强迫对流作用下AZ91镁合金α-Mg枝晶生长相场法模拟

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

摘要:

在合金凝固过程中，熔体流动会显著改变枝晶生长的热动力学，从而影响构件的微观组织和力学性能。本工作建立了强迫对流作用下Mg-9.0wt%Al-1.0wt%Zn合金α-Mg枝晶生长的相场-格子Boltzmann耦合模型，主要研究了熔体对流对α-Mg枝晶生长的影响。结果表明，熔体对流会导致枝晶生长的不对称形态，上游的枝晶生长速率大于下游，且流速越大枝晶的不对称形态越显著。通过对不同流速方向的模拟，发现枝晶臂长度会随流速方向与水平方向夹角的增大而增大，而溶质富集层厚度则会随夹角的增大而减小，当夹角为90°时，枝晶臂受到剪切力最大，偏转角度也最大。此外，三维模拟结果证实，强迫对流作用下α-Mg枝晶的不对称生长行为在三维模拟中同样存在，表现为下游溶质富集程度更大，而凝固潜热主要集中在上游。

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.