Microstructure and Mechanical Properties of Arc Zone and Laser Zone of TC4 Titanium Alloy Laser–TIG Hybrid Welded Joint

Abstract

As a high-efficiency and high-quality welding technology, laser-tungsten inert gas (laser–TIG) hybrid welding has been widely used in the aerospace and marine equipment industries. Through laser–TIG hybrid welding of TC4 titanium alloy, the effect of the current on the weld formation, the microstructure and mechanical properties of the arc zone, and the laser zone was studied. The results show that the molten pool in the arc zone will flow periodically, and the flow becomes more intense with an increase in the current, which will result in a finer grain size in the arc zone than in the laser zone, having the effect of eliminating pores. The spacing of the α′ martensite beams in the laser zone is narrower, with an average spacing of 0.41 μm. The β phase increases gradually with the increase in the current, which will lead to a downward trend in the average hardness of both zones. The average hardness value of the laser zone, containing more α′ martensite and less β phase, is slightly higher than that of the arc zone. The hardness uniformity of the laser zone is also significantly better than that of the arc zone. The tensile strength of the joint shows a trend of increasing first and then decreasing, and the joint with I = 50 A presented the highest tensile strength of 957.3 MPa, approaching 100% of the base metal, and fractured in the fusion zone.