Microstructure characterization and mechanical performance of laser powder bed fusion processed AlMgScZr alloy: Effect of heat treatment

Abstract

Laser powder bed fusion (LPBF) of aluminum alloys produces a particularly unique microstructure compared to conventional casting and forging products. Generally, the heat treatments employed in traditional fabrication techniques may not be suitable for LPBF. To mitigate this dilemma, this work systematically investigated the hardening behavior of various heat-treated temperatures and hold durations carried out on LPBF fabricated AlMgScZr alloy. The microstructure and mechanical performance in the as-built and heat-treated conditions were also compared and discussed. Results demonstrate that the resultant static mechanical performance is exceptionally excellent with ultimate tensile strength (UTS) exceeding 550 MPa along with a sound fracture elongation even after heat treatment. These outstanding properties are strongly related to the fine equiaxed grains microstructure and a high fraction of secondary Al3(Sc, Zr) precipitations. Importantly, these fine equiaxed grains almost maintained ungrowth even after heat treatment owing to the pinning effect of secondary Al3(Sc, Zr) precipitations. This AlMgScZr alloy demonstrates high tensile strength and appreciable ductility due to fine grain strengthening, solid solution strengthening and secondary phase strengthening. As such, by the synergetic effects of Sc and Zr microalloying and optimal heat treatment conditions, the high strength and decent ductility of LPBF fabricated AlMgScZr alloy can be achieved, extending its further application in aerospace industry. This strategy can also be employed to other LPBF fabricated engineering materials, providing a foundation for expanding industrial applications of LPBF fabricated parts.