Bonding Environments in a Creep–Resistant Mg–RE–Zn Alloy

Density functional theory (DFT) based first principle calculations was used to examine the effect of transitional element Zn addition on the bonding environment of Mg–Gd solid solutions. Our calculations reveal that Zn strongly interacts with Gd, while simultaneously disperses the p-orbital valence electron density of Zn along the [0001]_Mg and \( \left\langle { 1 1 {\bar{\text{2}}}0} \right\rangle_{\text{Mg}} \) directions of hcp-Mg lattice. These results suggest that Zn addition stiffens the Mg–Mg bonds between the {0002}_Mg-basal planes, and along \( \left\langle { 1 1 {\bar{\text{2}}}0} \right\rangle_{\text{Mg}} \). The enhanced bonding between the Mg basal planes may potentially drives basal precipitation in Mg–Gd–Zn alloys seen in experiments. On the other hand, bond stiffening along \( \left\langle { 1 1 {\bar{\text{2}}}0} \right\rangle_{\text{Mg}} \) noticeably increased the vacancy migration barrier for basal plane diffusion in Mg. This increase has bearing on the high temperature creep properties, because vacancy diffusion is a dominant creep deformation mechanism at operation temperatures of 150–300 °C for Mg-alloy parts. Thus, our calculations predict that Zn addition to Mg–Gd alloy will strongly influence its microstructure and creep response.