Interfacial behaviour of 6061/AI 2 0 3 metal matrix composites

Ultramicroindentation and electron probe microanalysis (EPMA) techniques were used to evaluate the behaviour of the interfaces between the particles and matrix in two aluminium based metal matrix composites. Three distinct regions were observed from ultramicroindentation corresponding to the particle, interface, and matrix. It was noted that although the hardness of the interface was consistently higher than that of the matrix, both regions exhibited age hardening behaviour. Elastic moduli values, estimated from the ultramicroindentation data, also showed that both the matrix and interfacial region exhibited age hardening behaviour, again with the interfacial region exhibiting higher stiffness than the matrix. Data from EPMA indicated that magnesium enrichment occurred in the interfacial region between the particle and the matrix and the extent of this enrichment increased with aging time. It is suggested that the high dislocation density in the matrix regions adjacent to particles, associated with differential coefficients of thermal expansion between the two phases, leads to enhanced precipitation in these regions.