Effects of heat treatment on the microstructure and mechanical property of Mg[sbnd]6Zn[sbnd]1Cu-0.5Ce alloy

Abstract

The microstructure and mechanical properties of Mg6Zn1Cu-0.5Ce alloy under different heat-treated conditions were investigated by using OM, XRD, SEM, TEM and the tensile test. The results indicate that the alloy is mainly composed of α-Mg, CuMgZn, MgZn2, and Mg12Ce phases. After T4 treatment at 405 °C for 24 h, the eutectic phases dissolve into α-Mg matrix sufficiently and the coarse residual eutectic phases transform into fine and discontinuous particles. After T6 treatment at 160 °C for 20 h, the fine and dispersible precipitates including β1′ rods, β2′ discs and granular phase precipitate. The β1′ rods and granular precipitates are identified as MgZn2 phases and CuMgZn phases, respectively. Artificially aged alloy is strengthened mainly by β1′ rods that is perpendicular to the basal plane and granular CuMgZn phase, which hinders the movement of dislocations and grain boundaries. Conducting aging treatment at lower temperature is beneficial to increase the density of precipitates and improve the mechanical property. The tensile strength, hardness and elongation reach the value of 256 MPa, 84 HV and 12.5%, respectively. In addition, the main characteristic of fracture is transformed from the intergranular and cleavage fracture to transgranular and quasi-cleavage fracture after heat treatment.