Study on Friction Stir Welding and Electron Beam Welding of Mg-Li Alloy

Experimental study on friction stir welding (FSW) and electron beam welding (EBW) of a new α+β dual phase Mg-Li alloy is carried out, providing reference for the application of this alloy in precision manufacturing. The evolution characteristics of microstructure and mechanical properties of the welded joint are analyzed in detail by optical microscope, scanning electron microscope and microhardness testing. Results show that by using proper process parameters, the α+β dual phase in the nugget zone of Mg-Li alloy FSW are both refined apparently and transformed into equiaxed grains. Moreover, the volume fraction of α-phase is relatively reduced. When the welding velocity is 15 mm/ s, the focus current is 500~540 mA and the welding current is 8~10 mA, Mg-Li alloy of 5 mm thickness is welded with full penetration. Equiaxed grains are obtained and the α-phase is dispersively distributed in the grain boundary of β-phase. By using the two processes, the microhardness (HV) of the weld zone is both approximately 13 higher than that of the base metal. In conclusion, FSW and EBW both can achieve sound joint of Mg-Li alloy with good appearance, microstructure and mechanical properties.