Dissimilar friction stir welds in AA5083-AA6082. Part I: Process parameter effects on thermal history and weld propertie
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INTRODUCTION
FRICTION stir (FS) welding is a relatively new joining technique developed by TWI, Cambridge, in 1991.[1] The technique has been optimized for aluminum alloys, although it has also been applied to the joining of magnesium,[2] titanium,[3] and steel.[4,5] The process takes place in the solid state and appears to offer a number of advantages over conventional fusion welding techniques, such as no need for expensive consumables such as filler wire and gas shields, ease of automation on simple milling machinery, good mechanical properties of the resultant joint, and low distortion.[6,7] In addition, since welding occurs by the deformation of material at temperatures below the melting temperature,[8,9] it is possible to avoid problems commonly associated with the joining of dissimilar aluminum alloys.[10] Successful trials have been performed on the joining of various aluminum alloy series.[11–14] However, few systematic studies have been performed on dissimilar welds, and the relationships between the various weld parameters and the resulting weld properties have not been identified. The aim of this study was to investigate the extent of the so-called processing window—the range of FS welding speeds (rotation and traverse) within which good-quality welds could be produced between the dissimilar alloys AA5083 and AA6082. The approach has been to produce two sets of welds based around identical combinations of rotation and traverse speeds, with the relative positions of the alloys reversed. Furthermore, a limited number of similar material (AA5083–AA5083 and AA6082–AA6082) welds have been produced for comparison. The welds were instrumented to measure the forces and torque acting on the tool as well as the temperature within the backing plate M.J. PEEL, Post-Doctoral Fellow, A. STEUWER, Post-Doctoral Fellow, and P.J. WITHERS, Professor, are with the Materials Science Centre, Manchester University, Manchester, U.K. M.J. PEEL and A. STEUWER, Post-Doctoral Fellow, are with FaME38 at the ESRF-ILL, Grenoble, France. Contact e-mail: [email protected] T. DICKERSON, Post-Doctoral Fellow, Q. SHI, Post-Doctoral Fellow, and H. SHERCLIFF, Senior Lecturer, are with the Engineering Department, Cambridge University, Cambridge, U.K. Manuscript submitted September 27, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS A
during welding. Several welds were fitted with thermocouples to measure the thermal profile at specific points within the plate. Subsequently, the processing window has been evaluated in terms of (a) the forces acting on the tool, (b) the macroscopic material flow, with emphasis on the absence of defects, (c) the resulting microstructure, and subsequently (d) the mechanical properties of the welds. Simple models have been developed to aid the evaluation of these properties against the rotation and traverse speed variations. The first is a numeric thermal model that has been calibrated against experimental data and provides estimations of thermal data throughout the plate over the weld cycle. In addition, a hardening model has
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