Effect of Heat Treatment on Microstructure and Properties of Titanium Alloy Welded Joint by Laser Welding with Flux-Cored Wire

Ti-6Al-4V titanium alloy plate was welded by a laser beam with self-developed titanium alloy flux-cored wire. The welded joint was solution treated at 920 degrees C for 1 h and aging treated at 650 degrees C for 2 h, and its microstructure and properties were compared with those of the alpha s-welded joint. The results show that the heat-treated welded joint is composed of a typical tri-modal microstructure containing alpha(p) phase, alpha(s) phase colony, and alpha(gb) phase, as well as punctate distributed residue beta phase. alpha' martensite microstructure in the alpha(s)-welded joint is not found in the heat-treated joint, which makes the strength, plasticity, and toughness well balanced and maintained. The strength of the heat-treated welded joint is reduced, while elongation and impact toughness at room temperature are enhanced. The tensile fracture of the heat-treated welded joint is surrounded by massive shear lips. The dimples are deep and uniform, presenting as microvoid coalescence ductile fracture. In the alpha(s)-welded joint, the proportion of large-angle grain boundaries with misorientation between grains in the weld zone greater than 15 degrees accounts for 83.78%, and in the heat-treated welded joint, the proportion is about 90.21%. Through XRD test, it is discovered that the alpha(s)-welded weld is mainly composed of alpha' martensite, with a small amount of extremely weak multi-angle alpha phase diffraction peak. In the heat-treated weld, the central angle position of alpha phase diffraction peak is consistent with that of a' martensite in the as-welded weld, with a sharp beta phase (110) diffraction peak observed as well.