Effect of copper addition on precipitation behaviors and mechanical properties of Mg-Zn-Cu alloys with respect to high zinc

The current work deals with the precipitation behaviors and mechanical properties of the high zinc content of the Mg-Zn-Cu system alloys using gravity casting. Differential scanning calorimetry (DSC) was conducted to describe the solidification process and precipitation behaviors. Thermodynamic calculations were carried out to determine the precipitation conditions using the Thermo-calc software. The microstructures were characterized by an optical microscope (OM), scanning electron microscope (SEM), electron probe micro analysis (EPMA), transmission electron microscopy (TEM), and confocal laser scanning microscope (CLSM). Tensile tests and micro-hardness tests were applied to investigate the mechanical properties. The results substantiated that the MgZnCu phase precipitates in Cu-containing alloys and that the precipitate content, as well as the precipitate temperature, increased with the Cu content from 0 to 3 wt.% according to the thermodynamic calculations and the DSC results. The measured micro-hardness of the alloy was 53.2, 57.9, 55.8, and 52.5 VHN, respectively. The ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) revealed a λ-like trend of the alloys, and Mg-7Zn-1Cu alloy exhibits the optimum tensile properties with the UTS of 258.9 MPa, YS of 126.2 MPa, and the EL of 14.2%.