Grain Refinement Mechanism and Effective Nucleation Phase of Al-5Ti-1B Master Alloy

Abstract

The Al-5Ti-1B, Al-10Ti, Al-4B master alloys and TiB2 powder were applied to refine the pure aluminum, respectively. The effects of the TiAl3 phase, TiB2 particle, and AlB2 phase on the grain size of pure aluminum were compared. The grain refinement mechanism of the Al-5Ti-1B grain refiner was studied. The results showed that the TiAl3 phase was an effective heterogeneous nucleus of the α-Al grain. But the TiAl3 phase in the Al-5Ti-1B grain refiner was not the heterogeneous nucleus of the α-Al grain due to its re-melting in the Al melt. The separate TiB2 particle or AlB2 phase was not the heterogeneous nucleus of the α-Al grain. However, the TiB2 coated by the TiAl3 phase can be the effective heterogeneous nucleus of the α-Al grain. The grain refinement mechanism of the Al-5Ti-1B grain refiner can be summarized as follows: when the Al-5Ti-1B grain refiner is added into the Al melt, the TiAl3 phases are re-melted to release the Ti atoms, while the TiB2 particles are remaining in the Al melt. During the solidification of the Al melt, the Ti atoms are segregating on the surface of TiB2 particles to form the TiAl3 phases. The TiB2 particles coated by the TiAl3 phases then reacts with the Al melt to generate α-Al crystal nucleus.