The "Lazy S" feature in Friction Stir Welding of AA2099 Aluminum-Lithium alloy
Klages, Holli K.
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The addition of Lithium to Aluminum-Lithium (Al-Li) alloys results in reduced density as well as increased stiffness and strength, and so these materials are attractive for selected aerospace structures. Friction Stir Welding (FSW) of Al-Li alloys may provide high join efficiency in such structures but potential FSW defects must be understood. This thesis examines the occurrence of the "Lazy S" feature, which may be a defect. Welds were made after various treatments of the faying surfaces and with different FSW procedures. These welds were examined and their microstructures were characterized by optical microscopy and orientation imaging microscopy. Microhardness data were acquired as well. The Lazy S feature arises as the faying surfaces are deformed and spread out during FSW. Inadequate bonding along these surfaces will constitute a weld defect.
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