Opposite effects of Zn addition on the creep resistance at low and high temperatures for as-cast Mg-15Gd alloy

The effect of Zn addition on the mechanical properties in Mg-rare earth (RE) alloys has been controversial. In this study, we selected the as-cast Mg-15Gd (wt.%) alloy as a model system to illustrate the effect of Zn addition on the microstructures and creep properties. The results revealed that the main strengthening phase transformed from β' in the Mg-15Gd alloy to long-period stacking ordered (LPSO) structure in the Mg-15Gd-1Zn (wt.%) alloy. At low temperatures (≤285 °C) when the creep mechanism was dislocation slip, the prismatic β' phase hindered the movement of dislocations, leading to better creep resistance of the Mg-15Gd alloy. On the contrary, at high temperatures (>285 °C) when the creep was controlled by dislocation climbing, the Mg-15Gd-1Zn alloy with lower stacking fault energy and basal LPSO phase exhibited better creep resistance. These findings inspire us to design the composition of Mg-RE alloys in different service environments for better performance.