Welding in the World最新文献

This study compares the paste/slurry formed by different filler mixing ratios (filler metal powder: DM water [wt.%/wt.%]) used to fabricate dip-brazed joints for Al-64430. Eight different filler ratios were selected, namely 1:5, 1:4, 1:3, 1:2, 1:1, 5:4, 2:1 and 3:1. The fabricated samples were tested for bump test, microhardness, tensile strength and surface deformation. Maximum microhardness and tensile strength were observed at a 5:4 mixing ratio. Both the values increased until the 5:4 mixing ratio (450% increase in microhardness and a 5400% increase in tensile strength compared to a 1:4 mixing ratio sample), after which they declined (3% decrease in microhardness and a 35% decrease in tensile strength). Surface deformation of the samples remained almost constant throughout, although these values were 10–20 times less than those of samples produced by conventional welding operations. Microstructural analysis revealed dendrite formation at the brazed joints. Voids and cracks were also detected in some samples. Al-Si eutectic matrix and (alpha)-aluminium were visible at the joint. SEM analysis was carried out to determine the silicon state in the matrix, which displayed the presence of both primary and eutectic silicon. EDX analysis showed that the silicon concentration at the joint increased as the filler ratio increased, and this silicon concentration played a major role in determining the strength and hardness of the joints.

Laser-MIG hybrid multi-layer welding was performed upon the 20-mm thick 6082-T6 aluminum alloy butt-joints. The weld formation, microstructure, and mechanical properties of the welded joints were studied in details. The results indicated that the well-formed weld without obvious incomplete fusion and cracks could be obtained by using the optimal welding parameters, only very few porosities appeared in the filling layer and covering layer. The equiaxed crystals and columnar crystals were respectively observed in the weld center and near the fusion in the weld metal; their sizes and widths of each layer were different. The microhardness values of the weld metal and heat-affected zone are lower than those of the base metal; the lowest microhardness value appeared in the heat affected zone. The order of microhardness values in the weld center from high to low was filling layer, backing layer, and covering layer; their microhardness values were 74 HV, 70 HV, and 67 HV, respectively. The average tensile strength of the joints reached up to 235.2 MPa, which was 79.7% of the base metal. The tensile specimen fractured near the fusion line in the heat affected zone and the fracture propagated approximately parallel to the fusion line, and the tensile fracture showed a typical plastic fracture mode. The median fatigue limit and safety fatigue limit of the welded joints were 99 MPa and 93 MPa, respectively. The fatigue specimen fractured in the weld metal, and the crack initiated in the backing layer.

Through the analysis of the magnetic field around the arc, the feasibility of controlling the arc shape and performance by the external axial magnetic field is clarified. Combined with the derived mathematical expression of the alternating axial magnetic field generated by the energized solenoid, the magnetic field and its distribution were simulated with COMSOL Multiphysics and MATLAB software, and the effects of the magnetic head structure and parameters on the magnetic field and its distribution were determined. A magnetic head was designed and manufactured according to the simulation results, and the welding process experiments were carried out. The experimental results show that the high-frequency axial magnetic field can significantly compress the arc and improve the welding penetration.

CrS/NbC reinforced Co-based self-lubricating composite coatings were successfully prepared on the surface of Cr12MoV steel by high-frequency micro-vibration (HFMV) assisted laser cladding technology. The microstructure, phase composition, microhardness, and wear resistance of the composite coatings were studied by means of X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), microhardness tester, and friction-wear tester. The results show that there were excellent metallurgical bonding and free of pores and cracks in the CrS/NbC Co-based self-lubricating composite coating with 10% WS₂ prepared by laser cladding at 552 Hz vibration frequency. The appropriate vibration frequency could cause strong convection in the molten pool and refine the microstructure, which made NbC hard particulates and CrS lubricants to be evenly distributed in the composite coating. In particular, the refined CrS and NbC in the upper area of the coating were combined with each other to form a dense network microstructure. Moreover, the hardness of the coating prepared at the vibration frequency of 552 Hz was significantly improved due to its excellent microstructure compared with the without vibration and 985 Hz vibration frequencies and the maximum hardness reached 652.8 HV_0.5. Its wear resistance was also significantly improved, and the friction coefficient of the coating was reduced to 0.451. Only abrasive wear and slight adhesive wear were observed on the coatings surface, and the tearing layer and wear loss of grinding defects were significantly reduced.

Climate change exacerbates the need for resource-efficient and cost-effective production processes across manifold industries, including the field of electrical connections. This specific field is characterized by a conflict of objectives, i.e., weight reductions while maintaining joint strength and electrical conductivity. From a material point of view, the use of aluminum as a conductor material is suitable for this application, as it is lighter than copper, a classical conductor material. Electrical conductors are often used in the form of flexible cables, so-called stranded wires. This type of conductor as well as the fact that the sole use of aluminum in electrical systems is not feasible, e.g., because the predetermined connection terminals of power electronic components are made of copper, creates a substantial demand for dissimilar aluminum-copper cable arrester joints. However, traditional fusion-based welding processes have proved incapable of reliably producing these dissimilar aluminum-copper joints because of thermophysical effects and chemical incompatibilities, the latter eventually leading to the formation of intermetallic phases. These phases adversely affect the quality of the joint in terms of both mechanical and electrical performance. Yet, magnetic pulse welding, a pressure welding process, is ideally suited for producing dissimilar metal joints on the basis of a low energy input during the welding process. Consequently, the formation of intermetallic phases is restrained. However, magnetic pulse welding has not been sufficiently investigated for the reliable contacting of stranded cables to tubular arresters. As a result, this paper focuses on the fabrication of tubular stranded cable arrester joints using magnetic pulse welding. To shed light on possible material combinations, aluminum-to-aluminum and copper-to-copper joints as well as their dissimilar counterparts are welded. Subsequently, the joints are characterized with regard to their microstructure and quasi-static material strength. Electrical characterization comprises the four-wire Kelvin measurement method to evaluate the resistance of the electrical joints. The results demonstrate that magnetic pulse welding is ideally suited to join the aforementioned material combination and joint configuration due to its process characteristics eventually leading to material continuity. As a result, the stranded wires are welded to the tubular arresters rather than crimped. Consequently, a comparative analysis of the joint properties with those of the joining partners shows that the measured electrical resistances and mechanical tensile forces may be considered very good.

Welding of AlSi10Mg alloys fabricated by additive manufacturing (AM) has been recently conducted to meet the demands for joining or repairing them. However, high susceptibility to porosity occurring in weld metal (WM) poses a significant challenge for fusion welding of AM AlSi10Mg alloys. The laser metal deposition (LMD) process has emerged as a promising welding solution due to its low dilution rate for reducing the porosity. In this study, LMD welding of AM AlSi10Mg alloys was carried out employing different heat inputs with five and eight tracks. The study systematically assessed the impact of heat input on porosity, microstructure, and mechanical properties of the welded joints. The results show that the decrease of heat input from 180 to 75 J/mm results in a substantial reduction in porosity from 7.0 to 2.1%. This reduction leads to a 29.4% increase in ultimate tensile strength (UTS) and an 11.7% increase in elongation index (EI). Furthermore, the upper region of joints with eight tracks possessing low heat input displays lower porosity and superior mechanical properties than the bottom region with relatively high heat input. The WM with eight tracks exhibits refined α-Al cells and Si-rich eutectic phases, improved connectivity of Si-rich networks, and increased solid solution strengthening, compared to the five-track joints with higher heat input. As a result, low heat input of the upper region in the LMD welded joints has been effective in minimizing hydrogen pores, enhancing WM microstructure, and improving the mechanical properties of welded joints in AM AlSi10Mg alloys.

Weld defect detection is an important task in the welding process. Although there are many excellent weld defect detection models, there is still much room for improvement in stability and accuracy. In this study, a lightweight deep learning model called WeldNet is proposed to improve the existing weld defect recognition network for its poor generalization performance, overfitting, and large memory occupation, using a design with a small number of parameters but with better performance. We also proposed an ensemble-distillation strategy in the training process, which effectively improved the accuracy rate and proposed an improved model ensemble scheme. The experimental results show that the final designed WeldNet model performs well in detecting weld defects and achieves state-of-the-art performance. Its number of parameters is only 26.8% of that of ResNet18, but the accuracy is 8.9% higher, while achieving a 24.2 ms inference time on CPU to meet the demand of real-time operation. The study is of guiding significance for solving practical problems in weld defect detection, and provides new ideas for the application of deep learning in industry. The code used in this article is available at https://github.com/Wanglaoban3/WeldNet.git.

Keyhole Tungsten inert gas (K-TIG) welding can realize single-sided welding and double-sided forming. However, due to the influence of gravity, undercuts always occur in K-TIG horizontal welding. In order to expand the application scenarios of K-TIG and achieve automatic welding, a magnetic controlled K-TIG horizontal automatic welding system is proposed in this paper. A longitudinal magnetic field is used to weaken the influence of gravity and improve welding quality. The OCR (Object-Contextual Representations)-SVM (support vector machines) model is proposed to identify the welding penetration states during K-TIG horizontal welding, whose accuracy rate is 93%. In order to solve the problem of slow convergence and poor learning of difficult-to-learn classes, a loss function called Unified Focal loss was used, which achieves a mIoU (the mean of Intersection over Union) score of 91.48%.