Modeling of macrosegregation due to thermosolutal convection and contraction-driven flow in direct chill continuous casting of an Al-Cu round ingot

Macrosegregation in direct chill (DC) continuous casting of an Al-4.5 wt pet Cu round ingot is numerically simulated. The model incorporates descriptions of heat transfer, solute redistribution, and melt convection on the system scale with microscopic relations for grain growth, solutal undercooling, and microsegregation. Simulations are conducted to study the effects of mushy zone permeability, thermosolutal convection, and solidification contraction on the macrosegregation pattern in a DC casting. The results indicate that centerline segregation can be either positive or negative, depending upon the grain density in and permeability of the mush. In addition, it is shown that the flow induced by solidification contraction not only causes inverse segregation at the ingot surface, but also has a significant influence on the macrosegregation across the central portion of the ingot. A comparison with temperature and macrosegregation patterns measured in a previous experiment shows reasonable agreement. Several areas for future model improvements are identified.