Microstructure evolution in the conventional single side and bobbin tool friction stir welding of thick rolled 7085-T7452 aluminum alloy

The microstructure evolution during the conventional single side friction stir welding (SS-FSW) and the bobbin tool FSW (BB-FSW) of 7085-T7452 alloy thick plate was extensively studied by using the state-of-the-art materials characterization techniques. The Electron backscattering diffraction result...

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Bibliographic Details
Published in:Materials characterization 2018-04, Vol.138, p.48-55
Main Authors: Xu, W.F., Luo, Y.X., Fu, M.W.
Format: Article
Language:English
Subjects:
ALUMINIUM ALLOYS
Aluminum alloy
BACKSCATTERING
Electron backscattering diffraction
ELECTRON DIFFRACTION
FRICTION
Friction stir welding
GRAIN REFINEMENT
HEAT
MATERIALS SCIENCE
MICROSTRUCTURE
OPTIMIZATION
RECRYSTALLIZATION
Single side and bobbin tool
THICKNESS
WELDED JOINTS
WELDING
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Summary:The microstructure evolution during the conventional single side friction stir welding (SS-FSW) and the bobbin tool FSW (BB-FSW) of 7085-T7452 alloy thick plate was extensively studied by using the state-of-the-art materials characterization techniques. The Electron backscattering diffraction results reveal that a significant grain refinement and a larger percentage of high angle grain boundaries (HAGBs) exist in the weld nugget zone (WNZ) and the thermal-mechanical affected zone (TMAZ) compared with the base material. Meanwhile, more obviously inhomogeneous refined grains and HAGBs in WNZ along the thickness direction and a larger percentage of low angle grain boundaries (LAGBs) were observed in SS-FSW joint than that in BB-FSW joint. The change of the average grain size is the result of friction heat and strain rate of plastic deformation combined with a certain degree of recrystallization. Moreover, the recrystallization is mainly controlled by the strain rate during the FSW process. The presence of Cube and Cube ND after welding shows that the discontinuously dynamic recrystallization (DDRX) is a major factor in the final microstructural response. The research and findings help the understanding of the mechanism of microstructure homogenization and further optimizing the welding process for application. •Comparison of microstructure evolution via EBSD of SS-FSW and BB-FSW was investigated.•Friction heat, strain rate and degree of recrystallization affected grain size.•Discontinuously dynamic recrystallization occurred in the weld nugget zone.•The degree of recrystallization was mainly controlled by the strain rate.
ISSN:1044-5803
1873-4189
DOI:10.1016/j.matchar.2018.01.051