Phase field modeling of β ₁ precipitation in WE54 alloy

WE54 (Mg-5wt%Y-2w1%Nd-2wt%HRE), which has high strength and lightweight at elevated temperatures, has been identified as one of the most successful magnesium alloys. The strength of WF54 can be achieved via precipitation strengthening by aging at 150-250°C during which precipitations of intermediate phases β ₁ and β′ and equilibrium phase β take place. In order to understand the microstructure evolution of β ₁ phase and its effects on dislocation gliding, a phase field model of β ₁ precipitation has been 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 the β ₁ precipitates are quantitatively determined. The interactions between precipitates and gliding basal dislocations and corresponding effects on the strength of the alloy have been investigated.