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Based on die casting AZ81 alloy, this article focuses on the effects of adding alloying elements (0.5%Pb, 0.5%Pb+0.5%Sn、0.5%Pb+1.0%Sn) on its microstructure and mechanical properties at room temperature and 180℃. 1) In the alloy of AZ81-0.5%Pb-1.0%Sn, there was polygon Mg2Sn phase at grain boundary. In the meantime, Pb and Sn suppressed the formation of precipitation Mg17Al12 at grain boundary to a certain extent, which contributed to the medium temperature resistance. 2) At room temperature, the tensile strength and yield strength of the alloys increased with the increase of Sn. The tensile strength and yeild strength of die casting AZ81-0.5Pb-1.0Sn at room temperature were 211 MPa and 150.5 MPa, respectively. 3) At 180℃,the tensile and yeild strength increased with the increase of Sn as well. The tensile strength and yeild strength of die casting AZ81-0.5Pb-1.0Sn alloy at 180℃ were 200.5 MPa and 145.2 MPa, respectively. 4) The Pb-Sn made the fracture mechanism transferred from plasticity to brittleness.