Abstract: The bending properties of the linear friction welded joints between TC11 and TC17 dissimilar titanium alloys was analyzed, and the weak areas of the bending plasticity of the weld zone was investigated. The mechanism of the welded joint's bending fracture was studied by hardness testing, microstructure and fracture morphology analysis. Especially, the sliding line on the bending workpiece surface was analyzed. By utilizing ultrasonic shock and high-temperature solid solution & aging heat treatment after welding, the methods that improve the bending plasticity of welded joints were explored. The results shown that the bending performance test could better characterize the macroscopic properties of the linear friction welding joints of TC11 and TC17 dissimilar titanium alloys. The bending angle of the linear friction welding joint after aging heat treatment is only 38% of the bending angle of TC17 base material and 30% of TC11 base material. It is found that bending plasticity is a weak property in the joint. The weld zone and the deformation zone on the TC17 side are the weak areas of the joint's bending plasticity, and the fracture has brittle fracture characteristics. The fracture type in the weld zone is the intergranular fracture with fine equiaxed grains. The welding interface has a significant hindrance to the slip on the TC17 side, where microscopic cracks are easily formed. The morphology of the bending fracture initiation in the deformation zone of TC17 contains shear dimples that are formed by large-area sliding shear. The grains in the TC17 side deformation zone are elongated, which prompts the formation of long slip lines and significant dislocation aggregation. Therefore, the deformation zone on the TC17 side is most likely to crack during the bending test. After implementing ultrasonic impact treatment to the welded joints, a deformation layer that is about 20 μm thick is formed on the surface of the test piece, and the bending angle of the joint increases 34%. With the high-temperature solid solution & aging treatment after welding, the bending plasticity of the joint was improved. The highest average bending angle reaches 31.2°, which represents an 82% increment. Analysis and improvement of the macroscopic plastic properties of the linear friction welded joints of the titanium alloys is represented as a significant topic of research.

Key words: titanium alloy, linear friction weld, bending performance, ultrasonic impact, high-temperature heat treatment