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The plunging depth of 0.05mm was optimum for joint formation of 0.5mm thick Al-6061 sheet by micro friction stir welding. Increasing rotational velocity from 1500rpm to 2000rpm was ...beneficial to sound surface formation, while the taper pin with three flats owned wider process window than the single taper pin. The minimum ratio of thickness reduction of 2% was attained, which enhanced the area of load bearing. The taper pin with three flats owing to the severe stirring actions resulted in the finer grain size, improving tensile property. The maximum tensile strength by the taper pin with three flats reached 217MPa, equivalent to 90% of base material.
Different challenges associated with dissimilar micro-friction stir welding result in improper material intermixing, which affects joint integrity. The present work used a triple-spiral micro-grooves ...featured tool to mitigate this issue while joining 0.5 mm thick AA6061-T6 and ALCLAD 2024-T3 alloy sheets. The extent of material intermixing and its flow due to the introduction of micro-grooves on the shoulder-end surface was assessed by analyzing process responses, and weld characteristics. This investigation was further extended for different micro-groove depths (0.06 mm, 0.09 mm, and 0.12 mm). Apart from the types of material flow (continuous and discontinuous) through the micro-grooves, the difference in the interaction volume with the shoulder-end surface also affected the process responses and the weld characteristics. The defect-free welds obtained in different cases were considered for detailed microstructural analysis at the center of the stir zone and the junction of the two materials to correlate with the weld performance. It was found that finer grains (1.954 ± 0.973 μm), a high percentage of recrystallized grains (84.5%), and high angle grain boundaries (61.5%), with high texture intensity (3.301) were obtained in the stir zone of the weld produced by the highest micro-groove depth (0.12 mm) tool. This was attributed to the high degree of material intermixing at the highest micro-groove depth since it facilitated a higher volume of material to be directed both in the thickness direction and from one side of the weld to another. As a result, improved tensile properties with the highest mean joint efficiency of 77.18% were obtained where the weld fractured from the heat-affected zone of the AA6061 side.
•Effects of different micro-groove depths were investigated.•Material movement at tool-workpiece interface due to different depths was explained.•Microstructural analysis (recrystallization and texture evolution) was studied.•Highest joint efficiency of 77.18% was obtained in the case of 120-CCS-MG.
Dissimilar micro-friction stir welding (dissimilar μFSW) can be a preferred choice for joining dissimilar materials having thickness ≤ 1000 μm. The technique's potential applications are in ...miniaturized components, where the inherent benefits of the process, such as low temperature, low distortion, and clean joining, are advantageous compared to fusion welding. However, the challenges associated with dissimilar μFSW hinder its full potential applications in the relevant industries. The challenges are particularly a combination of two different characteristics of the process (i) the complexities of simultaneously fulfilling the dissimilar materials' demands due to the vast differences in the two materials' mechanical and thermal properties and (ii) the problems due to reduced sheet thickness. In this regard, the present work is a comprehensive and timely review of the research works done on dissimilar μFSW targeted at easily acquainting the research community about the know-how and the state of the art of the process. The review is broadly divided into three crucial parts: the process inputs/requisites, process mechanics, and process performance. The details about the μFSW tool, process parameters, and relative sheet positioning are discussed under the heading process inputs/requisites. Concerning the process mechanics, the intermetallic compound formation, defect generation, and material mixing are discussed. The joints' resulting performance is shown by detailing the essential properties such as formability, residual stresses, fatigue, hardness, and tensile strength. Additionally, several future research directions are presented at the end of this critical review to motivate further improvements in this joining technique and instigate its utility in relevant industries.
•Two thermal management strategies implemented for joining 0.5 mm (500 µm) thick dissimilar aluminum alloys.•Underlying physics assessed through coupled Eulerian-Lagrangian formulation for proper ...utilization of strategies.•Temperature distribution, material flow velocity symmetry, and material intermixing were analyzed.•Macro and microstructure, and weld performance, showed good agreement with numerical results.•Ductile failure occurs, yielding highest joint efficiency of 77.3% as a combined effect of two strategies.
The increased heat dissipation rate from thin sheets and differences in material properties lead to difficulties in controlling the heat input in dissimilar micro-friction stir welding (dissimilar µFSW). As a result, improper material mixing and defect formation significantly increase, which deteriorates weld performance and escalates its rejection rate. This issue of thermal mismanagement is mitigated in the present work by utilizing suitable material positioning and tool offset strategies during the dissimilar µFSW of 0.5 mm thick AA 2024-T3 and AA 6061-T6. To date, post-weld analysis was predominantly utilized to derive the physics for explaining these strategies in dissimilar µFSW. However, for proper utilization of these strategies, it is important to comprehend the underlying process physics by investigating the parameters that evolved during the process, such as temperature distribution, material flow velocity, and material intermixing. The literature currently available lacks a systematic investigation in this direction. For this purpose, a 3-D thermo-mechanical model based on coupled Eulerian-Lagrangian formulation was employed in this study. The numerical results showed that an optimal temperature difference between the advancing and retreating sides facilitates achieving a higher degree of velocity symmetry with a uniform higher magnitude of velocity vectors. Importantly, this degree of velocity symmetry showed a good agreement with experimentally determined weld characteristics, namely macro and microstructures, and mechanical performance. By appropriate thermal management, a joint efficiency of 77.3 % (weld strength = 243.58 MPa) was obtained upon tensile loading, and the weld fractured from the heat-affected zone of the AA 6061-T6 side, exhibiting characteristics of ductile failure.
Friction stir welding FSW is a promising technique for joining various similar and dissimilar materials with an application of frictional heat source generated by a non-consumable rotating tool for ...achieving high quality welds. In this article, FSW process is focused on the development of micro-friction stir welding μFSW, which is observed on very thin sectional materials of thickness 1000 μm 1 mm or less. The joining of precipitation-hardened aluminium alloy to pure-copper sheets of 0.8 mm thickness each were carried out on a semi-automatic vertical milling machine using a zero-pin length tool configuration. A mild steel backing plate is designed for fixture mechanism to hold the welding sheets on machine. Weld-process parameters coded for tool-rotational speed, tool-travel speed and tool-plunge depth are examined for predicting better joint characteristics. Mechanical responses such as tensile strength, yield strength, percentage-elongation and micro-hardness are recorded for better weld joints at weld-nugget zone WNZ interface. Microstructural features are observed on achieved mechanical responses of welded joints using scanning electron microscope SEM and energy dispersive X-ray EDX analyzer.
This study utilized high rotational speeds (5500, 8500, and 10,000 rpm) and various traverse speeds (300, 600, and 900 mm/min) to carry out micro-friction stir welding on 0.8 mm thick plates of ...5052–0 and 5052-H32 aluminum alloys. The weld heterogeneity was assessed through microstructural analysis and tensile testing under various process parameters. It was found that high rotational speeds generate enough heat to provide grain growth within the stirring zone. Moreover, the stirring zone showed a sizeable population of equiaxed grains, measuring less than 5 μm, that resulted in an improved mechanical strength of the joint. The joint efficiencies in the 5052-O and 5052-H32 alloys were significantly improved. The joint efficiencies of yield strength for 5052-O and 5052-H32 ranged between 129 and 139%, and 118% and 124%, respectively. The joint efficiencies of tensile strength for 5052-O varied between 102 to 109%, while in 5052-H32 they ranged from 93 to 100%. A comparison of the micro friction stir welding parameter to conventional thick plate friction stir welding showed that the former provided superior properties.
Triple-spiral micro-grooves on the tool-shoulder end-surface is a feature recently being used for improving material flow during micro-friction stir welding (μFSW). However, its effect on process ...responses in comparison to the plain tool-shoulder end-surface lacks recognition, which has been targeted in the present work. An additional contribution to the knowledge base of μFSW tools having such features is also made by investigating the effect of imparting different cross-sections (rectangular, circular, right-trapezoidal type I and right-trapezoidal type II) to the micro-grooves, on the process responses. Forces, temperature, and material flow pattern were mainly the process responses analyzed through experiment and FEA simulation of μFSW in 0.5 mm thick AA6061-T6 sheets at a tool rotation of 1900 rpm and welding speed 500 mm/min. Furthermore, the welds’ quality was assessed by its surface topography, microstructure, and tensile property. The physics of the interaction between shoulder end-surface and plasticized sheet material showed that besides the triple-spiral shape, it was the cross-section of micro-grooves (mainly the orientation angle and shape of micro-grooves’ wall) that crucially determined the mechanical, thermal, and flow characteristics of the plasticized sheet material, ultimately affecting the process responses. The possibility of low-temperature welding with enhanced material mixing had been achieved with the micro-grooved tools. A higher amount of plastic deformation was also seen, with these tools, through X-ray tomographic images of the deformed copper foils placed transverse to the welding direction. Moreover, a remarkable improvement in the weld surface finish was obtained using the micro-grooved tools. Among the four micro-grooved tools, the right-trapezoidal type II cross-section showed the best performance by yielding moderate process loads along with the best weld surface finish and tensile property.
Micro friction stir welding (μFSW) was successfully performed to join the ultra-thin 6061-T4 sheet with the thickness of 0.5mm. The optimum plunging depth of 0.05mm was obtained and reduction ratio ...was lower than 0.2%. Based on better dynamic flow induced by the triflat pin, the good surface appearance at the wider process window was obtained, while the grain size at the nugget zone was finer than that by the taper pin. Increasing welding speed caused that tensile property increased firstly and then decreased with high welding speed than 500mm/min. The maximum values of tensile strength and elongation of the μFSW joint using the triflat pin reached 220.3MPa and 11.7%, which were 91.9% and 54.4% of base material, respectively.
Aluminium honeycomb core is a thin-walled cellular structure extensively used in crash resistance applications in automotive industry. To overcome current challenges in adhesive-bonded honeycomb, new ...fabrication route using micro friction stir lap welding has been proposed. With a specific energy absorption capacity as high as 28.2 kJ/kg in flatwise impact testing, fabricated honeycomb demonstrated its potential for industrial applications. The structure exhibited no weld cracks or cell wall delamination, unlike adhesive-bonded honeycombs. However, in friction stir welding of thin sheets (0.5 mm), achieving an optimized heat input is challenging due to limited scope for variation in process parameter and tool design. Therefore, control of heat outflow by proper selection of backing plate material is the alternative approach for achieving desirable joint performance. Experiments with backing plates having a range of thermal diffusivities demonstrated that joint produced with mild steel backplate exhibited maximum shear-tensile strength. Conversely, joint with aluminium backplate exhibited poor plastic flow of material. Effective sheet thickness and lap width were predominantly affected by heat accumulation in weld, resulting in different failure modes.
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