Microstructural control and hardening response of Mg–6Zn–0.5Er–0.5Ca alloy

The effects of heat treatment on microstructures and hardening response of Mg–6Zn–0.5Er–0.5Ca (wt%) alloy were investigated by optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM) in this paper. The results show that the Mg–6Zn–0.5Er–0.5Ca alloy contains Mg₃Zn₆Er₁ quasicrystalline phase (I-phase) and Ca₂Mg₆Zn₃ phase under as-cast condition. Most of the Ca₂Mg₆Zn₃ phases and I-phases dissolve into matrix during heat treatment at 475 °C for 5 h. After the as-solution alloy was aged at 175 °C for 36 h, a large amount of MgZn₂ precipitate with several nanometers precipitate. It is suggested that the trace addition of Ca results in refining the size of the precipitate, and the presence of the nanoscale MgZn₂ phase is the main factor to improve the peak-aged hardness greatly to 87 HV, which increases about 40 % compared with that of as-cast alloy.