Effect of process parameters on mechanical properties of friction stir welded 2195 Al-Li alloy joints

The weldability and mechanical properties of friction stir welded 2195 Al-Li alloy were studied in this paper.The results showed that sound welds have been successfully obtained over a wide range of parameters. The tensile strength of welded joints has a different reduction, compared to the base material. With the increasing of the rotation speed, the tensile strength and the elongation rate increased first, and decreased after reaching extremes. With the increasing of the welding speed,the tensile strength firstly increased to a maximum value and then decreased. The maximum tensile strength was 432.8 MPa,which reached to 77% of that of the base metal,when the rotation speed was 600 r/min and the welding speed was 200 mm/min. There is a hardness decrease area on both sides of HAZ just beyond TMAZ. Welding parameters affect the weakest zone of microhardness. The joints were mostly fractured at the heat-affected zone near the HAZ/TMAZ interface. With the change of the heat input, the fracture can be classified into two types. Mode 1:Fracture occurred in the heat affected zone, showing ductile fracture, with equiaxed dimple pattern and a lot of plastic slip. Mode 2:weld fracture occurs in the nugget, showing ductile-brittle mixed fracture.