Structure and Mechanical Property of Friction-Stir Weld Joint of 2195-T8 Al-Li Alloy Plate

The tensile properties of friction stir weld (FSW) joint of 2195-T8 Al-Li alloy plate with 5 mm thickness prepared by straight-cylindrical (SC) pin and threaded-cylindrical (TC) pin at different rotational speeds and welding speeds were investigated. The structures of the FSW joint were detected. Results show that when prepared by SC pin at improper welding speed, continuous hole is formed in the FSW joint along the welding direction, leading to lower joint strength. TC pin alleviates the formation of hole in the weld, and the joint strength is enhanced with the rotational speed increasing from 700 to 1100 r/min at a given welding speed of 120 mm/min. The grains in the nugget zone (NZ) are recrystallized, but their size is inhomogeneous. The precipitates of T1 (Al2CuLi) and theta' (Al2Cu) in the NZ are completely dissolved. All theta' precipitates but most T1 precipitates are dissolved in the thermo-mechanically affected zone (TMAZ). Meanwhile, dislocations are formed in the NZ.