Creep Behavior of AZ91 Magnesium Alloy

Effects of intermetallic phases on the creep behavior of AZ91 magnesium alloy have been studied. Thermally stable intermetallic phases such as Mg2Si and Mg3Sb2 are introduced deliberately in AZ91 alloy by the adding Si and Sb (0.5% Si, 0.5% Sb and 0.5% Si+0.2% Sb, all are in wt %). Creep tests were carried out at 150 and 200°C with an initial stress of 50 MPa on the as cast samples. It is found that the β-Mg17Al12 intermetallic phase in the AZ91 alloy suffers sever cracking and facilities cavity formation due to its low melting point and incoherency with Mg matrix, which results in poor creep resistance. On the other hand, the creep behavior of AZ91 alloy is greatly improved with the presence of Mg2Si and Mg3Sb2 intermetallic phases because of their better thermal stabilities. These intermetallic phases strengthen the grain b undary against sliding and hence, reduce the possibility of void formations during creep. Furthermore, they also promo e more number of continuous Mg17Al12 precipitates near the grain boundaries during creep, which in turn restricts the creep deformation.