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. 2019 Oct 1;12(19):3215.
doi: 10.3390/ma12193215.

Texture Evolution in AA6082-T6 BFSW Welds: Optical Microscopy and EBSD Characterisation

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Free PMC article

Texture Evolution in AA6082-T6 BFSW Welds: Optical Microscopy and EBSD Characterisation

Abbas Tamadon et al. Materials (Basel). .
Free PMC article

Abstract

One of the difficulties with bobbin friction stir welding (BFSW) has been the visualisation of microstructure, particularly grain boundaries, and this is especially problematic for materials with fine grain structure, such as AA6082-T6 aluminium as here. Welds of this material were examined using optical microscopy (OM) and electron backscatter diffraction (EBSD). Results show that the grain structures that form depend on a complex set of factors. The motion of the pin and shoulder features transports material around the weld, which induces shear. The shear deformation around the pin is non-uniform with a thermal and strain gradient across the weld, and hence the dynamic recrystallisation (DRX) processes are also variable, giving a range of observed polycrystalline and grain boundary structures. Partial DRX was observed at both hourglass boundaries, and full DRX at mid-stirring zone. The grain boundary mapping showed the formation of low-angle grain boundaries (LAGBs) at regions of high shear as a consequence of thermomechanical nature of the process.

Keywords: AA6082-T6; EBSD; bobbin friction stir welding; microstructure; optical microscopy.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic of the fully-featured Bobbin-Tool (tri-flat threaded pin and spiral scrolled shoulders).
Figure 2
Figure 2
Weld cross-section of the AA6082-T6 plates, (1) Base Metal; (2) Middle Stirring Zone; (3) Flow-arms; (4) Sub-shoulder region; (5) Advancing Side (AS) Hourglass border and (6) Retreating Side (RS) Hourglass border. The two dashed-lines in the middle are representative of the position of the pin, the dashed-line in the corners of the cross-section are representative of the width of the shoulders.
Figure 3
Figure 3
Crystallography directions in Aluminium alloys, (a) Schematic of ED, ND and TD reference directions, applied for EBSD analysis; (b) IPF colour triangle. (Source for (b) Ex EBSD machine).
Figure 4
Figure 4
Base Metal microstructure, (a) Optical microscopy and (b) EBSD colour map.
Figure 5
Figure 5
The microstructure of the Mid-Stirring Zone (SZ) region, (a) Optical microscopy and (b) EBSD colour map.
Figure 6
Figure 6
The microstructure of Flow layer patterns, (a) Optical microscopy and (b) EBSD colour map.
Figure 7
Figure 7
The microstructure of the Sub-shoulder region, (a) Optical microscopy and (b) EBSD colour map.
Figure 8
Figure 8
The microstructure of the AS Hourglass border, (a) Optical microscopy and (b) EBSD colour map.
Figure 9
Figure 9
The microstructure of the RS Hourglass border, (a) Optical microscopy and (b) EBSD colour map.
Figure 10
Figure 10
The micropatterns of the presence of low-angle grain boundaries (LAGBs, for 2°–10°) (af) in blue colour, for different regions of the weld; Base Metal (BM) (a); AS Hourglass border (b); Flow-arms (c); Sub-shoulder region (d); Mid-SZ (e); RS Hourglass border (f).
Figure 11
Figure 11
The micropatterns of the presence of high-angle grain boundaries (HAGBs, more than 10°) (af) in red colour, for different regions of the weld; BM (a); AS Hourglass border (b); Flow-arms (c); Sub-shoulder region (d); Mid-SZ (e); RS Hourglass border (f).
Figure 12
Figure 12
The Euler map micropatterns of the presence of HAGBs with post processing using a 15° angle, for different regions of the weld; BM (a); AS Hourglass border (b); Flow-arms (c); Sub-shoulder region (d); Mid-SZ (e); RS Hourglass border (f).

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