Effect of mischmetal additions and solution heat treatments (T4) on the microstructure and mechanical properties of thixocast ZK60-RE magnesium alloys

Solution treatments (T4) at 380 °C for 16 h and 500 °C for 8 h were performed for ZK60 magnesium alloys modified with addition of 0.5, 1.5 and 2.5 wt% of mischmetal (combination of rare-earth (RE) elements). The compression behaviour was investigated at room temperature and at 300 °C correlated with the microstructure and differential scanning calorimetry (DSC) data. The ascast microstructure is formed by -Mg matrix with globular grains reinforced by a semi continuous network of Mg-Zn, Mg-Zn-RE and Mg-RE intermetallic particles. Solution-treated alloys show lower yield strengths due to partial dissolution of precipitates. Work hardening was not observed for the alloys compressed at 300°C with the compression speed of 10^-3 s^-1, whereas it was observed for the compression speed of 10^-2 s^-1 for the all as-cast, ZK60-1.5RE-T4 at 380 °C and ZK60-1.5RE-T4 at 380 °C.