The production of AlSi alloy-SiCp composites via compocasting: some microstructural aspects

Aluminiumsilicon alloy (Al-5%Si-0.2%Mg) based composites containing different volume fractions of reinforcing SiC particles are produced using the compocasting route. The particles of SiC were incorporated by a special stirrer and the slurry was poured into a permanent die of certain dimensions, preheated to various temperatures, in order to obtain different cooling rates during the solidification of the composite ingots. The microstructural characteristics such as dendrite arm spacing, SiC particle distribution, porosity and phases present in the microstructures of the composites were investigated by using light microscope, scanning electron microscope with microprobe attachment and X-ray diffractometer. High incorporation levels were obtained by using reasonably short mixing times. The ingots cast into moulds having temperatures of 80°C and below showed homogeneous SiC particle distribution. The samples with SiC volume fraction lower than 17% contained little porosity, and no formation of harmful Al4C3 was observed in any of the samples produced.