Effect of Ultrasonic Melt Treatment on Solidification Microstructure of Al–5Ti–1B Alloy Containing Numerous Inoculant Particles

The effect of ultrasonic melt treatment (UST) on the solidification microstructure of an Al–5Ti–1B alloy containing high-volume fractions of Al 3 Ti and TiB 2 particles is investigated for various UST times with different melt holding times. The as-cast Al–5Ti–1B alloy is composed of TiB 2 and polygonal Al 3 Ti particles (present prior to UST), plate-like Al 3 Ti particles, and Al grains (formed during UST and/or solidification). The UST causes a size reduction and homogeneous distribution of the TiB 2 -agglomerated region containing many submicron-sized TiB 2 particles pushed to the grain boundaries. The UST slightly decreases the size and improves the distribution of polygonal Al 3 Ti particles enriched in the TiB 2 -agglomerated region. Unlike the TiB 2 and polygonal Al 3 Ti particles, which exhibit a minor refining effect, the plate-like Al 3 Ti particles show a significant refinement with UST application. The UST has a significant effect on the size distribution of Al grains by inducing the formation of medium-sized grains at the expense of small and large grains; however, it only has a slight effect on grain refinement. The degree of microstructure modification increases with increasing UST time but decreases with melt holding time after UST. The mechanisms for the refinement and dispersion of the TiB 2 and Al 3 Ti particles and Al grains are discussed considering fragmentation, nucleation, and growth behaviors induced by the UST and subsequent solidification. Graphic abstract