Densification, microstructure, mechanical properties, and thermal stability of high-strength Ti-modified Al-Si-Mg-Zr aluminum alloy fabricated by laser-powder bed fusion

Abstract

Micrometer-sized, irregularly shaped Ti particles (0.5wt% and 1.0wt%) were mixed with an Al-Si-Mg-Zr matrix powder, and a novel Ti-modified Al-Si-Mg-Zr aluminum alloy was subsequently fabricated via laser-powder bed fusion (L-PBF). The results demonstrated that the introduction of Ti particles promoted the formation of near-fully equiaxed grains in the alloy owing to the strong grain refinement of the primary (Al,Si)₃(Ti,Zr) nanoparticles. Furthermore, the presence of (Al,Si)₃(Ti,Zr) nanoparticles inhibited the decomposition of Si-rich cell boundaries and the precipitation of Si nanoparticles in the α-Al cells. The ultimate tensile strength (UTS), yield strength (YS), and elongation of the as-built 0.5wt% Ti (0.5Ti) alloy were (468 ± 11), (350 ± 1) MPa, and (10.0 ± 1.4)%, respectively, which are comparable to those of the L-PBF Al-Si-Mg-Zr matrix alloy and significantly higher than those of traditional L-PBF Al-Si-Mg alloys. After direct aging treatment at 150°C, the precipitation of secondary nanoparticles notably enhanced the strength of the 0.5Ti alloy. Specifically, the 0.5Ti alloy achieved a maximum UTS of (479 ± 11) MPa and YS of (376 ± 10) MPa. At 250°C, the YS of the L-PBF Ti/Al-Si-Mg-Zr alloy was higher than that of the L-PBF Al-Si-Mg-Zr matrix alloy due to the retention of Si-rich cell boundaries, indicating a higher thermal stability. As the aging temperature was increased to 300°C, the dissolution of Si-rich cell boundaries, desolvation of solid-solution elements, and coarsening of nanoprecipitates led to a decrease in the UTS and YS of the alloy to below 300 and 200 MPa, respectively. However, the elongation increased significantly.

Keywords

laser-powder bed fusion / Ti-modified Al-Si-Mg-Zr alloy / microstructure / mechanical property / thermal stability

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