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College Park, Maryland      June 6 - 10 , 2004

MP29: De-Convoluting the Influences of Plastic Deformation and Heat on Residual Stresses during Friction Stir Welding of 6061-T6 Aluminum Plates

W. Woo (Material Science and Engineering Department, University of Tennessee, Knoxville, TN 37996, USA), H. Choo (Material Science and Engineering Department, University of Tennessee, Knoxville, TN 37996, USA; Metals and Ceramics Division, Oak Ridge National Laboratory), D. W. Brown (Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA), Z. Feng (Metals and Ceramics Division, Oak Ridge National Laboratory), P. K Liaw (Material Science and Engineering Department, University of Tennessee, Knoxville, TN 37996, USA), S. A. David, C. R. Hubbard (Metals and Ceramics Division, Oak Ridge National Laboratory)

Friction-stir welding (FSW) is a solid-state joining process that makes a strong metallurgical bonding through (1) a severe plastic deformation caused by rotation of a stirring pin and (2) frictional heat generated from pressing shoulder. However, the deformation and heat necessary for the joining are also the major sources of residual stresses in the welds, which are detrimental to the integrity of the joined component.

Three different weld specimens were prepared from 6061-T6 Aluminum plates: (Case 1) a plate processed only with pin, (Case 2) a plate processed only with the pressing shoulder, and (Case 3) a plate processed with both stirring pin and the pressing shoulder, i.e., a regular friction-stir weld. The longitudinal, transverse, and through-thickness strain components were measured across the weld line using neutron diffraction and converted to stresses. The comparison among the three cases shows distinctly different residual-stress profiles clearly revealing de-convoluted effects from the different welding parameters, i.e., deformation, heat, or the combination, for the first time. The relationships between the welding parameters and residual stresses will be discussed to provide a phenomenological understanding of the micro-mechanism of the residual stress formation during the FSW.

Acknowledgements: This work benefited from the use of the Los Alamos Neutron Science Center (LANSCE) at the Los Alamos National Laboratory. This facility is funded by the US Department of Energy under Contract W-7405-ENG-36. This work is supported by the NSF International Materials Institutes program under DMR-0231320.

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