Engineering

Abstract: The secondary dendrite arm spacing (SDAS) is a critical microstructural parameter that directly influences the local mechanical performance of AlSi casting alloys. Although the power-law relationship between cooling rate and SDAS is widely acknowledged, the existing literature lacks a standardized framework for selecting the most appropriate solidification thermal interval for calculating this characteristic cooling rate. This study introduces an optimized methodological approach by evaluating solidification kinetics across two distinct thermal regimes: a standard non-isothermal sand mold (no chill) and an accelerated cast iron insert configuration (with chill). Cooling curves of a primary hypoeutectic AlSi7Mg0.3 alloy were continuously recorded via ten calibrated K-type thermocouples along a wedge-shaped casting profile, and the corresponding local SDAS values were quantified using light optical metallography. By mathematically evaluating six distinct thermal analysis boundaries, the results demonstrate that conventional global intervals (e.g., liquidus-to-eutectic) yield lower predictive accuracy (R² ≈ 0.75) due to the accumulation of thermal "noise" from the early fluidic stage and the final eutectic reaction. In contrast, the localized interval bounded strictly between the Dendrite Coherency Point and the Rigidity Temperature (TDCP-TRigidity) achieved excellent correlation for both the baseline slow-cooling regime (R² = 0.8509) and the accelerated regime (R² = 0.9547). This optimized window successfully isolates the exact kinetic timeframe of secondary dendritic evolution and effectively eliminates localized calculation anomalies across the entire spectrum of cooling rates. Thermodynamic analysis reveals a sharp cooling asymmetry in the wedge geometry, where the local solidification timescale collapses by a factor of 34 at the chill base. This extreme kinetic restriction limits the characteristic solute diffusion distance(L≈D.t)) by a factor of nearly six, providing a quantitative physical basis for the significantly flatter coarsening slope (-14.85) under accelerated cooling compared to the baseline regime (-32.63), while simultaneously shifting the eutectic silicon morphology from coarse acicular plates to a highly refined, fibrous structure. The proposed methodology establishes a physically grounded, highly accurate microstructural prediction tool suitable for advanced foundry engineering and casting simulations.

Abstract: The growing use of binder jetting in foundry practice creates a need for effective recovery of the fine silica sand used in additively manufactured molds. This study compares mechanical and thermal reclamation of spent furfuryl-resin sands originating from binder-jetted molds (US-1) and conventionally manufactured molds (US-2) after ductile iron casting. Mechanical reclamation was conducted at rotor speeds of 280–560 rpm for 10–30 min, whereas thermal reclamation was performed at 600–1000 °C. Reclaim quality was assessed using loss on ignition (LOI), pH, dust generation, grain morphology, and bending strength. Conventional spent sand was more susceptible to mechanical treatment, reaching a maximum reclamation efficiency index of 41.1%, compared with 31.5% for binder-jetted sand. Thermal treatment was markedly more effective, reducing LOI to 0.14% for US-1 and 0.29% for US-2 and increasing reclamation efficiency to 94.8% and 89.8%, respectively. High-temperature thermal reclamation is therefore particularly suitable for fine-grained binder-jetted sand, whereas excessive mechanical treatment may promote grain crushing and dust formation.

Abstract: Diamond-like carbon (DLC) coatings are widely used to improve corrosion resistance, but the same coating can behave very differently depending on the metal substrate. This study focuses on how the substrate affects coating performance. Titanium-doped (Ti-DLC) and tungsten-doped (W-DLC) films were deposited by magnetron sputtering using the same process. Both were deposited on two substrates: 316L stainless steel and Ti6Al4V. The coatings were characterized by SEM, EDX, water contact angle, and Raman spectroscopy. Corrosion behavior was evaluated in 3.5 wt% NaCl by poten-tiodynamic polarization and electrochemical impedance spectroscopy (EIS). Wettability shifted in opposite directions on the two substrates: 316L became more hydrophilic after coating, while Ti6Al4V became more hydrophobic. Raman spectroscopy showed that the two dopants produced a similar degree of carbon disor-der on 316L, but diverged on Ti6Al4V. Ti-DLC was the most ordered film of the four coatings and W-DLC formed a more disordered one, suggesting that titanium and tungsten promote carbon ordering differently depending on the substrate. Both films reduced the corrosion current density compared to the bare metal. By EIS, every coated specimen also showed a higher polarization resistance than its bare substrate. On each substrate, Ti-DLC outperformed W-DLC, but with different degrees of improvement. On 316L, the less corrosion-resistant one, gained more from coating in relative terms, while Ti6Al4V reached the highest corrosion resistance. This substrate dependence likely reflects differences in dopant amount and interfacial bonding.

Abstract: This study investigates the fabricability, microstructures, mechanical and corrosion behavior of multi-material structure (MMS) composed of niobium alloy (NbZr1) and titanium alloy (Ti64) using a wire-arc directed energy deposition process. The microstructure of NbZr1 alloy primarily consisted of equiaxed grains oriented in the rolling direction, while the deposited Ti64 microstructure exhibited ‘banding’ morphology and a basket weave structure composed of α phase lamellae in a β matrix. The MMS interface revealed good metallurgical bonding and was free from defects such as cracks, pores and intermetallic phases. Niobium diffusion from the NbZr1 into the Ti64 alloy resulted in formation (β-Ti + Nb) solid solution which imparted strength to the MMS. The hardness testing showed that microhardness values follow the trend: NbZr1 substrate > MMS interface > Ti64 deposit. The NbZr1–Ti64 multi-material structure developed in this study exhibited a balanced combination of ductility (22.73% elongation) and moderate tensile strength (254.18 MPa), outperforming most reported NbZr1-Ti64 MMS studies. All tensile specimens failed in ductile manner on NbZr1 side. The MMS demonstrated superior corrosion resistance, exhibiting the lowest corrosion current density and corrosion rate compared to its individual counterparts.

Abstract: The ferromanganese industry, critical for global steelmaking, faces increasing pressure to adopt sustainable practices due to its high energy consumption and carbon footprint. High-carbon ferromanganese (HCFeMn) slag, a significant by-product, represents both an environmental challenge and a valuable resource for metal recovery. This study employs a multi-metric approach to assess the technical, environmental and operational performance of aluminothermic reduction smelting of HCFeMn slag in a 200 kW DC arc furnace, with focus on energy, material, and emissions assessment. For materials, the focus was on reductant efficiency, elemental accountability, elemental recovery, elemental deportment and slag-to-metal ratio. The environmental indicators studied includes CO2-equivalent emissions per ton of product, dust and particulate emissions, NOx/SOx emissions. The consumption of electrodes and refractory was also studied. The innovative process proposed in this study also aims to valorize metallurgical residues into high-value manganese alloy products while minimizing environmental burdens. A total of 2009 kg of HCFeMn slag was smelted and reduced by recycled aluminium scrap (202 kg) over 20 taps, while fluxing with burnt lime (382 kg). The campaign recorded an average gross specific energy requirement of 0.87 kWh kg−1 of charge across 20 taps, with tap-by-tap values ranging from 0.74 to 0.98 kWh kg−1. When compared to conventional submerged-arc SiMn furnaces ( 4,000–4,500 kWh t−1), this corresponds to an approximate 79–81 % reduction in specific energy consumption. The attained aluminium reductant efficiencies ranged from 55.14 to 91.89 % (the campaign average being ∼60 %), with Mn recovery of 47–81 % and Fe recovery progressing from 33–38 % to over 90 % across successive taps. The observed high slag-to-metal ratio (SMR) (4.79–6.68 kg/kg) is attributed to the operating strategy of using slag as a feed, rather than a process deficiency. This high SMR contrasts with the 1.0–1.3 kg/kg typical of SiMn industrial operations. The emissions from the current 200 kW DC arc furnace study were approximately 1.35 t CO2-eq t−1 alloy (Eelec=1.20 t CO2-eq t−1; EAl−prod=0.15 t CO2-eq t−1), marking a decrease of 60–65 % when compared to conventional carbothermic HCFeMn production (3.0–4.0 t CO2-eq t−1) and an 80 % decrease when compared with the full cradle-to-gate SiMn benchmark (6.94 t CO2-eq t−1). Direct process CO2 emissions were negligible, owing to the absence of fossil reductants in the burden. SO2 emissions of 0.312 kg t−1 alloy and particulate emissions of 10.4 kg t−1 alloy (pre-abatement) were measured, well below industrial SiMn off-gas emission intensities, while the use of recycled scrap aluminium, which requires up to 95 % less energy than primary aluminium, underpins the low embodied-carbon contribution. The integration of aluminothermic reduction in a DC arc furnace offers a robust, efficient and environmentally sustainable alternative route for the recovery of manganese from industrial HCFeMn slag, validating the current-study process at Technology Readiness Level 6. The primary contribution of this study is the application-level demonstration of the current process at a 200 kW DC arc furnace pilot scale, and bridging the gap between laboratory concepts and industrial-scale implementation. The study further compares the Pyrosim simulation values to campaign data, slag and alloy chemical analyses and specific energy requirement.

Abstract: The high-speed steel (HSS) substrate was coated with CrC, NbC, TiC, and VC layers using the thermo-reactive diffusion (TRD) process at 900 and 1100 °C for 2 and 4 hours. The experimental design was implemented according to the Taguchi L8 orthogonal array. The coating morphology was examined by scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS), while the phase composition was identified by X-ray diffraction (XRD). The effects of coating type, temperature, and time on coating thickness, microhardness, coefficient of friction, and specific wear rate were evaluated using analysis of variance (ANOVA). SEM and EDS analyses showed that coatings produced at lower temperatures and shorter times exhibited non-uniform layer thickness, localized porosity, and irregular carbide formation, whereas coatings applied at higher temperatures and longer times resulted in uniform layers, homogeneous elemental distribution, and improved surface morphology. XRD analyses confirmed that the coatings consisted of high-intensity carbide phases and that the chemical composition of the substrate influenced the resulting coating phases. Phase composition analysis revealed the presence of residual phases such as Cr₇C₃ and Cr₂₃C₆ in the coatings. Coating thickness and hardness increased with increasing temperature and time. Analysis of variance revealed that coating type (45.13%) and temperature (42.34%) were the dominant factors affecting coating thickness, whereas temperature (39.92%) and coating type (37.77%) had the greatest contributions to hardness. The friction coefficient was predominantly influenced by coating type (87.98%), whereas the specific wear rate was mainly affected by temperature (34.99%) and coating type (33.37%). NbC coatings exhibited the lowest performance among the investigated coatings across all evaluated properties.

Abstract: Laser powder bed fusion (LPBF) enables fabrication of complex bimetallic structures, such as combustion chambers, that require a thermally conductive internal channel supported with a high-strength structural jacket. Inconel625 (IN625) served as the substrate, with GRCop-42 deposited with varying laser power and laser scanning speeds to create the IN625-GRCop-42 interface. Hot isostatic pressing (HIP) was performed to evaluate defect mitigation and Vickers microhardness testing assessed the mechanical properties across the bimetallic interface. Microstructure characterization revealed porosity across the full processing window and HIP was unsuccessful in eliminating the defects, indicating that densification is primarily achieved by LPBF process optimization. Microhardness testing proved that the as-printed samples showed higher microhardness values than the as-HIPped samples due to the fine microstructure, high dislocation density and residual stresses caused by the LPBF process. As-HIPped samples showed recrystallization and grain coarsening due to the decrease in microhardness compared to the as-printed samples. These results highlight the importance of LPBF process optimization in achieving strong, thermally stable IN625-GRCop-42 bimetallic interfaces. This study aims to investigate the microstructural and mechanical behavior of the IN625 and GRCop-42 dissimilar metal interface fabricated using the LPBF process and the effects of HIP on the bimetallic microstructure.

Abstract: This study develops novel multicomponent Al–Mg–Si–Zr–Cu-based alloys for high-pressure die casting (HPDC) with improved mechanical properties and thermal sta-bility. Four compositions were designed through Zn and Cr additions, supported by thermodynamic modelling. Phase formation and microstructure were analysed by XRD and SEM/EDS, while density, electrical conductivity, hardness, and mechanical behaviour under tensile and compressive loading at room temperature and 200 °C were evaluated. Hardness increased from 166 to 214 HV3 with Zn and Cr due to the formation of complex intermetallic phases. The Al–Mg–Si–Zr–Cu alloy showed the best balance of strength and ductility under tensile loading, whereas Zn and Cr additions reduced tensile performance. In compression, Zn significantly improved strength, reaching an ultimate compressive strength of 697 MPa. Compared with the reference AlSi9Cu3 alloy, the new alloys achieved up to 30% higher yield strength, 13% higher ultimate tensile strength, and im-proved thermal stability. Among the studied compositions, Al72Mg10Si5Zr3Cu10 showed the best overall performance, while Al67Mg10Si5Zr3Cu10Zn10 was optimal for compres-sion-dominated applications.

Abstract: The empirical descriptors of high-entropy alloys and oxides, from the mixing entropy and atomic-size mismatch to the Miedema enthalpies and the Ω, Φ, and φ stability parameters, are quoted in nearly every design study, yet they are reimplemented ad hoc by individual groups, by closed web calculators, and now inside language-model agent frameworks, where fabrication of property values is a documented failure mode. The resulting numbers disagree and cannot be traced or reproduced. We present HEA-Bench, an open calculator in which every descriptor is a closed-form expression over a curated, literature-cited element-property table, with the six canonical phase-prediction rules reported alongside their thresholds and sources rather than as predictions. One calculation core is delivered as a dependency-free Python library, a zero-install browser application, an offline desktop executable, and a Model Context Protocol server that exposes it to AI agents as deterministic tools, returning every value with its unit, citation key, and version so an agent’s reasoning trace can be audited. The implementation reproduces published per-alloy and per-oxide anchor values to their printed precision and extends to high-entropy oxides in four structure families. The numerical instability of Ω near zero mixing enthalpy is quantified and exposed as a callable check.

Abstract: Neodymium (Nd) and dysprosium (Dy) are two critical rare earth elements for fabricating NdFeB permanent magnets, which have crucial applications in modern technologies. The increasing global demand for Nd and Dy emphasizes new efficient processes for their recovery and purification, which are technologically challenging due to their close physical and chemical properties. Through systematic exploration, it was found that Lewatit VP OC 1026 resin impregnated with di-(2-ethylhexyl) phosphoric acid (D2EHPA) had a strong adsorption preference for Dy³⁺ over Nd³⁺, which is highly suitable for Dy-Nd separation from their mixed solutions under optimized conditions. The loaded resin could be eluted using dilute sulfuric solutions for recycling to the adsorption process. By employing a multistage adsorption-elution process analogous to distillation, efficient Dy-Nd separation and purification were realized from their mixed solution, with a prospective purity of 99.13% and recovery of 97.45% for Dy and a prospective purity over 99.96% and recovery of above 99.90% for Nd, despite the large concentration disparity between Dy and Nd where Nd concentration is over 26 times of that of Dy. This research demonstrates that efficient recovery and purification of metals from aqueous solutions can be achieved using selective resin adsorption processes analogous to distillation, despite large concentration differences of the metals in the solutions, which presents new alternative approaches.

Abstract: Metallic powder systems containing niobium play a key role in the development of advanced materials for structural, biomedical, energy, and surface-engineering applications. The incorporation of niobium into metallic powders influences particle behavior during processing, phase stability, microstructural evolution, and the resulting mechanical and corrosion properties of consolidated materials. This review examines the scientific and technological advances related to niobium-containing metallic powders, covering powder production routes, particle characterization methods, processing techniques, and performance evaluation. Publications on powder metallurgy, additive manufacturing, thermal processing, surface modification, and corrosion-resistant materials were analyzed to identify relationships among powder characteristics, processing conditions, and material performance. The available evidence indicates that niobium contributes to grain refinement, precipitation control, microstructural stabilization, improved resistance to wear, and localized corrosion. The element also expands the applicability of metallic powders in functional coatings, biomaterials, engineered surfaces, and components manufactured from particulate feedstocks. Current challenges involve powder homogeneity, process reproducibility, economic considerations, and the prediction of long-term service behavior. The analysis highlights niobium's contribution to the design of high-performance metallic powder systems and identifies research directions for developing materials with enhanced reliability and industrial applicability.

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.