Study of the channel segregation using a two-phase columnar solidification model

Abstract

A two-phase columnar solidification model was used to study the formation mechanism of the channel segregation in a Sn-10 wt.% Pb benchmark ingot. The two phases considered in the current model are the melt and columnar phase. The morphology of the columnar dendrite trunks is approximated as step-wise cylinders with constant primary dendrite arm spacing. The growth kinetics of the columnar trunks is governed by the diffusion of the rejected solute element surrounding the columnar trunks. From the 3D modelling result one can 'visualize' the dynamic formation sequence of the channel segregation. The final channel segregation pattern shows a discontinuous and lamellar- or plume-structure. The formation mechanism of the channels is due to the disturbed flow, which can accelerate and retard the local solidification rate in the mushy zone and near the solidification front. This study has also verified that the channel segregation can form in the condition without remelting, namely, remelting is not a necessary condition for channel segregation.