The influence of Si and Mg rich phases on the mechanical properties of 6061 Al-matrix composites reinforced with Al2O3

Besides altering the kinetics of precipitation, the reinforcements with alumina particles appear to alter the relative proportions of the various phases formed in the matrix alloy during ageing. Alumina also seems to reduce the volume fractions of hardening phase in these materials, especially at higher contents. One reason for this effect could be the dislocation relief of the matrix strain associated with the early precipitates. Additionally, the diffusion of Mg and its subsequent incorporation into the reinforcement at the Al2O3/Al interface could also result in Mg depletion from the matrix, accounting for the reduction of the beta (Mg2Si) particle sizes. Magnesium incorporation into interfacial alumina to form MgAl2O4 has been observed in these materials. This paper shows that the nature and morphology of the second phases depend the heat treatment conditions on. (C) 2002 Kluwer Academic Publishers.