Creep studies of AZ91D pressure die casting

Creep properties of pressure die cast AZ91D magnesium alloy (9% Al-1% Zn) were investigated in the temperature range of 150-180°C and load range of 30-100 MPa. The pressure die cast material is characterized by a small grain size of about 10 μm. Creep tests were performed under constant load and under varying load. Creep rates were found to be a few orders of magnitude lower than these of pure magnesium but higher than these found by the authors in previous study for ingot casting. Elongations to fracture were found to be at least 1.5 times than these of pure magnesium. No steady state stage was observed, however a minimum creep rate was reached after approximately one third of the creep life of the specimens. The stress exponent was found to be 6.9 for 150°C and 5.4 for 180°C and was independent of temperature and stress. Transmission electron microscopy (TEM) contrast experiments show dislocation existence on other planes than the basal planes.