Effect of substituting Gd with 3 wt% Nd on high temperature creep behaviors of peak-aged Mg-10Gd-0.4Zr casting Mg alloy

Abstract

In this paper, the high temperature creep behaviors of peak-aged Mg-10Gd-0.4Zr and Mg-7Gd-3Nd-0.4Zr casting alloys were investigated. The results showed that substituting Gd with 3 wt% Nd promoted precipitation of the β′ phase with higher number densities and larger aspect ratios, which led to the higher tensile mechanical properties of the peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy at both room and elevated temperatures. The peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy had better tensile creep properties at temperatures of 200 °C–225 °C. However, the peak-aged Mg-10Gd-0.4Zr casting alloy showed better creep resistance when the creep temperature ≥250 °C. The creep mechanism for the peak-aged Mg-10Gd-0.4Zr casting alloy was dislocation climb assisted by grain boundary diffusion under all experimental conditions, while the creep mechanism of the peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy transformed from dislocation glide at 200 °C–225 °C into dislocation cross-slip above 250 °C. Due to the faster transformation from β′ phase into β1 phase in peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy, the blocking effect of precipitation on dislocation movement was weakened. And a larger number of basal < a > dislocations accumulated in the grain boundary region, leading to precipitate free zones (PFZs) widening more obviously in the peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy, and which well explained the reason why the creep resistance of peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy deteriorated rapidly above 250 °C.