Abstract: Ansys software was used to simulate the welding and post-weld heat treatment(PWHT) process of the TC4 titanium alloy, and the changes of microstructure and residual stress of the welded and heat treated alloy were analyzed. The results show that during the welding process, the temperature of each layer of the weld varies due to different heat inputs. The peak temperature of the first layer weld is the lowest (2183.6 ℃), and the fifth layer is the highest (2337.8 ℃). Due to the different characteristics of thermal cycles experienced by each layer, the size of martensite in each layer of the weld zone changes from 19.5 μm to 96.2 μm. The weld zone after welding is mainly composed of α_m phase, a small amount of β phase, some α_t phase and precipitated α_g phase. After the PWHT, the α_m phase in the joint transforms into a secondary (α+β) phase, and it is XRD observed that the (0002)_α diffraction peak undergoes peak splitting, a new peak (110)_β appears at 2θ=39.6°, the full width at half maximum decreases by 5.56%-43.75%, indicating that the crystallinity of TC4 titanium alloy is improved with the elimination of residual stress. The residual stress after welding is mainly concentrated near the weld seam, which is a fracture prone location. The residual stress along the direction perpendicular to welding is symmetrically distributed, which is basically the same as the distribution of temperature field. After the PWHT, all the residual stresses are reduced.

Key words: TC4 titanium alloy, numerical simulation, TIG welding, post-weld heat treatment, microstructure