Microstructural zones and tensile characteristics of friction stir welded joint of TC4 titanium alloy

TC4 titanium alloy was friction stir welded using a W-Re pin tool, and the defect-free weld was produced with proper welding parameters. The joint consists of stir zone, heat affected zone and base material. The stir zone is characterized by equiaxed dynamically recrystallized a phases and transformed β phases with fine a+β lamellar microstructure. The microstructure of the heat-affected zone is similar to that of the base material, but there is an increase in the volume fraction of β. Transverse tensile strength of the joint is 92% that of the base material, and the joint is fractured in the stir zone and the fracture surface possesses typical plastic fracture characteristics. The stir zone is the weakest part of the joint, through which the tensile characteristics of the TC4 joint can be explained.