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

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 degrees C (above liquidus), 790 to 750 degrees C (cross liquidus) and 750 to 710 degrees 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.