G. J. Grant, R. Davies, D. Herling, E. Stephens, Battelle Pacific Northwest National Laboratory, Richland, WA; D. Waldron, Advanced Joining Technologies, Inc., Santa Ana, CA

Summary:

Post-weld forming of a welded structure or sheet is rarely done in manufacturing. The process is not considered viable for many material systems due to the limited ductility of the joint itself. For fusion welded materials, the joint is composed of generally coarse-grained weld metal showing solidification microstructure. Limited ductility can lead to flow localization during plastic deformation, and early failure of the weld in forming operations. Friction Stir Welding (FSW) produces a fundamentally different weld metal microstructure that shows grain refinement, increased ductility, and in some materials, increased strength and toughness relative to the base materials. High ductility of the FSW weld metal, and matched parent/weld flow stress can resist localization and fracture in the welded region allowing Friction Stir Welded assemblies to be successfully formed.

Friction stir welded sheet materials are already seeing application in tailor welded blanks; sheet materials welded together to form a blank for later stamping operations. Parts manufactured in this way can display cost or weight savings, and often are used to replace assemblies fabricated from multiple separate parts. Applications are also under study to join sheet materials into larger sheets that are later formed into continuous complex curvature parts for aircraft or other applications. This presentation will outline some of the efforts to characterize the ductility and forming performance of Friction Stir Welded assemblies for automotive and aircraft applications. Data will be presented on the formability of welded assemblies of Aluminum sheet materials (5xxx and 6xxx). Weld process parameters can be optimized for formability performance and data on process/performance relationships will also be presented.