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基于Al-Bi过偏晶合金凝固通过难混溶区阶段产生的液-液相分解及分离的运动行为,采用两相体积平均法,对质量、动量、能量、组分及液滴密度守恒方程进行数值模拟,计算中考虑了形核、扩散长大、Stokes运动及Marangoni运动等多种复杂物理现象的耦合作用,分析了两相运动速度、第二相尺寸分布、第二相体积分数分布以及液滴密度分布对过偏晶合金凝固的显微组织演变及宏观偏析的影响。结果表明,过偏晶合金凝固过程中显微组织演化在不同阶段的主要影响因素不同:凝固初始阶段主要以形核和扩散长大为主;凝固中期和后期第二相迁移运动行为将逐渐占主导作用。凝固过程中,铸件顶角位置首先获得过冷度驱动形核,并以较快的形核速率达到最大形核密度。随着凝固过程不断地进行,第二相小液滴受到的Marangoni力约为Stokes粘滞阻力的两倍,开始由铸件顶角和边缘低温区向中心高温区聚集。凝固时间为1 s时,铸件顶角和边缘第二相小液滴的生长直径和第二相体积分数大于铸件中心位置,而凝固时间为5和7 s时,第二相小液滴直径随铸件中心距离变化的曲线斜率随凝固过程的进行而逐渐变缓,长大速率逐渐变慢。
Based on the kinetic behaviors of liquid-liquid phase decomposition and separation of Al-Bi peritectic alloy during the phase of immiscible zone solidification, two-phase volume average method was used to study the mass, momentum, energy, composition and droplet density conservation equation The numerical simulation is carried out. The coupled effects of various complex physical phenomena such as nucleation, diffusion growth, Stokes motion and Marangoni motion are taken into account. The distributions of velocity, phase size distribution, volume fraction distribution of the second phase, Effect of Droplet Density Distribution on Microstructure Evolution and Macrosegregation during Solidification of Transgranular Alloys. The results show that the main influencing factors of microstructure evolution during the solidification of the transgranular alloy are different in different stages: the initial stage of solidification mainly takes place in the nucleation and diffusion growth; the migration phase of the second phase in the middle and later phases of solidification will gradually account for Leading role. In the process of solidification, the top corner of the casting first gets undercooled nucleation and reaches the maximum nucleation density at a faster nucleation rate. As the solidification progressed, the second phase droplets received a Marangoni force approximately twice that of Stokes viscous resistance and started to accumulate from the apex of the casting and the low temperature region of the edge toward the central high temperature region. When the solidification time is 1 s, the growth diameter and the second phase volume fraction of the second phase in the top corner and the edge of the casting are larger than the center of the casting. When the solidification time is 5 and 7 s, the droplet diameter of the second phase The slope of the curve of casting center distance changes slowly with the progress of the solidification process, and the growth rate becomes slower.