Deformation characteristics and microstructural evolution in friction stir welding of thick 5083 aluminum alloy
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The microstructure development in the weld key-hole along the plate thickness was investigated through scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) techniques. A fundamental understanding of the contact condition at the tool/workpiece interface in a TriflatTM designed friction stir welding (FSW) tool is presented. The development of grain structure for “stop-action” weld reveals that the plasticized material undergoes complex interacting flows due to the presence of threads and flats. The localized high material velocities induce a significant increase in the strain rate within thread space and thereby tune the Zener-Hollomon parameter. An interesting analogy is drawn between the evolution of the secondary shear zone (SSZ) in a typical metal cutting and the steady state FSW processes. The presence of different morphology of the material filling the thread space is linked to the local variation of the contact state variables along weld thickness. It was found that the contact state is governed by the intrinsic interface characteristics and the mechanical property of the material. It was also shown that the presence of larger particles (> 0.5 μm) is responsible for the formation of high angle boundaries (HAGBs) and random recrystallization texture within the stir zone, reflecting random grain orientation due to particle-stimulated nucleation (PSN).
KeywordsFriction stir welding Particle-stimulated nucleation Stop-action weld Deformation state Weld key-hole
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The authors would like to thank the staffs of the welding workshop of the Joining and Welding Research Institute of Osaka University for their cooperation and support. The authors also express their sincere thanks to Dr. Probir Saha at Indian Institute of Technology (IIT) Patna for the valuable suggestions in this work.
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