等轴球晶凝固多相体系内热溶质对流、补缩流及晶粒运动的数值模拟 Ⅱ．模型的应用

MODELLING OF THE THERMO-SOLUTAL CONVECTION, SHRINKAGE FLOW AND GRAIN MOVEMENT DURING GLOBULAR EQUIAXED SOLIDIFICATION IN A MULTI-PHASE SYSTEM Ⅱ. Application of Model

利用等轴球晶三相凝固模型模拟了A356铝合金半固态浆料冷却斜槽法制备过程,研究了晶粒密度、尺寸及固相分数的分布与工艺参数的关系．结果表明,在斜槽浇注处晶粒形核密度最大,在斜槽末端晶粒尺寸、固相分数最大,在铸型中这三者的最终分布大致均匀．适当降低浇注温度有助于提高斜槽上形核密度和固相分数及降低晶粒尺寸．此外,还模拟了热溶质对流及补缩流在Al-4％Cu(质量分数)合金等轴球晶凝固过程所起的作用,以及晶粒运动及补缩流对合金自由表面和宏观偏析形成的影响．结果表明,凝固初期热对流及补缩流为主导,凝固中期热溶质对流为主导,凝固后期补缩流为主导;晶粒运动受阻程度直接影响自由表面形状,补缩流考虑与否导致完全不同的宏观偏析图．实验测得晶粒尺寸与模拟结果分布较相似,但其绝对值存在较大差异．

The developed three-phase model of globular equiaxed grain solidification has been applied to the cooling channel process of semi-solid slurry of A356 aluminum alloy. The effects of the processing parameters on the grain density, size and solid fraction have been studied. The results show that, grain density has its maximum at the pouring position of the cooling channel, the grain size and solid fraction have their maximum at the end of the cooling channel. Their distributions are almost uniform in the mold after rheocasting process. Decreasing proper pouring temperature is helpful to increase the grain density and solid fraction, and to decrease the grain size. In addition, the flow pattern of Al-4%Cu （mass fraction） solidification has been numerically investigated, showing that the thermal convection and feeding flow dominate the flow pattern at the beginning of solidification and the thermo-solutal convection dominates the middle and the feeding flow controls the end. Additionally, the effects of grain movement and feeding flow on the formation of free surface and macrosegregation have been studied. The results show that the obstacle of grain movement directly affects the shape of free surface, and completely different macrosegregation maps are obtained with considering feeding flow and without. The developed model has been validated by comparing the grain size between the measurement and simulation.