Investigation on microstructure and creep properties of as-cast and aging-treated Mg–6Sn–5Al–2Si alloy

This study examined the high temperature mechanical properties of as-cast, solution-treated and aging-treated Mg–6Sn–5Al–2Si alloy. The microstructure of as-cast Mg–6Sn–5Al–2Si alloy mainly consisted of α-Mg, Mg17Al12, Mg2Si and Mg2Sn phases. After solution heat-treatment, most of the Mg17Al12 phases were dissolved into the matrix. In the case of aging heat-treatment, finely distributed Mg17Al12 and Mg2Sn phases were evenly formed inside the grains. The ultimate tensile strength of solution treated Mg–6Sn–5Al–2Si alloy at 25 °C was decreased due to the reduced volume fraction of Mg17Al12 phase. However, the creep resistance was increased by solution heat-treatment because of complete dissolution of the thermally unstable Mg17Al12 phase into the Mg matrix. On the other hand, both the tensile strength at 25 °C and creep resistance of the peak-aged Mg–6Sn–5Al–2Si alloy were improved as compared to those of the as-cast alloy. It seems that the improved mechanical properties were associated with finely distributed Mg17Al12 and Mg2Sn phases.