Search Results (52)

Understanding the limitations of cold-formed aluminum alloys in practice applications is essential, particularly due to the risk of substructural changes and a reduction in strength when exposed to elevated temperatures. In this study, the thermal stability of the ultra-fine-grained (UFG) structure formed by equal channel angular pressing (ECAP) at room temperature and the mechanical properties of the AlSi7MgCu0.5 alloy were investigated. Prior to ECAP, the plasticity of the as-cast alloy was enhanced by a heat treatment consisting of solution annealing, quenching, and artificial aging to achieve an overaged state. Four repetitive passes via ECAP route A resulted in the homogenization of eutectic Si particles within the α-solid solution, the formation of ultra-fine grains and/or subgrains with high dislocation density, and a significant improvement in alloy strength due to strain hardening. The main objective of this work was to assess the microstructural and mechanical stability of the alloy after post-ECAP annealing in the temperature range of 373–573 K. The UFG microstructure was found to be thermally stable up to 523 K, above which notable grain and/or subgrain coarsening occurred as a result of discontinuous recrystallization of the solid solution. Mechanical properties remained stable up to 423 K; above this temperature, a considerable decrease in strength and a simultaneous increase in ductility were observed. Synchrotron radiation X-ray diffraction (XRD) was employed to analyze the phase composition and crystallographic characteristics, while transmission electron microscopy (TEM) was used to investigate substructural evolution. Mechanical properties were evaluated through tensile testing, impact toughness testing, and hardness measurements. Full article

Cu-Fe in situ composites often face challenges in achieving high strength during cold rolling due to the inefficient transformation of partial Fe phases into fibrous structures. To uncover the underlying mechanisms, this study systematically investigates the co-deformation behavior of Cu and Fe phases in a Cu-10Fe alloy subjected to cold rolling at various strains. Through microstructure characterization, texture analysis, and mechanical property evaluation, we reveal that the Cu matrix initially accommodates most applied strain (ε_vm < 1.0), forming shear bands, while Fe phases (dendrites and spherical particles) exhibit negligible deformation. At intermediate strains (1.0 < ε_vm < 4.0), Fe phases begin to deform: dendrites elongate along the rolling direction, and spherical particles evolve into tadpole-like morphologies under localized shear. Concurrently, dynamic recrystallization occurs near Fe phases in the Cu matrix, generating ultrafine grains. Under high strains (ε_vm > 4.0), Fe dendrites progressively transform into filaments, whereas spherical Fe particles develop long-tailed tadpole-like structures. Texture evolution indicates that Cu develops a typical copper-type rolling texture, while Fe forms α/γ-fiber textures, albeit with sluggish texture development in Fe. The low efficiency of Fe fiber formation is attributed to the insufficient strength of the Cu matrix and the elongation resistance of spherical Fe particles. To optimize rolled Cu-Fe in situ composites, we propose strengthening the Cu matrix (via alloying/precipitation) and suppressing spherical Fe phases through solidification control. This work provides critical insights into enhancing Fe fiber formation in rolled Cu-Fe systems for high-performance applications. Full article

The present study was performed on real-life I4-aluminum cylinder heads produced industrially by applying the lost foam technique to Al-Si-Mg alloys (356 and 357). This work, in addition, introduces a new Al-Cu alloys coded 220 alloy. The main aim of this study is to analyze the effects of liquid metal treatment on the hardness and tensile properties of such castings. The effects of liquid metal treatment (modification with 200 ppm Sr, grain refining with 150 ppm B and degassing using pure Ar) of the castings produced by the lost foam technique on the tensile strength and hardness properties were evaluated. Hydrogen plays an important role in the formation of porosity. At the same time, the foam mold leaves an impression on the casting surface taking the shape of fine holes. In addition, segregation of hydrogen occurs in front of the solidification front. Thus, the porosity is a combination of hydrogen level and the solidification rate. Gains of 17% and 24% are observed for the hardness and yield strength for alloy 357 compared to alloy 356, caused by the difference in their magnesium (Mg) contents in the sense that, in the T6 heat-treated condition, precipitates in the form of ultra-fine Mg₂Si phase particles are formed. The enhancement in the mechanical properties of the used alloy depends mainly of the volume fraction of the precipitated Mg₂Si particles. The hardness of alloy 220 increases by 18% and the yield strength by 15% compared to that measured for alloy 356. In this case, the hardening phase Al₂Cu is responsible for this increase. Thus, this study demonstrates that liquid metal treatments significantly enhance the hardness and yield strength of Al-Si-Mg and Al-Cu alloys, with the gain attributed to refined microstructures and reduced porosity. Full article

Application of rare earths (RE) as grain refiners is well-known in the technology of aluminum alloys for the automotive industry. In the current study, Al-2.4%Cu-0.4%Mg alloy (coded 220) and Al-7.5%Si-0.35%Mg alloy (coded 356.1), were prepared by melting each alloy in a resistance furnace. Strontium (Sr) was used as a modifier, while titanium boride (TiB₂) was added as a grain refiner. Measured amounts of Ce and La were added to both alloys (max. 1 wt.%). The alloy melts were poured in a preheated metallic mold. The main part of the study was conducted on tensile testing at room temperature. The results show that although RE would cause grain refining to be about 30–40% through the constitutional undercooling mechanism, grain refining with TiB₂ would lead to approximately 90% refining (heterogenous nucleation mechanism). The addition of high purity Ce or La (99.9% purity) has no modification effect regardless of the alloy composition or the concentration of RE. Depending on the alloy ductility, the addition of 0.2 wt.%RE has a hardening effect that causes precipitation of RE in the form of dispersoids (300–700 nm). However, this increase vanishes with the decrease in alloy ductility, i.e., with T6 treatment, due to intensive precipitation of ultra-fine coherent Mg₂Si-phase particles. There is no definite distinction in the behavior of Ce or La in terms of their high affinity to interact with other transition elements in the matrix, particularly Ti, Fe, Cu, and Sr. When the melt was properly degassed using high-purity argon and filtered using a 20 ppi ceramic foam filter, prior to pouring the liquid metal into the mold sprue, no measurable number of RE oxides was observed. In conclusion, the application of RE to aluminum castings would only lead to formation of a significant volume fraction of brittle intermetallics. In Ti-free alloys, identification of Ce- or La-intermetallics is doubtful due to the fairly thin thickness of the precipitated platelets (about 1 µm) and the possibility that most of the reported Al, Si, and other elements make the reported values for RE rather ambiguous. Full article

Commercially pure Cu features excellent electric conductivity but low mechanical properties. In order to improve the mechanical properties of Cu, strengthening elements can be added to prepare alloys or composites featuring enhanced performances. This study focuses on the detailed characterization of the microstructure of a Cu composite strengthened with Al₂O₃ particles during high shear strain processing. The Cu-Al₂O₃ mixture was prepared by powder metallurgy and directly consolidated by the intensive plastic deformation method of hot rotary swaging. Samples cut from the consolidated piece were further processed by the severe plastic deformation method of high pressure torsion (HPT). The primary aim was to investigate the effects of varying degrees of the imposed shear strain, i.e., the number of HPT revolutions, microstructure development (grain size and morphology, texture, grain misorientations, etc.) of the consolidated composite; the microstructure observations were supplemented with measurements of Vickers microhardness. The results showed that the added oxide particles effectively hindered the movement of dislocations and aggravated grain fragmentation, which also led to the relatively high presence of grain misorientations pointing to the occurrence of residual stress within the microstructure. The high shear strain imposed into (the peripheral region of) the sample subjected to four HPT revolutions imparted equiaxed ultra-fine grains and an average Vickers microhardness of more than 130 HV0.1. Full article

Ultrafine copper powders were prepared by the air-jet milling of copper oxide (CuO) powders and a subsequent hydrogen (H₂) reduction. After milling, the particle size and grain size of CuO powders decreased, while the specific surface area and structural microstrain increased, thereby improving the reaction activity. In a pure H₂ atmosphere, the process of CuO reduction was conducted in one step, and followed a pseudo-first-order kinetics model. The smaller CuO powders after milling exhibited higher reduction rates and lower activation energies compared with those without milling. Based on the unreacted shrinking core model, the reduction of CuO powders via H₂ was controlled by the interface reaction at the early stage, whereas the latter was limited by the diffusion of H₂ through the solid product layer. Additionally, the scanning electron microscopy (SEM) indicated that copper powders after H₂ reduction presented a spherical-like shape, and the sintering and agglomeration between particles occurred after 300 °C, which led to a moderate increase in particle size. The preparing parameters (at 400 °C for 180 min) were preferred to obtain ultrafine copper powders with an average particle size in the range of 5.43–6.72 μm and an oxygen content of less than 0.2 wt.%. Full article

The corrosion properties of an EN AC AlSi9Cu3(Fe) alloy (reference sample (RS)) and samples produced by recycling chips of RS by direct hot extrusion (DHES) and subsequent thixoforming (TFS) were tested in 0.5 M NaCl solution. The plastic deformation changes the microstructure of RS, and brittle, coarse Si particles and intermetallic compounds (IMCs) were effectively broken into ultrafine-grained particles and redistributed homogeneously into the α-Al matrix in DHES. TFS exhibits a globular structure, and polyhedral clusters rich in Si and IMCs were observed along the grain boundary. Electrochemical measurements combined with surface characterisation show that the microstructure significantly influences the tested samples’ corrosive properties. It was confirmed that corrosion resistance increased in the following order: RS < TFS < DHES. Similarly, the corrosion potential becomes nobler, the corrosion current decreases, the passive area increases, and the oxide layer becomes more stable (higher resistance and thickness). Also, the percentage of the surface affected by corrosion and the volume of pits reduce. The effect of microstructure is particularly pronounced in the level of the corrosion current and the volume of pits formed. The corrosion current of DHES and TFS decreases by 4–5 times, while the pit volume of DHES and TFS decreases by several orders of magnitude compared to RS. The corrosion stability of DHES and TFS in relation to RS is a consequence of the comminution of the Si particles and the IMC. The refined and homogeneous microstructure contributes positively to forming a stable oxide film on DHES and TFS and increases their corrosion resistance in an aggressive environment. The applied recycling method represents an innovative and sustainable process for the recycling of semisolid materials, with lower energy consumption and less greenhouse gas emissions compared to conventional recycling. The fact that the products obtained through recycling have a significantly higher corrosion resistance further increases the economic and environmental impact of the process. Full article

In this work, to explore potential substitutions for the Co binder phase, ultrafine-grain WC-based cermets with various binder phases of Co, Ni and AlCoCrNiFeCu HEA were prepared using the SPS method. Based on SPS, WC-based cermets were fabricated at higher speed, showing fine carbide particles less than 410 μm. The microstructure, mechanical properties and wear properties were systematically evaluated. By comparison, the grain size of WC was the lowest for WC-10Co, while WC-10 HEA cermet held the coarsest WC particles. The hardness and fracture toughness of WC-10 HEA were the best among all three samples, with values of 93.2 HRA and 11.3 MP·m^1/2. However, the bending strength of WC-10HEA was about 56.1% lower than that of WC-10Co, with a value of 1349.6 MPa. The reduction in bending strength is attributed to the lower density, formation of a newly Cr-Al rich phase and coarser WC grains. In dry sliding wear conditions, WC-10 HEA showed the lowest wear rate (0.98 × 10⁻⁶ mm³/(N·m)) and coefficient of friction (0.19), indicating the best wear resistance performance. This reveals that WC-based cermet with a HEA binder phase has superior wear performance due to the higher hardness and good self-lubricating effect of the wear products. Full article

A theoretical model is suggested that describes the effect of deformation temperature on the yield stress of an ultrafine-grained (UFG) Al-Cu-Zr alloy structured with severe plastic deformation. Within the model, nanoprecipitates (NPs) of Al₂Cu act as sources of lattice dislocations in the presence of a number of extrinsic grain-boundary dislocations (EGBDs) near the NPs. It is shown that the number of EGBDs near the NPs decreases with a drop in the deformation temperature that increases the yield stress of the Al-Cu-Zr alloy. The proposed model is in good quantitative agreement with available experimental results. Full article

In this study, Cu-10 wt% Fe alloy in as-cast state was modified using friction stir processing (FSP). The microstructure evolution of Cu-10 wt% Fe alloys in different states was characterized in detail using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that due to dynamic recrystallization, the FSPed Cu-10 wt% Fe alloy obtained a uniformly equiaxed ultrafine microstructure with low density of dislocation, high proportion of high-angle grain boundaries (HAGBs), and high degree of recrystallization. Fine equiaxed grains with an average size of 0.6 μm were produced after FSP. Many fine-precipitate Fe-phases with an average size of 20 nm were uniformly distributed in the Cu matrix. The FSPed samples possessed excellent mechanical properties, such as high Vickers hardness (163.5 HV), ultimate tensile strength (538.5 MPa), and good elongation (16%). This single-pass FSP method does not require subsequent aging treatment and provides a simple and efficient way to improve the properties of Cu-Fe alloys. Full article

The research presented in this paper focused on optimising the process of unconventional plastic forming by hydrostatic extrusion (HE) with post-processing heat treatment of a copper alloy (CuCrZr) for electro-discharge machining (EDM) applications. The treatment was carried out in such a way as to obtain a material with an improved microstructure, characterised by a significant increase in hardness and strength while maintaining a high electrical conductivity, thus achieving the main goal of reducing electrode wear in the EDM process. As part of the research, a material with an ultrafine-grained structure was obtained with an average grain size of d₂ = 320 nm and a much higher strength of UTS = 645 MPa compared to the material in the initial state (UTS = 413 MPa). The post-processing treatment (ageing) allowed us to obtain a material with a high electrical conductivity after the HE process, at 78% IACS. The electrodes made of CuCrZr subjected to HE had a reduced electrical discharge wear in relation to electrodes made of the initial material. The best results were obtained for electrodes made of the material subjected to a five-stage HE process combined with ageing at 480 °C for 1 h. The electrical discharge wear in these electrodes was reduced by more than 50% compared to electrodes made of non-deformed copper. Full article

This paper studies the feasibility of fabricating pseudo-alloys based on a W-Cu system through vacuum sintering of spherical bimetallic particles synthesized using the electric explosion of copper–tungsten wires in argon. The effects of the sintering temperature on the structure and hardness of the fabricated composites was studied. In terms of the structure of the samples, tungsten particles of predominantly spherical shapes with sizes ranging from submicrons to 80–90 µm were uniformly distributed throughout the copper matrix. Based on the analysis, the volume fractions of tungsten and copper were approximately equal. The calculated average phase compositions for all the samples were 58.9 wt% for W, 27.3 wt% for Cu, and 13.8 wt% WO₂. When the annealing temperature increased from 1100 °C to 1250 °C, the wetting of tungsten by molten copper improved, which resulted in the porosity of the copper matrix being at the minimum, as observed in the contact zone. Due to good wetting and a decrease in the viscosity of copper, rearrangement of the solid phase of the tungsten in the bulk of the composites improved, and the density and hardness of the pseudo-alloy increased. The formation of coarse tungsten grains is caused by the fact that submicron and micron particles are growing in size and merging into agglomerates during the course of liquid-phase sintering, and this happens because of the high surface activity of ultrafine particles. Further research will be devoted to solving the discovered problems. Full article

This paper studies the effect of the laser melting process (LMP) on the microstructure and hardness of a new modified AlCuMgMn alloy with zirconium (Zr) and Yttrium (Y) elements. Homogenized (480 °C/8 h) alloys were laser-surface-treated at room temperature and a heating platform with in situ heating conditions was used in order to control the formed microstructure by decreasing the solidification rate in the laser-melted zone (LMZ). Modifying the AlCuMgMn alloy with 0.4 wt% Zr and 0.6 wt% Y led to a decrease in grain size by 25% with a uniform grain size distribution in the as-cast state due to the formation of Al₃(Y, Zr). The homogenization dissolved the nonequilibrium intermetallic phases into the (Al) matrix and spheroidized and fragmentized the equilibrium phase’s particles, which led to the solidification of the crack-free LM zone with a nonuniform grain structure. The microstructure in the LMZ was improved by using the in situ heating approach, which decreased the temperature gradient between the BM and the melt pool. Two different microstructures were observed: ultrafine grains at the boundaries of the melted pool due to the extremely high concentration of optimally sized Al₃(Y, Zr) and fine equiaxed grains at the center of the LMZ. The combination of the presence of ZrY and applying a heating platform during the LMP increased the hardness of the LMZ by 1.14 times more than the hardness of the LMZ of the cast AlCuMgMn alloy. Full article

Applications of Copper (Cu) range from small scale applications such as microelectronics interconnects to very large high-powered applications such as railguns. In all these applications, Cu conductivity and ampacity play vital roles. In some applications such as railguns, where Cu also plays a structural role, not only is high conductivity needed, but high strength, high ductility, and high wear resistance are also critical. Current technologies have achieved their full potential for producing better materials. New approaches and technologies are needed to develop superior properties. This research examines a new fabrication approach that is expected to produce Cu with superior mechanical strength, enhanced wear resistance, and increased electrical conductivity. Materials with refined grain structures were obtained by breaking down the coarse-grained Cu particles via cryogenic ball milling, followed by the consolidation of powders using cold isostatic pressing (CIP) and subsequent Continuous Equal Channel Angular Pressing (C-ECAP). The mixture of fine and ultrafine grains, with sizes between 200 nm to 2.5 µm and an average of 500 nm, was formed after ball milling at cryogenic temperatures. Further processing via C-ECAP produced nanostructured Cu with average grain sizes below 50 nm and excellent homogenous equiaxed grain shapes and random orientations. The hardness and tensile strength of the final Cu were approximately 158% and 95% higher than the traditional coarse-grained Cu bar, respectively. This material also displayed a good electrical conductivity rate of 74% International Annealed Copper Standard (IACS), which is comparable to the current Cu materials used in railgun applications. Full article

Designing a composite, possibly strengthened by a dispersion of (fine) oxides, is a favorable way to improve the mechanical characteristics of Cu while maintaining its advantageous electric conductivity. The aim of this study was to perform mechanical alloying of a Cu powder with a powder of Al₂O₃ oxide, seal the powder mixture into evacuated Cu tubular containers, i.e., cans, and apply gradual direct consolidation via rotary swaging at elevated temperatures, as well as at room temperature (final passes) to find the most convenient way to produce the designed Al₂O₃ particle-strengthened Cu composite. The composites swaged with the total swaging degree of 1.83 to consolidated rods with a diameter of 10 mm were subjected to measurements of electroconductivity, investigations of mechanical behavior via compression testing, and detailed microstructure observations. The results revealed that the applied swaging degree was sufficient to fully consolidate the canned powders, even at moderate and ambient temperatures. In other words, the final structures, featuring ultra-fine grains, did not exhibit voids or remnants of unconsolidated powder particles. The swaged composites featured favorable plasticity regardless of the selected processing route. The flow stress curves exhibited the establishment of steady states with increasing strain, regardless of the applied strain rate. The electroconductivity of the composite swaged at elevated temperatures, featuring homogeneous distribution of strengthening oxide particles and the average grain size of 1.8 µm², reaching 80% IACS (International Annealed Copper Standard). Full article