Effect of Heat Treatment on Microstructure and Tensile Property of Laser-Powder-Bed-Melted Al-Mn-Mg-Sc-Zr Alloy.

This study explored the effects of T5 and T6 heat treatments on the microstructure and tensile properties of a laser powder bed fusion (LPBF)-fabricated Al-Mn-Mg-Sc-Zr alloy. The as-built condition exhibited a bi-modal grain structure of equiaxed and columnar grains. Specimens after T5 heat treatment also had a bi-modal microstructure with slight grain growth and the precipitation of secondary Al3Sc, which enhanced the yield strength via precipitation hardening but reduced ductility. In contrast, T6 treatment triggered recrystallization, and the microstructure was only coarse equiaxed α-Al grains. This microstructure change was accompanied by coarsened primary Al3X and Al6(Mn, Fe) precipitates, partial Mg2Si dissolution, and significant secondary Al3Sc particle growth. Consequently, T6-treated specimens showed lower strength than their T5 counterparts and the poorest ductility due to brittle fracture induced by the stress concentration effect of coarse precipitates at grain boundaries.