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 me lt mechanical agitation on the performance of aluminum grain refinemen t master alloys were investigated using small ingot castings. The resu lts confirm that the presence of dissolved Ti in the melt is the key f actor 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 colum nar-equiaxed transition in master alloy treated melt is more sensitive to heat transfer variation rather than to the number of TiB2 particle s 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.