Age Hardening and Microstructure of ZA84 Magnesium Alloy with the Combined Addition of Cr and Bi

Abstract The age hardening and microstructure of ZA84 magnesium alloy with the combined addition of Cr and Bi was studied by SEM and HRTEM. The results show that a trace amount of Cr and Bi has a significant enhancement effect on the hardness of aging. When the ZA84-0.2Cr-0.5Bi alloy was aged at 160 °C, during the early aging period, the matrix has serious lattice distortion and a large number of crystal defects. The microstructure at the peak aging consists of a large number of rod-like or blocky β′ 1 -MgZn 2 phases and granular Bi 2 Mg 3 phases, and the peak hardness HV value is 924.8 MPa. When ageing proceed, the precipitates coarsening results in the hardness value reduction.