A magnesium based alloy containing at least 86 wt % Mg; 4.8 to 9.2 wt % aluminum, 0.08 to 0.38 wt % manganese, 0.00 to 0.9 wt % zinc, 0.2 to 1.2 wt % calcium, 0.05 to 1.4 wt % strontium, and 0.00 to 0.8 wt % rare earth elements. The alloy may also comprise up to 0.02 wt % zirconium and up to 0.001 wt % beryllium.