Effect of second phases on the high temperature mechanical properties of squeeze cast Mg-Al alloys

Effect of second phases on high temperature tensile properties of several squeeze cast Mg-Al alloys have been investigated. The alloys were chosen to have different types of second phases in the microstructure; precipitates (AM60 and AZ91D) and dispersoids (AZ61-0.7Si-0.2Ca and AZ61-0.7Si-0.1P). It shows that AZ91D alloy shows the largest decrease in strength with increasing temperature. The sudden hardness drop Of Mg17Al12 phase at 200degreesC is responsible for such behavior, in addition to the decrease in the volume fraction and coarsening Of Mg17Al12 precipitates when exposed at high temperatures. On the other hand, the AZ61-Si-Ca and AZ61-Si-P alloys show less degree of change in strength with temperature than AZ91D alloy, This is mainly due to the presence of thermally stable Mg2Si dispersoids in the microstructure. It has also been shown that the AZ61-Si-Ca and AZ61-Si-P alloys have small strain rate sensitivity values at high temperature, suggesting that these alloys have improved creep resistance over AZ91D alloy.