LIU_2010_Transactions-of-Nonferrous-Metals-Society-of-China.pdf

Microstructural zones and tensile characteristics of friction stir welded joint of TC4 titanium alloy LIU Hui-jie (刘会杰), ZHOU Li (周 利) State Key Laboratory of Advanced Welding Production Technology, Harbin Institute of Technology, Harbin150001, China Received 13 October 2009; accepted 5 March 2010 Abstract: 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 α phases and transformed β phases with fine α+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. Key words: friction stir welding; titanium alloy; microstructural zones; tensile characteristics 1 Introduction Since the introduction of titanium and titanium alloys in the early 1950s, TC4 titanium alloy has in a relatively short time become backbone material for the aerospace, energy, and chemical industries due to its excellent comprehensive properties[1]. With the increase in the use of TC4 titanium alloy, the demand for high performance joints has become more and more stringent. Almost all conventional welding technologies have been applied to join TC4 titanium alloy. However, the application of fusion welding tech