Metals

16 pages, 1656 KB

Open AccessArticle

Effect of Mechanical Activation on Electrochemical Properties of Chalcopyrite in Iron-Containing Sulfuric Acid Solutions

by Yuxin Li, Zuyuan Tian, Xu Wang and Congren Yang

Metals 2025, 15(10), 1075; https://doi.org/10.3390/met15101075 (registering DOI) - 25 Sep 2025

Abstract

Mechanical activation significantly enhances the leaching of chalcopyrite, a process that is fundamentally electrochemical in nature. Thus, a comprehensive understanding of its impact on the electrochemical behavior of chalcopyrite in leaching systems is crucial. This study examines the effect of mechanical activation on [...] Read more.

Mechanical activation significantly enhances the leaching of chalcopyrite, a process that is fundamentally electrochemical in nature. Thus, a comprehensive understanding of its impact on the electrochemical behavior of chalcopyrite in leaching systems is crucial. This study examines the effect of mechanical activation on the electrochemical and semiconductor properties of chalcopyrite in H₂SO₄ solutions containing Fe²⁺ or/and Fe³⁺ at pH = 1.5. Mechanical activation was carried out using a planetary ball mill at 700 rpm for durations ranging from 0 to 2.5 h to reduce particle size and induce lattice distortion, thereby increasing its electrochemical activity. In iron-containing electrolytes, mechanically activated chalcopyrite is more readily reduced, releasing Fe²⁺ and leading to a higher surface concentration of Fe²⁺, which consequently increases the diffusion coefficient at the solid–liquid interface. Mott–Schottky analysis revealed a decrease in flat band potentials (from 261.7 mV to 131.2 mV in 0.1 mol/L Fe³⁺ after 1.0 h of activation) and an elevation in Fermi levels. As a result, mechanical activation markedly accelerates the corrosion rate of chalcopyrite in ferric solutions—the corrosion current increased from 40.27 µA to 70.71 µA in 0.1 mol/L Fe³⁺ after 1.0 h of activation. These findings provide valuable insights for developing strategies to enhance mineral dissolution, and advance the hydrometallurgical processing of chalcopyrite. Full article

(This article belongs to the Section Extractive Metallurgy)

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14 pages, 4290 KB

Open AccessArticle

Mechanisms of Fine Mud Covering and Enhanced Dispersion for a Rutile Middling

by Yang Wang, Yongxing Zheng, Liuyi Ren, Shaojun Bai, Lingyun Huang and Jieli Peng

Metals 2025, 15(10), 1074; https://doi.org/10.3390/met15101074 - 25 Sep 2025

Abstract

Electric separation is usually adopted to separate and purify rutile and zircon. However, fine mud covering over the target minerals either reduces the conductivity of rutile or improves the conductivity of zircon. Therefore, the conductivity difference between zircon and rutile becomes smaller, leading [...] Read more.

Electric separation is usually adopted to separate and purify rutile and zircon. However, fine mud covering over the target minerals either reduces the conductivity of rutile or improves the conductivity of zircon. Therefore, the conductivity difference between zircon and rutile becomes smaller, leading to the difficulty of separation and purification of both minerals. In this paper, the mechanisms of fine mud covering and enhanced dispersion for a rutile middling were illustrated by theoretical calculations of Derjaguin–Landau–Verwey–Overbeek (DLVO) and the extended DLVO (EDLVO), respectively. The fine mud was initially characterized by chemical multi-element analysis, X-ray diffractometer (XRD) analysis, electron probe micro analysis (EPMA), and laser particle size analyzer. The results showed that the gangue was mainly composed of goethite, quartz, calcite, and kaolinite and the average particle size of the fine mud reached 11.06 μm. The DLVO theoretical calculation revealed that the covering ability of fine-grained gangue ranked as follows: quartz < goethite < kaolinite < calcite. Compared with the zircon, the fine-grained gangue was more likely to cover the surface of rutile. The EDLVO theoretical calculation suggested that the addition of sodium silicate or sodium hexametaphosphate promoted detachment of the gangue from the surface of rutile and zircon and the shedding order was quartz > kaolinite > calcite > goethite. Moreover, the sodium hexametaphosphate had a better dispersion effect than the sodium silicate. Full article

(This article belongs to the Special Issue Advances in Sustainable Utilization of Metals: Recovery and Recycling)

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17 pages, 4731 KB

Open AccessArticle

Effects of Ceramic Particulate Type and Porosity on the Corrosion Behavior of Open-Cell AlSn6Cu Composites Produced via Liquid-State Processing

by Mihail Kolev, Vanya Dyakova, Yoanna Kostova, Boriana Tzaneva, Hristina Spasova and Rositza Dimitrova

Metals 2025, 15(10), 1073; https://doi.org/10.3390/met15101073 - 25 Sep 2025

Abstract

The corrosion behavior of open-cell AlSn6Cu-based composites, one reinforced with SiC particles and the other with Al₂O₃ particles, was investigated. The composites were fabricated via liquid-state processing, employing both squeeze casting and the replication method, and they produced in two [...] Read more.

The corrosion behavior of open-cell AlSn6Cu-based composites, one reinforced with SiC particles and the other with Al₂O₃ particles, was investigated. The composites were fabricated via liquid-state processing, employing both squeeze casting and the replication method, and they produced in two distinct pore size ranges (800–1000 µm and 1000–1200 µm). Corrosion performance was systematically evaluated through gravimetric (weight loss) measurements and electrochemical techniques, including open-circuit potential monitoring and potentiodynamic polarization tests. Comprehensive microstructural and phase analyses were conducted using X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The results revealed that both reinforcement type and pore architecture have a significant impact on corrosion resistance. Al₂O₃-reinforced composites consistently outperformed their SiC-containing counterparts, and pore enlargement generally improved performance for the unreinforced alloy and the Al₂O₃ composite but not for the SiC composite. Overall, the optimal corrosion resistance is achieved by pairing a coarser-pore architecture (1000–1200 µm) with Al₂O₃ reinforcement, which minimizes both instantaneous (electrochemical) and cumulative (gravimetric) corrosion metrics. This study addresses a gap in current research by providing the first detailed assessment of corrosion in open-cell AlSn6Cu-based composites with controlled pore architectures and different ceramic reinforcements, offering valuable insights for the development of advanced lightweight materials for harsh environments. Full article

(This article belongs to the Special Issue Microstructure and Characterization of Metal Matrix Composites)

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11 pages, 18277 KB

Open AccessArticle

Experimental Study on Electric Separation of Ti/Zr-Bearing Minerals in Gravity Separation Concentrate After Thermal Activation Roasting

by Yang Wang, Yongxing Zheng, Hua Zhang, Xiang Huang, Xiangding Wang and Zhenxing Wang

Metals 2025, 15(10), 1072; https://doi.org/10.3390/met15101072 - 25 Sep 2025

Abstract

To solve the problem of purifying concentrates of rutile and zircon, a new method of electric separation after thermal activation roasting at 800 °C was proposed to strengthen the separation of Ti/Zr-bearing minerals. The results showed that the grade of TiO₂ in [...] Read more.

To solve the problem of purifying concentrates of rutile and zircon, a new method of electric separation after thermal activation roasting at 800 °C was proposed to strengthen the separation of Ti/Zr-bearing minerals. The results showed that the grade of TiO₂ in the conductor increased by 2.55~6.45% and the content of ZrO₂ decreased by 0.83~2.60% after thermal activation roasting and electronic separation, in contrast with electronic separation without roasting. To further explore the mechanism of activation roasting, the electrical conductivity, the phase evolution, and the microstructure of the gravity separation concentrate (GSC), pure rutile and pure zircon before and after roasting were investigated. The results of conductivity testing showed that the roasting pretreatment significantly improved the conductive difference between rutile and zircon, thus strengthening their separation performance. The XRD results revealed that the thermal activation roasting made the anatase in the GSC transform into rutile, thus enhancing the conductivity. Meanwhile, the crystallinity of both of the pure minerals was improved. The SEM results showed that the GSC particles formed loose and porous sinters, suggesting the reconstruction of the unstable anatase into rutile. Small amounts of cracks and protrusions occurred on the surface of both pure minerals, ascribed to the dehydration and deoxygenation at a high temperature. Full article

(This article belongs to the Special Issue Advances in Sustainable Utilization of Metals: Recovery and Recycling)

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16 pages, 4416 KB

Open AccessArticle

High-Pressure Die Casting (HPDC) Process Parameters Optimization for Al-Mg-Fe Aluminum Alloy Structural Parts Manufacturing

by Mikel Merchán, Alejandro Pascual, Ane Jiménez, José Carlos García, Eva Anglada, Haize Galarraga and Naiara Ortega

Metals 2025, 15(10), 1071; https://doi.org/10.3390/met15101071 - 24 Sep 2025

Abstract

The increasing adoption of High-Pressure Die Casting (HPDC) technology in the production of automotive body structure components is driven by its potential for efficiency and performance. This technology, however, involves complex physical phenomena with numerous parameters that significantly influence casting quality. In this [...] Read more.

The increasing adoption of High-Pressure Die Casting (HPDC) technology in the production of automotive body structure components is driven by its potential for efficiency and performance. This technology, however, involves complex physical phenomena with numerous parameters that significantly influence casting quality. In this study, three key die casting parameters—plunger or shot speed, vacuum application, and intensification pressure (IP)—have been evaluated following a Design of Experiment (DoE) approach. The results demonstrate that IP application is instrumental in reducing porosity within the cast specimens, thereby enhancing their mechanical strength and elongation. Furthermore, the combined application of vacuum and IP yields further improvements in elongation by minimizing porosity. These findings are particularly relevant for silicon-free alloys, which eliminate the need for post-casting heat treatments to achieve the required mechanical properties. By optimizing HPDC processes, manufacturers can reduce rejection rates, lower production costs, and improve the overall efficiency of their operations, contributing to the production of high-quality and cost-effective components for the automotive industry. Full article

(This article belongs to the Special Issue Advanced Metal Casting Processes: Latest Research, Insights, and Challenges)

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11 pages, 2526 KB

Open AccessArticle

Specific Features of Using High-Silica Flux Ore in Copper Smelting Units

by Bagdaulet Kenzhaliyev, Sergey Kvyatkovskiy, Sultanbek Kozhakhmetov, Bulat Sukurov, Maral Dyussebekova and Anastassiya Semenova

Metals 2025, 15(10), 1070; https://doi.org/10.3390/met15101070 - 24 Sep 2025

Abstract

This study explores the application of high-silica flux ore in copper smelting and converting processes at the Zhezkazgan Copper Smelting plant. Pilot-scale experiments and SEM analyses were performed to assess its influence on slag composition, temperature regime, and metal recovery. The results demonstrated [...] Read more.

This study explores the application of high-silica flux ore in copper smelting and converting processes at the Zhezkazgan Copper Smelting plant. Pilot-scale experiments and SEM analyses were performed to assess its influence on slag composition, temperature regime, and metal recovery. The results demonstrated that replacing conventional flux with high-silica ore reduced flux consumption by 19%, increased converter slag temperature from 1124 to 1174 °C, and decreased copper content in converter slag from 10% to 4.5%. SEM micro-analysis revealed the formation of lead-containing silicate rims around matte inclusions, which hinder their settling at low temperatures. However, when the slag temperature exceeded 1400 °C, these rims were destroyed, facilitating separation and reducing residual copper. These findings highlight the potential of high-silica fluxes (>90% SiO₂) to improve both energy efficiency and metal recovery in process of copper matte converting, offering practical recommendations for industrial operations. Full article

(This article belongs to the Section Extractive Metallurgy)

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28 pages, 1204 KB

Open AccessReview

Factors Affecting the Surface Roughness of the As-Built Additively Manufactured Metal Parts: A Review

by Simone Paggetti, Enrico Bedogni and Paolo Veronesi

Metals 2025, 15(10), 1069; https://doi.org/10.3390/met15101069 - 24 Sep 2025

Abstract

Nowadays, additive manufacturing technologies continue to increase in number, and with them, the various challenges they bring for the optimal design of components. However, many relevant applications require that a certain surface finishing level is reached; in particular, surface roughness should stay below [...] Read more.

Nowadays, additive manufacturing technologies continue to increase in number, and with them, the various challenges they bring for the optimal design of components. However, many relevant applications require that a certain surface finishing level is reached; in particular, surface roughness should stay below a certain threshold. The aim of this work is to provide, for each of the most used metal additive manufacturing technologies, a short review of parameters affecting as-built surface roughness, indicating possible correlations with process parameters. The identified correlations, summarized visually as tables, could serve as starting guidelines for the design and production of parts with controlled surface roughness or having a surface roughness suitable for the application of possible surface finishing post-processes. Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing for Metallic Materials and Their Applications (3rd Edition))

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17 pages, 3675 KB

Open AccessArticle

High-Performance Porous Aluminum Alloys from Recycled A356 Scrap: Synergistic Foaming Approach Using TiH₂ and Na₂B₄O₇·10H₂O

by Jinwoo Baek, Hyuncheul Lee, Jaehui Bang and Eunkyung Lee

Metals 2025, 15(10), 1068; https://doi.org/10.3390/met15101068 - 24 Sep 2025

Abstract

Porous aluminum alloys are widely used for lightweight structural materials such as marine structures, energy absorbers, and buoyant components. However, the conventional foaming agent TiH₂ presents limitations such as high cost and elevated decomposition temperatures, which increase manufacturing costs and restrict industrial [...] Read more.

Porous aluminum alloys are widely used for lightweight structural materials such as marine structures, energy absorbers, and buoyant components. However, the conventional foaming agent TiH₂ presents limitations such as high cost and elevated decomposition temperatures, which increase manufacturing costs and restrict industrial applicability. In addition, the utilization of recycled raw materials such as aluminum machining chips has emerged as an important challenge in material development for resource efficiency and sustainability. To address these issues, porous aluminum alloys were fabricated in this study using recycled A356 aluminum chips by incorporating TiH₂ and a low-cost alternative foaming agent, Na₂B₄O₇·10H₂O (borax), either individually or in combination. The effects of foaming agent content (1, 1.5, and 3 wt.%) on pore characteristics, microstructure, hardness, and corrosion resistance were systematically investigated. TiH₂ induced an increase in porosity due to hydrogen generation and also promoted grain refinement, which contributed to the improvement of hardness and corrosion resistance, while Na₂B₄O₇·10H₂O exhibited effective pore formation and hardness improvement at 1–1.5 wt.% but tended to deteriorate corrosion resistance as its content increased. In particular, combined addition of both agents at 1.5 wt.% showed excellent pore formation and corrosion resistance properties, with a relatively high pore area fraction (2.38%), porosity (27.0%), SDAS (48.1 ± 4.8 µm), hardness (59.35 ± 6.4 HV), corrosion potential (−1.039 V), pitting potential (−0.709 V), and corrosion current density (4.956 μA/cm²). This study demonstrated that Na₂B₄O₇·10H₂O (borax) foaming agent can be an economic alternative to TiH₂, and shows that the performance of porous aluminum alloys can be effectively improved by optimizing the combination of recycled raw materials and foaming agents. Full article

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21 pages, 3073 KB

Open AccessArticle

Treatment of Na₂SO₄-Containing Wastewater Generated During the Recycling of Spent Lithium-Ion Batteries: Comparative Study on the Operating Modes of Bipolar Membrane Electro-Dialysis

by Minhyuk Seo, Youngjae Lee, Junhee Kim, Jaehyuk Chang, Yeonchul Cho and Jaewoo Ahn

Metals 2025, 15(10), 1067; https://doi.org/10.3390/met15101067 - 23 Sep 2025

Abstract

The recycling of spent lithium-ion batteries generates Na₂SO₄-containing wastewater, resulting in environmental problems and resource losses. This study investigates a treatment method employing bipolar membrane electrodialysis (BMED) to recover H₂SO₄ and NaOH from such wastewater. The [...] Read more.

The recycling of spent lithium-ion batteries generates Na₂SO₄-containing wastewater, resulting in environmental problems and resource losses. This study investigates a treatment method employing bipolar membrane electrodialysis (BMED) to recover H₂SO₄ and NaOH from such wastewater. The acid and base recovery efficiencies, energy consumption, operational stability, and economic feasibility of two BMED configurations, i.e., two- and three-compartment systems, were systematically compared. The current density, initial concentrations of the feed, and initial concentrations and volumes of the acid and base were optimized under constant current conditions. The three-compartment system exhibited higher acid purity and stability, whereas the other system exhibited lower energy consumption and membrane degradation. Under optimal conditions, both systems successfully recovered H₂SO₄ and NaOH from the Na₂SO₄-containing wastewater. A techno-economic analysis based on a lab-scale process revealed that the two-compartment system exhibited cost effectiveness while the three-compartment system showed long-term operational stability. These findings suggest that BMED is a viable and effective solution for the treatment of Na₂SO₄-containing wastewater generated from battery recycling processes. Full article

(This article belongs to the Special Issue Advances in Mineral Processing and Hydrometallurgy—3rd Edition)

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15 pages, 3956 KB

Open AccessArticle

Novel Alloy Designed Electrical Steel for Improved Performance in High-Frequency Electric Machines

by Carl Slater, Xiyun Ma, Gwendal Lagorce, Juliette Soulard and Claire Davis

Metals 2025, 15(10), 1066; https://doi.org/10.3390/met15101066 - 23 Sep 2025

Abstract

The increase in electrification and desire for greater electrical motor efficiency under a range of operating conditions for different products (e.g., household appliances, automotive and aerospace) is driving innovative motor designs and demands for higher performing electrical steels. Improvements in the magnetic, electrical [...] Read more.

The increase in electrification and desire for greater electrical motor efficiency under a range of operating conditions for different products (e.g., household appliances, automotive and aerospace) is driving innovative motor designs and demands for higher performing electrical steels. Improvements in the magnetic, electrical and/or mechanical properties of electrical steels are required for high-volume electric motors and recent advances include steels with increased silicon (Si) content (from <3.5 wt% Si up to 6.5 wt%). Whilst the 6.5 wt% Si steels provide increased motor performance at high frequencies, the formation of a brittle BCC B2/D03 phase means that they cannot be cold-rolled, and therefore the production route involves siliconization after the required thickness strip is produced. The advances in computationally driven alloy design, coupled with physical metallurgical understanding, allow for more adventurous alloy design for electrical steels, outside the traditional predominantly Fe-Si compositional space. Two alloys representing a new alloy family called HiPPES (High-Performing and Processable Electrical Steel), based on low cost commonly used steel alloying elements, have been developed, cast, rolled, heat-treated, and both magnetically and mechanically tested. These alloys (with nominal compositions of Fe-3.2Mn-3.61Si-0.63Ni-0.75Cr-0.15Al-0.4Mo and Fe-2Mn-4.5Si-0.4Ni-0.75Cr-0.09Al) offer improvements compared to current ≈3 wt% Si grades: in magnetic performance (>25% magnetic loss reduction at >1 kHz), and in tensile strength (>33% increase in tensile strength with similar elongation value). Most importantly, they are maintaining processability to allow for full-scale commercial production using traditional continuous casting, hot and cold rolling, and annealing. The new alloys also showed improved resilience to grain size, with the HiPPES materials showing a <5% variance in loss at frequencies greater than 400 Hz for grain sizes between 55 and 180 µm. Comparatively, a commercial M250-35A material showed a 40% increase in loss for the same range. The paper reports on the alloy design approach used, the microstructures, and the mechanical, electrical and magnetic properties of the developed novel electrical steels compared to conventional ≈3 wt% Si and 6.5 wt% Si material. Full article

(This article belongs to the Special Issue Electrical Steels)

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23 pages, 24962 KB

Open AccessArticle

Effect of Piston Velocity on Microstructural Consistency and Critical Regions in a High-Pressure Die Cast AlSi9Cu3(Fe) Alloy Component

by Dana Bolibruchová, Marek Matejka, Richard Pastirčák and Radka Podprocká

Metals 2025, 15(10), 1065; https://doi.org/10.3390/met15101065 - 23 Sep 2025

Abstract

High-pressure die casting (HPDC) is a highly efficient method for producing aluminum parts that require high dimensional accuracy and complex shapes. However, the quality of the resulting castings, specifically their porosity and microstructure, is critically dependent on the setting of process parameters. Any [...] Read more.

High-pressure die casting (HPDC) is a highly efficient method for producing aluminum parts that require high dimensional accuracy and complex shapes. However, the quality of the resulting castings, specifically their porosity and microstructure, is critically dependent on the setting of process parameters. Any deficiencies in these aspects can lead to a significant reduction in the mechanical properties of the components. This article deals with the influence of plunger speed during high-pressure die casting on microstructure homogeneity and the occurrence of porosity in critical areas of AlSi9Cu3(Fe) alloy castings. Numerical simulations and experimental evaluation demonstrated that with increasing plunger speed, there is a transition from a transitional to a laminar flow regime to a fully turbulent regime, which affects the homogeneity of the alloy and its solidification. Turbulent flow minimizes shrinkage porosity in castings but increases the risk of gas porosity and oxide inclusions due to reoxidation processes, leading to the entrainment of air and oxide layers. Microporosity analysis showed that the lowest occurrence of shrinkage-type pores was found at a plunger speed of 4 m/s due to rapid filling and shorter solidification time. The optimal plunger speed range is between 3 and 3.6 m/s, ensuring a compromise between microstructure stability and minimization of porosity in critical areas. Full article

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

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19 pages, 8169 KB

Open AccessArticle

Preparation of a Porous Tri-n-decylamine Modified Adsorbent for the Efficient Removal of Uranium and Iron from Rare Earth

by Zihang Yi, Lifeng Chen, Shichang Zhang, Juan Liu, Zhifu Ye, Mohammed F. Hamza, Yuezhou Wei and Shunyan Ning

Metals 2025, 15(10), 1064; https://doi.org/10.3390/met15101064 - 23 Sep 2025

Abstract

The presence of impurities Fe and trace radioactive U in rare earth elements (REEs) may lead to a significant decline in the performance of high-purity rare earth products. For deep removal from REEs in a green and efficient way, an amine-functionalized silica-based adsorbent, [...] Read more.

The presence of impurities Fe and trace radioactive U in rare earth elements (REEs) may lead to a significant decline in the performance of high-purity rare earth products. For deep removal from REEs in a green and efficient way, an amine-functionalized silica-based adsorbent, TNDA/SiO₂-P, was prepared by a simple vacuum impregnation method, which had a high organic loading rate of 31.2 wt.%. The experimental results showed that it exhibited good adsorption selectivity for uranium and iron, with separation factors SF_U/REE = 20147 and SF_Fe/REE = 88128 in 5 M HCl. The adsorption kinetics was fast, with equilibrium obtained in 120 min. The 0.1 M HCl can desorb U and Fe efficiently. The deep removal of U and Fe from REEs including Sc can be achieved through chromatographic column separation with high enrichment. FT-IR, XPS and DFT calculations mutually confirmed that protonated TNDA/SiO₂-P exhibited a selective mechanism for uranium and iron in complex anion species in the hydrochloric acid system. This demonstrates its potential for efficiently removing trace impurities U and Fe from REEs. Full article

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13 pages, 5218 KB

Open AccessArticle

Extraction of Titanium from Blast Furnace Slag: Research on the Crushing Process of TiC-Bearing Slag

by Dongsheng Wang, Yanqing Hou and Wenming Guo

Metals 2025, 15(10), 1063; https://doi.org/10.3390/met15101063 - 23 Sep 2025

Abstract

TiC-bearing slag is an intermediate product in the titanium extraction process following the “high-temperature carbonization and low-temperature chlorination” method. It exhibits complex grinding characteristics, and traditional grinding methods often yield issues such as broad particle size distribution (PSD) and overgrinding, adversely affecting process [...] Read more.

TiC-bearing slag is an intermediate product in the titanium extraction process following the “high-temperature carbonization and low-temperature chlorination” method. It exhibits complex grinding characteristics, and traditional grinding methods often yield issues such as broad particle size distribution (PSD) and overgrinding, adversely affecting process efficiency. In this study, TiC-bearing slag was investigated as the raw material. Through methods such as SEM-EDS, MLA, and scientific experiments, we established quantitative relationships between mechanical inputs and product granulometry. The results indicate that the coexistence of TiC and pyroxene-group minerals leads to poor grinding selectivity, causing TiC to resist fracturing while pyroxene minerals are prone to overgrinding. Furthermore, the experiments demonstrated that high circulating-load grinding combined with staged sieving is most effective for producing narrow PSD products. This research explores the methods and paths for achieving controlled narrow PSD of TiC-containing slag in the crushing process, and providing data support for the selection of industrial-scale grinding processes. Full article

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13 pages, 5067 KB

Open AccessArticle

Investigation of Corrosion Resistance in Powder-Coated 6060 Aluminum Alloy: Effects of Powder Coating and Pre-Anodizing Followed by Powder Coating

by Aikaterini Baxevani, Eleni Lamprou, Azarias Mavropoulos, Fani Stergioudi, Nikolaos Michailidis and Ioannis Tsoulfaidis

Metals 2025, 15(10), 1062; https://doi.org/10.3390/met15101062 - 23 Sep 2025

Abstract

This study investigates the corrosion resistance of EN AW 6060 aluminum alloy powder-coated samples, with and without pre-anodizing treatment. The samples were exposed to a 3.5% NaCl solution, which is known for its strong corrosive effects, and their corrosion behavior was evaluated using [...] Read more.

This study investigates the corrosion resistance of EN AW 6060 aluminum alloy powder-coated samples, with and without pre-anodizing treatment. The samples were exposed to a 3.5% NaCl solution, which is known for its strong corrosive effects, and their corrosion behavior was evaluated using two electrochemical techniques: Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy (EIS). The aim was to assess the effectiveness of powder coatings in enhancing corrosion resistance and to examine the role of surface preparation and prior treatments. Polarization tests provided corrosion current densities and corrosion rates, while EIS data were analyzed using equivalent electrical circuits to evaluate the integrity of the protective layers. The results show that powder coatings significantly improves corrosion resistance compared to uncoated aluminum and the combination of pre-anodizing followed by painting offers the highest protection. These findings confirm the improved performance achieved through multilayer surface treatments and support the application of powder coatings acting as a durable barrier against environmental factors. Full article

(This article belongs to the Section Corrosion and Protection)

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17 pages, 6302 KB

Open AccessArticle

Low-Alloyed Spring Steel: Nanostructure and Strength After Austempering

by Mikhailo Brykov, Vasily Efremenko, Isabella Gallino, Ivan Petrišinets, Oleksii Kapustyan, Olexandr Klymov, Alexey Efremenko and Vasyl’ Girzhon

Metals 2025, 15(10), 1061; https://doi.org/10.3390/met15101061 - 23 Sep 2025

Abstract

Carbide-free bainite microstructures were developed in 0.6 wt.%–2 wt.% Si spring steel via austempering at 250 °C. Heat treatment included austenization with subsequent isothermal holding at 250 °C, varying the holding duration to 1.0, 1.5, or 2.0 h with final cooling in water. [...] Read more.

Carbide-free bainite microstructures were developed in 0.6 wt.%–2 wt.% Si spring steel via austempering at 250 °C. Heat treatment included austenization with subsequent isothermal holding at 250 °C, varying the holding duration to 1.0, 1.5, or 2.0 h with final cooling in water. X-ray diffraction, SEM investigation, tensile test, and hardness measurement were employed to study the microstructure and phase compositions of the samples. It was found that nanostructured bainite developed in the experimental steel. The distribution of distances between phase borders was determined via digital processing of SEM micrographs, and the mode distance was found to be 30 nm. The analytical estimation of possible strengthening showed that the yield strength of the nanobainite obtained should be in the gigapascal range, and the tensile testing results demonstrated that a 2 GPa yield strength was developed in the sample after isothermal treatment at 250 °C for 1 h. Investigations of the fracture surface and microstructure of the cross-section near the fracture zone confirmed the ductile mode of failure. Full article

(This article belongs to the Special Issue Advances in High-Strength Steels: Microstructure, Mechanical Properties and Applications)

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11 pages, 1206 KB

Open AccessArticle

Analysis of Strain Hardening Stages of AISI 316 LN Stainless Steel Under Cold Rolling Conditions

by Tibor Kvačkaj, Jana Bidulská, Ľuboš Kaščák, Alica Fedoríková and Róbert Bidulský

Metals 2025, 15(10), 1060; https://doi.org/10.3390/met15101060 - 23 Sep 2025

Abstract

In the present investigation, stress–strain curves and strain hardening rates on samples rolled at ambient temperature with thickness reductions of 0%, 10%, 30%, and 50% were studied. On the processed samples, static tensile tests at ambient temperature were performed. Transformation of the engineering [...] Read more.

In the present investigation, stress–strain curves and strain hardening rates on samples rolled at ambient temperature with thickness reductions of 0%, 10%, 30%, and 50% were studied. On the processed samples, static tensile tests at ambient temperature were performed. Transformation of the engineering stress–strain curves to true stress–strain curves and their numerical processing by first derivation (θ = dσ/dε) was carried out. Dependencies θ = f(ε_T) characterizing the strain hardening rates were derived. From the curves and the true stress–strain and strain hardening rates, the three stages describing different rates of strain hardening were identified. A rapid increase in true stress and a rapid decrease in the strain hardening rate in Stage I were observed. Quasi-linear dependencies with an increase in true stress but with a slow, gradual decline in the strain hardening rate in Stage II were obtained. Slowly increasing true strains, accompanied by a decrease in strain hardening rates and their transition to softening, led to the formation of plastic instability and necking in Stage III. The endpoints of the strain hardening rate depending on the cold rolling deformations lie in the following intervals: θ_{Stage I} ∈ <1904;3032> MPa, θ_{Stage II} ∈ <906;−873> MPa, θ_{Stage III} ∈ <−144;−11,979> MPa. While in Stage I and Stage II, the plastic deformation mechanism is predominantly dislocation slip, in Stage III, the plastic deformation mechanism is twinning accompanied by dislocation slip. Full article

(This article belongs to the Special Issue Numerical Simulation and Experimental Research of Metal Rolling)

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Metals, Volume 15, Issue 10 (October 2025) – 16 articles

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