Effects of processing parameters on the performance of Al grain refinement master alloys Al-Ti and Al-B in small ingots

The effects of the Ti/B ratio, the melt holding temperature and the melt mechanical agitation on the performance of aluminum grain refinement master alloys were investigated using small ingot castings. The results confirm that the presence of dissolved Ti in the melt is the key factor for effective grain refinement. Homogenizing the distribution of heterogeneous nuclei in the melt by mechanical agitation can further enhance the performance of Ti-B based master alloy. When the amount of dissolved Ti in the melt is less than the peritectic point, the columnar-equiaxed transition in master alloy treated melt is more sensitive to heat transfer variation rather than to the number of TiB2 particles retained in the melt. Slow cooling is recommended to avoid columnar growth. As the holding temperature increases, inoculation fade occurs. (C) 1997 Elsevier Science S.A.