J. Brown, B. M. Tweedy, C. A. Widener, D. A. Burford, W. Horn, G. Talia, Wichita State University, Wichita, KS
Riveting and resistance spot welding are the dominant fastening methods for thin gauge materials in the Aerospace and Automotive industries. Sealants are often used to prevent corrosion in the crevice created at the faying surface of a lap joint. Previous experimentation has shown the capability of Friction Stir Welding (FSW) in lap joints through a sealant in 7075 series aluminum. This experiment investigates the capability of welding though sealants in swept Friction Stir Spot Welding (FSSW) in 2xxx series thin gauge aluminum. Swept FSSW differs from plunge and retract or refill FSSW, which involve no translation of the pin tool in the plane of the workpiece. Swept FSSW has the typical plunge and retract motion with the addition of a closed loop translation that increases the shear area, while maintaining the characteristics of a discrete fastener system. The aluminum sheets include a sealant and are pre-treated with various surface coatings. The uncured sealants were applied to the faying surface of the test coupons shortly before joining. The results are also compared to bare sheets in the untreated condition. A single pin tool has been selected for use in this experiment. The pin tool was selected after several developmental experiments involving a number of different pin tool designs. The pin tool chosen was the one which showed the most promise of successfully welding through the sealants and surface treatments. The welds were mechanically tested through static tension per the NASM 1312-4 specification. To determine the susceptibility to corrosion, the weld coupons were corroded using the ASTM B117 salt spray test method, followed by metallographic analysis. Work in this area is important to support increased implementation of FSSW in production applications as a replacement for other discrete fastening methods, like riveting and resistance spot welding.
Summary: The purpose of this investigation is to evaluate the ability of swept friction stir spot welding to join thin gauge aluminum alloys through various faying surface sealants and treatments using static tension and corrosion testing.
