The effect of plastic deformation applied to AISI 316L in low-temperature vacuum carburizing without surface activation was investigated. To create a difference in the deformation states of each specimen, solution and stress-relieving heat treatment were performed using plastically deformed AISI 316L, and the deformation structure and the carburized layer were observed with EBSD and OM. The change in lattice parameter was confirmed with XRD, and the natural oxide layers were analyzed through TEM and XPS. In this study, the carburized layer on the deformed AISI 316L was the thinnest and the dissolved carbon content of the layer was the lowest. The thickness and composition of the natural oxide layer on the surface were changed due to the deformed structure. The natural oxide layer on the deformed AISI 316L was the thickest, and the layer was formed with a bi-layer structure consisting of an upper Cr-rich layer and a lower Fe-rich layer. The thick and Cr-rich oxide layer was difficult to decompose due to the requirement for lower oxygen partial pressure. In conclusion, the oxide layer is the most influential factor, and its thickness and composition may determine carburizing efficiency in low-temperature vacuum carburizing without surface activation.

Wire-arc additive manufacturing (WAAM) has emerged as a promising technology for producing large-scale, high-strength aluminum due to its high efficiency and geometric flexibility. However, repeated thermal cycling and non-equilibrium solidification during WAAM often induce microstructural heterogeneity and mechanical anisotropy. In this study, the effects of interlayer hammering on the microstructural evolution and tensile anisotropy of WAAM-fabricated AA7075 alloy were systematically investigated. The results confirm that interlayer hammering restores the structural continuity of the matrix by fragmenting the continuous defects and Mg-Zn-Cu-rich phase networks along the fusion boundaries. Furthermore, interlayer hammering refines the grains beneath the fusion line and weakens the solidification texture, thereby mitigating local stress concentrations. Consequently, the tensile anisotropy was substantially reduced; at the highest hammering strain, the discrepancy in yield strength and tensile strength between the building direction and the longitudinal direction was reduced to within 10%, with a simultaneous enhancement in elongation. These findings suggest that the anisotropic mechanical behavior of WAAM-fabricated AA7075 is governed not only by defect density but also by the spatial connectivity of interfacial features. Moreover, the direction-dependent mechanical behavior was found to originate from the formation of a periodic coarse- and fine-grained microstructure, signifying a transition from defect-dominated to microstructure-governed anisotropy. This study provides a mechanistic basis for controlling anisotropy via microstructural design, thereby enhancing the structural reliability of WAAM-fabricated 7xxx-series aluminum alloys.

Recycling of aluminum casting alloys is increasingly important for sustainable manufacturing, however, the accumulation of Fe impurities during recycling promotes the formation of brittle, plate-like β-Al₅FeSi intermetallic compounds, severely limiting alloy performance. In this study, the role of melt thermal history in governing Fe-rich intermetallic phase transitions was systematically investigated in an A356 (Al-7Si-0.35Mg) alloy containing 0.4 wt.% Fe.,Thermal-rate treatment (TRT), involving superheating the melt to 800 °C for 60 min prior to solidification, was applied in combination with controlled cooling conditions ranging from gravity casting to rapid solidification by melt spinning. The results show that TRT suppresses the formation of monoclinic β-Al₅FeSi and promotes the formation of metastable cubic α-AlFeSi with a Chinese-script morphology, even in the absence of chemical modifiers or grain refiners. The tendency for α-AlFeSi formation increases with cooling rate, indicating a strong coupling between liquid-state condition and solidification kinetics.,Rapid solidification experiments were conducted to quench liquid-state solute configurations and elucidate the underlying mechanism. Transmission electron microscopy reveals that, under the TRT condition, the early formation of discrete Fe-rich intermetallic phases is strongly suppressed. Instead, Fe and Si are retained as solute-enriched distributions along cell boundaries and within cell interiors, indicating delayed intermetallic formation during the initial stage of solidification. Atom probe tomography provides atomic-scale evidence for this liquid-state modification. The results show that TRT alters the nanoscale distribution of Fe and Si by suppressing solute clustering and promoting a more homogeneous solute configuration in the melt. Partial radial distribution function analysis shows a pronounced reduction in Fe-Si correlations toward values approaching a random distribution after TRT, indicating weakened chemical short-range order in the liquid state. This modified liquid-state solute distribution facilitates preferential nucleation of α-AlFeSi, suppresses β-Al₅FeSi formation, and kinetically inhibits the peritectic transformation from α-AlFeSi to β-Al₅FeSi during subsequent solidification.