Modeling of the Sump Profile During DC and MC-DC Casting Based on a Functional Packing Fraction

The sump profile during direct-chill (DC) casting provides critical information for understanding the solidification mechanism. In this work, the influence of the solid packing fraction (SPF) at the dendrite coherency point on the sump profile of DC and melt-conditioned direct-chill (MC-DC) casting is taken into account in the numerical model. It was found that the value of SPF has a significant influence on the sump profile, and that a constant value of SPF in the model cannot achieve a precise prediction of the sump profile in MC-DC casting simulation. Thus, a SPF as the function of grain size is proposed based on the data from the literature to improve the model. The results indicate that the improved model with the packing fraction function can predict a more accurate sump profile. The reason is the relationship between the grain feature and the SPF. In the model, the coarse dendritic grain structure is set as a low packing fraction value of about 0.3, but the fine globular grain structure is set as a high packing fraction value of about 0.6. The improved model has been verified by traditional DC casting and MC-DC casting of an AA6063 aluminum alloy.