Microstructure and Mechanical Properties of Magnetically Controlled Narrow Gap TIG Welding Joint of Titanium Alloy Thick Plate

The microstructure factors affecting the mechanical behavior of magnetically controlled narrow gap TIG welded joint of Ti-6Al-4V alloy thick plate were systematically studied. The microhardness distribution and tensile properties at room temperature of the 100mm thick Ti-6Al-4V joint were measured. The strain distribution during tensile process was recorded by digital image correlation technology. Through comprehensive microstructure characterization, the influence of joint microstructure heterogeneity on the mechanical behavior was revealed. The results show that the tensile strength of the joint reaches 893 MPa, the joint strength coefficient is 94%, and the elongation is only 3.8%. The microstructure of heat affected zone is composed of three characteristic structures and shows a significant microstructural heterogeneity. Recovery and partial recrystallization occurs in the heat affected zone near the base metal, which exhibits the lowest hardness and strength. Yield and necking first occur in this area during tensile process. The significant microstructural heterogeneity of the joint leads to serious strain localization during tensile process, which makes the overall elongation of the joint deteriorate significantly.