1 School of Materials Science and Engineering, Tianjin University, Tianjin 300350, China 2 Tianjin Key Laboratory of Advanced Joining Technology, Tianjin University, Tianjin 300350, China 3 School of Mechanical Engineering, Tianjin University, Tianjin 300350, China 4 China Academy of Launch Vehicle Technology, Beijing 100076, China
Friction pull plug welding is one of the key technologies in the manufacturing process of rocket tank.The geometrical shape and its effect on microstructure and mechanical properties of friction pull plug welding for the 8 mm thick 2219-T87 aluminum alloy were studied. The results show that the geometry of hole and forming ring has an important effect on the interface quality of the joint. When the welding parameters are 7000 r·min-1 rotation speed, 35 kN axial tensile force and 16 mm axial feed, the use of tapered straight hole can effectively prevent the neck of plug during the welding process, so as to eliminate the lack of bonding defect. The stepped shaped forming ring can improve the stress state of interface and prevent the weak bonding defects. The microstructure analysis shows that dynamic recrystallization occurs at the base material side adjacent to the interface, and obvious plastic deformation occurs at the thermo-mechanical affected zone. The microstructure adjacent to the bonding interface is obviously softened by the welding thermal cycle and the rotary extrusion of the plug; and the lowest hardness value is about 90HV, which occurs in the thermal mechanical affected zone. When the joint has weld defects, the tensile strength of the joint significantly reduces compared with that of base material.The tensile strength and elongation of the joint without weld defects can reach 360.1 MPa and 6.45%, respectively, the joint coefficient is 0.828, and the fracture mode is ductile fracture.
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