Global and Local Mechanical Properties and Microstructure of Friction Stir Welds with Dissimilar Materials and/or Thickn
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-MADE Blanks (TMBs) are sheet metals with possibly different thicknesses or materials that are joined prior to forming. The possibility of having different thicknesses and materials in a single assembly facilitates optimal distribution of material and results in effective and lean joints. Although TMBs have found numerous applications in the automotive industry, their applications are limited in the aircraft industry. That is because the high welding temperatures of fusion welding adversely affect the mechanical properties of precipitation-hardened aluminum alloys. New techniques such as machining,[1] adhesive bonding,[2,3] and alternative welding methods such as friction stir welding (FSW) have been suggested for production of TMBs in the aircraft industry. In FSW, welding temperatures are well below the melting point,[4] hence minimizing the adverse effects. The microstructure and, thus, the mechanical properties of sheets are nevertheless affected by the welding process.[4] FSW blanks exhibit highly heterogeneous microstructural features[5] and mechanical properties.[6] The link between heterogeneous microstructure and AMIR ABBAS ZADPOOR, Assistant Professor, formerly with the Materials Innovation Institute (M2i) and the Faculty of Aerospace Engineering, Delft University of Technology, is with the Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology. Contact e-mail: [email protected] JOS SINKE, Assistant Professor, and RINZE BENEDICTUS, Professor, are with the Faculty of Aerospace Engineering, Delft University of Technology, Delft 2629HS, The Netherlands. Manuscript submitted September 15, 2009. Article published online September 22, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
heterogeneous mechanical properties as well as the plasticity features of FSW TMBs must be known, because any application of the technology requires availability of such data as input for material selection, structure design, and manufacture planning. There has been a vast body of research addressing the different aspects of FSW blanks including some studies of FSW blanks with dissimilar materials or different thicknesses. A summary of the studies on dissimilarmaterial FSW is presented in Table 24 of Reference 4. For some representative samples of the more recent studies of FSW with dissimilar materials, see References 7 through 11. There has also been considerable recent interest in FSW with dissimilar thicknesses (e.g., References 12 through 15). Very limited knowledge of FSW blanks with simultaneously dissimilar alloys and thicknesses is available in the open literature. The main purpose of this article is to provide an integrated study of the different types of FSW TMBs and to contribute toward understanding how the thickness and material difference affect the microstructure and global and local mechanical properties of FSW TMBs. An extensive test matrix comprising ten different configurations (Table I) is considered. The designed test matrix allows for the study of not only the independent effects of di
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