Effect of homogenization temperature on the microstructure and mechanical properties of extruded Mg-7Sn-1Al-1Zn alloy

The effect of homogenization temperature (HT) on the microstructure and tensile properties of extruded Mg-7Sn-1Al-1Zn (TAZ711) alloy was investigated by conducting homogenization heat-treatment at 400, 450, and 500 °C for 24 h, followed by indirect extrusion. The results obtained through this revealed that second phases are nearly fully dissolved by homogenization at 500 °C, but undissolved Mg₂Sn particles remain after homogenization at 450 and 400 °C. Furthermore, the increase in large undissolved particles with decreasing HT helped to promote dynamic recrystallization (DRX) during extrusion by particle stimulated nucleation (PSN), thus resulting in an increase in the area fraction of DRXed grains in the extruded alloy. A decrease in the amount of Sn supersaturated in the matrix, however, suppressed the formation of fine Mg₂Sn precipitates during extrusion, which in turn led to an increase in the size of DRXed grains due to a reduction in grain boundary pinning by precipitates. Ultimately, this meant that although the yield and ultimate tensile strengths gradually improved with increasing HT due mainly to a decrease in the DRXed grain size, an increase in texture intensity, and an increased number of fine Mg₂Sn precipitates, the elongation deteriorated due to crack initiation at twins formed within coarse non-DRXed grains.