This paper investigated the optimal deformation temperature T c , and the optimal Zener-Hollomon parameter Z c , of both as-extruded Mg8Al and Mg-8Al-2RE alloys, to examine the capacity of these alloys for deformation. Additionally, an equation that involves the ZenerHollomon parameter Z was derived to evaluate the flow stress of these magnesium alloys at various temperatures and strain rates and was validated using a statistical method. These alloys were prepared by melting and casting in a vacuum induction furnace, and extruded at 633 K with a reduction ratio of 90 : 1. Tensile tests were performed at 473 to 723 K and at strain rates ranging from 8:3 Â 10 À4 to 8:3 Â 10 À1 s À1 . The implications of the experimental data were discussed in detail.