自然对流作用下Al-Si合金凝固过程的组织演变模拟

通过实验观察Al-Si合金的凝固组织,测量枝晶组织的二次枝晶臂间距,并分析温度对凝固组织的影响。在相场模型中引入重力引起的自然对流以预测实验条件下Al-Si合金凝固组织的演变。模拟结果与实验结果吻合良好,验证了本文中提出的模拟方法的可靠性。基于本文的耦合模型,开展一系列不同溶质含量合金柱状晶和等轴晶组织生长的二维和三维模拟,发现合金中溶质含量对凝固组织的演变几乎没有影响,而溶质膨胀系数对枝晶尖端移动速度有显著影响。本文中采用的算法极大地加快计算效率,因此,大规模的数值模拟使难以直接通过同步辐射实验观察的Al-Si合金凝固组织演变过程的研究成为可能。

Simulation on microstructure evolution of Al-Si alloy under effect of natural convection during solidification

The solidification microstructure of Al?Si alloy was observed in the experiment, the second dendrite arm spacing (SDAS) was measured, and the effect of temperature on the microstructure was analyzed. Phase-field (PF) model incorporating natural convection caused by gravity was employed to simulate the microstructure evolution of Al?Si alloy under the experimental conditions. Good agreements between the experimental and simulation results verified the reliability of the simulation approach proposed in this study. Based on the proposed model, a series of simulation cases (2D and 3D) were performed to investigate the evolution of columnar and equiaxed dendritic structures. It was found that the solute content of the alloy had little impact on the microstructure evolution, while the solute expansion coefficient had obvious effect on the dendrite tip velocities. Significant improvement of computational efficiency was achieved via novel algorithms, making it possible to perform massive simulation for studying the evolution of solidification microstructures, which is hard to be directly observed in experiments via synchrotron radiation for Al?Si alloy.