Growth pattern and orientation selection of magnesium alloy dendrite: From 3-D experimental characterization to theoretical atomistic simulation

Abstract

Based on synchrotron X-ray tomography and EBSD techniques, it was found that magnesium alloy dendrite exhibits a typical 3-D growth pattern with eighteen-primary branches, of which six grow along 〈112¯0〉 in the basal plane and the other twelve along 〈112¯3〉 in non-basal planes. The underlying mechanism behind such growth pattern was investigated by determining the surface energy related anisotropy along different crystallographic orientations via atomistic simulation in light of density functional theory and hcp lattice structure. Results showed that the surface energy exhibits an orientation-dependent behavior, and these specific crystallographic planes perpendicular to which lay the preferred growth directions of α-Mg dendrite always exhibit higher surface energy. Accordingly, the orientation selection of α-Mg dendrite growth was confirmed to be 〈112¯0〉 and 〈112¯3〉, which agreed well with the experimental findings. A geometrical model was developed to illustrate the 3-D growth pattern of the α-Mg dendrite based on its outer contour shape at equilibrium energy state.