Effect of aging prior to extrusion on the microstructure and mechanical properties of Mg-7Sn-1Al-1Zn alloy

The effect of aging prior to extrusion (APE) on the microstructure and mechanical properties of Mg-7Sn-1Al-1Zn (wt.%) alloy was investigated under various extrusion conditions. The extruded alloy exhibited a partially or fully recrystallized (DRXed) structure with fine Mg₂Sn precipitates, with the fraction and size of the DRXed grains decreasing with a reduction in extrusion temperature and ram speed. The numerous precipitates formed by APE also reduces the size of the DRXed grains and increases the overall amount of precipitate in the extruded alloy, thereby improving the yield and tensile strength regardless of the extrusion conditions. The ductility of the alloy was also improved by APE when extruded at relatively high temperature and speed, which is attributed to the suppressed formation of coarse banded Mg₂Sn; however, a deterioration in ductility was observed at low ram speed and/or low extrusion temperature due to the reduction in the fraction of DRXed grains and increased amount of Mg₂Sn precipitates. Furthermore, the extruded alloy with APE showed superior strength and ductility to that aged after extrusion, indicating that APE is the more effective means of improving the mechanical properties of extruded alloy.