Microstructure and mechanical properties of TC4 titanium alloy K-TIG welded joints
(1. School of Mechanical and Transportation Engineering, Guangxi University of Science and Technology, Liuzhou 545006, China;
2. School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510640, China;
3. SAIC Liuzhou Automobile Transmission Co., Ltd., Liuzhou 545006, China)
2. School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510640, China;
3. SAIC Liuzhou Automobile Transmission Co., Ltd., Liuzhou 545006, China)
Abstract: The 12 mm-thick Ti-6Al-4V (TC4) titanium alloy plates were welded using keyhole tungsten inert gas (K-TIG) welding at various heat inputs. The microstructure, grain boundary (GB) characteristics and mechanical properties of the weld metal zone (WMZ) were analyzed. The test results show that the K-TIG welds are well formed, and no obvious defects are observed when the heat input is 2.30-2.62 kJ/mm. When the heat input gradually increases, α laths increase in length, and α′ phase and residual β phase are reduced. The electron backscatter diffraction (EBSD) test results indicate that the high-angle GB proportion in the WMZ increases with the increase of heat input. The tensile strength of the WMZ gradually decreases and the elongation of the WMZ increases when the heat input increases from 2.30 to 2.62 kJ/mm. The impact toughness of the WMZ increases as the heat input increases.
Key words: K-TIG welding; heat input; α′ phase; high-angle grain boundary; Charpy impact fracture surface