Influence of ultrasonic treatment on the formation of primary Al₃Zr in an Al-0.4 Zr alloy

Abstract

The effect of ultrasonic treatment on the formation of primary Al₃Zr was investigated by applying ultrasound to an Al–0.4Zr alloy. Three temperature ranges were selected, i.e., 830 to 790 °C (above liquidus), 790 to 750 °C (cross liquidus) and 750 to 710 °C (below liquidus) for ultrasonication. Using the scanning electron microscopy, both the size and morphology of the primary Al₃Zr particles were examined. It was found that the size was significantly reduced and the morphology changed from large throwing-star shape to small compact tablet shape. The mechanisms for refinement of primary Al₃Zr were discussed. It is suggested that sonocrystallization theory via activation of aluminium oxide particles is responsible for the refinement of primary Al₃Zr when ultrasonic melt treatment (UST) is applied within the fully liquid state. The refinement of primary Al₃Zr particles when UST is applied in the slurry (growth stage) is due to the sonofragmentation.