建立了模拟二元合金树枝晶生长的三维元胞自动机模型, 以Al-4%Cu(质量分数)为模型合金, 模拟了合金过冷熔体中树枝晶的生长过程, 研究了来流对枝晶生长的影响. 结果表明, 来流对合金过冷熔体中三维树枝晶生长影响显著, 迎流侧枝晶尖端生长速度随来流速度的增大而增大, 枝晶尖端半径随来流速度的增大而减小; 随着来流速度的增大, 枝晶尖端选择参数减小; 在给定过冷度条件下, 随界面能各向异性的增大, 来流对枝晶尖端选择参数的影响增强; 对于给定的合金(或界面能各向异性), 来流对枝晶尖端选择参数的影响随着过冷度的增大而增强.
The dendrite morphology is determined by the interaction between the capillarity effect and the transports of heat and solute, and is significantly altered by the presence of fluid flow during solidification. A lot of numerical models have been developed to investigate the effect of fluid flow on the dendritic growth of pure materials. But up to date, only a few researches were carried out on the effect of fluid flow on the dendritic growth of alloys. The effect of fluid flow on three dimensional (3D) dendrite tip selection parameter of alloys remains an unsolved scientific problem. A 3D cellular automaton (CA) model for dendritic growth of alloys was developed in this paper. 3D CA is solved in coupling with a momentum transport model in order to predict the evolution of dendritic morphology during solidification of alloys in the presence of flow. The dendrite growth with a forced flow in an undercooled melt of an Al-4%Cu (mass fraction) alloy was simulated. The effect of forced flow on dendritic growth was investigated. The results show that a forced flow affect the three dimensional dendritic growth of an alloy significantly. The growth of the primary and secondary arm in the upstream direction is much greater than that in the downstream direction. The growth direction of the primary arm perpendicular to the flow direction tilted into the upstream direction. The dendrite tip of the primary arm perpendicular to the flow direction shows an asymmetric morphology. The degree of the tilt and the asymmetry of the tip become stronger with the increase of the forced flow velocity. With the increase of the flow velocity the growth velocity of the upstream dendrite tip increases, the radius and the selection parameter of the upstream dendrite tip decrease. For a given undercooling, the effect of forced flow on the selection parameter of the upstream dendrite tip becomes stronger with the increase of the anisotropy of the interfacial energy. For a given alloy, the effect of forced flow on the selection parameter of the upstream dendrite tip also becomes stronger with the increase of undercooling.
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