Effect of ultrasonic treatment on the Fe-intermetallic phases in ADC12 die cast alloy

The ultrasonic treatment temperatures were varied from about 100 °C above the liquidus temperature down to the Al–Si eutectic temperature, for different treatment times (0–15 s). The results showed that the ultrasonic melt treatment was very effective to convert the long plate-like Fe-intermetallic phases (up to 200 μm length) to a highly compacted fine polyhedral/globular form (<15 μm size). The critical ultrasonic treatment temperature to affect the morphology of Fe intermetallics was found to be in the range of 596–582 °C. The eutectic Si was mostly not affected by ultrasonic treatments carried out in this study (in the temperature range of 670–581 °C and for up to 10 s). It was also observed that the nucleation undercooling, which is a measure of nucleation efficiency, at the start of solidification was lowered from ∼2.9 to ∼0.4 °C by ultrasonic treatment. The variation of horn temperature within 20 °C above pouring temperature to 10 °C below it had no noticeable effect. The ultrasonically treated samples showed better tensile properties than the untreated samples, due to the change in morphology of the Fe-intermetallic particles.