近液相线半连续铸造中凝固组织的多尺度模拟

建立了描述连续铸造过程的温度场模型及相变模型,通过固相率变化将宏观和介观尺度上的模拟耦合起来.利用外推边界条件对Al-Cu合金在近液相线半连续铸造过程的稳态温度场进行了计算;根据连续铸造特点,提出了用液/固相变区域中元胞的平均过冷度作为形核计算的基本参数,避免了铸件中心区域的多余形核问题.对Al-(3.5~10)%Cu合金、铸造速度为2.0 mm/s的液相线铸造的凝固组织进行了模拟,并且ZL201合金的模拟结果与实验吻合.计算表明:合金成分对半固态合金组织的形成有较大影响,当合金质量分数在(8~10)%时可获得晶粒大小和分布良好的合金组织.

Multi-scale Simulation of Microstructural Evolution in Near Liquidus Semi-continuous Casting

The models of temperature fields and phase transformation of Al-Cu alloy were developed for its continuous casting, where the change in solid fraction is available to couple the macro-scale simulation with meso-scale one. The steady state temperature field was calculated by the extrapolated non-physical boundary we proposed in the near liquidus semi-continuous casting process. The average undercooling of the cells in liquid/solid phase transformation region was taken as the principal parameter to calculate the nucleation rate in the melt by virtue of Rappaz's model, thus avoiding the extra estimation of the nucleation of the core of continuous castings. The solidifying process of Al-(3.5-10)wt% Cu alloys was simulated during liquidus casting at a casting speed 2 mm/sec. As a commonly used Al-Cu alloy, the ZL201 alloy was also simulated and the result is consistent with experimental result. The calculation showed that the content of alloying elements has great influence on the semisolid microstructural formation. When the mass fraction of Cu is 8%-10%, a microstructure can be obtained with favorable grain size and its distribution.