Precipitation hardening in Mg-Ca-Zn alloys

Based on thermodynamic calculations, four alloys in the system Mg-Ca-Zn produced by gravity die casting were solution treated and aged at 175 °C for different times. The scanning electron microscopy and X-ray diffraction analyses of the solutionized alloys were in good agreement with the thermodynamic calculations. In these Mg-Ca-Zn alloys, the hardness increases with aging time up to 8 hours followed by typical overaging, during which the hardness decreases. According to the calculations and scanning transmission electron microscopy analyses, the change in the hardness can be correlated to the precipitation of Ca₂Mg₆Zn₃.