The deformation mechanisms of FCC metals such as aluminium are well understood and documented. For HCP metals however, there is not as much information available. This is due to the complexity of HCP crystal deformation. In order to understand the mechanical properties of magnesium and its alloys, their deformation mechanisms must first be analysed.Magnesium is a soft metal, but can be strengthened by alloying with aluminium and zinc, such as the AZ91 alloy. The composition of AZ91 is 8.1-9.3% Al, 0.4-1.0% Zn and 0.1% maximum Cu.