Study on the Microstructure Changes of Hypereutectic Aluminum Casting Alloy Using Ultrasonic Vibration Process

Abstract

The microstructure changes using the ultrasonic vibration process method and Al-P refiner on permanent mold castings of hypereutectic aluminum alloy (Al-20Si) were studied using optical microscopy. The Al-P refiner refined the primary silicon phase from a large polyhedral shape to a smaller polyhedral shape, but had no effects on the morphology of the eutectic silicon phase. However, in samples subjected to ultrasonic vibration during the solidification process, both primary and eutectic silicon phases were significantly refined and modified respectively. Furthermore, the aluminum phase was also significantly changed. Small polyhedral silicon particles and globular aluminum grains were formed in the region near the probe (zone one). In the region far away from the probe (zone two), the primary silicon refined as in zone one, while the partly eutectic phase changed to globular alpha aluminum phase and polyhedral silicon phase.