Search Results (95)

The adjustable-ring-mode (ARM) scanning laser was used to perform butt welding on 0.5 mm thick TA1 titanium alloy and 304 stainless steel (SS304) thin sheets, with 1.2 mm diameter AZ61S magnesium alloy welding wire as the filling material. Microhardness test results show that the hardness distribution presented a trend of being higher in the base metals on both sides and lower in the middle filling area, with no hardening observed in the weld zone. For all specimens subjected to horizontal and axial weld bending tests, the bending angle reached 108° without any cracks occurring. When the ring power was in the range of 800–1000 W, or the scanning frequency was between 100 and 200 Hz, all the average tensile strengths of the welded joints were more than 80% of that of the AZ61S filling material (approximately 240 MPa); the maximum average tensile strength stood at 281.2 MPa, which is equivalent to 93.7% of the AZ61S. As the ring power or scanning frequency increased further, the tensile strengths of the joints showed a decreasing trend. The remelting effect of the trailing edge of the ARM laser under high energy conditions, or the scouring of the turbulent molten flow induced by the scanning beam, damages the weak links at the newly formed solid–liquid interface and increases the Fe concentration in the molten pool. This leads to a thicker FeAl interface layer during growth, thereby resulting in a decline in the mechanical properties of the welded joints. Full article

Assurance of the integrity of every weld joint is highly desirable, and defect detection methods that can be applied to welds at high temperatures immediately after welding are required. The laser ultrasonic (LU) method, which generates ultrasonic waves in the target via pulsed laser irradiation, is a well-known technique for non-contact defect detection during welding. Ultrasonic waves excited in ablation mode exhibit large amplitudes and predominantly surface-normal propagation, which has driven extensive research into their application for weld inspection. However, owing to the size and weight of conventional equipment, such systems have largely been limited to bench-top experimental setups. To address this, we developed an LU robotic system incorporating a compact, lightweight laser source and an improved signal-processing system. We conducted experiments to measure signals and to detect backside slits in flat plates and blowholes in lap-fillet welds. Additionally, a method to improve the sensitivity of laser interferometers was investigated and demonstrated on smut-covered areas near weld beads. Full article

Resistance spot welding of aluminum alloys causes the electrode materials to degrade rapidly. This is due to diffusion processes occurring between the sheet materials and the copper electrodes at process temperatures of up to 600 °C. This significantly limits the electrode life, resulting in less than 60 weld cycles before the joint quality becomes insufficient. Thin-film diffusion barriers can increase electrode life and improve joint quality. This article describes the generation of barrier layers of nickel and tungsten using physical vapor deposition. These layers directly influence the welding process by altering the electrical resistance and friction coefficients in the contact area. Nanoindentation is used to determine the specific properties of the barrier layers within the 2.5–3 µm layer thickness range. Hardness and modulus of elasticity are determined by indentation tests. Scratch tests determine the friction coefficients and adhesion strength of the coating against plastic deformation. Nanoindentation is also used to investigate the degradation process of the electrode base material and barrier layers. This reveals which damage mechanisms occur with uncoated electrodes and demonstrates how thin-film diffusion barrier coatings can prevent aluminum diffusion. Full article

This paper addresses the mechanical characterization of dissimilar overlap joints made by autogenous laser welding between thin sheets of low-carbon steel (CS) and austenitic stainless steel (SS) with an optimized welding technology able to produce sound overlap joints. This involved applying the laser beam from the CS-side to reduce the SS overheating. The research is focused on the analysis of combined tensile-shear behavior of the weld and of the heat-affected zones. During testing, the applied tensile-shear load rotates the weld connecting the CS and SS plates. The rotation angle transmitted to the free ends of the plates, together with relevant strain fields, were measured by using a digital image correlation system, VIC-2D. Thus, it was found that the weld acts as a non-linear hinge which experiences a sudden loss of stiffness when strain concentrations develop from the weld ligament edges towards the loaded sides of the plates. The welded joint fails by yielding localization and necking in the CS plate, far from the weld. This mode of failure is a consequence of the weld and heat-affected zone strength mismatches of 1.09 and 1.33, respectively. These values are consistent with the hardness profile and the documented microstructural heterogeneities. Full article

Welding is a technological variant of the electric resistance spot-welding process in which the machined protrusion on the surface is heated and rapidly deformed, and the small molten zone formed at the interface is then forged to form the weld spot. The paper analyses the effects of projection welding parameter values for thin, low-carbon aluminized steel sheets. Two sets of 16 welded samples having three or five protrusions were performed and analyzed using the Taguchi method. The microstructural aspects were analyzed in cross sections made through the welded points, highlighting the expulsion or accumulated effects of the Al-Si alloy protective layer and the formation of intermetallic compounds. To estimate the effect of welding parameters, the samples were subjected to tensile strength tests, and the fracture mode was evaluated. It was found that the values of the breaking forces were close for the two types of samples analyzed, for identical values of the welding regime parameters, but the elongation at break was double in the case of samples with five protrusions. The breaking force increased from 10.9 kN for samples with three protrusions to 11.4 kN for samples with five protrusions, for the same values of welding parameters. Full article

Climate concerns are driving the automotive industry to adopt advanced manufacturing technologies that aim to improve energy efficiency and reduce vehicle weight. In this context, lightweight structural materials such as aluminium alloys have gained significant attention due to their favorable strength-to-weight ratio. Laser welding plays a crucial role in assembling such materials, offering high flexibility and fast joining capabilities for thin aluminium sheets. However, welding these materials presents specific challenges, particularly in controlling heat input to minimize distortions and ensure consistent weld quality. As a result, numerical simulations based on the Finite Element Method (FEM) are essential for predicting weld-induced phenomena and optimizing process performance. This study investigates welding-induced distortions in laser butt welding of 1.5 mm-thick Al 6061 samples through FEM simulations performed in the SYSWELD 2024.0 environment. The methodology provided by the software is based on the Moving Heat Source (MHS) model, which simulates the physical movement of the heat source and typically requires extensive calibration through destructive metallographic testing. This transient approach enables the detailed prediction of thermal, metallurgical, and mechanical behavior, but it is computationally demanding. To improve efficiency, the Imposed Thermal Cycle (ITC) model is often used. In this technique, a thermal cycle, extracted from an MHS simulation or experimental data, is imposed on predefined subregions of the model, allowing only mechanical behavior to be simulated while reducing computation time. To avoid MHS-based calibration, this work proposes using thermal cycles acquired in-line during welding via infrared thermography as direct input for the ITC model. The method was validated experimentally and numerically, showing good agreement in the prediction of distortions and a significant reduction in workflow time. The distortion values from simulations differ from the real experiment by less than 0.3%. Our method exhibits a slight decrease in performance, resulting in an increase in estimation error of 0.03% compared to classic approaches, but more than 85% saving in computation time. The integration of real process data into the simulation enables a virtual representation of the process, supporting future developments toward Digital Twin applications. Full article

Jointing is inevitable for CFRTP (carbon fiber reinforced thermoplastic) component applications in the automotive industry. In this study, commonly used jointing methods were applied to fasten CFRTP components. Three types of jointing methods. Ultrasonic welding, bolted joints, and adhesive joining, and three types of CFRTP materials, conventional cross-ply, ultra-thin prepreg cross-ply, and sheet molding compounds, were selected. The influence of the jointing methods on mechanical properties and damage patterns under bending load has been investigated. The finite element models were developed to predict the hazardous area and structural stiffness of jointed structures; the simulation results showed good agreement with experimental ones. The results indicate that the ultrasonic welding could reach similar bending stiffness compared to adhesive joining, whereas the stiffness of bolt jointed structures is relatively lower due to the contact separation induced by the bending deformation. Overall, the finite element model results correlated well with the experimental data. Full article

This study investigates the effect of welding speed on the microstructure and mechanical properties of pulsed laser lap-welded 0.2 mm 316L stainless steel sheets, commonly used in fuel cell bipolar plates. Welding speeds ranging from 6 to 26 mm/s were tested while other laser parameters remained constant. Results show that increasing welding speed reduces heat input, overlap factor, and weld dimensions. A transition from full to partial penetration occurs beyond 6 mm/s, with no visible heat-affected zone. The weld microstructure features columnar ferrite near fusion boundaries and globular ferrite in the center. Tensile–shear tests reveal that welds maintain higher strength than the base metal up to 22 mm/s, with all fractures occurring in the base material. An optimal speed range of 10–14 mm/s ensures defect-free joints with improved mechanical performance. These findings provide practical guidance for thin-gauge stainless steel welding in fuel cell applications. Full article

This study explores the friction stir welding (FSW) of thin aluminum sheets, focusing on alloys 1050 and 5754. FSW, a solid-state joining technique, offers advantages like minimal deformation and high joint strength, but optimizing welding parameters is crucial for sound welds. In order to investigate the optimum welding parameters, the Taguchi method was employed, in which key parameters such as rotational and welding speed were optimized to enhance tensile strength and weld quality. The tensile testing of the welded specimens revealed that the optimal combination—1000 RPM rotational speed and 250 mm/min welding speed—produced the highest tensile strength and weld quality. The results highlight the importance of parameter optimization in ensuring strong, stable welds, with rotational speed having the most significant influence. Additionally, excessive rotational speeds were found to weaken welds due to excessive heat input, while a slower welding speed contributed to greater weld stability. Full article

In order to further study the effect of welding residual stress on the fatigue strength of a TC4 titanium alloy sheet during laser welding, a laser welding butt joint model for TC4 titanium alloy sheets was established using ABAQUS (2022) software. The temperature and residual stress fields generated during the welding process were comprehensively simulated, and the melt pool shape and residual stress magnitudes were experimentally verified. The experimental parameters included a laser power range of 900–1200 W, welding speeds of 12.5 and 25 mm/s, and a double-sided welding approach with a cooling interval of 20 s between passes. The findings indicate that welding residual stress is primarily concentrated around the weld and the heat-affected zone, predominantly as tensile stress, with the maximum value observed at the weld’s initiation point, reaching 920 MPa—close to the material’s tensile strength limit. Under ideal conditions (without considering welding residual stress), the fatigue life at the weld area is estimated to reach 188,799 cycles, while the fatigue life of the base material without welding is calculated to be 167,109 cycles. However, when accounting for welding residual stress, the fatigue strength of the sheet decreases significantly, with the minimum fatigue life occurring at the weld toe, measured at 10,471 cycles. This study demonstrates that welding residual stress has a substantial impact on the fatigue life of TC4 titanium alloy sheets, particularly in the heat-affected zone, where the fatigue life is reduced by nearly 94% compared to the ideal condition. These results provide critical insights for improving the fatigue performance of laser-welded TC4 titanium alloy components in engineering applications. Full article

A mechanically robust flexible transparent conductor with high thermal and chemical stability was fabricated from welded silver nanowire networks (w-Ag-NWs) sandwiched between multilayer graphene (MLG) and polyimide (PI) films. By modifying the gas flow dynamics and surface chemistry of the Cu surface during graphene growth, a highly crystalline and uniform MLG film was obtained on the Cu foil, which was then directly coated on the Ag-NW networks to serve as a barrier material. It was found that the highly crystalline layers in the MLG film compensate for structural defects, thus forming a perfect barrier film to shield Ag NWs from oxidation and sulfurization. MLG/w-Ag-NW composites were then embedded into the surface of a transparent and colorless PI thin film by spin-coating. This allowed the MLG/w-Ag-NW/PI composite to retain its original structural integrity due to the intrinsic physical and chemical properties of PI, which also served effectively as a binder. In view of its unique sandwich structure and the chemical welding of the Ag NWs, the flexible substrate-cum-electrode had an average sheet resistance of ≈34 Ω/sq and a transmittance of ≈91% in the visible range, and also showed excellent stability against high-temperature annealing and sulfurization. Full article

The P91 martensitic steel and 304L austenitic stainless steels are two mainly used structural steels in power plants. The major problem in conventional multipass tungsten inert gas (TIG) welding of P91/304L steel is high heat input and joint distortion, increased cost and time associated with V groove preparation, filler rod requirement, preheating and welding in multiple passes, and labor efforts. Hence, in this study, a novel approach of robotically operated activated flux TIG (A-TIG) welding process and thin AlCoCrFeNi_2.1 eutectic high entropy alloy (EHEA) sheet as the interlayer was used to weld 6.14 mm thick P91 and 304L steel plates with 02 passes in butt joint configuration. The joints were qualified using visual examination, macro-etching, X-ray radiography testing and angular distortion measurement. The angular distortion of the joints was measured using a coordinate measuring machine (CMM) integrated with Samiso 7.5 software. The quality of the A-TIG welded joints was compared to the joints made employing multipass-TIG welding process and Inconel 82 filler rod in 07 passes. The A-TIG welded joints showed significant reduction in angular distortion and higher productivity. It showed a 55% reduction in angular distortion and 80% reduction in welding cost and time compared to the multipass-TIG welded joints. Full article

Electron backscattered diffraction (EBSD) characterization was conducted on the typical regions in friction-stir-welded dissimilar Al/Mg joints of 2 mm thick sheets with/without ultrasonic assistance. The effects of ultrasonic vibration (UV) on the grain size, recrystallization mechanisms, and degree of recrystallization on both sides of the Al-Mg bonding interface and the intermetallic compounds (IMCs) were investigated. It was found that on the Mg side of the weld nugget zone (WNZ), the primary dynamic recrystallization (DRX) mechanisms were discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), with geometric dynamic recrystallization (GDRX) playing a secondary role. On the Al side of the WNZ, CDRX was identified as the primary mechanism, with GDRX as a secondary contributor. While UV did not significantly alter the DRX mechanisms in either alloy within the WNZ, it promoted the aggregation and rearrangement of dislocations. This led to an increase in high-angle grain boundaries (HAGBs) and an enhanced degree of recrystallization in the welds. The average grain size in both the Al and Mg alloys of the WNZ followed a pattern of initially increasing and then decreasing along the thickness direction, reaching a maximum in the upper-middle part and a minimum at the bottom. The influence of UV on the average grain size in the WNZ was minimal, with only slight grain refinement observed, and the minimum refinement degree was only 0.9%. The Schmid factor (SF) on the WNZ and thermo-mechanically affected zone (TMAZ) boundary regions of the advancing side (AS) indicates that the application of UV increased the likelihood of basal slip and extension twinning in the crystal structure. In addition, UV reduced the thickness of IMCs and improved the strength of the Al-Mg bonding interface. These results suggest a higher probability of fracture along the TMAZ and WNZ boundary on the AS when UV was applied. Full article

Friction stir welding (FSW) and ultrasonic vibration enhanced FSW (UVeFSW) experiments were conducted by using 6061-T6 Al alloy and AZ31B-H24 Mg alloy sheets of thickness 2 mm. The suitable process parameters windows were obtained for the butt joining of Al/Mg sheets. The effect of ultrasonic vibration on the macrostructure and mechanical properties of the dissimilar joints was studied. The results showed that the width of the weld nugget zone (WNZ) was enlarged to some extent and the hardness distribution in WNZ was more uniform in UVeFSW. In addition, the application of ultrasonic vibration effectively promoted the interpenetration degree of dissimilar materials in the WNZ so that the mechanical interlocking on the bonding interface of dissimilar Al/Mg materials was enhanced. The facture positions were changed from the bonding interface in FSW to the boundary between WNZ and the thermo-mechanical affected zone, and the ductile fracture zone was expanded. The highest ultimate tensile strength was 205 MPa at the process parameters set of 1200 rpm–50 mm/min in UVeFSW in this experiment. The average ultimate tensile strength of FSW/UVeFSW joints was 172.3 MPa and 184.4 MPa, respectively, and the average ultimate tensile strength was increased by 7.02% with the introduction of ultrasonic vibration. Full article

This study focused on the efficacy of employing a pulsed fiber laser in the curved cutting of thin, non-oriented electrical steel sheets. Experiments were conducted in paraffinic oil by adjusting the input process parameters, including laser power, pulse frequency, cutting speed, and curvature radius. The multiple output quality metrics included kerf width, inner and outer heat-affected zones, and re-welded portions. Analyses of the Random Forest Method and Response Surface Method indicated that laser pulse frequency was the most important variable affecting the cut quality, followed by laser power, curvature radius, and cutting speed. To improve cut quality, an innovative artificial intelligence (AI) approach incorporating a deep neural network (DNN) model and a modified equilibrium optimizer (M-EO) was proposed. Initially, the DNN model established correlations between input parameters and cut quality aspects, followed by M-EO pinpointing optimal cut qualities. Such an approach successfully identified an optimal set of laser process parameters, even beyond the specified process window from the initial experiments on curved cuts, resulting in significant enhancements confirmed by validation experiments. A comparative analysis showcased the developed models’ superior performance over prior studies. Notably, while the models were initially developed based on the results from curved cuts, they proved adaptable and capable of yielding comparable outcomes for straight cuts as well. Full article