New strategy to achieve fine recrystallized microstructure and strength-ductility synergy in extruded Mg-Al-Zn alloy

Abstract

A commercial Mg-3Al-1Zn (mass%) alloy was indirectly extruded, and the effect of homogenization on the microstructure and tensile property of the extruded alloy was investigated. The extrusion using the as-cast material resulted in a fine recrystallized grain structure, leading to a high 0.2 % proof stress of 275 MPa and moderate elongation to failure of 18.6 % after extrusion at 350 °C with a slow die-exit speed of 0.24 m/min. Moreover, the fine grain structure was maintained even after the extrusion at a relatively high speed of 2.4 m/min, resulting in a 0.2 % proof stress of 252 MPa, while the 0.2 % proof stress decreased to ∼200 MPa when homogenization was conducted before the extrusion. The microstructural characterization revealed that second-phase particles did not facilitate dynamic recrystallization (DRX), while the inhomogeneity of solute in the as-cast material promoted DRX, contributing to the formation of the fine recrystallized microstructure.