(1. 清华大学 材料学院，北京 100084；
2. 清华大学 汽车安全与节能国家重点实验室，北京 100084)
摘 要: 基于改进元胞自动机模型和流场传输模型，模拟对流作用下的镁合金等轴晶和柱状晶组织演变过程。采用改进元胞自动机模型模拟具有密排六方结构的镁合金的枝晶生长；采用投影法求解流场传输模型耦合质量守恒方程、动量守恒方程和溶质扩散方程。不仅模拟了镁合金中单枝晶、多枝晶和柱状晶在对流作用下的生长规律，还对不同入流速度下枝晶凝固前沿的溶质分布进行定量分析。模拟结果表明：迎流端枝晶生长较快，二次枝晶臂较为发达；背流端生长缓慢，二次枝晶臂较细小或没有二次晶臂。对流作用还会改变等轴枝晶扩散层的分布，在背流端扩散层呈拖曳特性。因此，对流作用对镁合金凝固组织的演变有重要影响。
关键字: 镁合金；枝晶生长；对流；元胞自动机
（1. School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China;
2. State Key Laboratory of Automobile Safety and Energy, Tsinghua University, Beijing 100084, China）
Abstract:A model, which is based on modified cellular automaton (CA) and momentum transport, was used to model equiaxed and columnar dendritic growth of magnesium alloys with convection. The CA model was used to simulate dendritic growth of Mg alloy (hexagonal close-packed structure). The modified projection method was used to solve the flow field transport model coupled mass conservation equation, momentum conservation equation and solute diffusion equation. The growth laws of the single dendrite, multiple dendrites and columnar grain in Mg alloy were simulated, and the solute distributions of dendritic solidification front with different inflow velocities were analyzed quantificationally. The simulation results show that the dendrite growth at the upstream tip is faster than that at downstream, and secondary arms stretches intensively on the primary arms at the upstream tip, rather than that at the downstream where only a few weak or no secondary arms stretches. The flow also changes the distribution of the diffusion layer, and the diffusion layer, which spreads heavily at the downstream. Therefore, the convection has a major impact on the evolution of solidification microstructure of Mg alloy.
Key words: magnesium alloys; dendrite growth; convection; cellular automaton
