Simulation of Macrosegregation and Shrinkage Cavity in an Al-4.5 Wt Pct Cu Ingot Using a Four-Phase Model

A four-phase dendritic solidification model is employed to calculate the formation of macrosegregation, as-cast structure, and shrinkage cavity of Al-4.5 wt pct Cu ingot. This model couples phenomena of thermal–solutal buoyancy, crystals sedimentation, shrinkage formation, heat transfer, nucleation and growth of equiaxed grains, and columnar-to-equiaxed transition. An additional air phase is introduced to feed the shrinkage cavity during the solidification. A laboratory scale ingot with Al-4.5 wt pct Cu is fabricated for the verification of the numerical simulation results. The predicted macrosegregation, characteristics of shrinkage cavity, and as-cast structure have a good agreement with the corresponding experimental results. Furthermore, various initial mold temperatures are investigated using this numerical model. It indicates that the initial mold temperature plays an important role in the macrosegregation formation by changing the solidification sequence. The higher the initial mold temperature is, the severer the macrosegregation that will occur. Meanwhile, the higher initial mold temperature is beneficial for the growth of equiaxed grains, which results in the final as-cast structures and an increased depth of shrinkage cavity.