Effect of Welding Wire Composition and Post-Welding Heat Treatment on Microstructure and Hardness of New Type α+β Titanium Alloy Welded Joint

Multi-layer and multi-pass tungsten inert gas shielded welding is used for α+β titanium alloy sheets belonging to the new type Ti-Al-Mo-V-Cr-Zr-Sn series. This method has the advantages of low connection temperature, little impact on thebase metal, and not limited by the size of material. The microstructures and Vickers hardness distributions of the welded joints prepared with two kinds of welding wires with different content of β stable elements are studied and analyzed. As the distance from the fusion zone decreases, the base material gradually changes from the Widmanstatten structure to basket-wave structure with the secondary α phase crossing, and the hardness of the heat affected zone is always higher than that of the base material and the fusion zone. The average hardness of the fusion zone of the welded joint of the welding wire with low β stable element contents is about 299.4HV. Reducing the β stable element contents of the welding wire can significantly coarse the α lamellas in the fusion zone, and the average hardness of the fusion zone reduces to 275.5HV. Three different post weld heat treatments are performed on the two kinds of welded joints. It is found out that there is no significant change in the sizes of the α lamellas in the fusion zone and the secondary α phases in the heat affected zone treated at 650 ℃ and 700 ℃. However, the α lamellas and secondary α phases coarsen when the joint is treated at 750 ℃, and the average hardness of the heat-affected zone of the welded joint is reduced to be close to that of the fusion zone and the base metal. The average hardnesses of the two welded joints are 311.7HV (welding wire with high contents of β stable elements) and 293.7HV (welding wire with low contents of β stable elements). Therefore, the element contents of the welding wire and the post weld heat treatment temperature can be changed to adjust the microstructure to control the hardness distribution of the welded joint.