Influence of Residual Titanium and Boron on Solidification of Recycled Al-7Si-0.3Mg Alloy Casting

This paper presents the influence of residual Ti and B on grain refinement process of recycled Al-7Si-0.3Mg alloy casting. Three sequences of casting process are followed; first, about 1kg of ingot was melted. The Al-5Ti-1B grain refiner was added into the melt. Then, it was poured into the graphite and steel molds. Second, the return scrap was continuously cast for 4 times (no addition of the grain refiner). Last, in order to clarify the influences of Ti and B on grain refining efficiency therefore the Al-10Ti or Al-3Ti-1B grain refiner was added during recycling process. It was found that the grain size of the sample was decreased from coarse equiaxed to fine grains by adding the Al-5Ti-1B grain refiner. However, grain sizes become coarser after increased the number recycling from 1 to 4 times, respectively. It was found that the concentration of both Ti and B gradually decreased by increased the number of recycling. The residual Ti and B in recycled scrap have minor effect on the nucleation site of grain refinement process. Grain size of recycled sample which was added the Al-3Ti-1B grain refiner has very finer grain compared to the Al-10Ti grain refiner. The TiB2 particle has powerful for a heterogeneous nucleation than the TiAl3 particle. 1