建立偏晶合金难混溶区凝固过程的两相数学模型, 模拟研究了有、无磁场Al--10%Bi过偏晶合金微观组织演变, 研究了温度、速度、第二相体积分数等物性参数对凝固组织宏观偏析的影响。结果表明, 在磁场作用下温度场为中心对称分布, 更有利于第二相液滴的均匀分布; 电磁力抵消了部分重力和Marangoni力, 使无磁场时外环流的速度场变为有磁场时斜向下的速度场, 且速度明显降低, 从而减轻了强对流导致的重力偏析; 在磁场的作用下, 试样底部第二相的体积分数减小, 凝固组织宏观偏析得到改善。
A two–phase mathematical model for the solidification process of monotectic alloys through the miscibility gap was established. The effect of magnetic field on the microstructural evolutions of an Al–10%Bi hypermonotectic alloy was investigated, and the effect of temperature, velocity and second phase volume fraction distribution on the macrosegregation were analyzed. The results showed that the centrosymmetric distribution of temperature field in the magnetic field was more advantageous to the uniform distribution of second phase droplets. Because partial gravity force and Marangoni force were counteracted by the Lorentz force, the velocity field changed from the outward circumfluence to the moving downward slope form in the magnetic field, and the velocity reduced obviously, thus the gravity segregation caused by strong convection was suppressed. Second phase volume fraction reduced in the specimen bottom in the magnetic field, and the macrosegregation was improved.
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