Search Results (150)

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

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 Welding (FSW) is widely used for high-strength aluminum alloys due to its solid-state bonding, which ensures superior weld quality and service stability. However, thermo-mechanical interactions during welding can induce complex residual stress distributions, compromising joint integrity. Previous studies have primarily focused on thermal load-driven stress evolution, often neglecting mechanical factors such as the shear force generated by the stirring pin. This study develops a three-dimensional thermo-mechanical coupled finite element model based on a moving heat source. The model incorporates axial pressure from the tool shoulder and torque-derived shear force from the stirring pin. A hybrid surface–volumetric heat source is applied to represent frictional heating, and realistic mechanical boundary conditions are introduced to reflect actual welding conditions. Simulations on AA6061-T6 aluminum alloy show that under stable welding, the peak temperature in the weld zone reaches approximately 453 °C. Residual stress analysis indicates a longitudinal tensile peak of ~170 MPa under thermal loading alone, which reduces to ~150 MPa when mechanical loads are included, forming a characteristic M-shaped distribution. Further comparison with a Coupled Eulerian–Lagrangian (CEL) model reveals stress asymmetry, with higher tensile stress on the advancing side. This is primarily attributed to the directional shear force, which promotes greater plastic deformation on the advancing side than on the retreating side. The consistency between the proposed model and CEL results confirms its validity. This study provides a reliable framework for residual stress prediction in FSW and supports process parameter optimization. Full article

This study’s novelty lies in providing first-time insights into the isolated role of Friction Stir Processing (FSP) travel speed on microstructure evolution and mechanical performance (micro-hardness, tensile properties, impact energy, and wear behavior) specifically in hypoeutectic as-cast Al-5 wt.% Si alloys, addressing a critical unaddressed gap in previous works (typically on near-eutectic compositions of Si > 6.5 wt.%). FSP, a solid-state technique, is highly effective for enhancing the properties of cast materials. The FSP was conducted at a fixed rotational speed of 1330 rpm and various travel speeds (26, 33, 42, and 52 mm/min). The FSP improves the mechanical properties of as-cast Al-5Si alloy by refining its grain structure. This leads to higher hardness, ultimate tensile strength (UTS), yield strength (YS), and strain at fracture and toughness compared to the as-cast condition. The specimen processed at 26 mm/min achieved the highest values of YS, UTS, toughness, and wear resistance. The fracture surfaces of the tensile and impact test specimens were examined using scanning electron microscopy (SEM) and discussed. Results indicated that the fracture surfaces revealed a transition from predominantly brittle fracture in the as-cast alloy to ductile fracture at 26 mm/min, changing to a mixed fracture mode at 52 mm/min. These findings underscore the critical importance of optimizing FSP travel speed to significantly tailor and enhance the mechanical performance of as-cast hypoeutectic Al-5Si alloys for industrial applications. Full article

This study investigates the mechanical and fatigue behaviour of friction stir composite joints fabricated from an aluminum alloy (AA6082-T6) and a glass fibre-reinforced polymer (Noryl^® GFN2) under different service temperature conditions. The joints were tested under both quasi-static and cyclic loading at three different temperatures (23, 75, and 130 °C). Fracture surfaces were analyzed, and the probabilistic S–N curves were derived using Weibull distribution. Results indicated that increasing the service temperature caused a non-linear decrease in both the quasi-static and fatigue strength of the joints. Compared to room temperature, joints tested at 75 °C and 130 °C showed a 10% and 50% reduction in average tensile strength, respectively. The highest fatigue strength occurred at 23 °C, while the lowest was at 130 °C, in line with the quasi-static results. Fatigue stress-life plots displayed a semi-logarithmic nature, with lives ranging from 10² to 10⁵ cycles for stress amplitudes between 7.7 and 22.2 MPa at 23 °C, 7.2 to 19.8 MPa at 75 °C, and 6.2 to 13.5 MPa at 130 °C. The joints’ failure occurred in the polymeric base material close to joints’ interface, highlighting the critical role of the polymer in limiting joints’ performance, as confirmed by thermal and scanning electron microscopy analyses. Full article

Surface roughness plays a vital role in determining surface integrity and function. Surface irregularities or reduced quality near the surface can contribute to material failure. Surface roughness is considered a crucial factor in estimating the fatigue life of structures welded by FSW. This study attempts to provide a deeper understanding of the nature of the surface formation and roughness of aluminum joints during FSW processes. In order to form more efficient joints, the frictional temperature generated was monitored until reaching 450 °C, where the transverse movement of the tool and the joint welding began. Hardness and tensile tests showed that the formed joints were good, which paved the way for more reliable surface roughness measurements. The surface roughness of the weld joint was measured along the weld line at three symmetrical levels using welding parameters that included a rotational speed of 1250 rpm, a welding speed of 71 mm/min, and a tilt angle of 1.5°. The average hardness in the stir zone was measured at 64 HV, compared to 50 HV in the base material, indicating a strengthening effect induced by the welding process. In terms of tensile strength, the FSW joint exhibited a maximum force of 2.759 kN. Average roughness (Rz), arithmetic center roughness (Ra), and maximum peak-to-valley height (Rt) were measured. The results showed that along the weld line and at all levels, the roughness coefficients (Rz, Ra, and Rt) gradually increased from the beginning of the weld line to its end. The roughness Rz varies from start to finish, ranging between 9.84 μm and 16.87 μm on the RS and 8.77 μm and 13.98 μm on the AS, leveling off slightly toward the end as the heat input stabilizes. The obtained surface roughness and mechanical properties can give an in-depth understanding of the joint surface forming and increase the ability to overcome cracks and defects. Consequently, this approach, using adaptive thresholding image processing coupled with grayscale histogram analysis, yielded significant understanding of the FSW joint’s surface texture. Full article

In this study, we examine the evolution of dislocation substructures influenced by the fatigue behavior of SSM 6063 aluminum alloy processed through friction stir welding (FSW). The findings indicate that dislocation substructures have a significant impact on fatigue life. Cyclic loading induced recrystallization in the stir zone (SZ), the advancing-side thermomechanically affected zone (AS-TMAZ), and the retreating-side thermomechanically affected zone (RS-TMAZ). The transformation of the α-primary aluminum matrix phase into an S/S’ structure and the precipitation of Al₅FeSi intermetallic compounds into the T-phase were observed. Furthermore, the precipitation of Si and Mg, the primary alloying elements, was observed in the Guinier–Preston (GP) zone within the SZ. Transmission electron microscopy (TEM) analysis revealed small rod-like particles in the T-phase, measuring approximately 10–20 nm in width and 20–30 nm in length in the SZ. In the AS-TMAZ, these rod-like structures ranged from 10 to 120 nm in width and 20 to 180 nm in length, whereas in the RS-TMAZ, they varied between 10 and 70 nm in width and from 20 to 110 nm in length. The dislocation substructures influenced the stress amplitude, which was 42.46 MPa in the base metal (BM) and 33.12 MPa in the FSW-processed SSM 6063 aluminum alloy after undergoing more than 2 × 10⁶ loading cycles. The endurance limit was 42.50 MPa for BM and 32.40 MPa for FSW. Fractographic analysis of the FSW samples revealed distinct laminar crack zones and shear fracture surface zones, differing from those of other regions. Both brittle and ductile fracture characteristics were identified. 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

This study investigates the influence of nano-sized reinforcements on aluminum matrix composites’ mechanical and tribological properties. Microstructural analysis revealed that introducing nanoparticles led to grain refinement, reducing the grain size from 129.7 μm to 41.3 μm with 2 wt.% TiO₂ addition. Furthermore, ultrasonic-assisted squeeze casting of AA6061 composites reinforced with TiO₂ and Al₂O₃ resulted in a 52% decrease in grain size, demonstrating nano-reinforcements’ effectiveness in refining the matrix structure. Despite these advantages, the high surface energy of nanoparticles causes agglomeration, which can undermine composite performance. However, ultrasonic-assisted stir casting reduced agglomeration by approximately 80% compared to conventional stir casting, and cold isostatic pressing improved dispersion uniformity by 27%. The incorporation of nano-reinforcements such as SiC, Al₂O₃, and TiC significantly enhanced the material properties, with hardness increasing by ~30% and ultimate tensile strength improving by ~80% compared to pure Al. The hardness of nano-reinforced composites substantially rose from 83 HV (pure Al) to 117 HV with 1.0 vol.% CNT reinforcement. Additionally, TiC-reinforced AA7075 composites improved hardness from 94.41 HB to 277.55 HB after 10 h of milling, indicating a nearly threefold increase. The wear resistance of Al-Si alloys was notably improved, with wear rates reduced by up to 52%, while the coefficient of friction decreased by 20–40% with the incorporation of graphene and CNT reinforcements. These findings highlight the potential of nano-reinforcements in significantly improving the mechanical and tribological performance of n-AMCs, making them suitable for high-performance applications in aerospace, automotive, and structural industries. Full article

The direct energy deposition arc process is widely used for fabricating medium and large components with moderate geometric complexity but often results in coarse microstructures and inconsistent hardness. This study introduces a hybrid manufacturing approach combining the friction stir burnishing process with the direct energy deposition arc by a gas–metal arc welding technique to refine the microstructure and enhance the microhardness of components fabricated from austenitic stainless steel 316L. Our former study used an aluminum alloy (A5052) friction stir burnishing tool, demonstrating significant microhardness improvement and grain refinement. However, it also faced notable challenges under high-heat and -friction conditions, including the effect of material adherence to the workpiece during processing. Therefore, this study introduces a newly developed friction stir burnishing tool made from copper (C1100) and compares its performance with the aluminum alloy tool regarding microhardness enhancement and microstructure refinement. The results indicate that the specimen processed by direct energy deposition arc combined with the copper friction stir burnishing tool demonstrated the best overall performance in grain refinement and hardness enhancement. Specifically, it achieved the highest average microhardness of 250 HV at 50 µm depths, compared to 240 HV for the aluminum alloy tool. The statistical analysis showed that both tools led to significant improvements over specimens processed without them. The statistical analysis confirmed a notable reduction in secondary dendrite arm spacing across all depths, with the copper tool demonstrating the most refinement. Additionally, a preliminary investigation of corrosion behavior revealed tool-dependent differences. Overall, this study offers a promising approach to improving additive manufacturing, particularly for industries with less stringent surface finish requirements. It could potentially reduce post-processing time and cost. Future research should explore different process parameters and assess long-term corrosion performance to develop this hybrid technique further. Full article

This study presents the optimization of the friction stir welding (FSW) process using polynomial regression to predict the maximum tensile load (MTL) of welded joints. The experimental design included varying spindle speeds from 600 to 2200 rpm and welding speeds from 100 to 350 mm/min over 28 experimental points. The resulting MTL values ranged from 1912 to 15,336 N. A fifth-degree polynomial regression model was developed to fit the experimental data. Diagnostic tests, including the Shapiro–Wilk test and kurtosis analysis, indicated a non-normal distribution of the MTL data. Model validation showed that fifth-degree polynomial regression provided a robust fit with high fitted and predicted R² values, indicating strong predictive power. Hill-climbing optimization was used to fine-tune the welding parameters, identifying an optimal spindle speed of 1100 rpm and a welding speed of 332 mm/min, which was predicted to achieve an MTL of 16,852 N. Response surface analysis confirmed the effectiveness of the identified parameters and demonstrated their significant influence on the MTL. These results suggest that the applied polynomial regression model and optimization approach are effective tools for improving the performance and reliability of the FSW process. 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

Despite the extensive use of 7xxx aluminum alloys in aerospace, intergranular corrosion is yet to be appropriately addressed. In this work, in situ rolling friction stir welding (IRFSW) was proposed to improve the corrosion resistance of joints via microstructural design. A gradient-structured layer was successfully constructed on the surface of the joint, and the corrosion resistance was improved by in situ rolling. The intergranular corrosion depth of the IRFSW joint was reduced by 59.8% compared with conventional joints. The improved corrosion resistance was attributed to the redissolved precipitates, the disappearance of precipitate-free zones, and the discontinuous distribution of grain boundary precipitates. This study offers new insights for enhancing the corrosion resistance of aluminum alloy FSW joints. Full article

Compared to base aluminum alloys, the surface composites of aluminum alloys are more widely used in the automotive, aerospace, and other industries. The ability to yield enhanced physical properties and a smoother microstructure has made friction stir processing (FSP) the method of choice for developing aluminum-based surface composites in recent times. In this work, the Goal Programming (GP) approach is adopted for the Multi-Objective Optimization of FSP processes with three Artificial Intelligence (AI)-based metaheuristics, viz., Artificial Bee Colony (ABC), Particle Swarm Optimization (PSO), and Teaching–Learning-Based Optimization (TLBO). Three parameters, copper percentage (Cu%), graphite percentage (Gr%), and number of passes, are considered, and multi-factor non-linear regression prediction models are developed for the three responses, Tool Vibrations, Power Consumption, and Cutting Force. The TLBO algorithm outperformed the ABC and PSO algorithms in terms of solution quality and robustness, yielding significant improvements in tool life. The results with TLBO were improved by 20% and 14% compared to the PSO and ABC algorithms, respectively. This proves that the TLBO algorithm performed better compared with the ABC and PSO algorithms. However, the computation time required for the TLBO algorithm is higher compared to the ABC and PSO algorithms. This work has opened new avenues towards applying the GP approach for the Multi-Objective Optimization of FSP tools with composite parameters. This is a significant step towards toll life improvement for the FSP of composite alloys, contributing to sustainable manufacturing. Full article