Effect of annealing temperature on mechanical properties of welds of Ti-6Al-4V titanium alloy

This study investigates the microstructure and mechanical properties of Ti-6Al-4V welds at different annealing temperatures, aiming to clarify the role of temperature in joining thin-walled titanium alloy pipes for aerospace applications. It is found that (1) with the same annealing temperature, Widmanstätten structures are observed in the welds by laser welding, and no Widmanstätten structure is observed in the welds by TIG welding. (2) The joint performance depends on the average grain size and the dislocation of the weld. When the annealing temperature is set as 650 °C, the tensile strength of the weld by laser is slightly higher (i.e., 0.9%) than that of the weld by TIG, and the microhardness of the weld by laser shows no difference from that of the weld by TIG. The average grain size of the weld by laser is 3.48% higher than that of the weld by TIG. The KAMave of the weld by laser is 14.8% lower than that of the weld by TIG. (3) When the specimens are joined by laser welding and the annealing temperature is increased from 650 to 800 °C, the weld microstructure transforms into a basketweave structure. Both microhardness and tensile strength of the weld are decreased significantly. The average grain size of the weld is increased by 8.73%, and the KAMave of the weld is decreased by 28.3%. In summary, the impact of the annealing temperature on the joint performance of the weld by laser welding is significantly greater than that of the weld by TIG.