Fracture Toughness of Ti-6Al-4V Titanium Alloy Welded by Keyhole Gas Tungsten Arc Welding Based on High Current

The welding of 20 mm Ti6Al4V medium plate titanium alloy was successfully realized by using keyhole gas tungsten arc welding technology. Fracture toughness of joints was investigated and researched in the paper. The fracture toughness of weld metal slightly increases about 10% than that of base metal. The microstructure of weld metal, microhardness of joint, crack propagation and fracture of weld metal has been studied. There is a large amount of disordered acicular martensite with dislocations in the weld metal, and the grain size is coarser and disordered than gas tungsten arc welding. The microhardness of the joint in weld metal and heat affected zone is basically the same, both higher than that in base metal, and most of the microhardness in weld metal and heat affected zone is distributed in the range of 330-370 HV 0.2 . The crack propagation path was zigzag with large angle deflection between 60 and 80°. The fracture is dominated by ductile fracture with a large number of dimples, and crystal facets in crack propagation zone. The coarse size of grain and fine acicular α ensure good strength and plasticity, which can improve the strength of weld metal and large the plastic zone at the crack tip, and the staggered directions of the phases makes crack propagation path zigzag. Therefore, the energy required for crack propagation is increased, and the fracture toughness of weld metal is improved.