Simulation of directional solidification with steep thermal gradients

The convection and macrosegregation predicted by a simulation of a directionally solidified binary alloy (Pb-23.2 wt%Sn) are presented, and the simulated macrosegregation is compared with the macrosegregation in an experimental casting. The casting was solidified at a rate of 6 μm s^-1 and a thermal gradient of approximately 7.2 × 10³ K m^-1; such thermal gradients are much greater than those previously simulated. The calculated results showed channels at the vertical casting surfaces and segregated internal pockets in the mushy zone, in agreement with the observation of freckles in the experimental casting.