Simulation of α-Mg Dendrite Growth in AZ91 Magnesium Alloy Under Forced Convection Using Phase Field Method

Abstract:

During the solidification process of alloys, the flow of molten metal can significantly alter the thermodynamics of dendrite growth, thereby affecting the microstructure and mechanical properties of the components. This work established a phase field-lattice Boltzmann coupling model for the growth of α-Mg dendrites in Mg-9.0wt%Al-1.0wt%Zn alloy under forced convection, mainly studying the effect of melt convection on the growth of α-Mg dendrites. The results show that melt convection leads to asymmetric dendritic growth, with the upstream dendritic growth rate greater than the downstream one. This asymmetric morphology of dendrites becomes more pronounced with the increase in flow velocity. Through simulations of different flow velocity directions, it is found that the length of the dendrite arm is increased with the increase in angle between flow velocity direction and horizontal direction, while the thickness of the solute enrichment layer is decreased with the increase in angle. When the angle is 90°, the dendrite arm experiences the maximum shear force and deflection angle. In addition, the three-dimensional simulation results confirm that the asymmetric growth behavior of α-Mg dendrites under forced convection also exists in the three-dimensional simulation, manifested as a greater enrichment of solutes downstream and a concentration of solidification latent heat mainly upstream.