Improvement of mechanical property on TC17 welded joints with backing plates by TIG + brazing hybrid welding

TIG welding is used for TC17 titanium alloy butt welding with backing plates. The silver-based brazing materials as interlayer is applied and a hybrid joint is obtained comprising two metallurgical bonding zones based on two different kinds of joining mechanisms. The microstructure and mechanical properties of welding specimens are compared under TIG welding and TIG + brazing hybrid welding methods. The microstructure evolution of different welded joints is characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and X-ray diffractometer (XRD). Microhardness test and shear punch test are employed to investigate the mechanical properties of each micro-zone in welded joints. The results show that the welding arc has been focused on the middle area of the two butt plates during the welding. Titanium alloy and brazing materials fusion welding process is realized at the titanium alloy-brazing materials interface, and interdiffusion reaction occurred in these regions. The microhardness distribution trends of welded joints under the two welding methods is similar, and base metal (BM) > heat-affected zone (HAZ) > weld metal (WM). The highest microhardness value is found in the brazed area (BA) with an average value of approximately 429 HV. The shear load of TIG + brazing hybrid welded joints in the WM is 1897 N and the 2256 N in the BA which is significantly higher than TIG welded joints.