Microstructural evolution during creep of Ca-containing AZ91

The influence of Ca addition on the microstructure and creep properties of AZ91 has been investigated in this work. Creep tests in compression in the temperature range between 150 and 200 deg. C and stresses between 70 and 200 MPa show an increase in creep resistance with an increasing Ca addition. Microstructural investigations with scanning electron microscopy show that with increasing amount of Ca the intermetallic phase gets more skeletal and finer and the creep resistance increases. Thermal treatment does not significantly influence creep properties of an AZ91 alloy with 5 wt.% Ca addition. In contrast to this, pre-deformation of this alloy leads to higher creep rates compared to as-cast samples. This can also be understood by microstructural investigations, as deformation leads to fracture of the skeletal intermetallic phase, which is surrounding the α-magnesium particles.