Stiffness loss and density decrease due to thermal cycling in an alumina fiber/magnesium alloy composite

Thermal expansion mismatch between a ceramic reinforcement and a metallic matrix can lead to thermal stresses under cyclic temperature conditions. This can lead to plastic deformation of the ductile metallic matrix, void formation at the reinforcement/matrix interface, and possible fracture of the reinforcement. Stiffness and density were used as damage parameters to study damage evolution as a function of thermal cycles in a unidirectional, continuous alumina fiber Al₂O_3f/ZE41A Mg alloy composite. Specimens were thermally cycled up to 3000 cycles between room temperature (22 °C) and 300 °C. The incidence of void formation increased with the number of cycles. Stiffness and density of this composite decreased with thermal cycling. Using Mackenzie's equation, the damage in elastic modulus was correlated to the damage in density of the composite. The damage rate in terms of modulus and density initially increased with number of cycles, and after a maximum, gradually decreased.