Continuously-casted Mg-9Al-1Zn-1Ca (in mass%) alloy (Mg-Ca alloy) and Mg-9Al-1Zn alloys (Ca-free Mg alloy) were forged at 573 K and their mechanical properties were investigated by tension tests at ambient temperature and 573 K. The forged Mg-Ca alloy showed higher 0.2% proof stress than the forged Ca-free Mg alloy. The high strength for the Mg-Ca alloy was attributed not only to grain refinement by hot forging, but also to the strengthening mechanisms arising from the difference in thermal expansion and geometrical incompatibility between Mg matrix and second phase. The Ca addition decreased the elongation to failure; however, the decrease was reduced for the forged specimens, compared to the unforged specimen. This results from segmentation of the second phases by the hot forging. Also, the forged Mg-Ca alloy showed a large elongation of 284% at 573 K
