铝合金铸件充型过程及氧化膜卷入的数值模拟

对于直接有限差分法，提出了单元表面无量纲距离、表面充填比率和体积充填比率，以描述铸件充型过程中自由表面的形状，建立了相应的充型过程数学模型，考虑了自由表面形状对动量、质量和能量传输的影响；提出了充型过程自由表面碰撞中表面氧化膜破碎，及其后破碎氧化膜流动的计算模型。对实验铝合金铸件进行了模拟应用，通过实际铸件充型过程的特殊X射线实时观察和记录。及实际铸件的气孔、收缩缺陷分布的检测，对模拟结果进行了验证分析。结果表明：充型过程模拟结果与X射线实时观察结果吻合较好，尤其是自由表面的变化；氧化膜卷入模拟结果与实际铸件气孔、收缩缺陷的分布存在一定的对应关系。

Numerical simulation of oxide entrapment and mold filling process of Al casting

Surface dimensionless distance, surface filled ratio and volume filled ratio for the direct finite difference method(DFDM) elements were proposed to describe the shape and position of free surface in simulation of mold filling process. The model of the process, taking into account the effect of free surface on transfer of momentum, mass and energy, was established. The method of estimating the breakup of oxide films on free surfaces during collision of the surfaces as well as judging movement of the entrapped broken oxide films was proposed. The model and method were applied to an experimental Al casting. By in-situ observation and recording actual mold filling process of the casting with special X-ray apparatus, and measuring porosities of the casting, the simulation results were further verified and analyzed. The simulation results indicate that mold filling are in good agreement with in-situ X-ray observation, especially in the evolution of free surface, and that the simulation results of entrapped oxides has some relationships with the distribution of porosities in the actual casting.