MMCs with controlled non-uniform distribution of submicrometre Al 2 O 3 particles in 6061 aluminium alloy matrix

By employing spherical agglomerate of submicrometre Al₂O₃ particles, a novel composite with controlled non-uniform reinforcement distribution was produced by the squeeze casting technique. The resulting composite has a microstructure in which composite spheres, consisting of Al reinforced by small Al₂O₃ particles, are uniformly distributed in a particle free Al matrix. The response of mechanical properties to the controlled non-uniform distribution of the reinforcement was investigated and the fracture mechanism was discussed in order to understand experimentally the influence of particle clustering on the deformation characteristics. It is demonstrated that a composite with such a controlled microstructure exhibits significant increase in ultimate tensile strength (UTS), elastic modulus, and also a slight increase in ductility compared to composite with a homogeneous microstructure at a given volume fraction. It is proposed that the composite spheres act as units of reinforcement when subjected to deformation and contribute positively to the modulus, UTS, and hardness. The higher ductility is attributed to the extensive ductile deformation of the Al matrix. In addition, the highly restrained deformation observed in the interagglomerate region can also be beneficial to the high strength.