(1. 清華大學(xué) 材料學(xué)院，北京 100084；
2. 清華大學(xué) 汽車安全與節(jié)能國家重點實驗室，北京 100084)
摘 要: 基于改進(jìn)元胞自動機模型和流場傳輸模型，模擬對流作用下的鎂合金等軸晶和柱狀晶組織演變過程。采用改進(jìn)元胞自動機模型模擬具有密排六方結(jié)構(gòu)的鎂合金的枝晶生長；采用投影法求解流場傳輸模型耦合質(zhì)量守恒方程、動量守恒方程和溶質(zhì)擴散方程。不僅模擬了鎂合金中單枝晶、多枝晶和柱狀晶在對流作用下的生長規(guī)律，還對不同入流速度下枝晶凝固前沿的溶質(zhì)分布進(jìn)行定量分析。模擬結(jié)果表明：迎流端枝晶生長較快，二次枝晶臂較為發(fā)達(dá)；背流端生長緩慢，二次枝晶臂較細(xì)小或沒有二次晶臂。對流作用還會改變等軸枝晶擴散層的分布，在背流端擴散層呈拖曳特性。因此，對流作用對鎂合金凝固組織的演變有重要影響。
關(guān)鍵字: 鎂合金；枝晶生長；對流；元胞自動機
（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
