To explore the crack formation mechanism of solid self-piercing riveted joints of Mg/Al dissimilar alloys, the mechanical properties of the magnesium alloy materials were characterized. The material constitutive model and GISSMO fracture failure model of the magnesium alloy were constructed, and a refined simulation model for the forming process of solid self-piercing riveting was established. The strain field distribution and material flow characteristics during the joint forming process were analyzed; the internal crack formation mechanism of the joint was revealed, and crack suppression was achieved through die structure optimization. The simulation and experimental results indicate that cracks are mainly generated in the piercing and extrusion stages of the riveting process; crack sources are initiated in the lower magnesium alloy sheet near the inner and outer edges of the die boss and the dissimilar material interface; under the combined extrusion of the punch and die boss, the crack sources on the upper and lower surfaces of the magnesium alloy sheet propagate towards each other and finally form macroscopic “bowl-shaped” cracks. The optimized beveled die reduces the peak effective plastic strain in the dangerous area, slows down the material flow rate, suppresses the generation of joint cracks, improves the material filling performance in the mechanical interlock region, and realizes the efficient and reliable joining of Mg/Al dissimilar alloys.
Laser welding technology has significant advantages in the precision machining and mass production of metal bipolar plates for fuel cells due to its characteristics of high precision and high efficiency. However, in the welding of ultra-thin metal bipolar plates, problems such as difficult-to-control weld quality and welding thermal deformation exist. To solve the above problems and optimize the welding process window more efficiently, a Gaussian surface-cylinder compound heat source model based on the non-penetrating welding of ultra-thin metal bipolar plates was constructed using COMSOL Multiphysics. A full factorial analysis scheme with four factors and five levels was constructed by adopting three parameters: penetration depth, weld width, and joint width. A BP neural network model was trained through JMP software combined with the actual weld pool morphology, making the modified simulation model closer to the actual welding weld pool. The test results show that when the modified laser heat source model is used for the welding process simulation, and the simulation results are compared with the actual bipolar plate welding test results, the relative errors between the simulation data and the test data are all within ±5%. This indicates that the model can well guide the actual engineering practice of the laser welding process for metal bipolar plates in the future.
To investigate the effects of different oscillation paths (no oscillation, 8-shaped, and triangular types) on the interface microstructure, intermetallic compound (IMC) layer thickness, tensile strength, and fracture behavior of Al/Ti dissimilar metal joints during the laser welding-brazing process, Al/Ti composite joints were prepared by laser welding-brazing technology. By using the oscillation path of the laser spot as the key process variable, the weld morphology and interface microstructure were characterized by optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy. Moreover, the mechanical properties and fracture mechanism of the joints were analyzed in combination with tensile tests. The results indicate that, compared with no oscillation, the 8-shaped and triangular oscillation paths can effectively increase the spreading length of the brazing filler metal on the surface of the Ti alloy and significantly inhibit the growth of interfacial IMC. Under the 8-shaped oscillation, the interfacial IMC thickness is the thinnest, ranging from 0.9 to 3.19 μm. element analysis confirms that Si aggregates at the Ti/Al interface, forming a Ti(Al, Si)3 ternary phase. In terms of mechanical properties, the tensile strength of the joint without oscillation is the lowest (119.19 MPa). The fracture occurs at the thicker Ti/Ti(Al, Si)3 interface or the Ti(Al, Si)3 layer, presenting typical brittle fracture characteristics. The oscillation paths effectively improve the joint strength by refining the IMC layer.
To address the problems of rotated objects, multiple scales, and large aspect ratios encountered in the coarse positioning of weld seams during welding automation, a coarse positioning method for weld seams based on an improved YOLOv11 oriented bounding box (YOLOv11-OBB) model was proposed. First, an OBB-RLSCD detection head was designed to capture rotational features using a combination of depthwise convolution and pointwise convolution, accurately capturing rotational features under a lightweight architecture and improving the detection efficiency and accuracy. Second, an adaptive lightweight downsampling module was adopted to improve the convolution, effectively retaining the key features of weld seams while reducing the amount of computation. Additionally, dynamic convolution was integrated into the C3k2 module to enable the convolution operation to adaptively adjust according to the input features. Finally, the PIoU loss function was introduced to optimize the positioning accuracy of rotated objects at the pixel level, enhancing the adaptability to complex scenes. The results indicate that the mean average precision of the model reaches 86.5%, which is higher than that of the original YOLOv11-OBB model; the number of parameters is reduced; the computation amount is reduced, and the inference speed reaches 89.7 frames/s, which meets the demand for real-time coarse positioning of welding robots. Meanwhile, the model is validated on the public dataset NEU-DET, and it still maintains high detection accuracy, which proves that the algorithm has good adaptability in different industrial scenarios.
Welding a lifting-eye plate onto underwater structures such as sunken ships to serve as anchoring points for underwater salvage can significantly improve salvage efficiency and reduce operational time. Under unmanned collaboration conditions, the welding robot needs to autonomously acquire the three-dimensional information of the lifting-eye plate and determine the welding position. Therefore, a three-dimensional reconstruction and welding guidance method for the lifting-eye plate based on instant neural graphics primitives (Instant-NGP) was proposed. Multi-view images of the lifting-eye plate were captured in an underwater hyperbaric dry chamber environment by a depth camera mounted on the welding robot, and the Instant-NGP algorithm was utilized to perform three-dimensional reconstruction within a large field of view. The three-dimensional point cloud of the lifting-eye plate was extracted, filtered, registered, coordinate-transformed, and mapped to the robot base coordinate system. The LO-RANSAC algorithm was used to perform planar segmentation on the point cloud on both sides of the weld groove; the weld seam centerline was obtained by calculating the intersection line of the fitted planes on both sides, and the trajectory starting point was determined by combining the point cloud boundary range of the groove region, thereby generating the initial welding guidance trajectory. Welding guidance and accuracy verification experiments were conducted through an experimental platform. The experiments indicate that the method can effectively accomplish the initial welding guidance; the average errors of the trajectory starting point in the x, y, and z directions are 1.17 mm, 1.09 mm, and 1.36 mm, respectively, meeting the requirements for the initial welding guidance of the underwater lifting-eye plate.
To study the dispersion of low-temperature fracture toughness and the discontinuous"Pop-in"phenomenon of multi-layer and multi-pass welds using Chinese welding materials for marine structural steel,the causes of the Pop-in phenomenon in the weld metals using Chinese welding materials were analyzed by comparing the fracture morphology,microstructure,EDSD crystallographic characteristics,and crack propagation paths of crack tip opening displacement(CTOD)specimens with two different thicknesses.The test results indicate that at-10 ℃,no Pop-in effect appears in the fracture toughness tests of the 60 mm-thick weld metals,and all CTOD values are above 500 μm;whereas the Pop-in effect occurs in all 100 mm-thick specimens,resulting in low fracture toughness with CTOD values of less than 100 μm.The microstructure of the 60 mm-thick specimens is composed of acicular ferrite and proeutectoid ferrite,while lath bainite appears in the microstructure at the mid-thickness position of the 100 mm-thick specimens.Moreover,there are few high-angle grain boundaries and abundant low-angle grain boundaries in the microstructure,which reduces the ability to hinder crack propagation and easily causes local microstructural embrittlement.The main reasons for the Pop-in effect in the 100 mm-thick weld metal CTOD specimens are the coupling of the thickness effect,local microstructural embrittlement,and inclusions.
A bypass-coupled three-wire indirect arc additive manufacturing process was adopted to simultaneously melt two dissimilar wires, namely ER50-6 low-alloy steel wire and ER316L stainless steel wire, to fabricate single-track multi-layer wall components of low-alloy high-strength steel. The arc morphology and metal transfer mode during the synchronized feeding of three wires were systematically investigated. Welding parameters were monitored and adjusted via an automatic wire feeding system to improve the forming accuracy and performance of the workpiece, and the strengthening mechanism of the mechanical properties of the additively manufactured components was explored. Experimental results indicate that when the welding current is 320 A; the welding height is 3 mm; the main wire feeding speed is 6.5 m/min; the side wire feeding speed is 5 m/min, and the welding speed is 8 mm/s, the wall surface is smooth; the forming accuracy is optimal; the metal deposition efficiency reaches 11.4 kg/h. During the rapid cooling process of the molten pool, the supercooled transformation of austenite occurs, accompanied by martensitic transformation and bainitic transformation. The multiphase microstructure synergistically improves the component performance. The average tensile strength of the components reaches 1 035 MPa; the elongation after fracture reaches 26%; the average micro Vickers hardness is 380 HV. All properties are in the qualified range of low-alloy high-strength steel. This process provides a novel and feasible idea for high-efficiency and high-performance arc additive manufacturing of low-alloy high-strength steel.
To study the interfacial microstructure and wear resistance of the tungsten-coated diamond reinforced nickel-based composite coating, tungsten-coated diamond particles and nickel-based brazing filler were used as coating materials, and a tungsten-coated diamond/nickel-based composite coating was prepared on the surface of H13 steel by an induction brazing process. The coatings were analyzed using a scanning electron microscope, an energy dispersive spectrometer, an abrasive wear testing machine, and a super-depth microscope. The results show that the content of tungsten-coated diamond has little effect on the interfacial bonding between the coating and the steel substrate, and no cracks or holes appear at the interface. The tungsten coating on the surface of the tungsten-coated diamond undergoes dissolution and diffusion, and a large amount of C-Cr and Ni-W compounds are distributed on the surface of the tungsten-coated diamond after brazing. The wear resistance of the coating shows a trend of first increasing and then decreasing with the increase of the content of tungsten-coated diamond. When the mass fraction of tungsten-coated diamond is 10%, the coating has the best wear resistance, with a wear loss of 250 mg.
As wide-bandgap power devices such as SiC/GaN have developed toward high power density, high current, and high voltage, higher requirements have been imposed on packaging substrates. Si3N4 ceramics have been widely used in electronic packaging due to their excellent mechanical properties. active metal brazing(AMB) has become an important metallization method for Si3N4 ceramic substrates because it enables high interfacial bonding strength and thick-copper-layer brazing. In this paper, the materials, processes, microstructures, and properties of copper-clad AMB-Si3N4 ceramic substrate were systematically reviewed. The material selection, fabrication processes, and interfacial reaction mechanisms of Si3N4 were summarized, and the failure behavior of substrates under thermal cycling was evaluated. Additionally, the performance differences among industrialized products both domestically and internationally were reviewed, along with the quality consistency challenges faced in the large-scale manufacturing of copper-clad AMB-Si3N4 ceramic substrate. Furthermore, the evaluation methods and major failure modes for void ratio, peel strength, warpage, and thermal cycling life were summarized. Finally, the development directions and engineering challenges of copper-clad AMB-Si3N4 ceramic substrates in high-temperature and high-power electronic packaging were discussed, providing a reference for promoting the industrialization of copper-clad AMB-Si3N4 ceramic substrates.
Penetration state is a critical indicator for evaluating welding quality, and it is closely related to molten pool morphology. To address the impact of operating condition fluctuations on welding quality, a quality monitoring system for the laser welding process based on molten pool profile point sets was developed. First, a laser welding experimental platform integrating welding processing, coaxial visual monitoring, and edge computing was established. Second, considering operational efficiency, a hybrid algorithm of maximum inter-class variance multi-threshold segmentation and edge detection based on a histogram pyramid was proposed to accurately extract the features of the high-temperature welding region and molten pool profile. Additionally, a multi-level representation mode based on polar coordinates was innovatively adopted to characterize the profile, thereby forming the molten pool profile point set. Finally, a deep convolutional network model VCAS-Net was constructed to achieve highly efficient and highly accurate mapping between the molten pool profile point set and penetration state. The results indicate that the model achieves an identification accuracy of 95.83%, and the processing time for a single image is 13.23 ms, which meets the requirements for high accuracy and real-time monitoring, and is suitable for industrial field applications
To meet the demand for"lightweight and high-performance"structures in fields such as aerospace and automotive and break through the bottleneck of a single technology in the fabrication of steel-aluminum reticulated bimetallic composites,a cold metal transfer melting-friction stir solid-phase synergistic additive manufacturing technology was adopted to fabricate steel-aluminum reticulated bimetallic composites,and the interface microstructure and properties of the fabricated steel-aluminum reticulated bimetallic materials were investigated.The results indicate that when the tool head's rotational speed is 600 r/min,the prepared steel-aluminum reticulated bimetallic composites exhibit a dense structure and excellent steel-aluminum interface bonding.Serving as the reinforcement of the steel-aluminum reticulated bimetallic composites,the steel mesh has an average hardness value of up to 257 HV,which significantly improves the overall hardness of the composites.The maximum tensile strength of the steel-aluminum reticulated bimetallic composites can reach 257.5 MPa,with an increase of 75.2%compared with the additive manufacturing specimens of pure aluminum alloy.The melting-solid phase synergistic additive manufacturing technology can provide theoretical and technical support for the fabrication and industrial application of steel-aluminum reticulated bimetallic composites.
In order to establish a fatigue life prediction method for welded joints considering the influence of defects, the defect detection and quantitative characterization of S47310 argon arc welded joints were conducted based on X-ray computed tomography (X-CT) technology, and a fatigue life prediction model for the joints was developed. Firstly, X-CT was used to detect microscopic defects in each micro-region of the weld and quantitatively characterize their morphology, size, and distribution pattern. The maximum characteristic size of welding defects was predicted through extreme value statistical analysis. The results show that the defect distribution in the heat-affected zone of the joint is relatively concentrated, and large-sized defects are mostly located near the surface of the specimen. The maximum value of the defect size φmax is approximately 162 μm. On this basis, considering the variation of threshold values and closure parameters with crack size a during short crack propagation, a modified NASGRO model was established based on fatigue crack growth tests of the heat-affected zone in the welded joint. Combined with the defect characterization results, the fatigue life of the joint at different stress levels was calculated using the modified model. The comparison with the S-N curve results of fatigue tests shows that the model prediction results all fall within a ± 2 scatter band, indicating high prediction accuracy. Furthermore, the modified model was used to expand the K-T diagram, and a defect-stress-life diagram of the welded joint was established, which can evaluate the fatigue life of the welded joint under different initial defect sizes.
To investigate the influence of Nb element on the microstructure and properties of the Fe-Cr-Ni coating, Fe-Cr-Ni-Nb coatings with Nb mass fractions of 0%, 0.05%, 0.1%, and 1.2% were prepared by laser cladding. The results show that with the increase of Nb content, the length of columnar crystals in the coating microstructure decreases; the number of cellular crystals increases, and the eutectic structure changes from spherical and fine rod-like to lamellar, strip-like, and network structures. The addition of Nb promotes the precipitation of Laves phase and NbC phase, and the precipitated phases mainly gather in the eutectic zone and form compounds with Cr. When Nb is not added, the eutectic structure is composed of Cr2B and FeNi solid solution; when the Nb mass fraction is 0.05% and 0.1%, Nb exists in the form of solid solution; when the Nb mass fraction is 1.2%, the Nb element is enriched, and Cr2Nb precipitates along the grain boundaries. Mechanical property test results indicate that with the increase of Nb content, the hardness of the coating increases significantly, and the hardness of the 1.2% Nb coating is 30% higher than that of the coating without Nb. Tensile test results show that with the increase of Nb content, the tensile strength and elongation after fracture first increase and then decrease. The 0.1% Nb coating exhibits the optimal tensile properties, with a tensile strength of 863.2 MPa and an elongation after fracture of 19.22%. Fracture analysis indicates that the coating exhibits quasi-cleavage fracture when Nb is not added; with the increase of Nb content, the dimple size increases, and the toughness improves; in the 1.2% Nb coating, cracks propagate along the Laves phase; the fracture mode transforms into ductile-brittle mixed fracture, and the toughness decreases.
The digital image correlation(DIC)method was employed for rapid,non-destructive measurement of residual stress of 6061aluminum alloy laser-MIG hybrid welded joints.In the process of the measurement of residual stress using the DIC method,dense grid markers were drawn on the surface of the test piece with a pencil,and the zero-mean normalized cross-correlation function insensitive to light intensity variation was selected to achieve precise matching of measurement points before and after hybrid welding.In the heat-affected zone and base metal zone of aluminum alloy laser-MIG hybrid welded joints,DIC method obtained results consistent with those measured by X-ray diffraction method.Moreover,the deviation between the results measured by both methods decreased with increasing distance from the weld center line.The residual stress distribution and morphology of the welded joints of 8 mm 6061 aluminum alloy plates under different hybrid heat source energy ratios were comprehensively analyzed,and the laser-MIG hybrid welding parameters were optimized.The results demonstrate that the maximum value(peak)of residual stress measured by DIC method increases with the increase of laser power proportion in the total energy input.When selecting welding parameters for MIG arc to laser energy ratios of 1.1,1.0,and 0.9,the measured peak magnitude of longitudinal stresses in the joint were 188 MPa,194 MPa,and 200 MPa respectively,while the measured peak magnitude of transverse residual stress were 84 MPa,89 MPa,and 93 MPa respectively.This ensures no excessive stress peaks will occur,and the joint has a small form factor,thus achieving satisfactory welding formation.
An optimization study on the process parameters of vacuum laser welding for Ta10W alloy lap joints was conducted, and the influence law of different process parameters on the weld formation was systematically analyzed. The microstructural features and mechanical properties of the Ta10W alloy weld were characterized, and the correlation between the microstructure and macroscopic performance was established. Experimental results demonstrate that when the ambient pressure is 20 Pa, the oxidation phenomenon of the welded joint can be significantly suppressed, and the weld surface formation quality is significantly improved. For the lap joint, a partial penetration weld format is required, and a combination of high-power and high-speed welding parameters is optimal. In this paper, for the specimen with a thickness of 1.5 mm, the optimal welding process parameters obtained under the vacuum environment are as follows: laser power of 5 kW, welding speed of 2.5 m/min, and defocus amount of + 3 mm. The microstructure of the T-shaped lap weld mainly consists of columnar crystals and equiaxed crystals; the columnar crystals are predominantly distributed in the upper region of the weld, and more equiaxed crystals exist in the central bottom region of the weld. Under the optimal process parameter conditions, the bonding interface width of the Ta10W alloy laser-welded lap joint is 1.29 mm; the joint shear strength reaches 389 MPa; all the specimen fractures occur in the weld zone.
In view of the problems of poor low-temperature impact toughness and non-uniform weld microstructure in X80 pipeline steel,X80 pipeline steel was welded by pulsed MAG welding with the addition of nano TiO2,and the effect of adding nano TiO2 on the weld microstructure and mechanical properties was investigated by inducing the nucleation of acicular ferrite through the in-situ synthesis of oxide inclusions.The results indicate that the weld microstructure with added nano TiO2 is mainly composed of acicular ferrite(AF),granular bainite(GB),and polygonal ferrite(PF).The Mn-Ti composite oxides induced by nano TiO2 serve as effective nucleation sites,driving AF to nucleate radially and increasing its content.The grain size is refined from 8.97 um to 5.14 um;the proportion of grain boundary angles greater than or equal to 45° increases by 7.5%;the proportion of low KAM values of less than 1 increases.The nucleation of AF promotes an increase in local dislocation density,which leads to higher partial hardness values.The average tensile strength of the weld with added nano TiO2 reaches 722.67 MPa,and the average low-temperature impact absorption energy at-40 ℃ is 82.91 J,which is an increase of 22.32%;the fracture morphology presents ductile fracture characteristics.The above study provides a new method for improving the microstructure and mechanical properties of pipeline steel welds.
The nozzle-to-safe-end joint of nuclear power equipment is a key welded structure in the primary circuit of nuclear power plants. It is usually formed by welding dissimilar metals of low-alloy high-strength steel and stainless steel using nickel-based alloy or stainless steel welding materials. Due to its long-term exposure to intense neutron irradiation and high-temperature and high-pressure water corrosion environments, more stringent requirements are imposed on its thermal stability, mechanical properties, interfacial connection reliability, and overall service life. At present, how to achieve high-quality welding of nozzle-to-safe-end joints remains a research focus and difficulty in China and internationally. Therefore, based on Chinese and international literature, the research status of dissimilar metal welding for nozzle-to-safe-end joints was systematically reviewed from four aspects: metallurgical issues, compatible welding materials, welding methods, and joint reliability. Furthermore, future research directions requiring in-depth study were discussed to provide a reference for subsequent studies on improving the quality and reliability of such joints.
In view of challenges such as minute defects and strong background interference in robotic welding, an intelligent defect detection algorithm fusing multi-scale edges and hybrid attention was proposed for the robotic welding information collection platform. First, a multi-scale edge enhancement module was designed to break through the limitations of the convolutional receptive field, strengthening the geometric contour perception of multi-scale irregular defects such as porosity and weld nodules. Second, a local-global channel attention mechanism was introduced to integrate local acuity with global contextual vision, dynamically filtering out background noise such as strong reflections and complex metal textures to acquire features with a high signal-to-noise ratio. Finally, a lightweight shared convolutional detection head was constructed, and by adopting group normalization and weight-sharing strategies, computational redundancy was substantially reduced while eliminating batch-size dependency. Tests indicate that compared with the baseline model, the number of parameters of the proposed algorithm is reduced by 6.6%; the mean average precision increases by 3.9% to reach 63.7%, and the inference speed reaches 135.5 frames per second. Heatmap visualization analysis confirms that the high-response areas of the network accurately converge on the faint targets and their geometric edges, successfully suppressing invalid background activations from the source. The proposed method achieves an excellent balance among precision, timeliness, and complexity, fulfilling the demand for highly reliable recognition.
To solve the problems of low efficiency and imbalanced duplex phase proportion of weld seam caused by complex thermal cycles in traditional arc welding of duplex stainless steel, a novel high-efficiency magnetically controlled laser-MIG hybrid welding technology for 2507 super duplex stainless steel was proposed. Xiris camera and high-speed imaging system were used to systematically study the plasma morphology and droplet transfer mode under different excitation parameters to elucidate the action mechanism of external excitation magnetic field in laser-MIG hybrid welding process. The results indicate that the addition of an external magnetic field changes the force state of plasma and droplet, thereby changing the plasma morphology and droplet transfer mode. Within a certain range, the applied external magnetic field can effectively regulate the plasma morphology, accelerate the droplet transfer frequency, simultaneously improve the droplet transfer stability, and improve the weld formation quality. When the excitation current is 1.0 A, and the excitation frequency is 75 Hz, the plasma presents a stably burning “bell shape”; the droplet transfer mode is stable jet transfer, and the weld formation quality is optimal.
To address the problems of low efficiency and poor accuracy of existing weld quality detection methods, a weld quality detection and evaluation method based on the binocular phase-shifting method was proposed. The point clouds of the weldment with a weld were first obtained based on the four-step phase-shifting method and the principle of binocular vision. Secondly, a model combining “rough extraction” and “fine extraction” was adopted to extract the weld point clouds from the weldment point clouds. Then, the ridge line of the weld point clouds was extracted; the direction line of the ridge line was fitted by the cubic B-spline curve fitting algorithm, and the cross-section point clouds of the weld were extracted accordingly. Finally, a multi-dimensional quantitative evaluation index system of weld quality was constructed, and the objective evaluation of weld forming quality was completed based on the geometric characteristics of the cross-section point clouds. A weld point cloud acquisition system was established, and experiments were conducted. The maximum deviation of the weld width obtained in the experiments is 0.287 mm, and the minimum deviation is 0.105 mm. The experimental results indicate that the proposed method can be applied to the detection and evaluation of various types of welds and has the advantages of strong stability and high precision, which can meet the application requirements of high-precision weld quality detection and evaluation in the industrial field.
