Effect of cryogenic treatment on the microstructure and mechanical properties of Mg-1.5Zn-0.15Gd magnesium alloy

The effect of cryogenic treatment on the microstructure and mechanical properties of Mg-1.5Zn-0.15Gd (at%) alloy were investigated. The result showed that numerous W phase particles precipitated from the Mg matrix after cryogenic treatment. With increasing cryogenic treatment duration from 1 min to 24 h, the volume fraction of W phase precipitate also increased, which agreed with the Kolmogorov-Johnson-Mehl-Avrami model. The kinetics of such precipitates was attributed to the additional space coming from the lattice contraction of Mg under cryogenic environment. After cryogenic treatment for 24 h, the ductility of alloy was enhanced by 79%, since the homogenous distributed W phase with nanoscale activated the nucleation of twins during deformation. One formation criterion of precipitation in Mg alloy under cryogenic environment was suggested. Cryogenic treatment could be efficient only for the formation of precipitate with a much lower atom density than the matrix.