Abstract:The microstructure of Mg-8Zn-4Al-1Ca aged alloy was investigated by TEM and HRTEM. The results show that the hardening produced in the Mg-8Zn-4Al-1Ca alloy is considerably higher than that in the Mg-8Zn-4A1 alloy. A dense dispersion of disc-like Ca₂Mg₆Zn₃ precipitates are formed in Mg-8Zn-4Al-1Ca alloy aged at 160 °C for 16 h. In addition, the lattice distortions, honeycomb-looking Moiré fringes, edge dislocations and dislocation loop also exist in the microstructure. The precipitates of alloy aged at 160 °C for 48 h are coarse disc-like and fine dispersed grainy. When the alloy is subjected to aging at 160 °C for 227 h, the microstructure consists of numerous MgZn₂ precipitates and Ca₂Mg₆Zn₃ precipitates. All the analyses show that Ca is a particularly effective trace addition in improving the age-hardening and postponing the formation of MgZn₂ precipitates in Mg-8Zn-4Al alloy aged at 160 °C.

Key words: Mg-8Zn-4Al-1Ca alloy; age hardening; Ca₂Mg₆Zn₃; Moiré fringe