Crystallographic Texture in Bobbin Tool Friction-Stir-Welded Aluminum
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Friction-stir welding (FSW) is a solid-state, continuous hot-shear joining process.[1] Apart from being a reliable joining technology for difficult-to-weld metals such as Al alloys, it also develops as an exciting approach to optimize local microstructures and thus local mechanical properties.[2] However, FSW creates an inhomogeneous texture distribution in the stirred zone (SZ); the regions that are influenced by the shoulder and by the probe have significantly different textures.[3,4] This may influence the integrity of the weld in subsequent performance.[4,5] To avoid such a problem, it is essential to change the characteristics of the material flow during welding. For example, stationary shoulder FSW was tried[3] to avoid the shoulder-dominated zone and obtain a uniform texture component through the whole plate. Although
JUNJUN SHEN and UCEU F.H. SUHUDDIN, Postdoctoral Researchers, SIYI HU, Master Student, and JORGE F. DOS SANTOS, Head of the Department, are with the Department of Solid-State Joining Processes, Materials Mechanics, Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max-PlanckStr. 1, 21502, Geesthacht, Germany. Contact e-mail: junjun.shen@ hzg.de FEIFAN WANG, Ph.D. Candidate, is with the Department of Solid-State Joining Processes, Materials Mechanics, Institute of Materials Research, Helmholtz-Zentrum Geesthacht, and also with the State Key Laboratory of Solidification Processing, Shaanxi Key Laboratory of Friction Welding Technologies, Northwestern Polytechnical University, Xi’an 710072, Shaanxi, People’s Republic of China. WENYA LI, Professor, is with the State Key Laboratory of Solidification Processing, Shaanxi Key Laboratory of Friction Welding Technologies, Northwestern Polytechnical University. Manuscript submitted March 6, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
this approach greatly reduces the shoulder-dominated zone, it still exists. Another approach is to increase the ratio of the shoulder diameter to weld thickness (or probe diameter) so that the contribution of the tool shoulder in material flow is increased; thereby the shoulder may generate a unique shoulder-induced texture. However, a recent study[6] has shown that probe-induced texture component is inevitable in regions close to the probe. Since bobbin tool FSW (BT-FSW) works with two shoulders, in comparison with the conventional FSW, the contribution of two shoulders would be much larger than the probe, especially in the case of a probe without any features. Therefore, BT-FSW may be a more effective way to produce a uniform texture within the SZ. While there has been considerable research on the crystallographic textures development during FSW, studies that focus on those produced by BT-FSW are limited. The present research investigates the local material flow in AA2198 after BT-FSW by electron backscatter diffraction (EBSD) technique, and discusses the crystallographic texture in the SZ. The material selected was a commercially available 3.2-mm-thick AA2198 Al alloy. The tool consisted of two convex scroll shoulde
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