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 TiB 2 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. [ABSTRACT FROM AUTHOR]