Microstructure and properties of 7075-T651 aluminum alloy friction plug welding joint

Friction plug welding (FPW) for 8 mm thickness 7075-T651 aluminum alloy sheets were carried out using 2219-T87 aluminum alloy as plug material, and the formation and microstructure characteristics of the FPW joints obtained by using different process were observed, and the properties were tested. The results show that defect-free joints can be obtained with optimized parameters, and equiaxed grains were formed at the friction interface between the plug and base material. According to the structure and morphology, the FPW joint can be divided into 6 zones: recrystallization zone, thermo-mechanical affected zone, plug thermo-mechanical affected zone, heat affected zone, plug heat affected zone and base metal. The microstructure of the thermo-mechanical affected zone grew and deformed, with the precipitation phase dissolved and coarsened. Local softening also occurred. In particular, the hardness value of the plug heat affected zone reached the lowest at about 90 − 95 HV. During the tensile test, fracture of the defect-free FPW joint happened at the plug center, with ductile features in terms of fracture mode. The maximum tensile strength and elongation of the FPW joints reached 343 MPa and 7.0%, reaching 63.8% and 77.8% of that of the base metal, respectively.