Abstract: The fatigue properties and the mechanical performance of AZ31B magnesium alloy with 8 mm thickness and its welded joint by TIG welding are studied. The results showed that the tensile strength of the base metal is 245.50 MPa and that of the butt joint, longitudinal fillet joint and transverse crossed joint are 193.55 MPa, 229.89 MPa and 227.39 MPa, respectively. The fatigue properties of AZ31B Magnesium alloy are evaluated, when the coefficient of stress cycle is zero. Under the condition of 2×106 cycles, the fatigue strength of the base metal is 57.81 MPa and that of the three types of joints are 24.60 MPa, 20.14 MPa and 17.25 MPa in turn. It is about 42.6%, 34.8% and 29.8% of that of the base metal, respectively. According to the standard of IIW, the FAT of the welded joint of magnesium alloy is about half of that of the aluminum alloy. So the fatigue properties are one of the key factors that obstructs the application of magnesium alloy for the structure suffered from the dynamic load.

Key words: AZ31B Mg alloy, Fatigue property, TIG welding, Welded joint