Densification, Microstructural, and Mechanical Properties of Al-Mn-Mg-Er-Zr Alloy Fabricated by Laser Powder Bed Fusion

To address the high cost of raw materials for laser powder bed fusion (L-PBF) processed high-performance Al-Mn-Mg-Sc-Zr alloy, a novel Er- and Zr-modified Al-Mn-Mg alloy was fabricated by L-PBF using pre-alloyed powder in this study. The large internal stress and the existence of the keyhole together caused cracks in most of the L-PBF processed samples. The as-built sample exhibited a heterogeneous grain structure, including main columnar α-Al grains in the inner region of the molten pool and a few ultrafine α-Al equiaxed grains at the fusion boundary. Al₃Er nanoparticles were attached to the Al₆Mn phase, and both mainly precipitated at the grain boundary of α-Al. The existence of Mn in the alloy reduced the grain refining effect of Er elements. The yield strength (YS), ultimate tensile strength (UTS) and elongation of the as-built alloy were 327 ± 5 MPa, 502 ± 3 MPa, and 12.2 ± 1% respectively. When the aging temperature was over 350 ℃, the primary precipitates in the sample grew up, and needle-shaped secondary Al₆Mn nanoparticles precipitated from α-Al. 350 ℃-6 h aging alloy exhibited maximum Vickers hardness of 171 ± 1 HV with YS, UTS and elongation of 339 ± 2 MPa, 508 ± 1 MPa and 8.1 ± 1%, respectively. During the tensile process of the alloy, micro-cracks mainly originated from the fusion boundary. At last, the authors also shared some prospects for future work.