Microstructure and properties of 2195 Al-Li alloy welded joints by friction stir welding

2195 Al-Li alloy-plates with 8 mm in thickness were welded by friction stir welding. The microstructures and fracture morphology of the welded joints were observed by optical microscopy and SEM,the mechanical properties at both room temperature and low temperature were studied. The results showed that the top of the joint was wide and the bottom was narrow,which looks like the shape of the letter V,and there are four zones in the joint which are weld nugget zone,thermo-mechanically affected zone,heat-affected zone and shoulder-affected zone. At the temperature of-196 ℃,the tensile strength and the elongation rate of welded joint are 71. 8% and 53. 8% of that of the base metal,respectively. The microhardness distribution of the cross section of the joint is W shape,the maximum and minimum hardness appears in the heat affected zone and the nugget zone,respectively. The tensile fracture location of the specimens is the heat-affected zone,the fracture mode is the form of ductile fracture.