| As a solid-phase connection technology,Friction Pull Plug Welding(FPPW)technology has a broad application prospect in the field of rocket tank defect repairing.In this paper,friction pull plug welding process of aerospace high strength aluminum alloy was studied systematically.The welding joint was designed and the welding process was simulated and analyzed.Friction Pull Plug Welding(FPPW)experiments were performed on 2A70-T6 aluminium alloy plates using 2219-T6 plugs.Based on the FPPW experiment of 6mm-8mm 2A70 aluminium alloy plates,joint geometry parameters and welding process parameters were optimized.And the FPPW experiment was carried out on the rocket tank successfully.Finally,the microstructure and mechanical properties of 2A70 aluminum alloy were analyzed.Force analysis and strength check of the plug was carried out to determine the minimum diameter range of the plug under different axial force.The FPPW 3d model of aluminum alloy was established by DEFORM software.The thermal field and flow field in the welding process were simulated and analyzed,and the geometric parameter optimization of FPPW joint was guided.The results showed that the friction heat and the plastic flow of materials were mainly concentrated at the friction interface between the plug and the base metal in the welding process.The size of forming hole of backing plate is very important for welding.Lack of bonding defect formed more likely near the weld bottom if the hole diameter was too large,and reduced the depth of the upper part of the forming hole may be helpful to improve the bottom forming.Process experiment results showed that for 8mm 2A70 aluminium alloy,the use of circular arc-shaped plug,cylindrical or cylindrical+tapered hole(taper hole length2 mm,straight hole length 6mm)and stepped tapered shaped forming hole of backing plate(the hole diameter is 30 mm,groove deep is 2 mm)can improve material flow and interface combination,and improve welding defects near the weld bottom.For6 mm 2A70 aluminum alloy,defect free joint can be obtained when used axial force of22 kN-30 kN,feed speed of 2mm/s-2.5mm/s and loading rate of 20 kN/s-40 kN/s to weld.For 8mm 2A70 aluminum alloy,fewer defects formed when used 40 kN axial force to weld.Further increase of axial force may lead to necking of plug and defect may increase significantly.Finally,the microstructure and mechanical properties of 2A70 aluminum alloy FPPW joint showed that the strength loss of the FG-TMAZ in FPPW joint was very limited due to the formation of ultra-fine grain.Both sides of the interface,the TMAZ and PM-HAZ,local softening occurred due to over-aging caused by the welding process,among which the PM-HAZ softened more obviously and had the lowest hardness.Eutectic network phase particles were found in both TMAZ and PM-HAZ.With axial force of 28 kN,rotating speed of 7000r/min,welding speed of 2.5mm/s,loading rate of 20 kN/s,and feeding displacement of 11 mm,the tensile specimen of the joint reached the highest performance,which obtained for 376 MPa ultimate tensile strength and 6.2% elongation.The fracture of the joint occurred in the PM-HAZ adjoining the bonding interface. |
