Structural Anatomy of Tunnel Void Defect in Bobbin Friction Stir Welding, Elucidated by the Analogue Modelling

Tamadon, Abbas; Pons, Dirk J.; Clucas, Don

doi:10.3390/asi3010002

Cited by 12 publications

(10 citation statements)

References 13 publications

(14 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…One line of thought is that they are cracks that propagate out from the edge of the tunnel void. This interpretation finds some support in the literature [44,45,49,61]. From this perspective the proposed explanation follows.…”

Section: Crack Formation Mechanismssupporting

confidence: 75%

“…The selected zones were only at the AS and mid-SZ. This is because the thermomechanical features are located here, and the literature shows that defects are invariably at the AS for BFSW [42][43][44][45]. The rotational and advancing motion of the tool on the AS border induces severe material shearing and compressive effect on the stirred mass.…”

Section: Regions Under Examinationmentioning

confidence: 94%

See 1 more Smart Citation

EBSD Characterization of Bobbin Friction Stir Welding of AA6082-T6 Aluminium Alloy

Tamadon

Pons

Clucas

2020

Advances in Materials Science

Self Cite

View full text Add to dashboard Cite

Electron Backscatter Diffraction (EBSD) was used to determine microstructural evolution in AA6082-T6 welds processed by the Bobbin Friction Stir Welding (BFSW). This revealed details of grain-boundaries in different regions of the weld microstructure. Different polycrystalline transformations were observed through the weld texture. The Stirring Zone (SZ) underwent severe grain fragmentation and a uniform Dynamic Recrystallisation (DRX). The transition region experienced stored strain which changed the grain size and morphology via sub-grain-boundary transformations. Other observations were of micro-cracks, the presence of oxidization, and the presence of strain hardening associated with precipitates. Flow-arms in welds are caused by DRX processes including shear, and low and high angle grain boundaries. Welding variables affect internal flow which affects microstructural integrity. The shear deformation induced by the pin causes a non-uniform thermal and strain gradient across the weld region, leading to formation of mixed state transformation of grain morphologies through the polycrystalline structure. The grain boundary mapping represents the differences in DRX mechanism I different regions of the weld, elucidates by the consequences of the thermomechanical nature of the weld. The EBSD micrographs indicated that the localised stored strain at the boundary regions of the weld (e.g. flow-arms) has a more distinct effect in emergence of thermomechanical nonuniformities within the DRX microstructure.

show abstract

Section: Crack Formation Mechanismssupporting

confidence: 75%

Section: Regions Under Examinationmentioning

confidence: 94%

EBSD Characterization of Bobbin Friction Stir Welding of AA6082-T6 Aluminium Alloy

Tamadon

Pons

Clucas

2020

Advances in Materials Science

Self Cite

View full text Add to dashboard Cite

show abstract

“…The welding speed sets were initially selected according to previous results for successful BFSW welds of aluminium, see [1,[10][11][12]14,20,27]. For aluminium plates, after running trials, the set of speeds of V (300 and 400 mm/min) and ω (650, 800 and 1000 RPM) were performed to obtain welds with no failure or material loss through the weld-line.…”

Section: Methodsmentioning

confidence: 99%

“…Therefore, the un-bonded layers of the deposited mass form the open tunnel void. The tunnel defect is representative of the continuous discontinuity at the bottom side of the AS weld region [27].…”

Section: Summary Of Outcomesmentioning

confidence: 99%

Flow-Based Anatomy of Bobbin Friction-Stirred Weld; AA6082-T6 Aluminium Plate and Analogue Plasticine Model

2020

Self Cite

View full text Add to dashboard Cite

Material flow transportation around the rotating tool and the mass deposition at the backside of the tool are critical characteristics of friction stir welding. To achieve an optimized weld structure, the history of the plastic deformation needs to be identified with a flow-based elucidation. In this study, an analogue model was applied to evaluate the formation of a banded structure using the bobbin tool, with a focus on the interaction between the tool-workpiece. The flow visualization in plasticine analogue was validated in comparison with the aluminium welds. The plastic flow mechanism was visualized both, at the surface and the cross-section of the weld-seam. The cross-section of the weld shows the details of the formation of tunnel voids, caused by the failure of the flow regimes. A physical model of the material flow was proposed to explain the formation mechanism of the tunnel void as a discontinuity during the mass refilling at the rear of the tool.

show abstract

“…By the advancing movement of the rotating tool through the joint interface, the softened and heated material of workpiece plates flows around the pin [11][12][13]. The plasticized mass at by the dark-field/bright-field illumination method the leading edge of the rotating tool transports to the trailing edge of the tool, where consolidates in form of the solid-phase weld [14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Analogue Modelling of Flow Patterns in Bobbin Friction Stir Welding by the Dark-Field/Bright-Field Illumination Method

Tamadon

Pons

Clucas

2020

Advances in Materials Science

Self Cite

View full text Add to dashboard Cite

The flow-inducing effect of the bobbin-tool features (tri-flat pin and scrolled shoulder) were replicated by a simple analogue model for aluminium welds by layered plasticine samples. Flow patterns of the weld zone were clarified by a typical stereomicroscopy instrument assisted by dark-field/bright-field illumination. The effects of the pin features, specifically threads and flats in centre of bond zone and scrolled shoulder in sides of stirred zone, were identified. This study shows that internal flow features for BFSW welds is transferable from the friction stir welding process to the functional metal forming processes such where the shearing can extensively affect the microstructure. The similarity between the flow pattern of the provided aluminium samples and the plasticine analogue can validate the accuracy of the flow model presented in this work.

show abstract

Structural Anatomy of Tunnel Void Defect in Bobbin Friction Stir Welding, Elucidated by the Analogue Modelling

Cited by 12 publications

References 13 publications

EBSD Characterization of Bobbin Friction Stir Welding of AA6082-T6 Aluminium Alloy

EBSD Characterization of Bobbin Friction Stir Welding of AA6082-T6 Aluminium Alloy

Flow-Based Anatomy of Bobbin Friction-Stirred Weld; AA6082-T6 Aluminium Plate and Analogue Plasticine Model

Analogue Modelling of Flow Patterns in Bobbin Friction Stir Welding by the Dark-Field/Bright-Field Illumination Method

Contact Info

Product

Resources

About