Engineering

Abstract: A study was conducted to characterize the performance of a HydroFloat® coarse particle flotation (CPF) cell using rougher tailings samples from an industrial copper mining operation. The work involved measuring internal hydrodynamic variables under a wide range of operating conditions. The effect of different operational and hydrodynamic conditions on the metallurgical performance of the HydroFloat® cell was also evaluated. Gas dispersion measurements, such as bubble size distribution, superficial gas velocity (J$_g$), superficial area flux (Sb), and residence time distribution (RTD), were recorded, enabling a detailed analysis of the cell's operation. Results show that copper recovery is strongly influenced by the superficial gas velocity (J$_g$) and the superficial liquid velocity (J$_l$). It was observed that the bubble diameter (d$_{32}$) remained relatively constant at 0.5 mm across all operating conditions, which is well below typical bubble sizes for conventional flotation cells. This suggests that contrary to what may be expected, in this kind of machine, small bubbles are able to float coarse particles. Bubble image inspection suggests that the HydroFloat{\textregistered} cell creates conditions conducive to bubble-particle aggregates, which would explain how small bubbles can float coarse particles. This study contributes to the understanding of CPF and establishes a framework for optimization in copper concentrators.

Abstract: One of the most common ways to improve the properties of aluminum casting alloys is through their modification. This study investigates the influence of titanium modification on the mechanical properties of Al-Si casting alloys. In this research, the Al-Si alloy which is widely used in the foundry industry, was selected as an object. The samples were liquefied in an induction furnace, and the liquid alloy was poured into sand-clay molds. The casting temperature was 750 °C. The titanium element was added to the liquid Al-Si foundry alloy in special packaging in the form of a powder from 0.1% to 0.3% of the charge and in the form of Al-10Ti master alloy from 0.1% to 0.2%. Then, samples were machined to prepare further investigations. During the research, mechanical properties including hardness and wear resistance analysis were conducted. Moreover, X-ray diffraction and microstructural analysis of the Ti modified Al-Si samples were carried out. Experimental results showed that the addition of titanium improved the mechanical properties of the samples. That is, the highest hardness was obtained at 0.1 wt.% Ti modified Al–10Ti master alloy, while titanium powder resulted in a more gradual increase in hardness. According to the wear resistance evaluations, addition of titanium within the range of 0.1–0.2 wt.% content was performed an optimal result. After, microstructural analysis, it is found that titanium promoted grain refinement and improved structural homogeneity, especially it is added in the form of Al-10Ti master alloy. The introduction of titanium into the aluminum alloy led to the formation of the Al₃Ti intermetallic compound, which contributed to the improvement of mechanical properties. These results demonstrate that the modification of Al–Si alloys with titanium can be reliably used to predict and improve mechanical properties based on comprehensive experimental analysis.

Abstract: During the continuous casting of high-titanium steel, traditional fluorine-containing mold fluxes are prone to causing fluoride contamination, equipment corrosion, and intensified slag-metal interface reactions. There is an urgent need to develop highly adaptable fluorine-free mold flux systems. In this study, titanium-containing blast furnace slag was used as the primary base material, while borax, soda ash, and witherite were selected as fluoride-substituting mineral raw materials. The effects of these mineral raw materials on the melting properties, crystallization behavior, crystalline phases, and microstructure of fluorine-free mold fluxes were systematically investigated, and an optimized mold flux design suitable for continuous casting of high-titanium steel was further developed. The results indicate that borax significantly reduces the melting temperature and viscosity and markedly suppresses the growth of crystalline phases such as calcium borosilicate, nepheline, and perovskite by weakening the polymerization degree of the silicate network, thereby substantially decreasing the crystallization ability of the mold flux. Soda ash primarily acts as a strong fluxing and network-depolymerizing agent, promoting the formation of low-polymerized structural units. It also enhances the tendency toward ordered atomic arrangement, thereby markedly increasing nepheline precipitation and the overall crystallization ratio. Witherite exerts a relatively mild effect on slag structure and phase evolution; its moderate addition helps synergistically reduce the melting point, viscosity, and crystallization ratio, thereby supporting performance stability. The optimized fluorine-free mold flux, designed on the basis of these findings, maintains a suitable initial crystallization temperature and critical crystallization cooling rate while exhibiting lower melting temperature, viscosity, and crystallization ratio than conventional fluorine-bearing flux. Moreover, the introduction of TiO2 reduces the chemical potential difference between Ti in the molten steel and the fluorine-free mold flux, thereby slowing down the rate of slag-metal interface reactions and improving compositional stability. The research results provide a theoretical basis for the industrial design of environmentally friendly mold fluxes for high-titanium steel and for improving billet quality.

Abstract: The escalating demand for sustainable metallurgical practices necessitates innovative approaches to manganese production. The smelting-aluminothermic reduction of hydrogen pre-reduced manganese ores in a direct current (DC) arc furnace offers a resilient and sustainable trajectory for optimizing manganese recovery efficiencies while minimizing waste generation under low-carbon operating conditions. This study presents a comparative of smelting-aluminothermic reduction of two Mn ores pre-reduced with hydrogen using two distinct approaches, namely, a packed-bed vertical retort and a plasma rotary furnace. A 200 kW DC arc furnace was used for smelting. The scope of this assessment integrates technical, environmental and operational metrics of smelting-aluminothermic reduction. For energy, the considered metrics are power stability metrics, specific energy requirement, furnace thermal efficiency and load factor/power-on time. The metrics considered for material are reductant efficiency, elemental accountability, elemental recovery, elemental deportment and slag-to-metal ratio. For process sustainability, refractory and electrode consumption were considered. The environmental indicators considered includes CO2-equivalent emissions per ton of product, dust and particulate emissions, NOx/SOx emissions. This research provides critical insights into the viability and environmental advantages of hydrogen pre-reduction coupled with smelting-aluminothermic reduction for cleaner manganese production.

Abstract: Mechanical locks were not quickly supplanted by electric locks. They are still being researched and improved, along with advanced electronic methods of attack. Reading pin lengths by detecting their natural frequencies (lock decoding) to forge a copy of the legitimate key can be done quickly using ultrasonic detectors, active or passive. Hence, advanced methods of defence must be further researched. One method is to make the lock’s pins out of functionally graded materials (FGM). A pin’s natural frequency (in the range 100 kHz-1 MHz) and hence its ultrasonic pulse transit/reflection time can be correlated to its length if it is made of a homogeneous material. The idea is to design pins made of functionally graded alloys, to achieve equal natural frequencies, but also desired positions of standing wave nodes regardless of the pin’s length. Mathematical models of pins vibrations must be devised first to enable calculations of FGM alloys composition. Two simple and fast mathematical models are first derived from finite-element model (FEM) of a pin. These models are used in an optimization procedure based on the Nelder-Mead simplex method to calculate optimal profiles of Young’s modulus and density along the pin’s longitudinal axis. A successful optimization procedure for 10 key pin lengths is performed, to make a pin-tumbler lock resistant to ultrasonic attacks.

Abstract: Grey cast iron brake discs remain standard in automotive braking systems due to their favorable thermal conductivity and mechanical strength. However, increasingly stringent environmental regulations, including Euro 7, necessitate enhanced surface durability to reduce particulate emissions and mitigate corrosion‑related degradation. In this context, Laser Metal Deposition (LMD) offers a promising route to engineer wear‑resistant coating systems with tailored microstructures. This study investigates phase formation and microstructural evolution in a 316L/430L‑WC multilayer coating deposited on grey cast iron (GJL) brake discs and subjected to brake‑shock testing to replicate thermomechanical load cycles representative of real braking conditions. X‑ray diffraction (XRD) performed on the interlayer region between the 316L and 430L‑WC layers revealed clear evidence of σ‑phase formation, indicating intermetallic transformations facilitated by thermal cycling. Microstructural characterization using scanning electron microscopy (SEM) and energy‑dispersive spectroscopy (EDS) identified localized enrichment of Cr‑ and Fe‑rich regions that support the XRD‑based interpretation of σ‑phase development. These results provide insights into phase transformations and elemental diffusion in LMD‑fabricated brake‑disc coatings. The findings advance the understanding of thermally induced transformations in multilayer steel systems and support the optimization of LMD coatings for high‑temperature and wear‑intensive applications through advanced analytical evaluation.

Abstract: The optimization and the engineering development of AM products both require ac-curate, non-destructive techniques to extract their mechanical performances. The In-strumented Indentation Test (IIT) has such a potential, although it currently lacks standard procedures that are suitable for analyzing materials which are affected by internal residual stress (RS). Additionally, nanoindentation testing suffers from the presence of indentation size effects (ISE), which hamper the possibility of correlating the measured mechanical performance at different indentation depths or peak loads. This paper presents a novel IIT methodology that is based on new indentation param-eters which are then used to assign the desired mechanical performances of an L-PBF 316L SS alloy obtained via multi-load nano- and macro-IITs. It has been proved that the new indentation parameters can be successfully correlated across different dimen-sional scales, i.e., from the nanoscale to the macroscale. The secant loading stiffness versus depth plot can be used to assess the susceptibility of RS to relax during indenta-tion, which is an important performance factor for the engineering design of AM components. The successful correlation that has been found between EBSD analysis (in terms of crystal anisotropy, grain size and GND density) and nanoindentation testing at three subregions of the core zone of the investigated deposit confirms the validity of the proposed methodology for the full determination of the 3Ps, that is, process, properties, and performance of advanced AM products.

Abstract: In hybrid Wire Arc Additive Manufacturing with interlayer Friction Stir Processing (UAMFSP), refined microstructures are produced in aluminum alloy builds; however, the thermal parameters governing layer-resolved defect evolution remain poorly understood. In this study, a first mechanistic framework is presented, identifying post-peak cooling rate as a governing parameter for porosity evolution in UAMFSP Al 4043 three-layer walls. In this study, a comprehensive multi-scale characterization of three-layer Al 4043 UAMFSP walls is presented, employing infrared thermography, quantitative optical grain morphology analysis (N = 10,346 grains, Layers 1–3), scanning electron microscopy from 250× to 35,000×, and image-based porosity quantification from calibrated SEM fields. A counterintuitive layer-dependent porosity gradient is reported, wherein the upper layer (L3) exhibited 80% higher porosity (2.90 ± 1.18%) and 107% higher pore density (4,283 ± 900 pores/mm²) than the bottom layer (L1), despite recording a 26% lower peak FSP surface temperature (195.1 vs. 263.2°C) (n = 3 fields per layer; Cohen’s d ≈1.7). Based on these results, the post-peak cooling rate, rather than peak temperature, is identified as a dominant controlling parameter for void consolidation quality, as evidenced by the observation that L3 cools at −12.3 °C/s versus −16.2 °C/s for L1, which is consistent with prolonged high-temperature dwell and reduced plastic-flow-assisted pore closure in the upper layer. It should be noted that the anomalously rapid cooling of L2 (−46.9 °C/s), attributed to a bilateral thermal gradient between the substrate and the air-cooled free surface, places it in a thermally distinct regime; accordingly, L2 is utilized exclusively for high-magnification SEM characterization in this study. High-magnification SEM imaging (12,000×–35,000×) revealed a frequent spatial co-location of sub-micron pores with fragmented Al–Si eutectic particles, which is consistent with preferential void persistence near particle–matrix interfaces. Furthermore, grain morphology exhibited evolve non-monotonically with build height, with mean circularity following the order L3 (0.645) > L1 (0.621) > L2 (0.569), and the equiaxed grain fraction ranging from 25.5% (L2) to 36.1% (L3) (ANOVA: F = 56.2, p = 5.15 × 10⁻²⁵), while the mean equivalent grain diameter remained below 3.4 μm across all layers. In summary, the outcomes of this study establish post-peak cooling rate, rather than peak temperature, as a governing parameter for void consolidation quality in UAMFSP builds. These outcomes are presented as a first mechanistic framework for this class of hybrid process, and are intended to motivate targeted controlled experiments, subsurface thermal characterization, and expanded porosity sampling in future investigations of multi-layer additive–deformation manufacturing of Al-based alloys.

Abstract: This study presents a comprehensive characterization of recycled aluminum briquettes produced by cold pressing of Al–Si–Mg alloy machining chips, along with an evaluation of their behavior during subsequent remelting. The objective was to assess the density, porosity, chemical composition, and metallurgical yield of the briquettes before and after melting, as well as to determine their suitability for use as deoxidizing additives in steelmaking. The cold-pressed briquette (Sample A) exhibited a low density of 2.29 g.cm-³ and a porosity of 12.1%, resulting from intergranular voids and residual lubricants. After melting and resolidification (Sample B), the density increased to 2.388 g.cm-3 and the porosity decreased to 8.15%. XRF chemical analysis confirmed a high degree of elemental homogeneity after melting with no indication of segregation, while SEM–EDS microstructural analysis verified the absence of significant intermetallic phases and revealed only a thin surface oxide layer. The metallurgical yield reached 94.2% with a low dross content (2.25%). The results demonstrate that, following appropriate preprocessing and optimized compaction, recycled aluminum briquettes constitute a stable and efficient secondary aluminum material suitable for steel deoxidation, and they can significantly reduce the environmental impact of metallurgical production.

Abstract: High Velocity Oxy-Fuel (HVOF) thermal spraying is widely used for the deposition of dense coatings with low porosity, high hardness, and superior fracture resistance. Tungsten carbide–cobalt (WC–Co) coatings are extensively employed in industrial and aerospace applications due to their excellent wear resistance and mechanical performance; however, further improvement in crack resistance and adhesion remains a key challenge. In this study, WC–Co+Ni composite coatings were deposited on ductile cast iron by HVOF, with particular emphasis on the role of Ni particle addition in tailoring coating microstructure and performance. Microstructural characterization was carried out using light, scanning, and transmission electron microscopy (LM, SEM, TEM), while phase composition and chemical analysis were determined by X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). The coatings exhibited a dense, low-porosity microstructure composed of partially molten Ni particles and fine WC and W₂C carbides embedded in a cobalt-based matrix, with locally nanocrystalline features. XRD analysis confirmed WC and W₂C as the dominant phases, with weak reflections indicating the possible formation of the η-phase (Co₆W₆C). Mechanical and tribological performance, evaluated by instrumented indentation and scratch testing, showed that Ni addition significantly enhances crack resistance, wear resistance, and coating–substrate adhesion. The results demonstrate that Ni-modified WC–Co coatings deposited by HVOF enable effective microstructural design, leading to improved durability and performance, which makes them promising candidates for advanced coating applications.

Abstract: Rapid solidification by melt‑spinning produces aluminum alloys with extremely refined microstructures but also introduces strong structural gradients across the ribbon thickness. In this work, the microstructural evolution of a rapidly solidified Al‑Cu‑Li‑Mg‑Sc‑Zr alloy was investigated during model homogenization using in‑situ STEM heating experiments and correlated with bulk electrical‑resistivity measurements. The as‑cast ribbons exhibit two distinct solidification zones: a near‑contact region consisting of columnar cells containing fine Cu‑rich spherical precipitates, and a central region composed of larger eutectic cells enriched in Al₂Cu and Al₇Cu₂Fe phases. Stepwise in‑situ annealing between 200 °C and 550 °C reveals a sequence of transformations, including matrix depletion due to precipitation of strengthening phases, coarsening and dissolution of primary phases, and the formation of Al₃(Sc,Zr) dispersoids. Above 500 °C, rapid dissolution of primary phases followed by their coagulation into a limited number of stable grain‑boundary particles eliminates the original two‑zone structure and results in a fully homogenized ribbon. Ex‑situ annealing confirms that the resulting microstructure is uniform across the ribbon thickness and enables consistent precipitation strengthening during artificial aging. Microhardness measurements from both ribbon surfaces reveal identical peak‑aged hardness, validating the effectiveness of the short‑time homogenization strategy for rapidly solidified Al‑Cu‑Li‑Mg-based alloys.

Abstract: This study explores the optimized extraction of platinum group metals (PGMs), particularly platinum (Pt) and palladium (Pd), along with associated base metals (Ni, Cu, Zn, and Pb) from UG2 ore. An integrated approach combining advanced mineral characterization and statistical optimization via Response Surface Methodology (RSM) was employed. X-ray fluorescence (XRF) revealed metal contents: Ni (0.28%), Cu (0.04%), Zn (0.04%), Pb (0.06%), and major gangue components Si (17.65%), Fe (13.33%), and Cr (7.37%). Complementary X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed mineral composition and textures favourable for flotation, while inductively coupled plasma optical emission spectroscopy (ICP-OES) indicated 0.05 g/t Au, 1.18 g/t Pt, and 1.41 g/t Pd in the run-of-mine sample. Optimization through a central composite design (CCD) identified ideal flotation conditions: collector dosages of 200 - 900 g/t, depressant dosages of 400 - 900g/t pulp pH of 8.5 to 9.5, and flotation time of approximately 10 minutes. Recoveries ranged from 6.8- 23.91% (Ni), 3.45- 100% (Cu), 9.46-100% (Zn), and averaged 80.10% (Pb). Post- flotation ICP-OES analysis demonstrated significant enrichment of PGMs, with Pt ranging between 12.01 to 16.51 mg/kg, Pd between 11.57 to 15.09 mg/kg, and gold peaking at 0.47 mg/kg for optimal runs. These findings highlight the effectiveness of integrating characterization techniques with statistical design to enhance PGM and associated base metals recovery, offering tailored solutions for improved economic viability and resource efficiency.

Abstract: Achieving high density in complex powder metallurgy components like spur gears is often hindered by friction-induced density gradients and ejection defects. This study investigates a novel elastic die system designed to mitigate these issues through controlled radial deformation. Spur gears were compacted using Ancorsteel 2000 powder under pressures of 400–700 MPa, utilizing a tapered elastic sleeve to apply radial compression. Green and sintered densities were measured, while porosity distribution was quantified via image analysis. Additionally, a 3D finite element simulation using FORGE software was conducted to model the thermo-mechanical behavior and stress distribution during the process. Experimental trials demonstrated that the elastic relaxation of the sleeve enabled free ejection of the compacts without requiring extraction force. Image analysis confirmed a homogenous porosity distribution across the gear teeth, and higher die pre-stressing strokes were found to correlate with increased sintered density. Finite element modeling accurately predicted critical stress concentrations of 700 MPa at the die-sleeve interface and validated the strain distribution. The results confirm that elastic die technology effectively eliminates ejection friction and improves density uniformity in complex gears, offering a viable solution for reducing tool wear and manufacturing defects in high-precision powder metallurgy.

Abstract: Despite the development of the new, modern non-metallic materials, the steel materials are largely used in various branches of industry, while in some applications they are still irreplaceable. It is expected that such a trend will remain for certain number of years. This is why the necessity is present for development of the new types of steels, which would possess even better properties. The Chromium-Molybdenum (Cr-Mo) steels, with high vanadium content, belong to the group of newer steels characterized by high values of hardness and toughness. In this research, the tests were performed on samples made from the X180CrMo12-1 steel with varying percentage of vanadium within the limits of 0.5-3%. Vanadium, as a carbide-forming alloying element, creates a carbide network of the M7C3 type around the metal matrix, and finely dispersed carbides of the V6C5 type within the metal matrix. This research was focused on determining the carbides’ composition, observing the shape of metal grains and carbide network, testing the material’s resistance to friction and wear, including the electrochemical characterization, as well. The objective was to determine the carbides microstructure and morphology, as well as to evaluate their impact on the material's characteristics. The experimental investigation was performed using the scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) and X-ray diffractometric analysis (XRD). Examination of the carbide composition confirmed that it was the M7C3 carbide.

Abstract: Softening behavior in the heat-affected zone (HAZ) of two X80 pipeline girth welds with different base metal microstructure, i.e. acicular ferrite (AF) dominated (X80-AF) and granular bainite (GB) dominated (X80-GB), were investigated in the present study. Hardness tests, transmission electron microscope (TEM), and electron backscattered diffraction (EBSD) were employed to analyze the softening behavior and corresponding microstructural evolution in the HAZ. The results indicated that softening in the HAZ of two girth welds primarily occurred in the fine-grained (FG) HAZ, while hardening was found in the coarse-grained (CG) HAZ. Due to its high dislocation density and refined interlocking structure, AF could effectively inhibit phase transformation and grain growth during reheating which resulted in smaller grains and lower softening rate in the FGHAZ. In contrast, coarse GB in the base metal was more prone to grain coarsening and hence engendered more pronounced softening. Therefore, for the microstructural design of high strength pipeline steels, increasing the proportion of refined AF is beneficial to the softening resistance and thereby elevates the service safety of pipelines.

Abstract: Copper-containing steel is widely used in ship plates and other marine engineering fields due to its excellent mechanical properties and good weldability. However, in hydrogen-containing media environments, ship plate steel is prone to hydrogen embrittlement during service. Existing research primarily focuses on steel grades with copper content below 3 wt.%, while the diffusion and trapping behavior of hydrogen in ultra-high copper steel with copper content exceeding 3 wt.% remains unclear. Therefore, this study designed an ultra-high copper content steel with a copper content of 6.01%, and investigated the diffusion behavior of hydrogen in the test steel under different hydrogen charging current densities through microstructure characterization, slow strain rate tensile testing, electrochemical hydrogen permeation, and internal friction tests. The results indicate that with an increase in hydrogen charging current density, the anti hydrogen embrittlement performance of the test steel is significantly improved without deteriorating its mechanical properties. At the same time, the hydrogen trap density increased by 167%, with the irreversible hydrogen trap density increasing by 76.3%, and the reversible hydrogen trap density increased significantly by 537.9%. A large number of microstructures, such as phase boundaries, grain boundaries, and dislocations, have formed inside the material, which have reversible trapping effects on hydrogen, effectively suppressing the migration of hydrogen in the crystal structure and reducing the embrittlement phenomenon caused by hydrogen. This study expands the application potential of copper containing steel in the field of ocean engineering, providing important reference for the future development of high-strength hydrogen embrittlement resistant copper steel with ultra-high copper content.

Abstract: The effect of a pre-nitriding treatment, applied prior to vacuum carburizing, on the carburizing efficiency of 20CrMnTi steel is investigated. The results demonstrate that pre-nitriding significantly enhances the vacuum carburizing efficiency of 20CrMnTi steel, refines the martensitic microstructure of the carburized layer, and promotes carbide precipitation. At the same carburized layer depth, the hardness and carbon content of the pre-nitriding samples are markedly higher than those of the without pre-nitriding samples. Specifically, the effective hardened depth and the surface hardness increase by approximately 0.15 mm and 75 HV500gf, respectively. These improvements are attributed to the formation of loose, porous nano-sized nitride particles on the surface during the pre-nitriding process, which substantially increases the surface roughness and pore volume. This surface morphology facilitates the adsorption and inward diffusion of carbon atoms during carburizing, and the presence of nitrogen in solid solution further enhances carbon diffusion.

Abstract:

Ti alloys are widely used in several fields, such as aerospace and biomedical, due to their high mechanical properties under severe loading conditions. Recently, the interest in these materials produced by additive manufacturing process has increased, but intensive research should be done to better characterise their properties. This work aims to study and compare the effect of surface properties, internal defects, microstructure, hardness and Hot Isostatic Pressing (HIP) treatment or in-Vacuum Heat Treatment (VHT) on fatigue properties of a Ti6Al4V produced by Selective Laser Melting (SLM) and Electron Beam Melting (EBM) additive manufacturing technologies. The samples were fully characterised using a wide range of techniques, in terms of microstructure (optical microscopy and SEM), mechanical properties (hardness mapping) and surface texture (confocal microscopy). The internal defects were evaluated using an image-based analysis approach. The uniaxial fatigue endurance limit properties were determined by a Dixon-Mood staircase approach and the failed samples near the fatigue limit were characterised by fracture surface and defect area analysis. A study of the applied load on the flaw areas was carried out to unveil the root causes of fatigue failure. The results showed that the fatigue properties of the as-printed samples were mainly determined by the surface roughness, whereas in the machined samples the internal defect dimension ruled the fatigue resistance of the material. The HIP used as a post-printing treatment is effective in substantially reducing the presence of internal pores, although local microstructural changes can take place only in the case of smooth surface. In conclusion, when properly developed in their melted parameters, both EBM and SLM technologies produce similar mechanical performance on comparable roughness levels, thus finding shared fields of application and fully eligible for the production of structural components.

Abstract: Copper-aluminum layered composites offer a promising combination of high conductivity, light weight, and cost-effectiveness, making them attractive for applications in electric vehicles, electronics, and power transmission. However, achieving reliable interfacial bonding while avoiding excessive work hardening and brittle intermetallic formation remains a significant challenge. In this study, a Cu18150/Al1060/Cu18150 trilayer composite was fabricated through a three-stage high-temperature oxygen-free rolling process. Subsequently, the produced composite was subjected to annealing treatments to systematically investigate the effects of rolling passes, annealing temperature/time on interfacial evolution and mechanical behavior. Results indicate that rolling passes primarily influence interfacial topography and defect distribution. Fewer passes lead to wavy, mechanically bonded interfaces, while more passes improve flatness but reduce intermetallic continuity. Annealing temperature critically governs diffusion kinetics; temperatures up to 400 °C promote the formation of a uniform Al2Cu layer, whereas 450 °C accelerates the growth of brittle Al4Cu9, thickening the intermetallic layer to 18 μm and compromising toughness. Annealing duration further modulates diffusion mechanisms, with short-term (0.5 h) treatments favoring defect-assisted diffusion, resulting in a porous, rapidly thickened layer. In contrast, longer annealing (≥1 h) shifts toward lattice diffusion, which densifies the interface but risks excessive brittle phase formation if prolonged. Mechanical performance evolves accordingly; as-rolled strength increases with the number of rolling passes, but at the expense of ductility. Annealing transforms bonding from a mechanical to a metallurgical condition, shifting fracture from delamination to collaborative failure. The identified optimal process, single-pass rolling followed by annealing at 420°C for 1 hour, yields a balanced interfacial structure of Al2Cu, AlCu, and Al4Cu9 phases, achieving a tensile strength of 258.9 MPa and an elongation of 28.2%, thereby satisfying the target performance criteria (≥220 MPa and ≥20%).

Abstract: The growing emphasis on environmental sustainability and the need for advanced manufacturing methods have accelerated progress in materials processing. Aluminum powder metallurgy (APM) is particularly promising due to aluminum’s low density, high strength-to-weight ratio, and the inherent benefits of the powder metallurgy (PM) process. However, the corrosion resistance of sintered aluminum components remains a significant concern. In this study, shot peening (SP) was employed as a surface modification technique to improve the corrosion behavior of Alumix 321 PM alloy. Sampleas of the as-sintered and shot peened Alumix 321 PM alloy, together with the wrought alloy counterpart AA6061, were characterized using non-contact optical profilometry, optical microscopy (OM), and scanning electron microscopy (SEM). Corrosion performance was evaluated in 3.5 wt.% NaCl solution using Tafel extrapolation (TE), cyclic polarization (CP), stair-step polarization (SSP), and electrochemical impedance spectroscopy (EIS). The results revealed that shot peening increased surface roughness and significantly reduced the corrosion rate from 0.079 mmpy to 0.004 mmpy for the unpeened and peened samples, respectively. While pitting was the dominant corrosion mechanism in the wrought alloy, the PM alloy exhibited a combination of pitting, crevice, and intergranular corrosion. These findings highlight the potential of SP in enhancing the durability of aluminum-based PM components, offering valuable insights for industrial applications.