Numerical study of the influence of mold filling conditions on the as-cast structure of Al-4 wt.% Cu ingots

In the last few decades research efforts were conducted to grasp good understanding about the origin of equiaxed and columnar grains formed during solidification. The morphological evolutions such as globular/cellular to dendritic or columnar-to-equiaxed transition were generally studied. Correspondingly, some empirical models were introduced. Nevertheless, no sufficient attention was paid to incorporation of such models together with macroscopic phenomena. A 5-phase mixed columnar-equiaxed solidification model recently proposed by the current authors was used to predict the macrostructure formation. However previous results showed that the initial melt conditions can influence the predicted structure particularly at low pouring temperature. In the current work, the impact of mold filling conditions on the final solidification structure is numerically verified in two stages: during pouring using 3-phase globular-equiaxed model; and after filling using the 5-phase mixed columnar-equiaxed model. The calculated results are compared to the as-cast structures obtained from experiments. The results demonstrated the significance of the `big bang' nucleation and the `premature' solidification occurred during pouring at low melt superheat on the as-cast structure.