Effect of Ti addition on B removal during silicon refining in Al-30%Si alloy directional solidification

To determine the effect of Ti addition on B removal during silicon refining by directional solidification of Al-30 wt.% Si alloy, five samples with different amount of Ti addition have been studied. The contents of B in primary Si flakes are reduced to less than 1 ppmw with excess Ti addition. An apparent segregation coefficient is used to characterize the B removal during the refining process, which is determined to be 0.0068 with 2000 ppmw Ti addition at a pulling rate of 0.05 mm s−1. Almost all the B atoms in the Al-Si melt with the excess Ti addition combine with Ti atoms to form TiB2 particles at the bottom part of the ingot (cold end) before the primary Si growth during directional solidification, resulting in a remarkable B removal rate in the refined primary Si flakes.