| The DC continuous casting of a grain refined Al-4.5%Cu round ingot with realistic boundary conditions is numerically simulated. The study uses a previously developed two-phase model that incorporates descriptions of heat transfer, solute redistribution, melt convection, and solid transport on the system scale with microscopic models of solutal undercooling, microsegregation and grain impingement. An efficient numerical algorithm for the solution of the model equations is developed. The numerical implementation is carried out in a commercial Computational Fluid Dynamics (CFD) code (PHOENICS) capable of solving two-phase equations.; The results of ten different numerical simulations are presented. These simulations explore the sensitivity of predictions to grain transport, grain density, contraction driven flow, pouring conditions and mold arrangements. The numerical results indicate that grain transport inhibits the formation of inverse segregation in the ingot shell and promotes negative centerline segregation. On the other hand, simulations with stationary solid (no grain transport) predict inverse segregation in the ingot shell. This inverse segregation is shown to be a result of contraction driven flow. Furthermore, centerline segregation is shown to depend on the permeability of the mushy zone. A relatively more permeable mushy zone is shown to positively segregate the ingot central region. A simple instantaneous nucleation model is implemented in a couple of simulations (with stationary solid). Fine grains at the ingot surface and relatively larger grains at ingot center were predicted.; Macrosegregation predictions in the case of stationary solid agree better with the experiment of Finn et al. (Finn, T. L., Chu, M. G., and Bennon, W. D., "The Influence of Mushy Region Microstructure on Macrosegregation in Direct Chill Cast Aluminum Copper Round Ingots," Micro/Macro Scale Phenomena in Solidification, ed. C. Beckermann, L. A. Bertram, S. A. Pien, and R. A. Smelser, HTD-Vol. 218/AMD-VoL 139, pp. 17-26, 1992). Nonetheless, grain transport cannot be neglected because the more severe centerline segregation reported by other investigators indicates the importance of grain transport. The aspects of the model that need improvement are identified. |
