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针对具有快速凝固特征的压铸工艺,通过热传导反算法得到较准确的压铸温度场,分析压铸镁合金凝固过程冷却曲线,建立了形核密度随冷却速率变化的形核模型.采用改进CA方法,建立了适用于镁合金hcp结构的枝晶生长模型.模型考虑了溶质扩散、成分过冷、曲率过冷以及界面各向异性等重要因素,实现了镁合金不同角度枝晶生长,再现了枝晶二次及三次枝晶臂生长,定向凝固不同温度梯度及凝固速率下的枝晶竞争生长以及三维枝晶生长等特征.应用所建立的形核及生长模型模拟了AM50镁合金“阶梯”压铸件不同压铸工艺下的凝固组织,模拟结果与实验结果相吻合.
Aiming at the die-casting process with rapid solidification characteristics, the accurate temperature field of die-casting is obtained by the inverse heat conduction method and the cooling curve of die-casting magnesium alloy is analyzed, and the nucleation model of nucleation density with cooling rate is established. The dendritic growth model suitable for hcp structure of magnesium alloy is taken into account.The model takes into account such important factors as diffusion of solute, undercooling, overcooling of curvature and anisotropy of interface, and realizes the growth of dendrite at different angles of magnesium alloy, Secondary and tertiary dendrite arms growth, different temperature gradient during directional solidification and dendritic growth and three-dimensional dendritic growth under the solidification rate were studied by using the established nucleation and growth model. Pieces of different die-casting process under the solidification structure, the simulation results and experimental results are consistent.