Effects of Ca addition on the hot tearing susceptibility of Mg-7Al-2Si-0.8Zn-0.5Sr-0.4Mn casting alloys were investigated.The hot crack samples were prepared by metal molds with the same length.Hot tearing susceptibility was evaluated using crack-rod critical diameter and hot tearing sensitive coefficient.The hot tearing behavior of constituent phase of the alloys were analyzed with the help of optical microscopy（OM）

scanning electron microscopy（SEM）and the detector of energy dispersive（EDX）.The results show that the microstructure of the alloys is refined with Ca addition.With 3.0% Ca addition

both the crack-rod critical diameter and hot tearing sensitive coefficient exhibit the minimum value

and fractured areas ofα-Mg dendrite and eutectic are zero and 100%

respectively.Furthermore

the eutectic phase is tended to enrich at the cracks

which establishes the ability to fill the cracks

decreasing the hot tearing susceptibility of alloy.The lower hot tearing susceptibility of the alloy is corresponding to the higher tensile strength.