Effects of elemental additions (Si and Sb) on the ageing behavior of AZ91 magnesium alloy

Effects of Si and Sb additions on the ageing behavior of AZ91 alloy have been investigated. Additions of Si and Sb lead to the formation of thermally stable Mg2Si and Mg3Sb2 intermetallic phases, respectively, which are stable even after solution treatment at 410 °C for 48 h. Ageing treatment of AZ91 alloy at 200 °C results in the formation of Mg17Al12 phases in two morphologies: (i) discontinuous and (ii) continuous. Further the results of the present study have shown that individual and combined additions of Si and Sb suppress the formation of discontinuous precipitate during ageing. Dense populations of continuous precipitates observed around the hard intermetallic phases reduce the amount of chemical driving force required for both the initiation and propagation of discontinuous precipitates. In spite of these observations, the hardness measurements of aged alloy samples indicate that the alloying additions do not improve the peak hardness of AZ91 significantly.