Understanding the mechanical heterogeneity of welded joints in ultra-high-strength steels is critical for predicting their performance and failure behaviour. In this study, digital image correlation was employed to extract local true stress–strain curves for individual sub-zones within laser-welded butt joints of S960MC steel. The local plastic behaviour of the weld metal, coarse-grained HAZ, and sub-critical HAZ was quantified using Voce hardening model, and XRD-based apparent dislocation density, complemented by residual stress measurements. Results confirm pronounced differences in strain hardening capacity among the sub-zones, with the sub-critical HAZ consistently exhibiting the lowest saturation stress and the most rapid exhaustion of its hardening reserve. Notably, the two investigated weld variants exhibited distinctly different failure modes attributed to differences in soft zone geometry, constraint effects, and residual stress distribution. These findings highlight the importance of accounting for local mechanical disparities and constraint effects when evaluating weld performance and predicting failure behaviour in statically loaded joints.
FSX-414 is a cobalt-based superalloy widely used in stationary gas turbine blades due to its high-temperature strength and oxidation resistance. However, service-induced degradation often necessitates repair welding to extend component life. In this study, the effect of filler metal selection on the microstructure and mechanical performance of GTAW-repaired FSX-414 was investigated. Four filler metals, namely FSX-414, HS25, HS188, and Mar-M918, were evaluated under identical welding conditions. The repaired joints were characterized using optical microscopy, SEM/EDS analysis, Vickers microhardness testing, and tensile testing conducted at both room and elevated temperatures. The results showed that filler metal composition significantly influenced dendritic morphology, carbide formation, hardness, and fracture behavior. The average weld metal hardness ranged from 367.5 HV for HS25 to 425 HV for HS188. Mar-M918 exhibited the best tensile performance, with the highest ultimate tensile strength and elongation, whereas FSX-414 showed the lowest values. Fractographic and microstructural observations indicated that variations in carbide precipitation and elemental segregation contributed to the observed mechanical behavior. Overall, Mar-M918 provided the most favorable strength–ductility balance, highlighting the critical role of filler metal selection in repair welding of FSX-414.
The increasing demands for high production rates, reduced costs, and more sustainable aircraft structures encourage the rapid introduction of thermoplastic composites in aerospace applications. A major challenge for their widespread implementation, especially in single-aisle aircraft programs, lies in meeting the required high production rates of up to 80–100 aircraft per month. Fast, automated manufacturing technologies such as thermoforming and welding are therefore essential to enable scalable industrialization. Continuous ultrasonic welding is such a high-speed joining technique. However, for stiff aerospace-grade composites, it remains challenging to achieve uniformly welded seams using current state-of-the-art control methods. This study investigated the potential for improving process robustness and weld quality in continuous ultrasonic welding of CF/LMPAEK adherends made from unidirectional plies by introducing a novel combined power-amplitude control method. Welds were produced using the state-of-the-art constant-amplitude and constant-power control methods, as well as the newly introduced approach, and were compared in terms of power and amplitude responses, heating uniformity, and resulting weld quality. A combined fuzzy power-amplitude control method was developed and implemented. Under the processing conditions investigated in this study, the proposed control method reduced extreme fluctuations in power and amplitude and was associated with improvements in weld strength and weld uniformity. Overall, the findings indicate that combined power-amplitude control is a promising approach for improving the robustness and quality of continuous ultrasonic welding of thermoplastic composites.
Flux-assisted laser welding of high-strength low-alloy (HSLA) steel was investigated to achieve deep penetration, microstructural control, and toughness enhancement in autogenous laser weld metal. A flux layer was applied to the steel plate surface, and welding was performed without inert shielding gas, whereas a conventional condition used Ar shielding. Compared with the Ar-shielded weld metal, which contained 0.003 mass% oxygen, the flux-assisted weld metal exhibited a markedly higher oxygen content of 0.047 mass% introduced through slag–metal reactions, resulting in a narrower bead width and significantly deeper penetration. The penetration enhancement is considered to be primarily attributed to oxygen-assisted modification of molten pool dynamics: oxygen, as a surface-active element, alters the temperature coefficient of surface tension and promotes inward Marangoni convection, thereby concentrating heat and momentum toward the pool axis. Moreover, oxygen addition through slag–metal reactions and the associated change in deoxidation balance transformed the inclusion population from Al–O-based inclusions to complex Ti–Al–Mn–Si–O oxides with Ti-enriched surface layers, providing intragranular nucleation sites for acicular ferrite. Consequently, the weld metal microstructure changed from coarse upper bainite to fine, randomly oriented acicular ferrite, leading to a substantial improvement in toughness in Charpy impact tests. These results demonstrate that flux-assisted laser welding enables simultaneous deep-penetration welding and microstructure–property improvement through oxygen-assisted control of Marangoni convection and oxide metallurgy.
With ongoing efforts to reduce vehicle weight, steel components in vehicles are substituted with aluminum. However, Resistance Spot Welding (RSW) of aluminum alloys is more challenging than that of steel due to their high thermal and electrical conductivity and the presence of an oxide layer. Although data-driven methods are prominent in RSW of steel structures and have demonstrated promising results for consecutive spot welds, their application in aluminum RSW remains limited. The analysis of the 159,210 welded spots generated in an experimental setup, shows that when welding multiple consecutive spot welds with the identical parameters (current, force, cap thickness and material), the weld diameter varies based on its position and the time between welds. This indicates temporal and hierarchical effects in the welding process of consecutive spot welds. Therefore, this work investigates Machine Learning (ML) algorithms that incorporate lagged features and sequenced data to predict the weld diameter and expulsion occurrence on the welding operation level. The best performing model (Extreme Gradient Boosting (XGBoost)) is capable of predicting weld diameter with an R2 of 0.9621 and expulsions with an accuracy of 98.55%. Finally, the contribution of features to the model predictions are quantified using Shapley Additive Explanations (SHAP) values. The results show that, although consecutive spot welds exhibit temporal and hierarchical dependencies, explicit feature modeling does not improve the prediction performance of the ML algorithms under the investigated experimental conditions, as these effects are sufficiently captured by the spot position.
Resistance spot welding (RSW) of aluminum to steel remains challenging due to the rapid formation of brittle Fe-Al intermetallic compounds (IMCs), which deteriorate weld integrity and mechanical performance. In the present study, an electroplated Ni interlayer (∼17 μm) was employed to control interfacial reactions and improve the joining behavior of dissimilar Al6061/St12 resistance spot joints. Microstructural characterization revealed that the Ni interlayer modified interfacial diffusion and suppressed the formation of thick and irregular Fe2Al5 layers typically observed in direct Al/steel welds. In the absence of Ni, a non-uniform Fe2Al5 layer with a thickness of up to ∼6 μm formed at the interface, promoting brittle interfacial fracture. In contrast, the introduction of the Ni interlayer resulted in a thinner and more uniform reaction zone (≤3 μm) consisting primarily of refined Fe-Al-Ni ternary phases. The modified interfacial structure significantly improved joint performance. Tensile-shear strength increased from 54 MPa to 93 MPa, while elongation improved from 0.80% to 3.15%. In addition, the absorbed energy increased from 0.25 J to 0.901 J. Fracture behavior transitioned from brittle interfacial failure to ductile tearing and partial plug failure in joints produced with the Ni interlayer. The findings demonstrate that electroplated Ni interlayer provides an effective approach for controlling interfacial reactions and enhancing weld performance in Al-steel joints, while maintaining compatibility with existing industrial RSW systems.
The integrity of the laser welding joints at the interface between battery tabs and busbars is crucial for ensuring the safety and efficiency of electric vehicles (EVs). Despite advancements in laser welding techniques, the effect of varying interface position on melt pool morphology, fluid flow, and keyhole stability remains unexplored. This study examined how different lap-joint interface positions affected fluid flow, melt pool depth and keyhole dynamics in AA1050 aluminum sheets, using a combination of experiments and numerical simulations. A wobbling pattern was employed to achieve the desired weld joint width, with a ring spot beam introduced to minimize spatter in the melt pool. The results reveal that the lap-joint interface position significantly alters heat distribution, melt pool convection patterns, and keyhole behavior. It was found in a lap-joint of 1 mm upper sheet and 3 mm lower sheet (1–3 mm) that early interaction with the interface promotes unstable fluid flow and keyhole fluctuations. In a 1.5–2.5 mm configuration, balanced heat transfer conditions were observed, resulting in deep penetration. In a 2–2 mm configuration, the penetration efficiency is reduced and susceptibility to porosity at the interface is increased. To gain further insight into the mechanisms leading to these observations, a 3D multiphysics simulation of laser wobbling with a ring spot beam was implemented. The model was validated against single-track experiments, and the results demonstrated that the interface position strongly influenced keyhole morphology and stability.
Direct friction welding of type 7075-T6 aluminum alloy (AA7075) to low carbon steel (LCS) is known to be challenging, primarily because the limited plasticity of AA7075 promotes crack initiation within the flash, and the resulting cracks can move toward the vicinity of the weld interface as welding proceeds. To determine the friction welding parameters required to produce joints whose strengths approach that of the LCS base metal, this study conducted a systematic examination of simultaneous friction welding with a commercially pure Ti (CP-Ti) insert metal between AA7075 and LCS. A CP-Ti insert thickness of 8 mm was found to be effective for producing joints without visible defects; however, insufficient heat generation at a short friction time of 0.7 s resulted in low tensile strength. Increasing the friction time improved joint performance, and the maximum strength reached 99% of the LCS base metal tensile strength, with an average of approximately 97% at a friction time of 2.5 s. Although slight necking appeared on the AA7075 side, fracture consistently initiated at the weld interface between the AA7075 side and the CP-Ti insert metal. Extending the friction time to 3.3 s caused a minor decline in joint strength. SEM-EDS and X-ray diffraction analyses showed no evidence of intermetallic compound interlayers at the weld interfaces, within their resolution limits. These results indicate that high strength can be achieved in the welded configuration involving AA7075, CP-Ti, and LCS through a simple single-step friction welding process, and they underscore the essential function of the CP-Ti insert metal in promoting joining between materials with inherently poor mutual weldability.
This study investigates dissimilar laser beam welding of 3 mm aluminium (EN AW‑1050A) to copper (CW004A) in an overlap joint under vacuum. A single-mode fiber laser with circular beam oscillation was used in a central composite face-centred (CCF) design of experiments (DoE) varying laser power, welding speed, chamber pressure and defocus. Weld seams were evaluated by top‑bead inspection, metallographic cross‑sections and scored metrics that guided selection of parameter sets for mechanical testing (peel and destructive shear‑tensile tests).Analysis of variance (ANOVA) shows that laser power, welding speed and chamber pressure are the primary factors controlling welding depth, seam width and seam area, while defocus showed no significant effect on these geometric response variables. Circular beam oscillation creates lateral energy maxima that produce characteristic penetration “spikes”. The calculated spatial energy distributions correspond to the observed penetration profile. Among the parameter sets selected for mechanical testing, P1 showed the most favourable peel-test behaviour, associated with a more homogeneous copper penetration profile, a larger seam width and a higher energy input per unit length (∼ 93 J/mm). Fractography by SEM and EDX showed the coexistence of Al-rich micro-ductile and Cu-rich brittle fracture regions on the investigated fracture surface, supporting an association between local composition and mixed ductile-brittle failure behaviour. Balanced processing conditions (≈ 1500 W, ≈ 20 mm/s, reduced chamber pressures of approximately 10–55 mbar) yielded the most favourable seams, whereas extreme settings increased defect risk or excessive mixing.
Wire-arc directed energy deposition (DED) with high heat input typically requires long inter-pass intervals to avoid deteriorating metallurgical and mechanical properties. However, this significantly extends process time, thereby sacrificing the manufacturing rate (MR). This trade-off is particularly pronounced in thin-walled structures due to low heat dissipation. While solid-contact active cooling (SCAC) can improve the metallurgical and mechanical properties of magnesium alloys in wire-arc DED, its potential for aggressive MR enhancement remains under-explored. This study experimentally reveals that SCAC enables the fabrication of AZ31 thin walls with a refined microstructure and acceptable tensile properties even under a very short interval (average 2.5 s) corresponding to an extremely high MR (882 cm3/h). While natural cooling (NC) exhibited continuous heat accumulation leading to bead sagging despite a 120 s interval (MR = 90 cm3/h), SCAC reached thermal equilibrium early, enabling nearly continuous deposition. Additionally, narrowing the gap between the cooling copper blocks reduced the molten pool volume. Furthermore, the refinement of grains and precipitates by SCAC promoted a transition from a predominant quasi-cleavage mode to an extensive ductile fracture mode. Consequently, SCAC increased the yield strength, tensile strength, and elongation by up to 12 MPa, 13 MPa, and 10%, respectively, along the travel direction. Microstructural analysis suggests that the yield strength enhancement is primarily governed by grain refinement. This work demonstrates that active cooling strategies, including but not limited to SCAC or magnesium alloys, possess the potential to maintain the overall mechanical properties while significantly enhancing productivity in wire-arc DED.
Friction stir additive manufacturing is a relatively new additive manufacturing technology with significant potential for fabricating large aerospace components (e.g., stiffeners or stringers). External cooling for this process is increasingly discussed because it can reduce mechanical degradation caused by reheating the lower layers during welding. In this article, an experimental study is described in which different cooling strategies (cooling plate, water spray, and water bath) were compared with a naturally cooled reference regarding their effects on workpiece temperatures, distortion, and hardness in specimens made of the aluminum alloy EN AW-6082-T6. In all specimens, distortion decreased with each additional layer, and hardness decreased from top to bottom, with several local maxima within the overlapping welds and in the welded part of the substrate. The cause of hardness loss was found to be grain and particle coarsening and a higher concentration of alloying elements in precipitation-rich areas. Compared to the naturally cooled reference, the water bath resulted in the lowest temperature during welding, lowest distortion, and highest hardness. The water spray also significantly affected the temperature and distortion, but its effect on hardness was small. In contrast, the cooling plate had the least effect on temperature and hardness, and it also negatively impacted distortion. Given the relatively low implementation effort and good results, future developments should focus on a system similar to the water spray, but with enhanced cooling of the trailing edge of the tool, e.g., cryogenic CO2 with nozzles attached to the machine's spindle.
Additive friction stir deposition (AFSD) is a solid-state additive manufacturing process that demonstrated its capability to repair high strength aluminum alloys without the deleterious effects related to rapid phase changes. This study investigated the influence of heat input on the bonding quality of a lubricant free, twin rod AFSD as deposited repair of simulated damaged 3 mm deep grooves on aluminum alloy 7050 plates to identify processing conditions that yielded improved ductility and tensile strength. Heat input was controlled by a novel temperature control scheme to maintain isothermal depositions at different traverse speeds where slower speeds generated higher heat input (HHI) and faster speeds generated lower heat input (LHI). While both repair conditions produced fully dense deposits that exceeded the mechanical properties of a non-repaired specimen, distinct fracture behavior was observed that affected the resulting mechanical response. The different hardness gradients across the repairs enabled distinct strain localization patterns that shifted from across the entire repair to within the deposit interface during tensile loading for the LHI and HHI repair respectively. The variability of ductility for the HHI condition suggested a sensitivity to processing parameters and underscored the critical role of thermal input in optimizing AFSD repair conditions for improved bonding.
The increasing demand for lightweight multi-material structures, particularly in automotive and aerospace applications, requires robust and efficient joining technologies. Mechanical joining methods based on locally formed pin structures offer a promising solution, as they enable the joining of dissimilar materials such as steel and aluminium as well as steel with fibre reinforced plastics without auxiliary elements. As single-pin connections have already been well researched, the focus has now shifted to applying this principle to multi-pin connections that are more relevant to practical applications. However, the forming behaviour of such systems remains insufficiently characterised.In this work the formation of multi-pin structures by forward extrusion and their implications for subsequent joining applications is being investigated. It is shown that multi-pin forming cannot be interpreted as a simple superposition of single-pin processes. Instead, the results reveal that local pin geometry is governed by interaction effects between neighbouring pins, even under constant process conditions. These interactions arise from competition for the locally available material, leading to systematic variations in pin height depending on pin spacing and arrangement. A distance-based interaction model is proposed, allowing the prediction of local pin height variations for configurations dominated by pin-to-pin interaction effects. The findings further demonstrate that, in addition to the local pin height, the homogeneity of the pin height distribution should be considered an important parameter, as it is expected to influence the reliability and predictability of the resulting mechanical joint. The presented approach provides a foundation for the design and optimisation of multi-pin joining systems for lightweight applications.
In mechanical joining, a wide variety of tool geometries and rivet types have been developed to meet different requirements. For example, this is due to the mechanical properties of sheet materials and the increasing number of material combinations that require joining. However, to address rising costs and sustainability demands or to react to supply chain disruptions, versatile joining processes are needed to reduce the amount of joining equipment required by adapting the process to the joining task. This study examines the influence of punch velocity on the clinching and semi-tubular self-piercing riveting processes, as well as on the binding mechanisms, joint geometric parameters, and joint properties. The aim is to determine the relevant range of punch velocities based on material properties, such as strain-rate dependence, and to assess whether punch velocity can be used as a control variable for versatile joining processes. To this aim, similar joints made of steel (HCT590X+Z), aluminum (EN AW-6014), and mixed joints of these materials are examined. The resulting joining forces are analyzed using force-displacement curves to evaluate the influence on the joining process. The form closure is examined using micrographs of the joints' geometric parameters. To characterize the force closure, the connection resistance is measured using the four-wire sensing method, and the load-bearing capacity is determined via a shear-tensile test.
Laser beam welding (LBW) is increasingly used for joining high-strength steels; however, its performance depends on coupled phenomena such as heat transfer, melting/solidification, phase transformation, and residual stress development, making process optimisation challenging. Although Computational Fluid Dynamics (CFD)-based approaches can capture these effects with high fidelity, they are often computationally expensive for industrial applications. This study presents a unified thermo-mechanical framework for remote LBW by combining a double conical-Gaussian volumetric heat source (DCVHS), adaptive thermal-to-mechanical coupling, and plasticity-based constitutive modelling. Unlike conventional thermo-mechanical welding models requiring manual definition of fusion-zone (FZ) and heat-affected zone (HAZ) domains, the proposed framework automatically identifies BM, HAZ, and FZ regions directly from the transient thermal field using temperature-based segmentation. These domains are subsequently used for automatic weld-joint generation through multi-point constraints (MPCs) and for zone-specific material properties assignment, enabling adaptive weld modelling under varying process parameters. A semi-empirical sigmoid regression model further enables prediction welding parameters such as laser power, welding speed, and penetration depth. Mechanical behaviour is evaluated using a plasticity model to predict tensile, lap-shear, and cross-tension performance of the joints. Validation through bead-on-plate and overlap welding experiments, metallography, microhardness mapping, and mechanical testing demonstrates good agreement between simulations and experiments, confirming the framework’s predictive capability and computational efficiency for weldability assessment and welding process optimisation.
During electrical machines manufacturing, quality control is often realised at the end of the line or at selected intervals. The manufacturing process for reliable terminations of machine windings is manual and error-prone, with up to 10% of the strands in terminations found to have incomplete connections. One solution lies in in-process monitoring and inspection of activities involved in the manufacturing. This research proposes the first framework for parallel bimodal quality prediction using real-time RGB images and thermal data from infrared images for process monitoring of thermally crimped wires. The framework demonstrated around 70% accuracy. The developed system simultaneously detects and classifies visible surface defects and hidden subsurface defects at a rate of 0.31 s per sample, while addressing key hindering issues associated with a single sensing modality. The non-destructive defect detection is achieved by combining visual and infrared thermal testing technologies. A Deep Learning Object Detector was trained on RGB images for surface defect identification, and two Long Short-Term Memory neural network models were designed and trained on time-series temperature profiles derived from infrared thermal images to predict hidden (subsurface) defects. Additionally, a novel crimping-score formula is proposed as a complementary diagnostic metric. This formula unifies the effects of individual crimping process parameters into a set of singular values, mapping them to sample quality. While independent of the proposed framework, this score provides manufacturers with an actionable path from parameter prescription to product verification, without interrupting the manufacturing process.
This study investigates the ultrasonic welding behavior and joint performance of woven carbon fiber reinforced polyphenylene sulfide (woven-CF/PPS) laminates using carbon nanotube (CNT) modified PPS energy directors. Single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT) were incorporated into PPS via controlled compounding processes, and their dispersion states were evaluated by scanning electron microscopy and volume resistivity measurements. The wet-kneading method was found to be essential for achieving homogeneous CNT dispersion, with the percolation threshold indicated at approximately 1.0 wt.% SWCNT. Ultrasonic welding behavior was characterized through in-situ monitoring of ultrasonic power and horn displacement. The welding process was classified into four stages: localized melting initiation, molten region expansion, full interfacial melting, and excessive melting accompanied by polymer squeeze-out. CNT addition promoted earlier melt propagation and increased the welded area ratio at shorter oscillation times. The maximum lap shear strength was achieved at an oscillation time of 0.9 s, corresponding to complete interfacial melting. In this study, the effects of CNT content and hybridization were further examined. MWCNT addition (0.5-1.0 wt.%) improved lap shear strength compared to pure PPS energy directors, whereas excessive SWCNT addition reduced strength due to re-agglomeration during melting. Hybrid incorporation revealed that 9:1 SWCNT:MWCNT ratio significantly reduced electrical resistivity and stabilized joint strength by enhancing nanotube interconnectivity. These results establish a process-structure-property relationship for CNT-modified energy directors and demonstrate the potential of hybrid CNT systems to improve joint strength and process stability in ultrasonic welding of thermoplastic composites.
With the latest advances in materials science, self-healing vitrimer adhesives with the ability to reform their polymer chain bonds with the application of external heating have emerged. These adhesives allow the manufacture of debond-on-demand and rebond-on-demand joints. This study presents a novel simulation approach that combines phenomenological modeling with finite element models of adhesive joints. The goal is to model the weakening of polymer chain bonds within the adhesive due to heating and estimate the required heating time to reach optimal debonding of the joint. The proposed phenomenological model is fitted to experimental stress-relaxation curves for the adhesive at different temperatures and implemented into finite element models with a user subroutine. Round-butt joints with aluminium adherends were manufactured and debonded at different heating temperatures to validate the proposed model. The finite element simulation results were compared to the experimental stress-displacement curves, showing that the proposed model was able to accurately predict the stiffness reduction of the adhesive for the temperature range that led to optimal debonding with purely cohesive failure in the experiments.
Laser welding of dissimilar aluminium-copper (Al-Cu) joints is a major challenge and a point of failure in EV battery pack manufacturing, predominantly due to non-uniform material mixing, intermetallic compound (IMC) formation, and the formation of defects such as porosity, cracking and voids. This study investigates the synergistic effect of varying the core-to-ring power ratio and travel speed on the metallurgical and mechanical properties of Al-Cu lap welds using a core-ring beam shaping and circular oscillation strategies. A systematic experimental approach was employed by varying the powers in the core and ring, as well as the travel speed, while keeping the oscillation conditions constant. Weld morphology, material mixing, and microstructural evolution were analysed using optical microscopy and SEM-EDS, whereas mechanical performance was evaluated through lap shear and axial fatigue testing. Results indicate that the core-to-ring ratio majorly controls the penetration depth and extent of material mixing, whereas travel speed influences cooling rates and defect formation. Higher core-to-ring ratios enhance penetration depth and bonding area but may promote excessive IMC formation and microcracking in the weld root, while higher travel speeds improve IMC distribution and reduce crack susceptibility. The highest lap shear strength was observed for sample C2 (C/R = 2, v = 300 mm/s), with an average peak load of 1208 +/- 18 N, attributable to improved Cu-Al mixing and a larger bonding area. Fatigue testing revealed distinct low- and high-cycle fatigue regimes, where samples with deeper penetration (B2 and C2) exhibited superior low-cycle fatigue performance, while sample C1 demonstrated the best high-cycle fatigue resistance owing to its homogeneous microstructure and absence of observable cracking. Higher travel speeds with an optimal core-to-ring ratio resulted in improved load-carrying capacity and fatigue resistance due to homogeneous mixing and reduced defect concentration.
Weak interfacial bonding remains a major limitation in developing hybrid structures for advanced mechanical and aerospace applications. This study integrates a systematic literature review with a comprehensive experimental investigation to evaluate the synergistic effects of laser-patterned superhydrophilic surfaces and TiO₂/SiO₂/MWCNT/PVCs nano multi-material reinforcement on interfacial bonding strength. From 263 reviewed papers (1996–2025), laser surface texturing (LST) and nanofiller addition emerged as dominant approaches to enhance adhesion in metal–composite systems. Experimentally, AA5052 aluminum substrates were modified using LST combined with etching–oxidation, forming circular micro-patterns that yielded superhydrophilic surfaces (Ra = 13.84 µm, contact angle = 0°, absorption time = 0.05 s). Hybrid joints were fabricated as Single Lap Joint (SLJ) through the Vacuum-Assisted Resin Infusion (VARI) one-step co-curing process, integrating six layers of carbon fiber reinforced polymer with epoxy resin containing 0–2.0 wt.% TiO₂/SiO₂/MWCNT/PVCs nano multi-materials synthesized via the sol–gel route from recycled solar-cell waste. Mechanical performance was evaluated by shear testing and Digital Image Correlation (DIC), while SEM–EDS, FTIR, and DSC confirmed morphological and chemical improvements. The optimal 1.5 wt.% reinforcement achieved a maximum shear strength of 19.5 MPa—an 11.3-fold enhancement— demonstrating a sustainable and cost-effective strategy for high-strength AA5052–CFRP hybrid bonding.
