Dendrite orientation selection in magnesium-based alloys

We study the directional solidification of Mg-Al alloys utilizing the phase field method. The hexagonal crystal structure of Mg-based alloys introduces a six-fold morphological symmetry, whose orientation with respect to the temperature gradient direction greatly influences the resulting microstructure. We find that different types of microstructure form as the cooling rate and anisotropy strength vary. Particularly, at high anisotropy strength and low cooling rates, main stalks cross at 60-degree angles that characterize the hexagonal crystal structure. As cooling rate is increased, a degenerate seaweed structure develops. Our results compare well with Haxhimali's work [11] wherein the competition between the first two cubic harmonics that characterize the surface energy anisotropy leads to the formation of various dendritic structures.