LAUSR

This investigation is an attempt to optimize the ultrasonic treatment (UST) temperature to refine the microstructure of A380 diecastings. As a preliminary estimation, isothermal UST was performed at the liquidus temperature, slightly above and at elevated temperature. This was followed by filling in a permanent mold. The ultrasonic vibrations were also applied to A380 at the same temperatures before being injected into the shot sleeve for diecasting. It was observed that in the isothermal treatment of both grain-refined and ungrain-refined alloys the UST at 600 °C and 595 °C changed the microstructure to a much finer and non-dendritic compared to UST at 620 °C. The effect was higher in the grain-refined alloy where Fe-phase transformed to a more globular form with UST at 600 °C and 595 °C. In case of diecasting without ultrasonic, coarse Si particles and massive Fe-intermetallics were observed. Applying UST to the melt of grain-refined alloy at high pouring temperatures (700 and 670 °C) did not show substantial effects on either Fe-intermetallics or Si particles. On the other hand, the grain-refined A380 alloy showed much finer grain sizes, highly globular Fe-phase and modified Si particles when UST is at lower pouring temperatures (640 and 620 °C). However, at pouring temperature of 675 °C, the unrefined alloy showed some grain refining while no effects on Fe-particles were observed.