Effect of ultrasonic vibration on microstructural evolution of the reinforcements and degassing of in situ TiB_2p/Al-12Si-4Cu composites

Some issues such as clustering of TiB₂ particles, formation of long rod-like Al₃Ti particles, as well as high porosity level usually associate with the fabrication of in situ TiB_2p/Al-alloy composites via conventional stir casting technique using Ti and B as reactants. High-intensity ultrasonic vibration was introduced in our research to solve the above issues. The process involved that the original in situ TiB _2p/Al-12Si-4Cu sample with large clusters of TiB₂ particles, large long rod-like Al₃Ti particles and high porosity was remelted at 850 °C, and then ultrasonic vibration was applied to the melt with an ultrasonic probe. The microstructural evolution of the samples treated by ultrasonic vibration with different time was examined by using SEM. After treated by ultrasonic vibration for 12 min, large clusters of TiB₂ particles were broken up effectively and TiB₂ particles were dispersed uniformly in the matrix, and long rod-like Al₃Ti particles were turned into blocky ones with the size of 10 μm due to the effect of ultrasonic stirring. In the meantime, the porosity in the composites decreased from about 6.5% to 0.86% due to the effect of ultrasonic degassing. Microhardness test suggested that a homogeneous microstructure of the composite was achieved after ultrasonic treatment. An effective approach using high-intensity ultrasonic vibration to optimize the microstructures of the particulate reinforced Al-alloy composites was proposed, and the mechanism of the effect of high-intensity ultrasonic vibration on the microstructural evolution of the reinforcements and degassing of composites was also discussed in our research.