Welding in the World最新文献

This investigation focused on the welding of Q690 bainitic steel using vacuum electron beam welding with currents of 350 and 500 mA, yielding samples with diverse microstructures and distinct fusion and heat-affected zones. Additionally, H₂S immersion tests were conducted to evaluate the susceptibility of the welded microstructure to hydrogen embrittlement. The results indicated different fracture sites in the samples welded under currents of 350 and 500 mA. Under the 350-mA welding current, fracture occurred in the coarse-grain heat-affected zone (CGHAZ) because of the high dislocation density in the bainitic ferrite plates and the low concentration of retained austenite in the CGHAZ. Under the 500-mA current, hydrogen embrittlement and fracture occurred in the upper bainite of the fusion zone because of the high welding-induced heat input that led to coarse precipitation and micro-void coalescence.

Rotary friction welding is a fast and efficient joining process with the possibility to join materials that are not weldable by conventional GMAW-processes. If done properly, the welds have a static and fatigue strength higher than the base material. However, in literature, there exists only sparse information on the design and assessment of these joints in terms of fatigue. The fatigue strength of two material combinations, S355-S355 and S355-1.4301, is investigated based on two specimen conditions, (1) with flash and (2) with flash mechanically removed. In the majority of tests, failure occurred outside the weld zone, in the base material. The derived endurable nominal stresses are compared to the design S-N curve of conventionally welded specimens and show a more than 50% higher fatigue strength.

Fatigue life evaluation of welded joints under multiaxial loading usually refers to stresses normal to the weld and shear stresses. Stresses parallel to the weld are not considered in most experiments or the well-known Gough-Pollard criterion. Hence, the Gough-Pollard criterion has recently been extended to include all stress components at the weld surface. In this paper, both the original and, for the first time, the extended Gough-Pollard criterion are applied to different welded specimens under multiaxial loading that includes stresses parallel to the weld. As shown, the original criterion is insufficient to evaluate such stress states. This is because the calculated fatigue life becomes less conservative as the stresses parallel to the weld become more significant. The extended criterion, on the other hand, shows greatly improved accuracy while significantly reducing the likelihood of non-conservative results. In conclusion, the extended Gough-Pollard criterion can describe fatigue life under multiaxial loading better than the original version and provides reliable and conservative results for welded joints. The main findings are valid for the nominal, the hot spot, and the notch stress concept.

Welding titanium to aluminum alloys is difficult and challenging due to the differences in their chemical and physical properties. The aim of this research is to investigate the effect of integrating a pure copper (Cu) interlayer on the mechanical behavior and the microstructure of the dissimilar TA6V/AU4G Rotary Friction Weld (RFW) joints. Tensile tests and microhardness measurements were conducted to demonstrate the mechanical behavior of the RFW joints. Microscopic observations were carried out to identify the structural nuances and quality of the weld joint. Energy Dispersive X-Ray (EDX) analysis was performed to reveal the interdiffusion phenomenon at the weld interfaces, and the present phases were identified through X-Ray Diffraction (XRD) analysis. The results suggest that adding a Cu-interlayer changes the flow direction of thermoplastically deformed material, leading to an increase in the Ultimate Tensile Strength (UTS) value up to 393.34 MPa. The microhardness profile of the TA6V/Cu/AU4G RFW joint is similar to that of the TA6V/AU4G joint, except for noticeable difference at the interface. In addition, the use of a Cu-interlayer has been shown to be more effective in preventing the formation of brittle TiAl₃ intermetallic compounds (IMCs) compared to direct TA6V/AU4G welds. The inclusion of a Cu-interlayer results in a significant improvement in joint efficiency by 105.32%, demonstrating the effectiveness of the Cu-interlayer in enhancing the mechanical properties of the dissimilar TA6V/AU4G RFW joints.

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.