPS, and 3D depth-of-field microscopy were employed to evaluate TETA-modified Li–Al LDH coatings at varying concentrations. Among them, the Li–Al LDHs without the addition of a TETA corrosion inhibitor decreased significantly at |Z|_{0.01 Hz} after immersion for 4 h. However, the Li–Al LDHs coating of 23.5 mM TETA experienced a sudden drop at |Z|_{0.01 Hz} after holding for about 60 h, and the Li–Al LDHs coating of 70.5 mM TETA also experienced a sudden drop at |Z|_{0.01 Hz} after holding for about 132 h. By contrast, at the optimal concentration (47 mM), after 24 h of immersion, the maximum |Z|_{0.01 Hz} reached 7.56 × 10⁵ Ω∙cm²—three orders of magnitude higher than pure Li–Al LDH coated AZ31 (2.55 × 10² Ω∙cm²). After 300 h of immersion, the low-frequency impedance remained above 10⁵ Ω∙cm², demonstrating superior long-term protection. TETA modification significantly improved the durability of Li–Al LDHs coatings, addressing the short-term protection limitation of standalone Li–Al LDHs. Li–Al LDHs themselves have a layered structure and effectively capture corrosive Cl⁻ ions in the environment through ion exchange capacity, reducing the corrosion of the interface. Furthermore, TETA exhibits strong adsorption on Li–Al LDHs layers, particularly at coating defects, enabling rapid barrier formation. This inorganic–organic hybrid design achieves defect compensation and enhanced protective barriers. Full article

(This article belongs to the Special Issue Metal Corrosion Behavior and Protection in Service Environments)

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