Simulation study of precipitation in an Mg–Y–Nd alloy

The high strength of magnesium alloy WE54 (Mg–5 wt.% Y–2 wt.% Nd–2 wt.% RE) is achieved through aging at 150–250 °C, during which precipitation of intermediate phases β1 and β′ and equilibrium phase β takes place. In order to understand the microstructure evolution of β1 phase and its effects on β′ and β precipitation, a phase field model of β1 precipitation is developed. Model inputs, including lattice parameters, precipitate–matrix orientation relationship, elastic constants and free energy data, are obtained from experimental characterization, ab initio calculations and thermodynamic databases. Through computer simulations, the equilibrium shape and spatial distribution of and stress field around β1 precipitates are quantitatively determined. The results show that the {11¯00} rather than {0 0 0 1} habit plane of β1 is determined by the coherency elastic strain energy minimization (e.g., the habit plane is close to an invariant plane). The elastic interactions among different precipitate particles are found to be responsible for the formation of various multi-particle configurations seen in experimental observations. The elastic interaction and spatial correlation between β1 and β′ precipitates are also investigated.