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The Refill Friction Spot Joining (RFSJ) is an emerging solid-state spot welding technology that thermo-mechanically creates a molecular-level bond between the work-pieces. RFSJ does not consume any filler or foreign materials so that no additional weight is introduced to the assembly. As the solid-to-liquid phase transition is not involved in RFSJ in general, there is no lack of fusion or material deterioration caused by liquefaction and solidification. Unlike the conventional friction stir spot welding, RFSJ produces a spot joint with a perfectly flush surface finish without a key or exit hole. Currently, the aerospace industry employs solid rivets for fastening the primary structures as they meet the baseline requirements and have well-established standards and specifications.

In the modern aircraft manufacturing, the cost reduction, the manufacturing time reduction, and the weight saving of aircraft are strongly demanded. The Refill Friction Spot Joining [1,2](FSJ, in other words FSSW, Friction Stir Spot Welding), which is one of innovative solid-state joining methodologies based on the Friction Stir Welding[3], is a promising technology that can replace rivets and fasteners. This technology is expected to offer cost reduction and weight saving for the aircraft manufacturing. In this study, to make stronger and reliable joints, the shoulder-plunging process of Refill FSJ was employed. The weldability of the Alodine or Chromic Acid Anodize coated materials along with a faying-surface sealant was investigated. The joint properties, such as tensile shear strengths and corrosion resistance, were evaluated.

New Refill Friction Stir Spot Welding (Refill FSSW) was performed for the aluminum alloys used for aircrafts. Joints were examined to evaluate its performances, such as tensile shear strength and strength of heat affected zone, with using various surface conditions. As a result of examination, significant lap shear strength by using shoulder plunging method was achieved with shorter process time. Even with the alodine coated aluminum alloys, strong and good quality joints can be made. And finally, actual prototype components were experimentally produced with Refill FSSW robot. Fine preproduction parts with no distortion and sufficient quality were obtained. Refill FSSW will be able to be regarded as suitable for fabrication of aircraft components.