INTERFACIAL STRUCTURE AND FRACTURE OF ALUMINUM-ALLOY A356-SIC PARTICLE METAL MATRIX COMPOSITE

The interfacial structure in a SiC particle reinforced aluminium alloy matrix composite has been investigated using analytical electron microscopy. It was established that no appreciable chemical reaction takes place at either silicon/SiC particle or aluminium/SiC particle interfaces. Segregation of certain alloy elements was observed using an electron microprobe. Depletion of magnesium was found to occur at the aluminium/SiC particle interfaces. Precipitation was observed on dislocations, particularly in the region of the SiC/aluminium interface. Microcracks were found at silicon/SiC particle interfaces and their probable causes are discussed. Fracture surfaces were carefully examined using scanning electron microscopy. The results imply that the silicon-SiC bonding is more brittle than the aluminium-SiC bonding. Cracks were also found in the fracture surfaces, which suggests that intergranular separation had occurred. The fracture surface tends to exhibit a more brittle morphology in the composite when compared with that in the alloy.