Microstructure, Texture, and Mechanical Properties of Thin Titanium Plates Jointed by Coaxial Laser-Plasma Hybrid Welding

The coaxial laser-plasma hybrid welding provides a novel method for the composition of two heat sources and achieves gently transitional butt joints with wider upper surfaces. The influence of hybrid welding parameters on the weld appearance and composite plasma behaviors had been proved with a significant composite heat source effect previously; the effect of microstructure on its mechanical properties has been investigated and explored in this paper. Finite element computation based on temperature field simulation is conducted to shed more light on the heat distribution characteristics of this novel hybrid welding method. The temperature in the hybrid-dominated region is much higher than that in the laser-dominated region. The tensile strength of the hybrid welded joints is higher than the standard requirement of base metal, and fractured at the base metal with an obvious necking, indicating as ductile fracture. The nanohardness results show the hardness rank order of the weld zone, heat-affected zone and base metal. It is revealed that the grain refinement of acicular α' martensite and fine α_g particles, the increase of distribution of the geometric necessary dislocations and the large angle grain boundary proportion in the weld zone contribute to an increase in hardness, tensile strength of the hybrid welded joint of Ti–6Al–4V. It also discloses the reason why the tensile fracture location is on the base metal. This work provides a theoretical and practical basis for the application of thin titanium alloy welding, especially at high welding speed.