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

• The precipitation process in Mg–10Gd–3Y–0.8Al (wt.%) alloy has been investigated.
• Particles with the 18R-type LPSO structure were observed in the solution state.
• Upon ageing at 250 °C, the precipitation sequence is: β″ → β′ → β1 (fcc) → β.
• The Al grain-refined alloy has a lower hardness than the Zr refined counterpart.

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.