On the mechanism of the formation of primary intermetallics under ultrasonic melt treatment in an Al-Zr-Ti alloy

Abstract

Ultrasonic melt treatment (UST) is known to induce grain refinement in aluminum alloys, especially when transition metals like Zr and Ti are present. The refinement of primary intermetallics (e.g. Al3Zr, Al3(Zr,Ti)) caused by UST may influence the subsequent solidification process when intermetallics act as nucleation sites. In this paper, an Al-Ti-Zr alloy is used to analyse the effect of different ultrasonic intensities on the formation of these primary intermetallics. The possible nucleation behaviour of Al3Zr particles during UST is also discussed and an edge to edge matching model is used to make a preliminary analysis of lattice mismatch between aluminum oxide and Al3Zr phase. The experimental results show that when UST is applied, the Al3(Zr,Ti) particles might nucleate on aluminum oxides and remain fine during solidification.