Search Results (94)

Aluminum spot welding is extensively applied in automotive, aerospace, and rail sectors due to its favorable strength-to-weight ratio. While resistance spot welding (RSW) has been the traditional method, its high residual stresses, electrode wear, and limited performance with high-strength aluminum alloys have driven interest toward alternative techniques. Friction stir spot welding (FSSW) offers significant advantages over RSW, linear friction welding (LFW), and hybrid processes, including solid-state joining that minimizes porosity, lower energy consumption, and the elimination of consumable electrodes. Compared to LFW, FSSW requires simpler fixturing and is more adaptable for localized repairs, while offering superior joint surface quality over hybrid laser-assisted methods. Despite these advantages, gaps remain in understanding the influence of process parameters on heat generation, microstructural evolution, and mechanical performance. This review consolidates advancements in tool design, thermal characterization, and weld property for aluminum alloys. It presents comparative insights into temperature distribution, weld strength, hardness variation, and metallurgical transformations reported across studies. By critically synthesizing the earlier works, this work identifies knowledge gaps and potential design improvements, aiming to support the development of more efficient and robust FSSW processes for industrial application. Full article

Achieving keyhole-free joints is critical in Friction Stir Spot Welding (FSSW). This study presents a new approach to eliminate this volumetric defect in AA6082-T6 FSSW sheet joints using a continuous multi-layer Friction Stir Deposition (CMFSD) technique, employing a newly designed AA6082-T6 consumable tool. FSSW was performed at various rotational speeds (350, 550, 750 and 950 rpm) with a 5 s dwell time. Comprehensive macro- and micro-scale evaluations, along with mechanical properties (hardness and tensile-shear load) of the produced joints, were conducted. Additionally, microstructures were examined using Optical Microscopy (OM), while fracture surfaces were analyzed via Scanning Electron Microscopy (SEM). Optimal FSSW conditions were identified at 550 rpm, yielding a stir zone (SZ) hardness of 94.6 ± 1.4 HV and a maximum tensile-shear load of 4.73 ± 0.27 kN. The keyhole was successfully refilled using AA6082-T6 rod material via CMFSD, resulting in a defect-free joint of the same base alloy. Electron Backscattered Diffraction (EBSD) technique was also used to examine the microstructural features. A comparative analysis revealed significant enhancements: the refilled FSSW joints exhibited a 46.5% increase in maximum tensile-shear load and a 66.66% improvement in elongation to failure compared to the highest-FSSW joint performance with the keyhole defect. Full article

In this study, under varying PDSP (plunging depths of stirring pin) and process parameters, refill friction stir spot welding tests were performed on 6061-T6 aluminum alloy, relying on a stirring tool with a 12 mm sleeve diameter and an 8 mm stirring pin diameter. The results manifested the internal defects in the weld zone when PDSP was 0, notwithstanding the alterations in process parameters. However, these flaws disappeared when PDSP was 0.5 mm and 1 mm. In the weld zone, PDSP exerted a dramatic effect on the internal metal flow state, particularly the curvature of the “Hook” shape and the width of the bonding ligament. It changed the downward bending of the ‘Hook’ into an upward one, influencing the fracture behavior of the weld zone and elevating the ULSF (ultimate lap shear force) by up to 20% (PDSP = 0.5 mm, welding speed = 30 mm/min, rotation speed is 1200 rpm). Besides, the PDSP intensified the PAZ (pin affected zone) pressure, induced more metal flowing into the SAZ (sleeve affected zone), thus reinforced the SAZ-TMAZ(thermomechanically affected zone) bonding strength, and upgraded the region’s microhardness. In summary, the PDSP is commendable for bolstering the weld zone’s performance, but excessively large PDSP values incur drastic indentations in the PAZ, which diminish the ULSF. Full article

This paper describes the development of a new hybrid composite for the metal joints of aluminium and glass fibre composite adherents. The aluminium adherend is manufactured using friction stir-formed studs that are inserted into the composite adherend in the through-thickness direction during the composite manufacturing process, where the dry fibres are displaced to accommodate the studs before the resin infusion process. The materials used were AA6082-T6 aluminium and plain-woven E-glass fabric reinforced epoxy, with primary applications in naval vessels. This joining approach offers a cost-effective solution that does not require complicated onsite welding. The joint design was developed based on a simulation test program with finite element analysis, followed by experimental characterisation and validation. The design solution was analysed in terms of the force displacement response, sequence of load transfer, and characterisation of the joint failure modes. Full article

The incorporation of multi-material design (MMD) to achieve lightweight vehicles requires Friction Stir Spot Welding (FSSW) to join steel with aluminum, magnesium, or composites. This study investigates the mechanisms, challenges, and performance of FSSW in MMD based on the information available in the literature. It also explores the effect of FSSW tool geometries and design on the spot weld formation and mechanical strength. Larger shoulder and pin diameters increase heat generation during welding. A concave shoulder profile produces a stronger weld compared to flat and convex profiles due to its ability to trap materials and transfer materials to the sheet interface efficiently for the development of a sound weld. Grooves such as Fibonacci and involute, and threads on P-FSSW and R-FSSW tools, also contribute to effective material flow during welding, hence assisting in heat generation. This review also provides recommendations on tool design for FSSW, P-FSSW, and R-FSSW. Full article

Friction stir welding (FSW) is a novel welding technique that produces a solid-state weld by generating frictional heat and plastic deformation at the weld spot with a revolving, non-consumable welding tool. Despite processing a wide range of industrial materials, FSW has concentrated on welding aluminum and its alloys because of its high strength-to-weight ratio and uses in the shipbuilding, aerospace, and other fabrication industries. Important FSW process factors that determine the mechanical qualities of the weldment are the tool tilt angle, tool traverse feed, tool pin profile, tool rotational speed (TRS), tool traverse speed (TTS), tool pin profile (TPP), and shoulder plunge depth. Variations in the required process parameters cause defects, which lower the weld quality of FSWed aluminum alloys (AA). Therefore, keeping an eye on and managing the FSW process is crucial to preserving the caliber of the weld joints. The current study aims to investigate the changes in the mechanical characteristics and microstructure of the FSWed AA5052-H111 and AA6061-T6 joints. To perform the FSW experiments, we varied TRS, TTS, and TPP on plates that were 5 mm thick and had a butt joint structure. Following welding, the microstructure of the weld zones was examined to observe how the grains had changed. The joint’s tensile strength reached a maximum of 227 MPa for the square-shaped TPP, and the micro-Vickers hardness test results showed a maximum of 102 HV at the weld nugget zone (WNZ). Full article

Understanding and optimizing the relationship between critical processing parameters (rotational speed and dwell time) and the resulting weld performance is crucial for the effective application of friction stir spot welding (FSSW) in joining aluminum alloys. FSSW is an increasingly important solid-state, clean technology alternative for joining lightweight alloys such as AA5052-H32 in various industries. To optimize this technique for lap joint configurations, the current study examines the influence of rotational speeds (500, 1000, and 1500 rpm) and dwell times (1, 2, and 3 s) on the heat input energy, hardness across weld zones, and tensile/shear load, using a full factorial Design-Expert (DOE) analysis. The FSSW responses of the numerical model were validated using the experimental results for the spot-welded joints. The findings indicate that the dwell time significantly affected the mechanical properties, while the tool rotational speed had a substantial effect on the heat input energy and mechanical properties. Fracture surfaces predominantly exhibited ductile failure with diverse dimple morphologies, consistent with the enhanced tensile properties under optimal parameters. The presence of finer dimples suggests a mixed-mode fracture involving shear. Full article

Friction stir spot welding (FSSW) is a solid-state joining technique increasingly favored in industries requiring high-quality, defect-free welds in lightweight and durable structures, such as the automotive, aerospace, and marine industries. This review examines the current advancements in FSSW, focusing on the relationships between microstructure, properties, and performance under load. FSSW offers numerous benefits over traditional welding, particularly for joining both similar and dissimilar materials. Key process parameters, including tool design, rotational speed, axial force, and dwell time, are discussed for their impact on weld quality. Innovations in robotics are enhancing FSSW’s accuracy and efficiency, while numerical simulations aid in optimizing process parameters and predicting material behavior. The addition of nano/microparticles, such as carbon nanotubes and graphene, has further improved weld strength and thermal stability. This review identifies areas for future research, including refining robotic programming, using artificial intelligence for autonomous welding, and exploring nano/microparticle reinforcement in FSSW composites. FSSW continues to advance solid-state joining technologies, providing critical insights for optimizing weld quality in sheet material applications. Full article

Simulation analysis is a key technical means for studying the internal metal flow patterns in refill friction stir spot welding zones. This study used DeformV11.0 software to establish an accurate and reliable numerical simulation model for 6061-T6 aluminum alloy refill friction stir spot welding. The microstructure of different stages during actual welding was obtained using the stop method, and combined with the simulation results, shows that the temperature in the spot welding zone is highest during the dwell stage, with a high degree of match between the temperature distribution and actual measurements. This stage is also crucial for affecting the refill process. The results indicate that the metal flow rate in the center of the spot welding zone is slow and the pressure is low, while the flow rate on both sides is fast, and the temperature and pressure are high. In addition, the metal in the weld zone flows plastically in a shear friction and in situ spinning manner, and the weld zone achieves connection in a form similar to “complete friction plug riveting”. A “spiral suction–refill injection layer stacking” model was established to describe the forming mechanism of refill friction stir spot welding. Full article

Over the past decade, friction stir spot welding (FSSW) has gained increasing attention, making it a competitor to conventional welding methods such as resistance welding, rivets, and screws. This type of welding is environmentally friendly because it does not require welding tools and is solid-state welding. This study attempts to demonstrate the importance of pin geometry on temperature distribution and joint quality by using threaded and non-threaded pins for similar and dissimilar alloys. To this end, thermal analysis of the welded joints was conducted using real-time monitoring from a thermal camera and an infrared thermometer, in addition to finite element method (FEM) simulations. The thermal analysis showed that the generated temperatures were higher in dissimilar alloys (Al-Cu) than in similar ones (Al-Al), reaching about 350 °C. In addition, dissimilar alloys show more pronounced FSSW stages through extended periods for each plunging, dwelling, and drawing-out time. The FEM simulation results are consistent with those obtained from thermal imaging cameras and infrared thermometers. The dwelling time was influential, as the higher it was, the more heat was generated, which could be close to the melting point, especially in aluminum alloys. This study provides an in-depth experimental and numerical investigation of temperature distribution throughout the welding cycle, utilizing different pin geometries for both similar and dissimilar non-ferrous alloy joints, offering valuable insights for advanced industrial welding applications. Full article

Despite the significant economic and environmental advantages of friction stir spot welding (FSSW) and its amazing results in welding similar and dissimilar metals and alloys, some of which were known as unweldable, it has some structural and characteristic defects such as keyhole formation, hook defects, and bond line oxidation. This has prompted researchers to focus on these defects and propose and investigate techniques to treat or compensate for their deteriorating effects on microstructural and mechanical properties under different loading conditions. In this experimental study, sheets of AA6061-T6 aluminum alloy with a thickness of 1.8 mm were employed to investigate the influence of reinforcement by graphene nanoplatelets (GNPs) with lateral sizes of 1–10 µm and thicknesses of 3–9 nm on the static and fatigue behavior of FSSW lap joints. The welding process was carried out with constant, predetermined welding parameters and a constant amount of nanofiller throughout the experiment. Cross-sections of as-welded specimens were tested by optical microscope (OM) and energy-dispersive spectroscopy (EDS) to ensure the incorporation of the nanographene into the matrix of the base alloy by measuring the weight percentage (wt.%) of carbon. Microhardness and tensile tests revealed a significant improvement in both tensile shear strength and micro-Vickers hardness due to the reinforcement process. The fatigue behavior of the GNP-reinforced FSSW specimens was evaluated under low and high cycle fatigue conditions. The reinforcement process had a detrimental effect on the fatigue life of the joints under cyclic loading conditions. The microstructural analysis and examinations conducted during this study revealed that this reduction in fatigue strength is attributed to the agglomeration of GNPs at the grain boundaries of the aluminum matrix, leading to porosity in the stir zone (SZ), the formation of continuous brittle phases, and a transition in the fracture mechanism from ductile to brittle. The experimental results, including fracture modes, are presented and thoroughly discussed. Full article

Refill friction stir spot welding (RFSSW) is an effective technique for achieving high-quality joints in metallic materials, with rotational speed being a critical parameter influencing joint quality. Current research on RFSSW has primarily focused on low-melting-point materials such as aluminum alloys, while limited attention has been given to pure copper, a material characterized by its high-melting-point and high-thermal-conductivity. This study aims to investigate the effects of rotational speed on the microstructure and mechanical properties of RFSSW joints in pure copper. To achieve this goal, welding experiments were conducted at five rotational speeds. The welding defects, microstructure, and hook morphology of the welded joints were analyzed, while the variations in axial force and torque during welding were studied. The influence of rotational speed on the microhardness and tensile-shear failure load of the welded joints was explored, and the fracture modes of the welded joints at different rotational speeds were discussed. The results indicated that the primary welding defects were incomplete refill and surface unevenness. Higher rotational speeds resulted in coarser microstructures in the stir zones. As the rotational speed increased, the hook height progressively rose, the peak axial force showed an increasing trend, and the peak torque continuously decreased. The high microhardness points in the welded joints were predominantly located at the top of the sleeve stir zone (S-Zone), while the low microhardness points were observed at the center of the pin stir zone (P-Zone) and in the heat-affected zone (HAZ). The tensile-shear failure load of the welded joints initially increased and then decreased on the whole with the rising rotational speed, peaking at 5229 N at a rotational speed of 1200 rpm. At lower rotational speeds, the fracture type of the welded joints was characterized as plug fracture. Within the rotational speed range of 1200 rpm to 1600 rpm, the fracture type transitioned to upper sheet fracture. The initial fractures under different rotational speeds exhibited ductile fracture. This study contributes to advancing the understanding of RFSSW characteristics in high-melting-point and high-thermal-conductivity materials. Full article

Friction stir spot welding (FSSW) technology relies on the generation of frictional heat during the rotation of the welding tool in contact with the workpiece as well as the stirring effect of the tool pin to produce solid-state spot joints, especially for lightweight materials. Although FSSW offers significant advantages over traditional fusion welding, the oxidation of the interfacial bond line remains one of the most challenging issues, affecting the quality and strength of the joint under both static and cyclic loading conditions. In this experimental study, inert argon gas was employed to surround the joint, aiming to prevent or minimize the formation of the interfacial oxides. Two welding processes were conducted with identical welding process parameters and welding tool geometry: the conventional process and another that employs an inert gas cover. Micrographs of as-welded specimens were analyzed using a computerized optical microscope to characterize the interfacial bond lines and an energy-dispersive spectroscope (EDS) was used to quantify the interfacial oxides. Specimens from both welding conditions were tested under static and cyclic loads to investigate the static and fatigue behaviors, respectively. The fatigue tested specimens were examined under different load levels to investigate the fatigue crack behavior and the modes of failure at low-cycle and high-cycle fatigue conditions. The optical micrographs showed significant improvement in bond line morphologies (33% enlarged fully bonded area) and both static and fatigue strengths (35% reduced partially bonded area) when the inert gas cover was used. The EDS analysis revealed a maximum reduction of the interfacial oxide of 41% in the bond line achieved in the argon-surrounded joints compared to specimens of the conventional welding process. Accordingly, an improvement of 14% in the static strength was reached, along with 60% and 26% in the fatigue strengths at low- and high-cycle fatigue conditions, respectively. Full article

To achieve carbon neutrality, a reduction in car body weight is essential. Multi-material structures that use lightweight materials such as carbon fiber-reinforced polymers (CFRP) and aluminum (Al) alloy are used to replace parts of steel components. This multi-material method requires specific joining techniques for bonding dissimilar materials. Friction stir spot welding (FSSW) is one of the joining techniques used for joining dissimilar materials, enabling rapid and strong joints. FSSW for bonding A5052 Al alloy and carbon fiber-reinforced thermosetting resin (CFRTS) utilizing composite laminates with integrally molded thermoplastic resin in the outermost layer has been developed. However, joints using this method cause pyrolysis due to excessive frictional heating at the tool’s bottom, which may affect joint strength and promote corrosion in Al alloy. Therefore, this study developed new tools, a concave-shaped tool without a probe, a concave-shaped tool with a probe and a conventional FSSW tool, and investigated the influence of heat distribution and joint strength using the three new tools. The newly developed concave-shaped tool with a probe suppressed 7% of maximum heat input, decreased the pyrolysis area of epoxy resin by 47%, and increased joint strength by 4%. Finite element analysis also showed the suppression of heat input through the newly developed concave-shaped tool with a probe, achieved by reducing the contact area between the tool and Al alloy. Full article

In this work, 2060 Al-Li alloy was joined by refill friction stir spot welding (RFSSW). The effects of the tool’s rotating speed and welding time on the microstructure and mechanical properties of the welded joints were studied. The results showed that joints without defects can be obtained within a wide range of welding parameters. Tiny voids were formed when using a low rotating speed of 1600 rpm, and incomplete refilling was obtained when using a short welding time of 1 s. Increasing the rotating speed from 1600 to 2000 rpm increased the grain size of the stir zone (SZ). When using a short welding time of 1 s, the grains of the SZ were not completely broken with high orientation differences in the grains. Higher hardness was obtained in the SZ when using a lower rotating speed and shorter welding time. Increasing the rotating speed increased the joint strength, while short and long welding times decreased the joint strength. Full article