中文摘要：

基于二元Al-Bi偏晶合金难混溶区间凝固过程的液-液相分解及分离机制,采用欧拉法求解该合金显微组织演化的数学模型。该模型考虑了实际凝固过程中导致第二相宏观偏析的诸多复杂因素,包括形核、扩散长大、Stokes运动、Marangoni运动及重力沉降的影响。模拟结果表明,无重力条件下Marangoni力驱动L2相小液滴向中心高温区迁移,而重力条件下却呈现轴对称环流运动形式;随着冷却过程的进行,L2相在重力作用下发生沉降聚积,铸件底部L2相体积分数和液滴直径增加显著;与重力条件相比,无重力条件更有利于晶核的形成。

英文摘要：

Base on the mechanism of liquid-liquid decomposition and separation in the immiscible gap during the solidification process of Al-Bi monotectic alloys, using Euler method to solve the numerical models on the microstructure evolution. These models include nucleation, diffusion growth, Stokes motion, marangoni motion and gravity sedimentation of L2 phase, which result in macrosegregation during the real solidification process. The simulation results indicated that Marangoni force drives the droplets to move from the cold towards the hot region under non-gravity conditions, however the droplets move as symmetry circumfluence pattern under gravity conditions. As cooling time proceeds, gravity-induced droplet sedimentation leads to volume fraction and diameter of L2 phase increase obviously at the lower corner. Comparing with gravity condition, Non-gravity condition is advantage for nucleation of L2 phase.