Research on microstructure and properties of heat-treated arc additively manufactured 7075 aluminum alloy components

Abstract In this study, thin-walled 7075 aluminum alloy samples were fabricated using Single-Bead Multi-Layer Wire Arc Additive Manufacturing (WAAM) with self-developed 7075 aluminum alloy welding wire and metal inert gas (MIG) welding. The samples underwent solid solution treatment followed by double-stage aging heat treatment. The metallographic structure, precipitate phases, and mechanical properties of the additive samples before and after heat treatment were investigated using optical microscopy (OM), electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The results indicate that, without heat treatment, the grains in the WAAM 7075 aluminum alloy samples exhibited a distinct weld structure with noticeable orientation. The precipitated phases, such as η (MgZn 2 ), S (Al 2 CuMg), and T (AlZnMgCu), were observed to form along the grain boundaries, with high-melting-point compounds like AlMnFeSi, Al 13 Fe 4 , and Mg 2 Si serving as nuclei. The weak fusion zones between adjacent weld beads contributed to poor mechanical properties in the as-deposited state, with no significant difference in mechanical performance between the Y(deposition direction) and X(cladding direction). After heat treatment, the η , S, and T phases were completely dissolved into the matrix, resulting in solid solution strengthening and aging. The interlaminar fusion zone (IFZ) grains recrystallized into equiaxed structures, improving the tensile strength and elongation in the cladding direction to 464.2 MPa and 13.11%, respectively. However, the presence of residual insoluble Fe and Si compounds limited further mechanical property improvements, and large pores densely distributed within the interlayer caused lower mechanical properties in the deposition direction compared to the cladding direction.