Search Results (26)

Aluminium remains relatively uncommon in civil structures; however, its durability and light-weight nature make it an attractive alternative for vehicular bridges. Recent applications use aluminium bridge decks supported by steel girders. However, galvanic corrosion and thermal incompatibility limit full and optimised behaviour. This research explores the use of Bobbin Tool Friction Stir Welding (BTFSW), which improves the welded aluminium behaviour while significantly improving fatigue detail classification, as it is critical for bridges. This configuration optimises material use, reduces structural weight, and supports Accelerated Bridge Construction (ABC) practices by enabling modular prefabrication and rapid installation. The findings highlight aluminium’s potential as a primary bridge material. Full article

Friction stir welding (FSW) is a solid-state welding process that uses a rotating tool to soften and stir the base metal, thereby joining it. A special type of tool that has attracted the interest of researchers is the so-called bobbin tool (BTFSW), which, unlike conventional tools with one shoulder, features two shoulders that envelop the base metal from both the top and bottom sides. As a result, significant tensile stresses develop on both sides of the weld, caused by the action of both tool shoulders. In this paper, this issue was addressed by applying laser shock peening (LSP), aiming to introduce compressive stresses, which can be useful as a post-processing technique for BTFSW on both weld sides. It was found that this process completely alters residual stresses in the treated area, from tensile to compressive, through shock waves that impart plastic deformation in the surface layer. It was shown that the LSP effect is more pronounced as the accumulated energy is higher. As a consequence, the microhardness values were significantly increased in the surface and subsurface layers, reaching a maximum depth of 480 to 780 µm for the lowest and highest accumulated laser energy, respectively, while surface roughness increased. While increasing compressive stresses and microhardness in the surface layer is beneficial from the point of view of fatigue resistance, increased roughness has a detrimental effect. Accumulated energy was hereby shown to have a higher effect compared to the maximal energy applied to the specimens. Full article

This study utilized a bobbin tool to friction stir weld aluminum 6082 workpieces under two sets of process parameters: a tool rotation speed of 280 rev/min with a weld velocity of 280 mm/min (280/280) and a tool rotation speed of 450 rev/min with a weld velocity of 450 mm/min (450/450). The weld microstructures were characterized through optical microscopy utilizing polarized light and through transmission electron microscopy (TEM) and scanning electron microscopy (SEM) coupled with chemical analysis by energy dispersive spectroscopy and electron back scatter diffraction. The microstructural studies were supplemented by hardness measurements (Vickers) performed on the same sections as the metallographic examinations. The produced weldments were free from cracks and any discontinuities. Fine, equiaxed grains that were several microns in size characterized the stir zones (SZs), and the advancing (AS) and retreating (RS) sides revealed distinct microstructural features. On the AS, the transition from the thermo-mechanically affected zone to the SZ was well defined and sharp, but on the RS, the transition appeared as a continuous, gradual change in microstructure. The lower weld energy (280/280) produced lower hardness in the stir zone than the higher energy weld (450/450), ~95 HV1 versus ~115 HV1; however, the 280/280 welds showed higher tensile strengths than the 450/450 welds, ~238 MPa as opposed to ~172 MPa. These behaviors in mechanical performance correlated with the temperature histories produced by each set of weld parameters in relation to the precipitation behavior of the alloy. The fracture characteristics of the weldments were notably different with the 450/450 sample fracturing in a quasi-brittle manner with slight plastic deformation and the 280/280 sample fracturing ductilely. A numerical simulation supported the investigation by elucidating the temperature and material flow behavior during the joining process. Full article

Bobbin tool friction stir welding (BT-FSW), or self-reacting tool friction stir welding (SR-FSW), refers to a solid-state welding process which that uses two opposing rotating shoulders (top and lower of the workpiece) connected with a fully penetrated pin. In fact, the bottom shoulder in the BT-FSW design replaced the backing plate used in the conventional tool friction stir welding (CT-FSW) to promote symmetrical solid-state joints. Compared to CT-FSW, the BT-FSW process has many advantages over the use of a conventional tool such as the welded structure is symmetric in thickness, low distortion of weld joint can be obtained, the elimination of root for welds, a backing plate is not required, and high force is not required for fixing the weld plates and possibility welding a closed or a hollow section (U and H shapes). The welding parameters of BT-FSW, such as tool pin profile, rotational speed, welding speed, and axial force, have a considerable effect on the microstructure and the mechanical properties of the resulting assembly. In the current study, two extrusions of aluminum alloy 6061-T6 with 8 mm were joined by the BT-FSW technique with a tool pin with threads and eight different welding parameters (tool rotation speed and welding speed). The maximum value of tensile strength was achieved using optimum welding conditions of a tool rotation speed of 850 rpm/min and a welding speed of 650 mm/min. The study also investigated the joint efficiency of the friction stir welded joint, defects at the weld zone, and fatigue life of BT-FSW samples at the optimized level. Full article

This article presents an optimal extrusion geometry for fabricating a bridge deck. The profile of the extrusion enables the possibility of welding onto another extrusion through butt joints only. This type of welding joint is optimal in terms of both the ultimate resistance and the fatigue performance. Thus, the aluminium deck will be manufactured by welding these extrusions together through the bobbin tool friction stir welding process, resulting in a full-penetration weld, free of the kissing bond and the flash toe defects, and in which the thermal input and the stirring are symmetrical on both outer sides of the butt joint. Therefore, this geometry addresses the shortcomings of both the MIG and the conventional FSW processes and significantly increases the lifespan of the aluminium deck. This article will present the scientific and technical approach, based on the Canadian standard CSA S6:19, and will present an example of application on an aluminium/glued laminated timber bridge. Full article

The two main process parameters of Bobbin tool friction stir welding (BT-FSW) are ω (rotational speed) and v (traverse speed). Both of these factors have a significant effect on heat input, microstructure, and mechanical properties. At present, most studies on friction stir welding adopt the control variable method to study the thermal cycling during the welding process and the mechanical properties of joints, and there are few studies on changing the two process parameters at the same time, because it can be difficult to assess the correlation between heat input and mechanical properties when changing both factors at the same time. In this study, the w/v ratio is defined as the thermal index, which is a characteristic value of heat input. The study uses ABAQUS 6.5 software to establish a BT-FSW CEL (coupled Eulerian–Lagrangian) thermal coupling model. This model explores the relationship between joint thermal cycles, microstructure, and mechanical properties for different w and v values with the same w/v ratio. The results show that increasing rotational and traverse speeds under the same w/v ratio leads to an increase in the peak temperature of the nugget zone (NZ). However, the peak temperature of the thermo-mechanically affected zone (TMAZ) and heat-affected zone (HAZ) remained almost constant. Joint strength was highest at a rotational speed of 750 r/min and a traverse speed of 650 mm/min, with a yield strength of 227 MPa. As rotational and traverse speeds increased, the recrystallized grain content of the NZ showed an increasing trend followed by a decreasing trend. The recrystallized grain content of the advancing side thermo-mechanically affected zone (AS-TMAZ) and retreating side thermo-mechanically affected zone (RS-TMAZ) showed a decreasing trend. Joint hardness had a “W” shaped distribution, with the highest average hardness value found in the NZ. Full article

Bobbin tool friction stir welding (BTFSW) is a variant of the FSW process which uses the special two-shoulder tool that forms the top and bottom of a weld surface. As such, a significant simplification of the welding setup is achieved. One of the dominant parameters of the BTFSW process is the interference between the tool shoulder pinch gap and the weld metal thickness. In this research, the influence of interference of the square pin tool with convex shoulders on process temperature, microstructure, tensile, impact, and bend performance were studied, and appropriate correlations were devised. The base metal was an aluminum–magnesium alloy in which the interference varied in the range of 0.1 to 0.5 mm. Wormhole defects and irregularities were found in all specimens except in the specimen welded with 0.4 mm interference. An optimal interference of 0.4 mm resulted in the best mechanical properties, which, in terms of tensile strength and reduction of area, were similar to the base metal. Furthermore, the impact strength was significantly higher, which was attributed to the grain refinement effect in the nugget zone. Full article

The use of the friction stir welding (FSW) process as a relatively new solid-state welding technology in the aerospace industry has pushed forward several developments in different related aspects of this strategic industry. In terms of the FSW process itself, due to the geometric limitations involved in the conventional FSW process, many variants have been required over time to suit the different types of geometries and structures, which has resulted in the development of numerous variants such as refill friction stir spot welding (RFSSW), stationary shoulder friction stir welding (SSFSW), and bobbin tool friction stir welding (BTFSW). In terms of FSW machines, significant development has occurred in the new design and adaptation of the existing machining equipment through the use of their structures or the new and specially designed FSW heads. In terms of the most used materials in the aerospace industry, there has been development of new high strength-to-weight ratios such as the 3rd generation aluminum–lithium alloys that have become successfully weldable by FSW with fewer welding defects and a significant improvement in the weld quality and geometric accuracy. The purpose of this article is to summarize the state of knowledge regarding the application of the FSW process to join materials used in the aerospace industry and to identify gaps in the state of the art. This work describes the fundamental techniques and tools necessary to make soundly welded joints. Typical applications of FSW processes are surveyed, including friction stir spot welding, RFSSW, SSFSW, BTFSW, and underwater FSW. Conclusions and suggestions for future development are proposed. Full article

Friction stir welding (FSW) is an effective solid-state joining process that has the potential to overcome common problems correlated with conventional fusion welding processes. FSW is used for the joining of metallic materials, in particular Al alloys (non-heat-treatable and heat-treatable). The heat produced by the friction between the rotating tool and the workpiece material generates a softened region near the FSW tool. Although the heat input plays a crucial role in producing a defect-free weld metal, it is a serious concern in the FSW of work-hardened non-heat-treatable Al alloys. In this group of alloys, the mechanical properties, including hardness, tensile properties, and fatigue life, are adversely affected by the softening effect because of grain growth and reduced dislocation density. Considering this challenge, work-hardened Al alloys have been limited in their industrial use, which includes aerospace, shipbuilding, automotive, and railway industries. The current comprehensive review presents the various approaches of available studies for improving the quality of FSW joints and expanding their use. First, the optimization of welding parameters, including the tool rotational and traverse speeds, tool design, plunge depth, and the tilt angle is discussed. Second, the incorporation of reinforcement particles and then underwater FSW are stated as other effective strategies to strengthen the joint. Finally, some supplementary techniques containing surface modification, bobbin tool FSW, copper backing, and double-sided FSW in relation to strain-hardened Al alloys are considered. Full article

In this study, five bobbin tools with different shoulder fillet radii were employed for the bobbin tool friction stir welding (BT-FSW) of A1050-O sheets to systematically evaluate the effects of shoulder fillet radius on the welding defect formation, flash formation, weld thickness, grain size of the stir zone, and tensile properties. The quality classifications of the joints’ appearance were summarized as process windows, and the appropriate welding condition range for each shoulder fillet radius was clarified. It was observed that an increase in the shoulder fillet radius decreased the welding defects and flash formation; however, it increased the minimum thickness of the weld except when the shoulder fillet radius was 0.5 mm. The grain size of the stir zone increased with increasing shoulder fillet radius from 0.5 mm to 6 mm. The ultimate tensile strength (UTS) of the stir zone decreased with increasing shoulder fillet radius from 0.5 mm to 1 mm, increased from 1 mm to 3 mm, and remained constant from 3 mm to 6 mm. The results indicate that a shoulder fillet radius larger than 3 mm is effective in decreasing flash formation and maintaining a constant weld thickness. Full article

The feasibility of producing welding joints between 6061-T6 aluminum and pure copper sheets of 6 mm thickness by conventional friction stir welding (CFSW) and bobbin tool friction stir welding (BTFSW) by using a slot-groove configuration at the joining surface was investigated. The microstructure of the welded samples was examined by using an optical microscope and X-ray diffraction. Furthermore, the mechanical properties of the weld samples are compared based on the results of the tensile test, hardness measurement, and fractography test. The slot-groove configuration resulted in the presence of a bulk-sized Al block on the Cu side. The microscopic observations revealed the dispersion of fine Cu particles in the stir zone. The presence of intermetallic compounds (IMCs) CuAl₂, which are hard and brittle, lowered the strength of the weld joints. The strength of the weld joints produced with BTFSW was superior to that of the C-FSW. The maximum hardness values of 214 HV and 211 HV are reported at the stir zone for BTFSW and CFSW, respectively. The fracture location of all the joints was at the intersection of the stir zone and the thermomechanically affected zone was on the Cu side. Full article

Bobbin tool friction stir welding (BTFSW) utilizes a special tool that possesses two shoulders interconnected by a pin instead of one: the top shoulder and the pin in the conventional FSW tool. This greatly simplifies the kinematics in the otherwise complicated setup of FSW since the bottom shoulder forms the bottom surface of the weld, without the need for a backing plate. Moreover, the tool enters the base metal sideways and travels, forming the joint in a straight line while rotating, without the need for downward and upward motion at the beginning and end of the process. This paper presents a study on the BTFSW tool geometry and parameters on the risk of wormhole defect formation in the AA5005 aluminum–magnesium alloy and the wormhole effect on mechanical properties. It was shown that higher stress imposed by the tool geometry on the joint has a significant influence on heating, an effect similar to the increased rotational speed. Optimal kinematic and geometrical tool properties are required to avoid wormhole defects. Although weld tensile strengths were lower (between ~111 and 115 MPa) compared with a base metal (137 MPa), the ductile fracture was obtained. Furthermore, all welds had a higher impact strength (between ~20.7 and 27.8 J) compared with the base material (~18.5 J); it was found that the wormhole defect only marginally influences the mechanical properties of welds. Full article

This work aims to optimize the performance evaluation characteristics such as the temperature at the weld center of the lap joint (Tw), the tensile shear load (TSL), and the hardness using an experimental design experiment for bobbin tool friction stir welding (BT-FSW) of AA1050 lap joints. BT-FSW is characterized by a fully penetrated pin and double-sided shoulder that promote symmetrical solid-state welds. This study contributes to improving the quality of 10 mm thick lap joints and addressing challenges to obtaining a sound weld deprived of any defects. Taguchi L9 orthogonal array (OA) experimental design was performed. Three different pin shapes (cylindrical, triangular, and square) and three levels of welding travel speeds of 200, 400, and 600 mm/min were selected as input controllable process parameters at a constant tool rotation speed of 600 rpm. A travel speed of 200 mm/min with square pin geometry significantly improves the TSL of the joint up to 6491 N. However, the hardness characteristic is optimized by using 600 mm/min travel speed and a cylindrical tool pin. The minimum temperature in the weld joint can be obtained using 600 mm/min or more with triangular pin geometry. From ANOVA results, it was seen that the BT-FSW of AA 1050 thick lap joints performance in terms of TLS and Tw were greatly influenced by travel speed; however, the tool shape influences the hardness more. For the validation of the models, BT-FSW experiments have been carried out for AA1050 using the applied processing parameters. Furthermore, regression models were developed to predict the Tw, TSL, and hardness. The calculated performance properties from the mathematical models were in an acceptable range compared to the measured experimental values. Full article