Microstructure and fracture characteristic of Mg–Al–Zn–Si3N4 composites

Magnesium matrix composites reinforced by three dimensional (3-D) network structure were fabricated by pressure-less infiltration technology. The 3-D network structure reinforcement and its composites exhibited special topology structure and different fracture characteristic. Metal matrix fractured in a ductile mode is manifested by small dimples and craters on the fracture surface. When the volume fraction of reinforcement is not in excess of 6%, the composite had an improved fracture toughness. This is because of the relatively homogeneous Si3N4 particles distributed in the metal matrix and the occurrence of interface reaction product such as MgAlO2 spinel phase. With the increases of volume fraction of reinforcement (>6%), the fracture toughness decreases slowly at the initial stages and then decreases rapidly towards the end. Therefore, the main fracture failure mechanisms consist of crack nucleation, growth, coalescence and crack propagation.