Refill friction stir spot welding of 7075-T6 aluminium alloy single-lap joints with polymer sealant interlayer

With the addition of a sealant interlayer, 7075-T6 aluminium alloy sheets were refill friction stir spot welded (RFSSW). Two sealants were used in the investigations: phenol-formaldehyde resin-based adhesive and epoxy resin-based tape. Single-lap RFSSW joints were made in 0.8- and 1.6-mm-thick sheets, which corresponds to the actual thicknesses of welded stringer of aircraft skin. The welding of the sheets with polymeric interlayer lowered the tensile pure/shear load capacity of the joint from approximately 9% to 28%, according to the variant of sealant application. However, the polymer interlayer increases considerably the protection of the weld against the corrosion environment. Considering that the main indicator of joint quality is a tight interlayer of sealant between the faces of joined sheets and simultaneously a minimum degree of imperfection induced in the joint microstructure by sealant material, it can be concluded that the most advantageous joint variant is that with a single interlayer of epoxy-based tape.