The effect of holding conditions in the conventional halide salt process on the performance of Al-Ti-B grain refiner alloys

Holding the molten alloy at 800 degrees C for 30 min under induction stirring in the conventional halide salt method gives the best performance. Higher temperatures, longer holding times and mechanical, instead of induction, stirring during holding lead to an extensive oxidation of the melt and thus to some loss of Ti which in turn hurts the grain refining efficiency. The variations in the performance of grain refiner alloys, however, cannot be accounted for by the Ti levels alone. Mixing of the spent K-Al-F salt is believed to wet the boride particles, impairing their potency as nucleation sites and leading to their agglomeration at the same time. It is thus inferred that even small amount of K-Al-F salt that remains on the molten alloy after decanting poses serious threat to the performance of the grain refiner alloy and is thus claimed to be responsible for the variation in the efficiency of the commercial grain refiner alloys. (c) 2006 Elsevier B.V. All rights reserved.