Properties of friction-stir-welded 7075 T651 aluminum
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Friction stir welding (FSW), a new welding technique invented at TWI, was used to weld 7075 T651 aluminum, an alloy considered essentially unweldable by fusion processes. This weld process exposed the alloy to a short time, high-temperature spike, while introducing extensive localized deformation. Studies were performed on these solid-state welds to determine mechanical properties both in the longitudinal direction, i.e., within the weld nugget, and, more conventionally, transverse to the weld direction. Because of the unique weld procedure, a fully recrystallized fine grain weld nugget was developed. In addition, proximate to the nugget, both a thermomechanically affected zone (TMAZ) and heat affected zone (HAZ) were created. During welding, temperatures remained below the melting point and, as such, no cast or resolidification microstructure was developed. However, within the weld nugget, a banded microstructure that influences room-temperature fracture behavior was created. In the as-welded condition, weld nugget strength decreased, while ductility remained high. A low-temperature aging treatment failed to fully restore T651 strength and significantly reduced tensile ductility. Samples tested transverse to the weld direction failed in the HAZ, where coarsened precipitates caused localized softening. Subsequent low-temperature aging further reduced average strain to failure without affecting strength. Although reductions in strength and ductility were observed, in comparison to other weld processes, FSW offers considerable potential for welding 7075 T651 aluminum.
KeywordsWelding Material Transaction Fracture Zone Friction Stir Welding Heat Affected Zone
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- 1.W.M. Thomas, E.D. Nicholas, J.C. Needham, M.G. Murch, P. Templesmith, and C.J. Dawes: “Friction Stir Butt Welding,” International Patent Application No. PCT/GB92/02203 and GB Patent Application No. 9125978.8, Dec. 1991, U.S. Patent No. 5,460,317, Oct. 1995.Google Scholar
- 2.C.J. Dawes and W.M. Thomas: TWI Bull. 6, 1995, vol. 124.Google Scholar
- 3.M. Ellis and M. Strangwood: TWI Bull. 6, 1995, vol. 138.Google Scholar
- 4.C.J. Dawes and W.M. Thomas: Weld. J. 1996, vol. 75 (3), p. 41.Google Scholar
- 5.O.T. Midling: Proc. 4th Int. Conf. on Aluminum Alloys, Atlanta, GA, Sept. 1994.Google Scholar
- 8.M.W. Mahoney: Rockwell Science Center, Thousand Oaks, CA, unpublished research, 1997.Google Scholar
- 9.Weld. Met. Fabr., 1995, June, p. 214.Google Scholar
- 10.Metals Handbook, 9th ed., ASM, Metals Park, OH, 1983, vol. 6, p. 373.Google Scholar
- 11.ASM Handbook, 1st ed., ASM, Materials Park, OH, 1993, vol. 6, p. 729.Google Scholar