Three-Dimensional Phase-Field Simulation and Experimental Validation of β-Mg17Al12 Phase Precipitation in Mg-Al-Based Alloys

A three-dimensional (3D) phase-field model has been developed to simulate the formation of lath-shaped beta-Mg17Al12 phase during hcp -> bcc transformation in Mg-Al-based alloys. The model considers the synergistic effects of the elastic strain energy associated with the lattice rearrangements that accompany the phase transformation, and the interface anisotropy (both in interfacial energy and interface mobility coefficient). By using the proposed model, the essential features of 3D morphology of the beta phase precipitate have been successfully predicted and experimentally validated using high-resolution transmission electron microscopy and atomic force microscopy. Furthermore, the spatial distribution of anisotropic elastic interaction field around a pre-existing beta precipitate has been quantitatively determined using 3D phase-field simulation, and the effects of the anisotropic elastic interaction energy on subsequent nucleation of beta phase near a pre-existing precipitate have been revealed. The results suggest that the anisotropic elastic interaction energy can promote the formation of new nucleus near the lozenge ends of the pre-existing precipitate, as explicitly substantiated by the experimental observations. The influence of different combinations of interface anisotropy and elastic strain energy on the thickness of beta phase precipitate has been elucidated. The correlation between microstructural design during precipitation and the alloy-strengthening mechanisms has also been discussed in terms of dislocation motion. Based on these results, possible strategies for strengthening Mg-Al-based alloys are proposed for magnesium alloy development and microstructural design.