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

摘要

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 〈1120〉_(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 〈1120〉_(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 〈1120〉_(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 ℃ for Mg-alloy parts. Thus, our calculations predict that Zn addition to Mg-Gd alloy will strongly influence its microstructure and creep response.