Influence of Al2O3 or ZrO2 particulate addition on the microstructure aspects of AlNi and AlSi alloys

Different metal/ceramic composites (Al7Si0.3Mg, Al3Ni, Al6Ni, Al9Ni) reinforced with Al₂O₃ or ZrO₂ were prepared by vortex method. Metallographic investigations reveal that in all the composites -Al did not nucleate on the reinforcement particulates. The particulates were generally observed to be located in the last freezing regions regardless of matrix alloy, particulate type or size. The reason for that was the mismatch in the thermal diffusivity between the ceramic particulates and matrix alloys. SEM micrographs show that the presence of the particulates in the AlSi alloy tends to modify the silicon eutectic. In contrast, the addition of the particulates into AlNi alloys did not result in a significant modification of the NiAl₃ phase, but it displaced the eutectic point to lower Ni content.