MECHANICAL-BEHAVIOR AND FAILURE MECHANISMS OF A BINARY MG-6-PERCENT-ZN ALLOY REINFORCED WITH SIC PARTICULATES

The mechanical behaviour in tension and fully reversed cyclic deformat ion as well as the fracture toughness were measured in an Mg-60%Zn all oy reinforced with 20 vol.% SiC particulates. The addition of the cera mic reinforcements led to significant improvements in stiffness (up to 62%) and strength, but the ductility and fracture toughness were dram atically reduced. The composite exhibited a strong response to artific ial aging, which increased the yield and tensile strength by 120 MPa o ver that of the as-received material. Cyclic strain hardening was obse rved in the solution heat treated condition, while the cyclic stress-s train curve was stable after artificial aging at high temperature. In addition, the cyclic yield strength in compression was always lower th an in tension owing to the presence of plastic deformation by twinning in compression, which reduced the resistance to plastic flow. The fai lure mechanisms were very similar in all cases, regardless of the heat treatment and loading condition. Porosity and the inability of the ma trix alloy to accommodate the large strain gradients induced by the pr esence of the SiC particulates were identified as the main causes of t he poor ductility and toughness of these composites.