Precipitation process in a Mg-Gd-Y alloy grain-refined by Al addition

The precipitation process in Mg-10Gd-3Y (wt.%) alloy grain-refined by 0.8 wt.% Al addition has been investigated by transmission electron microscopy. The alloy was given a solution treatment at 520 °C for 6 h plus 550 °C for 7 h before ageing at 250 °C. Plate-shaped intermetallic particles with the 18R-type long-period stacking ordered structure were observed in the solution-treated state. Upon isothermal ageing at 250 °C, the following precipitation sequence was identified for the α-Mg supersaturated solution: β″ (D019) → β′ (bco) → β1 (fcc) → β (fcc). The observed precipitation process and age hardening response in the Al grain-refined Mg-10Gd-3Y alloy are compared with those reported in the Zr grain-refined counterpart.