Mechanical behaviour and failure mechanisms of a binary Mg6%Zn alloy reinforced with SiC particulates

The mechanical behaviour in tension and fully reversed cyclic deformation as well as the fracture toughness were measured in an Mg6%Zn alloy reinforced with 20vol.% SiC particulates. The addition of the ceramic reinforcements led to significant improvements in stiffness (up to 62%) and strength, but the ductility and fracture toughness were dramatically reduced. The composite exhibited a strong rsponse to artificial aging, which increased the yield and tensile strength by 120 MPa over that of the as-received material. Cyclic strain hardening was observed in the solution heat treated condition, while the cyclic stress-strain curve was stable after artificial aging at high temperature. In addition, the cyclic yield strength in compression was always lower than in tension owing to the presence of plastic deformation by twinning in compression, which reduced the resistance to plastic flow. The failure mechanisms were very similar in all cases, regardless of the heat treatment and loading condition. Porosity and the inability of the matrix alloy to accommodate the large strain gradients induced by the presence of the SiC particulates were identified as the main causes of the poor ductility and toughness of these composites.