Abstract: | AZ91 magnesium alloy was adopted as master alloy and rare earths (RE) of 1%, 2% and 3% additions wereadded, respectively. The influence of RE on the microstructure was investigated. By casting fluidity spiral specimens, effect of RE on fluidity was achieved. The microhardness of the alloys was tested. By casting specimens in permanent mold,tensile properties of the alloys with different RE addition at ambient and elevated temperatures were studied. The fracturemechanisms of the alloys were studied by SEM. RE additions cause the formation of Al11 RE3 precipitation besides phasechange in the alloys. RE firstly decreases and then increases the fluidity. RE has little influence on ambient temperaturetensile properties but greatly improves high temperature tensile properties at 150 C. Tensile failure of the alloys are mainly brittle cleavage and/or quasi-cleavage fracture |