Objective The multi-layer multi-pass arc wel-ding process commonly employed for titanium alloys, is prone to welding quality issues such as numerous welding defects and significant post-weld deformation. Therefore, it is necessary to conduct research on the microstructure and properties of K-TIG (keyhole tungsten inert gas) welded joints in thick titanium alloys.

Method In response to the application requirements of titanium alloy components in rail transit industry, the technological issues of the commonly used TIG (tungsten inert gas) multi-layer multi-pass welding for titanium alloys are analyzed, and K-TIG welding technology is adopted to study the single-sided welding with double-sided forming process for 14-mm thick TC4 titanium alloys. Based on an analysis of the surface morphology, microstructure, mechanical properties, and microhardness of K-TIG welded joints under different process parameters, technical guidance is provided for titanium alloy K-TIG welded joints.

Result & Conclusion The heat input during the K-TIG welding process has a direct impact on the welding quality. Insufficient welding heat will lead to incomplete penetration of the weld seam, resulting in the formation of tunnel pores; excessive welding heat, on the other hand, will cause the weld seam to collapse. When the welding current is 550~600 A and the welding speed is 22~28 cm/min, the microstructure of the weld zone in the K-TIG welding of titanium alloy is mainly composed of high-temperature columnar β-titanium and basketweave α' acicular martensite. Under the optimal process conditions, the maximum tensile strength of the welded joint with a basketweave structure is close to the peak value, approximately 990.18 MPa, and its fracture location occurs at the interface between the heat-affected zone (HAZ) and the base metal. When the welding heat input is excessively high, the basketweave structure transforms into a Widmanstätten structure, which in turn leads to a decrease in the mecha-nical properties of the welded joint.