Microstructure, mechanical performance and nucleation mechanism of laser powder bed fused novel Sc/Zr/Ti-modified Al-Mg alloys

Abstract

In this study, the modification of 0.70 wt% ScH3alone did not substantially fine the grain and eliminate the hot-cracking of Al-Mg-Sc alloy, resulting in low strength of as-built material. In contrast, the 0.70 wt% ScH3 and 0.34 wt% ZrH2 modified Al-Mg alloy (hereafter denoted as Al-Mg-Sc-Zr1) was demonstrated to be an exceptionally effective inoculation for Al-Mg-Sc-Zr1 alloy, owing to the low lattice mismatch (0.4 %) between Al3(Sc,Zr) and α-Al. The considerable grain refinement was ascribed to the L12-Al3(Sc,Zr) nucleis, which efficiently promoted heterogeneous nucleants of α-Al grains, contributing to significant refined grain size. Consequently, the as-built Al-Mg-Sc-Zr1 alloy demonstrated outstanding tensile strength with sound elongation to fracture due to crack-free and fine grain strengthening. Additionally, compared with Al-Mg-Sc-Zr1 alloy, the further modification with more ScH3 and ZrH2 promoted substantial grain refinement via inoculation treatment of 1.15 wt% ScH3 + 0.55 wt% ZrH2. Moreover, the grain refinement effect of ScH3 and TiH2 modification was also studied and correlated to the resulted ultrafine equiaxed grains and performance. These results indicate that grain microstructure and mechanical properties of as-built Al alloys can be tailored by suitable inoculants which can be further employed to other engineering alloys.