Effect of heat treatment on microstructures and properties of vacuum laser welding Ti–6Al–4V titanium alloy

Vacuum laser welding of titanium alloys is currently being explored for use in UAVs and military-related fields, but the impact of post-weld heat treatment has been seldom studied. In this paper, the Ti–6Al–4V titanium alloy was welded by vacuum laser welding(VLW)with IPG 50 kW fiber laser, and analyze the microstructure and properties of the welds in as-welded state and post-welding heat treatment (850 °C/2h/FC(FC:furnace cooling)and 980 °C/10min/FC+720 °C/2h/FC).The results show that the microstructure of the as-welded weld is composed of primary columnar crystal (primary β phase) and grain boundary martensite (α′), and the microstructure of primary columnar crystal is composed of α'+ (α'+β). The proportion of high-angle grain boundary(HAGB) is 92.3%. The tensile strength is 1009 MPa, and the elongation is 9.3%. The average impact toughness at room temperature is 13J. The weld microstructure at 850 °C/2h/FC is composed of the acicular α phase and the α+β between the acicular α phases, the primary columnar crystals basically disappear, and the acicular α phases criss-cross weave into the net basket structure.The proportion of HAGB is 97.4%.The tensile strength is 988.3 MPa,and the elongation is 14.8%. The average impact toughness is 17J. The microstructure of the weld at 980 °C/10min/FC+720 °C/2h/FC is composed of the coarser acicular α phase and the (α+β) between the coarser acicular α phases. The proportion of HAGB is about 83.2%. The tensile strength is 586 MPa, and the elongation is 1.6%. The average impact toughness is 1.4J.