Microstructure and Fatigue Performance of Electron Beam Welded Joints of AZ31B Magnesium Alloy

In order to improve the microstructure and mechanical properties of magnesium alloy welded joints, a 10 mm thick AZ31B magnesium alloy plate was welded by the electron beam welding (EBW). The microstructure, element distribution, and phase composition of the EBW joints were then analyzed, and their static tensile properties and fatigue performance were measured. The results show that the microstructure and mechanical properties of the EBW butt joints all get improved. The crystal grains of the welding seam of are refined obviously. The mass fraction of Mg and Zn elements in the weld zone is decreased by 0.12% and 0.28%, respectively; while that of Al and Mn elements is increased by 0.24% and 0.14%, respectively. The fusion zone consists of single-phase α-Mg, and contains no obvious Mg17Al12 phase which has a low melting point and causes brittleness. The tensile strength of the EBW joints is 242 MPa, reaching the tensile strength of the base metals. Under 2×106 cycles and R=0.1, the fatigue strength of the EBW joints is 91 MPa, nearly 78.4% of the fatigue strength of the base metal.