Fracture of PM hot extruded and cast particle reinforced aluminium matrix composites

Particle reinforcement is an efficient way to improve, for example, the stiffness and wear resistance of aluminium alloys, but tends to severely reduce ductility and fracture toughness. To encourage the use of these materials by designers and maintain the toughness in manufacturing, tools are needed to account for such reduction. The fracture toughness of PM hot extruded and cast silicon carbide particle reinforced aluminum alloys was tested. Crack propagation was examined by scanning electron microscopy (SEM) of the fracture surfaces. SEM examination showed that a crack tends to propagate through regions where particles cluster to form a relatively brittle region. Tougher regions with less particles tend to retard crack propagation by bridging the crack. On the basis of these results, a model for fracture of particle reinforced metal matrix composites is proposed. In this fracture model, ductile ligaments are assumed to bridge the crack in a brittle matrix. The ratio of fracture toughness value of the brittle zone to that of the matrix alloy appears to be the main factor controlling the crack path and reduction in overall fracture toughness of these materials.