Role of Solute and Transition Metals in Grain Refinement of Aluminum Alloys under Ultrasonic Melt Treatment

Abstract

It is well known that several factors affect the as-cast microstructure through influencing either nucleation or growth during solidification. The effect of solute elements on grain refinement, which can be quantified by the growth restriction parameter Q, is of great importance for controlling the as-cast grain size in aluminum alloy. On the other hand, the ultrasonic melt treatment (UST) is one of potent grain refining methods in aluminum alloy. Our previous results showed that ultrasonic melt treatment results in a significant grain refining effect in an aluminum alloy when transition metals, such as Ti and Zr, are present in the melt. It was suggested that UST may increase the nucleating potency of Al3(Zr,Ti) intermetallics. In this paper, the growth restriction effect caused by segregating elements is considered in order to further study the efficiency and potency of grain refiner particles caused by ultrasonic treatment. The results show that the main effect of transition metals Zr and Ti is related to the maximum number of particles which are active nucleants under UST. With increasing Zr, the maximum number of potent particles increases, which produces a better grain refining effect.