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

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

doi:10.2478/adms-2020-0003

Cited by 9 publications

(8 citation statements)

References 33 publications

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“…The shear bands are regarded as the region of the localised plastic deformation [69,70]. During the DRX process, the nonhomogeneous deformation field (induced by the pin) causes an extensive grain deformation which leads to the large elongated grain transformation that makes up the flow-arm morphology.…”

Section: A Proposed Holistic Interpretation Of Grain Boundary Effects In Bfswmentioning

confidence: 99%

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

Tamadon

Pons

Clucas

2020

Advances in Materials Science

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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.

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Section: A Proposed Holistic Interpretation Of Grain Boundary Effects In Bfswmentioning

confidence: 99%

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

Tamadon

Pons

Clucas

2020

Advances in Materials Science

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“…The clockwise transverse transportation of the plasticised mass from the AS towards the RS around the proximity of the rotating tool causes a circulating flow condition which can be responsible for the lamella pattern [53,54]. As the generated heat at the middle of the SZ is in a higher rate compared to the sub-shoulder region [55], there are more suitable conditions for atoms to interact together and form intermetallic compounds, such as the ones within these lamella regions.…”

Section: Flow Mechanism Around the Rotating Toolmentioning

confidence: 99%

“…However, the elevated temperature can have some unpredicted effects in the uncontrolled formation of the IMCs phase in dissimilar Al-Cu welding. The mass flow model for the dissimilar joint also can be visualised by the analogue modelling of the multi-layered plasticine [53,54]. The transportation mechanism inside the plasticity region can be followed by the combined flow lines of the analogue model corresponding to the complexity of the tool profile.…”

Section: Implications For Future Workmentioning

confidence: 99%

Characterization of Dissimilar Al-Cu BFSW Welds; Interfacial Microstructure, Flow Mechanism and Intermetallics Formation

Tamadon

Abdali

Pons

et al. 2020

Advances in Materials Science

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The purpose of this study is to elucidate the flow features of the dissimilar Al-Cu welded plates. The welding method used is Bobbin Friction Stir Welding (BFSW), and the joint is between two dissimilar materials, aluminium alloy (AA6082-T6) and pure copper. Weld samples were cut from along the weld line, and the cross-sections were polished and observed under an optical microscope (OM). Particular regions of interest were examined under a scanning electron microscope (SEM) and analysed with Energy Dispersive X-ray Spectroscopy (EDS) using the AZtec software from Oxford Instruments. The results and images attained were compared to other similar studies. The reason for fracture was mainly attributed to the welding parameters used; a higher rotational speed may be required to achieve a successful BFSW between these two materials. The impact of welding parameters on the Al-Cu flow bonding and evolution of the intermetallic compounds were identified by studying the interfacial microstructure at the location of the tool action. The work makes an original contribution to identifying the solid-phase hybrid bonding in Al-Cu joints to improve the understanding of the flow behaviours during the BFSW welding process. The microstructural evolution of the dissimilar weld has made it possible to develop a physical model proposed for the flow failure mechanism.

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“…Tool pin shape has undergone several changes since the development of FSW in the year 1991. The very basic design i.e., cylindrical tool was found to create tunneling defects [9]. To avoid this defect formation, hexagonal and fluted tools were developed.…”

Section: Introductionmentioning

confidence: 99%

“…These shapes produce a pulsating action that will improve stirring. Tamadon et al, [9] used Bobbin tool to improve material flow. Thus, material mixing is a key factor to get defect free welds.…”

Section: Introductionmentioning

confidence: 99%

Numerical Studies on Temperature and Material Flow During Friction Stir Welding using Different Tool Pin Profiles

Bindu

Tide

Bhasi

2021

ARFMTS

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A three dimensional computational fluid dynamics (CFD) model has been developed to study the effect of tool pin profile on the material flow and temperature development in friction stir welding (FSW) of high specific strength AA 7068 alloy. Numerical simulations were carried out using a RNG k-e turbulence model. Three tool pin profiles, viz. cylindrical, conical and straight cylindrical threaded were considered for the simulation. The temperature distribution and material flow pattern obtained from the simulation were compared for different pin profiles. Simulation results predicted Temperature distribution and material maxing was better in straight cylindrical tapered thread pin welds. Weld joints were fabricated using the straight cylindrical threaded pin with the same parametric combinations as in the simulation. Peak temperature measured in the experiment was less than that obtained by simulation. Hardness measurements taken at different weld regions has showed that about 71% of that of the base metal hardness is obtained with the threaded tool pin. The microstructure study revealed a defect free weld joint. Precipitates distributed in the microstructure indicate sufficient heat input to join the material without dissolving precipitates. The developed numerical model is helpful in optimising FSW process parameters.

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

Cited by 9 publications

References 33 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

Characterization of Dissimilar Al-Cu BFSW Welds; Interfacial Microstructure, Flow Mechanism and Intermetallics Formation

Numerical Studies on Temperature and Material Flow During Friction Stir Welding using Different Tool Pin Profiles

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