中文摘要：

通过Al-7Si-0．36Mg合金定向凝固实验和元胞自动机模型，开展定向凝固枝晶形貌演化和一次枝晶臂间距选择过程的实验和模拟。结果表明：在给定的凝固条件下，一次枝晶臂间距范围是一个连续的变化区间。在恒定温度梯度和不同凝固速度条件下，测得Al-7Si-0．36Mg合金一次枝晶臂间距上限值（λmax）、下限值（λmin）和平均值（λave）以及生长速率之间的关系，且上限值和下限值的比值接近3。模拟结果与实验结果的吻合程度明显优于Hunt-Lu等解析模型的预测结果，表明CA模型在枝晶定向凝固过程枝晶形貌演化模拟和枝晶臂间距预测等方面的准确性。结合模拟研究和文献调研分析影响定向凝固一次枝晶臂选择的因素，包括抽拉速度V、温度梯度G、界面能大小、溶质扩散系数D_L、枝晶生长取向与热流方向的偏离角度θ等。

英文摘要：

The directional solidification dendritic morphology evolution and primary dendrite arm spacing selection process of Al-7Si-0.36Mg alloy were studied by directional solidification experiments and cellular automaton model. The results indicate that there is a continuous range of primary dendrite arm spacing under the given solidification condition. Under the condition of the given temperature gradient and various solidification velocities, the relationships between the primary dendrite arm spacing parameters （λmax, λave, λmin） Of Al-7Si-0.36Mg alloy and growth velocity were expressed, and λmax/λmin≈3. The simulated results show a quite good agreement with the experimental results, which is better than predicted results of Hunt-Lu model. The comparisons reveal that the present CA model has a high accuracy in simulating the evolution of dendrite morphology and predicting primary dendrite arm spacing in directional solidification. Based on the predictions and related literatures, the factors influencing the selection of primary dendrite ann spacing, such as growth velocity v, temperature gradient G, interracial energy effect, solute diffusion coefficient DL, as well as the deviation angle θ between the dendrite growth direction, and heat flux direction were analyzed.