Mechanism of the growth pattern formation and three-dimensional morphological transition of hcp magnesium alloy dendrite

Abstract

Based on an anisotropy function with the anisotropic strength determined via atomistic calculations, the mechanism of the three-dimensional (3D) growth pattern formation of magnesium alloy dendrite is investigated by performing phase-field simulations with the parallel adaptive-mesh-refinement algorithm. It is found that the 3D morphological transition of the $\ensuremath{\alpha}$-Mg dendrite is dependent on the growth parameters, including the partition coefficient, the anisotropic strength, and the supercooling during solidification. The $\ensuremath{\alpha}$-Mg dendrite exhibits growth tendency along both the basal and nonbasal directions, but the dendritic growth tendency along the basal direction is weaker. Consequently, the 3D morphology of the $\ensuremath{\alpha}$-Mg dendrite would transform from an 18-primary-branch pattern to a 12-primary-branch pattern if the local growth driving force on the basal plane is insufficient. During dendrite growth, the solute concentration increases as the distance from the dendritic nucleus center increases, and reaches the local maximum at the solid/liquid interface, beyond which it decreases before reaching a constant value. The simulation results agree well with those found in experiments and the existing solidification theory.