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The influences of processing parameters and tool feature on the microstructure of AA1100 and AA3003 aluminium alloys were investigated using bobbin friction stir welding (BFSW). The research includes flow visualization and microstructural evolution of the weld texture using the metallographic measurement method. Results indicated that the operational parameters of the welding (e.g. feed rate, rotating speed) and the geometry of the tool can directly affect the flow patterns of the weld structure. The microscopic details revealed by the optical and electron microscope imply the dynamic recrystallization including grain refinement and precipitation mechanisms within the stirring zone of the weld region. The microscopic observations for the weld samples show a better performance of the fully-featured tool (tri-flat threaded pin and scrolled shoulders) compared to the simple tool without inscribed surface features. The fully-featured tool resulted in a more uniform thermomechanical plastic deformation within the weld structure along with the precipitation hardening and the homogeneity of the microstructure.
Abbas Tamadon; Dirk J. Pons; Kamil Sued; Don Clucas. Internal Flow Behaviour and Microstructural Evolution of the Bobbin-FSW Welds: Thermomechanical Comparison between 1xxx and 3xxx Aluminium Grades. Advances in Materials Science 2021, 21, 40 -64.
AMA StyleAbbas Tamadon, Dirk J. Pons, Kamil Sued, Don Clucas. Internal Flow Behaviour and Microstructural Evolution of the Bobbin-FSW Welds: Thermomechanical Comparison between 1xxx and 3xxx Aluminium Grades. Advances in Materials Science. 2021; 21 (2):40-64.
Chicago/Turabian StyleAbbas Tamadon; Dirk J. Pons; Kamil Sued; Don Clucas. 2021. "Internal Flow Behaviour and Microstructural Evolution of the Bobbin-FSW Welds: Thermomechanical Comparison between 1xxx and 3xxx Aluminium Grades." Advances in Materials Science 21, no. 2: 40-64.
A variety of tool shoulder designs comprising three families i.e. blade, spiral and circular shaped scrolls, were produced to improve the material flow and restrictions to avoid the tunnel void. The bobbin tools were manufactured by 3D printing additive manufacturing technology using solid filament. The butt weld joint was produced by each tool using plasticine as the workpiece material. The apparent surface features and bi-colour cross-sections provided a physical flow comparison among the shoulder designs. For the bobbin friction stir welding (BFSW), the tool shoulder with a three-spiral design produced the most stability with the best combination of the flow patterns on surface and cross-sections. The circular family tools showed a suitable intermixing on the surface pattern, while the blade scrolls showed better flow features within the cross-sections. The flow-driven effect of the shoulder features of the bobbin-tool design (inscribed grooves) was replicated by the 3D-printed tools and the analogue modelling of the weld samples. Similar flow patterns were achieved by dissimilar aluminium-copper weld, validating the accuracy of the analogue plasticine for the flow visualization of the bobbin friction stir welding.
A. Tamadon; D. J. Pons; K. Chakradhar; J. Kamboj; D. Clucas. 3D-Printed Tool Shoulder Design for the Analogue Modelling of Bobbin Friction Stir Weld Joint Quality. Advances in Materials Science 2021, 21, 27 -42.
AMA StyleA. Tamadon, D. J. Pons, K. Chakradhar, J. Kamboj, D. Clucas. 3D-Printed Tool Shoulder Design for the Analogue Modelling of Bobbin Friction Stir Weld Joint Quality. Advances in Materials Science. 2021; 21 (1):27-42.
Chicago/Turabian StyleA. Tamadon; D. J. Pons; K. Chakradhar; J. Kamboj; D. Clucas. 2021. "3D-Printed Tool Shoulder Design for the Analogue Modelling of Bobbin Friction Stir Weld Joint Quality." Advances in Materials Science 21, no. 1: 27-42.
Need – There is a need to better understand the shear and plastic deformation that arises during clinch joint formation. Since microstructural texture preserves a history of deformation, grain structure has the potential to reveal the role of the operational parameters. Objective – This study elucidates the grain morphology of clinched joints using electron backscattering diffraction (EBSD) microscopy. Results – The main characteristics of grain morphology are equiaxed grains in the base material, with markedly elongated grain morphology and smaller grains in the necked region. Interpretation – The morphology is attributed to extensive plastic deformation causing the mechanochemical effect of dynamic recrystallization whereby localised recrystallization occurs along with transformation of grain morphology, followed by subsequent solutionizing and precipitation. Originality - An explanation is provided for the microstructural transformations during the clinching process.
Sia A. Nourani; Dirk J. Pons; Abbas Tamadon; Digby Symons. Microstructural deformation in the clinching process. Journal of Advanced Joining Processes 2021, 3, 100041 .
AMA StyleSia A. Nourani, Dirk J. Pons, Abbas Tamadon, Digby Symons. Microstructural deformation in the clinching process. Journal of Advanced Joining Processes. 2021; 3 ():100041.
Chicago/Turabian StyleSia A. Nourani; Dirk J. Pons; Abbas Tamadon; Digby Symons. 2021. "Microstructural deformation in the clinching process." Journal of Advanced Joining Processes 3, no. : 100041.
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.
A. Tamadon; D. J. Pons; D. Clucas. EBSD Characterization of Bobbin Friction Stir Welding of AA6082-T6 Aluminium Alloy. Advances in Materials Science 2020, 20, 49 -74.
AMA StyleA. Tamadon, D. J. Pons, D. Clucas. EBSD Characterization of Bobbin Friction Stir Welding of AA6082-T6 Aluminium Alloy. Advances in Materials Science. 2020; 20 (4):49-74.
Chicago/Turabian StyleA. Tamadon; D. J. Pons; D. Clucas. 2020. "EBSD Characterization of Bobbin Friction Stir Welding of AA6082-T6 Aluminium Alloy." Advances in Materials Science 20, no. 4: 49-74.
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.
A. Tamadon; M. Abdali; D. J. Pons; D. Clucas. Characterization of Dissimilar Al-Cu BFSW Welds; Interfacial Microstructure, Flow Mechanism and Intermetallics Formation. Advances in Materials Science 2020, 20, 52 -78.
AMA StyleA. Tamadon, M. Abdali, D. J. Pons, D. Clucas. Characterization of Dissimilar Al-Cu BFSW Welds; Interfacial Microstructure, Flow Mechanism and Intermetallics Formation. Advances in Materials Science. 2020; 20 (3):52-78.
Chicago/Turabian StyleA. Tamadon; M. Abdali; D. J. Pons; D. Clucas. 2020. "Characterization of Dissimilar Al-Cu BFSW Welds; Interfacial Microstructure, Flow Mechanism and Intermetallics Formation." Advances in Materials Science 20, no. 3: 52-78.
This work discusses the pressureless sintering of a boron carbide-titanium diboride (B4C– TiB2) nanocomposite via in-situ reaction of the boron carbide/titanium dioxide/carbon system. Attempting to sinter pure boron carbide leads to poor mechanical properties. In this work, the effect of adding TiO2 to B4C on mechanical properties of the boron carbide was investigated. Thermodynamic simulations were performed with HSC chemistry software to determine the phases which were most likely to form during the sintering process. The reaction thermodynamics suggested that during the sintering process, formation of TiB2 occurs preferentially over formation of TiC. For examination of the microstructural evolution of the samples, Scanning Electron Microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were utilized. The density, porosity, Young's modulus, microhardness and fracture toughness of the specimens were compared. Optimum properties were achieved by adding 10 wt% TiO2. In the sample possessing 10 wt% TiO2, the relative density, Young's modulus, hardness and fracture toughness were 94.26%, 428 GPa, 23.04 GPa and 5.19 MPa m0.5, respectively, and the porosity was decreased to 5.73%. Furthermore, phase analysis via XRD confirmed that the final product was free of unreacted TiO2 or carbon.
Mina Khajehzadeh; Naser Ehsani; Hamid Reza Baharvandi; Alireza Abdollahi; Mostafa Bahaaddini; Abbas Tamadon. Thermodynamical evaluation, microstructural characterization and mechanical properties of B4C–TiB2 nanocomposite produced by in-situ reaction of Nano-TiO2. Ceramics International 2020, 46, 26970 -26984.
AMA StyleMina Khajehzadeh, Naser Ehsani, Hamid Reza Baharvandi, Alireza Abdollahi, Mostafa Bahaaddini, Abbas Tamadon. Thermodynamical evaluation, microstructural characterization and mechanical properties of B4C–TiB2 nanocomposite produced by in-situ reaction of Nano-TiO2. Ceramics International. 2020; 46 (17):26970-26984.
Chicago/Turabian StyleMina Khajehzadeh; Naser Ehsani; Hamid Reza Baharvandi; Alireza Abdollahi; Mostafa Bahaaddini; Abbas Tamadon. 2020. "Thermodynamical evaluation, microstructural characterization and mechanical properties of B4C–TiB2 nanocomposite produced by in-situ reaction of Nano-TiO2." Ceramics International 46, no. 17: 26970-26984.
The effect of various tungsten carbide (WC) pin tools and operating parameters on the material structure and properties of an AA1100 friction stir welding (FSW) weld were evaluated. Three different pin shapes were employed (conical, square and threaded). For each tool shape, welds were generated for a set of tool (revolutions per minute, RPM) (710, 1120 and 1400) and advancing speeds (150, 250 and 400 mm/min). Weld samples were tested for mechanical strength by tensile testing. Morphology was examined using optical microscopy, and weld composition with scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). No weld contamination from the tools was observed. However, a number of structural defects, inherent to the FSW process, were observed (including tunnel voids, kissing bonds and swirling lines). These defects, associated with the stirring action, could not be eliminated. The results show how the operating parameters may be optimized to produce stronger welds.
Abbas Tamadon; Arvand Baghestani; Mohammad Ebrahim Bajgholi. Influence of WC-Based Pin Tool Profile on Microstructure and Mechanical Properties of AA1100 FSW Welds. Technologies 2020, 8, 34 .
AMA StyleAbbas Tamadon, Arvand Baghestani, Mohammad Ebrahim Bajgholi. Influence of WC-Based Pin Tool Profile on Microstructure and Mechanical Properties of AA1100 FSW Welds. Technologies. 2020; 8 (2):34.
Chicago/Turabian StyleAbbas Tamadon; Arvand Baghestani; Mohammad Ebrahim Bajgholi. 2020. "Influence of WC-Based Pin Tool Profile on Microstructure and Mechanical Properties of AA1100 FSW Welds." Technologies 8, no. 2: 34.
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.
A. Tamadon; D. J. Pons; D. Clucas. Analogue Modelling of Flow Patterns in Bobbin Friction Stir Welding by the Dark-Field/Bright-Field Illumination Method. Advances in Materials Science 2020, 20, 56 -70.
AMA StyleA. Tamadon, D. J. Pons, D. Clucas. Analogue Modelling of Flow Patterns in Bobbin Friction Stir Welding by the Dark-Field/Bright-Field Illumination Method. Advances in Materials Science. 2020; 20 (1):56-70.
Chicago/Turabian StyleA. Tamadon; D. J. Pons; D. Clucas. 2020. "Analogue Modelling of Flow Patterns in Bobbin Friction Stir Welding by the Dark-Field/Bright-Field Illumination Method." Advances in Materials Science 20, no. 1: 56-70.
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.
Abbas Tamadon; Dirk J. Pons; Don Clucas. Flow-Based Anatomy of Bobbin Friction-Stirred Weld; AA6082-T6 Aluminium Plate and Analogue Plasticine Model. Applied Mechanics 2020, 1, 3 -19.
AMA StyleAbbas Tamadon, Dirk J. Pons, Don Clucas. Flow-Based Anatomy of Bobbin Friction-Stirred Weld; AA6082-T6 Aluminium Plate and Analogue Plasticine Model. Applied Mechanics. 2020; 1 (1):3-19.
Chicago/Turabian StyleAbbas Tamadon; Dirk J. Pons; Don Clucas. 2020. "Flow-Based Anatomy of Bobbin Friction-Stirred Weld; AA6082-T6 Aluminium Plate and Analogue Plasticine Model." Applied Mechanics 1, no. 1: 3-19.
The potential position for tunnel defect within the structure of bobbin-tool friction stir welds was studied by analogue modelling. The welding process was simulated on layered plasticine slabs instead, compared to the aluminum plates. Observations in the modelled structure showed a high possibility for a continuous channelled discontinuity, like a tunnel-shaped void defect, in the entry zone of the weld, which mirrors the metal welding. The anatomy of tunnel defect in the entry zone was explained according to the mechanics of material during the plastic deformation process.
Abbas Tamadon; Dirk J. Pons; Don Clucas. Structural Anatomy of Tunnel Void Defect in Bobbin Friction Stir Welding, Elucidated by the Analogue Modelling. Applied System Innovation 2019, 3, 2 .
AMA StyleAbbas Tamadon, Dirk J. Pons, Don Clucas. Structural Anatomy of Tunnel Void Defect in Bobbin Friction Stir Welding, Elucidated by the Analogue Modelling. Applied System Innovation. 2019; 3 (1):2.
Chicago/Turabian StyleAbbas Tamadon; Dirk J. Pons; Don Clucas. 2019. "Structural Anatomy of Tunnel Void Defect in Bobbin Friction Stir Welding, Elucidated by the Analogue Modelling." Applied System Innovation 3, no. 1: 2.
Bobbin Friction Stir Welding (BFSW) is a thermomechanical process containing severe plastic deformation by mechanical stirring and Dynamic Recrystallization (DRX) during recooling. Here we report the three-dimensional characteristics of the micro-flow patterns within the aluminium weld structure. The Surface topography observations by Atomic Force Microscopy (AFM) show the stirred-induced microstructural evolution where the rearrangement of dislocations at the sub-grain scale, and the subsequent High- and Low-Angle Grain Boundaries (HAGBs, LAGBs) exhibit specific alterations in grain size and morphology of the weld texture. The dislocations interaction in different regions of the weld structure also was observed in correlation to the thermomechanical behaviour of the BFSW process. These micro-flow observations within the weld breadth give a new insight into the thermomechanical characteristics of the FSW process during the stirring action where the plastic flow has a key role in the formation of the weld region distinct from the base metal.
Abbas Tamadon; Dirk J. Pons; Don Clucas; Pons. AFM Characterization of Stir-Induced Micro-Flow Features within the AA6082-T6 BFSW Welds. Technologies 2019, 7, 80 .
AMA StyleAbbas Tamadon, Dirk J. Pons, Don Clucas, Pons. AFM Characterization of Stir-Induced Micro-Flow Features within the AA6082-T6 BFSW Welds. Technologies. 2019; 7 (4):80.
Chicago/Turabian StyleAbbas Tamadon; Dirk J. Pons; Don Clucas; Pons. 2019. "AFM Characterization of Stir-Induced Micro-Flow Features within the AA6082-T6 BFSW Welds." Technologies 7, no. 4: 80.
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.
Abbas Tamadon; Dirk J. Pons; Don Clucas; Kamil Sued. Texture Evolution in AA6082-T6 BFSW Welds: Optical Microscopy and EBSD Characterisation. Materials 2019, 12, 3215 .
AMA StyleAbbas Tamadon, Dirk J. Pons, Don Clucas, Kamil Sued. Texture Evolution in AA6082-T6 BFSW Welds: Optical Microscopy and EBSD Characterisation. Materials. 2019; 12 (19):3215.
Chicago/Turabian StyleAbbas Tamadon; Dirk J. Pons; Don Clucas; Kamil Sued. 2019. "Texture Evolution in AA6082-T6 BFSW Welds: Optical Microscopy and EBSD Characterisation." Materials 12, no. 19: 3215.
Bobbin friction stir welding with a double-sided tool configuration produces a symmetrical solid-state joint. However, control of the process parameters to achieve defect-free welds is difficult. The internal flow features of the AA6082-T6 butt-joints in bobbin friction stir welding were evaluated using a set of developed reagents and optical microscopy. The key findings are that the dark curved patterns (conventionally called 'flow-arms'), are actually oxidation layers at the advancing side, and at the retreating side are elongated grains with a high-density of accumulation of sub-grain boundaries due to dynamic recrystallization. A model of discontinuous flow within the weld is proposed, based on the microscopic observations. It is inferred that the internal flow is characterized by packets of material ('flow patches') being transported around the pin. At the retreating side they experience high localized shearing at their mutual boundaries, as evidenced in high density of sub-grain boundaries. Flow patches at the advancing side are stacked on each other and exposed to oxidization.
Abbas Tamadon; Dirk J. Pons; Don Clucas; Kamil Sued; Pons; Sued. Internal Material Flow Layers in AA6082-T6 Butt-Joints during Bobbin Friction Stir Welding. Metals 2019, 9, 1059 .
AMA StyleAbbas Tamadon, Dirk J. Pons, Don Clucas, Kamil Sued, Pons, Sued. Internal Material Flow Layers in AA6082-T6 Butt-Joints during Bobbin Friction Stir Welding. Metals. 2019; 9 (10):1059.
Chicago/Turabian StyleAbbas Tamadon; Dirk J. Pons; Don Clucas; Kamil Sued; Pons; Sued. 2019. "Internal Material Flow Layers in AA6082-T6 Butt-Joints during Bobbin Friction Stir Welding." Metals 9, no. 10: 1059.
One limitation of using silicon carbide (SiC) is the materials’ intrinsic brittleness. The mechanical properties of these ceramics can be improved through the use of additives during the sintering process. This research investigated the addition of boron carbide (B4C) on the Liquid Phase Sintered (LPS) SiC-Al2O3-Y2O3 system. The aim was to determine the effects on both the mechanical properties and microstructure of the LPS-SiC composite with varying levels of B4C as an additive. The Silicon Carbide preparation was composed of a 10 wt.% mixture of Alumina (Al2O3) and Yttria (Y2O3) at a 3:2 molar ratio, with different concentrations of boron carbide between 0 - 6 wt.%. In addition, 1 wt.% of carbon powder was added to the precursors to prevent oxidation during sintering. All precursors were milled for 2 h at 200 rpm and then samples were sintered by the pressureless technique for 1 h at 1900 °C in an argon atmosphere. A relationship was observed between the measured mechanical properties, the porosity and various phases formed in within the structure of the ceramic composite. The grain size and distribution of the B4C reinforcement phase provides a mechanism for the observed strengthening and increase in fracture toughness. Increasing the B4C content up to 5 wt.% enhanced the strength and fracture toughness of the composite samples, however increasing beyond 5 wt.% led to a decrease in these properties. Furthermore, a microstructural explanation of the grain-effects is proposed by considering the crack-growth micro-patterns. This work clarifies the link between the mechanical properties and microstructural characteristics of the SiC-Al2O3-Y2O3 composite with B4C additive. The strengthening mechanism of B4C additives was also explored in the microscopic scale.
Mostafa Bahaaddini; Hamid Reza Baharvandi; Naser Ehsani; Mina Khajehzadeh; Abbas Tamadon. Pressureless sintering of LPS-SiC (SiC-Al2O3-Y2O3) composite in presence of the B4C additive. Ceramics International 2019, 45, 13536 -13545.
AMA StyleMostafa Bahaaddini, Hamid Reza Baharvandi, Naser Ehsani, Mina Khajehzadeh, Abbas Tamadon. Pressureless sintering of LPS-SiC (SiC-Al2O3-Y2O3) composite in presence of the B4C additive. Ceramics International. 2019; 45 (10):13536-13545.
Chicago/Turabian StyleMostafa Bahaaddini; Hamid Reza Baharvandi; Naser Ehsani; Mina Khajehzadeh; Abbas Tamadon. 2019. "Pressureless sintering of LPS-SiC (SiC-Al2O3-Y2O3) composite in presence of the B4C additive." Ceramics International 45, no. 10: 13536-13545.
Bobbin friction stir welding (BFSW), with its fully penetrated pin and double-sided shoulder, can provide high rates of heat generation. This produces solid-state thermo-mechanical grain refinement. In this paper, the microstructure evolution of the welded joints of AA6082-T6 obtained using BFSW process was investigated with a focus on grain refinement. Two sheets of the AA6082-T6 alloy were butt-welded with a fixed-gap bobbin tool. The microstructure at a mid-weld transverse cross-section was evaluated using optical microscopy and electron backscatter diffraction (EBSD). Significant grain refinement was observed, with a decrease in grain size from 100 μm in directional columnar grain morphology of the base metal, to an ultrafine size—less than 10 μm—for the equiaxed grains in the stirring zone. The EBSD results showed that with BFSW processing, secondary phase precipitation patterns were produced that are distinct from the primary artificial age-hardening precipitates created by the T6 tempering cycle. The severe plastic deformation and heat generation appear to accelerate dynamic recrystallization and precipitation during the BFSW process. The microstructural studies confirmed that the BFSW process can provide a highly efficient thermodynamically activated grain refinement in the solid-state without requiring additional processes such as heat treatment or external means of grain refinement.
Abbas Tamadon; Dirk J. Pons; Kamil Sued; Don Clucas. Thermomechanical Grain Refinement in AA6082-T6 Thin Plates under Bobbin Friction Stir Welding. Metals 2018, 8, 375 .
AMA StyleAbbas Tamadon, Dirk J. Pons, Kamil Sued, Don Clucas. Thermomechanical Grain Refinement in AA6082-T6 Thin Plates under Bobbin Friction Stir Welding. Metals. 2018; 8 (6):375.
Chicago/Turabian StyleAbbas Tamadon; Dirk J. Pons; Kamil Sued; Don Clucas. 2018. "Thermomechanical Grain Refinement in AA6082-T6 Thin Plates under Bobbin Friction Stir Welding." Metals 8, no. 6: 375.
Bobbin friction stir welding (BFSW) is an innovative variant for the solid state welding process whereby a rotating symmetrical tool causes a fully penetrated bond. Despite the process development, there are still unknown variables in the characterization of the process parameters which can cause uncontrolled weld defects. The entry zone and the exit zone consist of two discontinuity-defects and removing them is one of the current challenges for improving the weld quality. In the present research, the characteristic features of the entry and exit defects in the weld structure and formation mechanism of them during the BFSW processing was investigated. Using stacked layers of multi-colour plasticine the material flow, analogous to metal flow, can be visualised. By using different colours as the path markers of the analogue model, the streamline flow can be easily delineated in the discontinuity defects compared with the metal welds. AA6082-T6 aluminium plates and multi-layered plasticine slabs were employed to replicate the entry-exit defects in the metal weld and analogue samples. The fixed-bobbin tool utilized for this research was optimized by adding a thread feature and tri-flat geometry to the pin and closed-end spiral scrolls on both shoulder surfaces. Samples were processed at different rotating and longitudinal speeds to show the degree of dependency on the welding parameters for the defects. The analogue models showed that the entry zone and the exit zone of the BFSW are affected by the inhomogeneity of the material flow regime which causes the ejection or disruption of the plastic flow in the gap between the bobbin shoulders. The trial aluminium welds showed that the elimination of entry-exit defects in the weld body is not completely possible but the size of the defects can be minimized by modification of the welding parameters. For the entry zone, the flow pattern evolution suggested formation mechanisms for a sprayed tail, island zone and discontinuity-channel. For the exit zone a keyhole-shaped discontinuity is discussed as a structural defect.
Abbas Tamadon; Dirk J. Pons; Kamil Sued; Don Clucas. Formation Mechanisms for Entry and Exit Defects in Bobbin Friction Stir Welding. Metals 2018, 8, 33 .
AMA StyleAbbas Tamadon, Dirk J. Pons, Kamil Sued, Don Clucas. Formation Mechanisms for Entry and Exit Defects in Bobbin Friction Stir Welding. Metals. 2018; 8 (1):33.
Chicago/Turabian StyleAbbas Tamadon; Dirk J. Pons; Kamil Sued; Don Clucas. 2018. "Formation Mechanisms for Entry and Exit Defects in Bobbin Friction Stir Welding." Metals 8, no. 1: 33.
BACKGROUND—The solid-phase joining of A6082-T6 plates by bobbin friction stir welding (BFSW) is problematic. Better methods are needed to evaluate the microstructural evolution of the weld. However, conventional Al reagents (e.g., Keller’s and Kroll’s) do not elucidate the microstructure satisfactorily, specifically regarding grain size and morphology within the weld region. APPROACH—We developed innovative etchants for metallographic observations for optical microscopy. RESULTS—The macrostructure and microstructure of A6082-T6 BFSW welds were clearly demonstrated by optical microscopy analysis. The microetching results demonstrated different microstructures of the Stir Zone (S.Z) distinct from the Base Metal (B.M) and Heat Affected Zone (HAZ) & Thermo-mechanical Affected Zone (TMAZ). The micrographs showed a significant decrease in grain size from 100 μm in B.M to ultrafine 4–10 μm grains for the S.Z. Also, the grain morphology changed from directional columnar in the B.M to equiaxed in the S.Z. Furthermore, thermomechanical recrystallization was observed by the morphological flow of the grain distortion in HAZ and TMAZ. The etchants also clearly show the polycrystalline structure, microflow patterns, and the incoherent interface around inclusion defects. ORIGINALITY—Chemical compositions are identified for a suite of etchant reagents for metallographic examination of the friction-stir welded A6082-T6 alloy. The reagents have made it possible to reveal microstructures not previously evident with optical microscopy.
Abbas Tamadon; Dirk J. Pons; Kamil Sued; Don Clucas. Development of Metallographic Etchants for the Microstructure Evolution of A6082-T6 BFSW Welds. Metals 2017, 7, 423 .
AMA StyleAbbas Tamadon, Dirk J. Pons, Kamil Sued, Don Clucas. Development of Metallographic Etchants for the Microstructure Evolution of A6082-T6 BFSW Welds. Metals. 2017; 7 (10):423.
Chicago/Turabian StyleAbbas Tamadon; Dirk J. Pons; Kamil Sued; Don Clucas. 2017. "Development of Metallographic Etchants for the Microstructure Evolution of A6082-T6 BFSW Welds." Metals 7, no. 10: 423.