Friction pull plug welding process and joint quality evaluation for large-scale aluminum alloy rocket tanks

To meet the demand for high-quality repair welding during the manufacturing and service of rocket tanks, an implementation scheme for friction pull plug welding (FPPW) of rocket tanks was proposed. This scheme mainly covered defect localization, welding head attitude adjustment, defect removal, and in-situ repair welding. The quality of the repaired joint was verified by nondestructive testing, leak-tightness testing, microstructural observation, and mechanical property testing. The results show that the scheme can achieve high-quality plug hole machining and stable repair welding formation. The joint exhibits sound macroscopic morphology without defects such as cracks, lack of fusion, and pores, and its leak-tightness testing results meet the leak detection requirements of tanks. Different microstructural regions are formed within the joint, and dynamic recrystallization eliminates the original interface between the plug and the tank materials, realizing metallurgical bonding. The tensile results show that the joint achieves an ultimate tensile strength of 322.2 MPa, a joint efficiency of 0.80 relative to the 2219-T6 plug material, and an elongation after fracture of 8.2%. The fracture surface shows dimple features, and the fracture mode is mainly ductile fracture. This study can provide a reference for the engineering application of the FPPW technology in the repair welding of rocket tanks.