基于枝晶间流动的Darcy定律, 考虑了凝固过程氢的宏观扩散与传输, 建立了耦合氢宏观偏析的铝合金铸件微观孔洞形成的数学模型, 并进行了实时熔炼的Al-4.5%Cu(质量分数)铸件的垂直向上凝固实验, 铸件微观组织和孔洞的分析结果表明: 铸件沿着高度方向包括了柱状晶、柱状晶向等轴晶转变(CET)和等轴晶3个区域; 柱状晶区域内微观孔洞体积分数存在递减的分布规律, 且邻近底部冷模的试样微观孔洞体积分数最大．采用所建立的模型对实验铸件微观孔洞形成进行了模拟, 模拟结果与实验结果吻合较好; 而当忽略氢宏观偏析时, 模拟结果与实验结果存在较大误差．研究表明, 氢的宏观偏析对微观孔洞的形核与分布具有重要影响．
Based on Darcy’s law for interdendritic flow, the present study developed a mathematical model for hydrogen porosity formation in Al castings, which specially considers the hydrogen macrosegregation including hydrogen diffusion and transport in macroscopic scale. An upward unidirectional solidification experiment of Al-4.5wt%Cu casting with in-situ melting was carried out. The microstructure analysis showed that the casting included columnar, CET (columnar-to-equiaxed transition), and equiaxed regions in upward direction. It was found that there exist a decreasing distribution of porosity in the columnar region and porosity with high content in casting part next to the bottom chill. The proposed model was applied to the experimental casting. The simulation results were in well agreement with the experiment results. It was indicated that the simulation without the hydrogen macrosegregation can’t well predict the microporosity in the casting, and that the hydrogen macrosegregation had significant influence on the predicted porosities, especially their nucleation and distribution.
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