中文摘要：

通过引入溶质再分配、溶质扩散、界面能各向异性和界面曲率，构建了描述合金凝固微观组织形态演变的2D元胞自动机模型。并用该模型研究了Al-4．5mass％Cu合金凝固过程中树枝晶长大过程。结果表明：该模型较好地描述了枝晶生长、晶间和枝晶偏析。凝固过程中的溶质再分配直接影响着树枝晶的生长形貌和微观偏析形成。成份过冷是液／固界面失稳的主要原因，激发二次晶或三次晶产生。二次晶生长是相互竞争的过程，在成分过冷和曲率过冷作用下，二次晶根部溶质富集程度大，出现明显的“颈缩”。在枝晶生长过程中，枝晶间会形成小范围、高溶质浓度的孤立液体区域，形成晶间偏析或点偏析，树枝晶形貌对晶间偏析程度影响较大。在各枝晶臂上，先凝固部分溶质浓度较后凝固部分溶质浓度低，并且中心溶质浓度较边缘处溶质浓度低，形成枝晶偏析，枝晶偏析在枝晶的亚稳态生长阶段更显著。

英文摘要：

By adopting solute redistribution, solute diffusion, anisotropy of interface tension and interface curvature, a 2D cellular automaton model describing microstructure evolution during alloy solidification is developed. The presented model can finely depict dendrite growth, dendrite segregation and interdentritic segregation. The solute redistribution severely affects dendritic morphology and micro-segregation formation. Concentration undercooling is the main reason for the instability of solid/liquid interface and the formation of high-order dendrite arms. The growth of secondary dendrites is competitive, and the ＇ neck shrinkage＇ is evident under the effects of concentration undercooling and curvature undercooling. There exist some small molten pools with higher solute concentration in inter-dendrite area, which will be the sources of interdendritic segregation or point segregation, and the segregation degree is evidently affected by the dendritic morphology. On the dendrite arms, concentration of the early solidified parts is lower than that of the later solidified parts, and the center is lower than that of the edges, so the dendrite segregation is produced which is prominent at the stage of metastable dendritic growth.