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 degrees C/2h/FC(FC:furnace cooling) and 980 degrees C/10min/FC+720 degrees C/2h/FC).The results show that the microstructure of the as-welded weld is composed of primary columnar crystal (primary 8 phase) and grain boundary martensite (alpha ' ), and the microstructure of primary columnar crystal is composed of alpha'+ (alpha'+8). 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 degrees C/2h/FC is composed of the acicular alpha phase and the alpha+8 between the acicular alpha phases, the primary columnar crystals basically disappear, and the acicular alpha 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 degrees C/10min/FC+720 degrees C/2h/FC is composed of the coarser acicular alpha phase and the (alpha+8) between the coarser acicular alpha 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.