INTERFACE STRUCTURE AND FRACTOGRAPHY OF A MAGNESIUM-ALLOY, METAL-MATRIX COMPOSITE REINFORCED WITH SIC PARTICLES

The interfacial structure in SiC-particle-reinforced, as-cast and heat -treated magnesium-alloy-matrix composites was investigated using anal ytical electron microscopy. No extensive chemical reactions were obser ved between the magnesium and the SiC particles or the SiC and the eut ectic phase. However, most of the eutectic phase appeared to nucleate at the surface of the SiC particles. In addition to the lamellar eutec tic, a fine eutectic and Mg2Si particles have been identified at the S iC surface using nanoprobe micro-analysis. As with the aluminium base composite, precipitation was observed to take place on dislocations, a nd dense precipitation was found to occur in the stress fields around the SiC particles. Examination of the fracture surface indicated that the bonding between the SiC/eutectic is stronger than between the SiC/ magnesium matrix. Intergranular cracks have been observed both in the fracture surface and also in a polished and etched section. The fractu re surface tends to exhibit a more brittle morphology in the composite than is observed in the alloy.