Some aspects of grain refining of Al-Si cast alloys

A study on the effect of different grain refiners and addition technique in Al-7%Si alloys was carried out. The results show that the Al₃Ti phase reacts with silicon (Si) in the molten alloy forming a new compound (Al,Si)₃Ti. This reaction is independent of the grain refiner addition technique. The temperature of the liquid metal causes a significant change in the Al₃Ti phase morphology, which precipitates in the form of platelets at 750°C and in a dendritic form at 950°C. It has also been observed that while (Al,Si)₃Ti phase platelets precipitate within the α-aluminum dendrites, the TiB₂ or AlB₂ particles are rejected into the surrounding interdendritic regions. The results also reveal that addition of 100ppm B will reduce the initial grain size by ~ 85%, which is more than the reduction obtained with the addition of 0.2%Ti in the form of Al-10%Ti (about 65%).