Welding in the World最新文献

To control the formation and grain structural characteristics in the welding process, an alternating current (AC)-assisted double-wire feeding strategy was applied to a traditional gas tungsten arc welding (GTAW) process. During this process, two filler wires were connected to AC power and fed to the molten pool in a nonplanar and symmetric manner from one side. The influences of the AC, AC frequency, and arc current on various parameters, including the molten droplet size, droplet transition frequency, and deposited bead formation, were evaluated. The research revealed that this method could be implemented to effectively achieve a well-formed weld bead, especially at high ACs. Microstructural analysis indicated that the grain size decreased with increasing AC frequency. Finally, the underlying mechanism of grain refinement resulting from the addition of AC to the double filler wire was discussed.

The present study investigates the cold metal transfer (CMT) welding of a novel hybrid aluminium composite (AA6061-T6/ 2wt.% TiB₂/ 0.5wt.% La₂O₃) fabricated via stir casting. It analyzes the effect of welding parameters, i.e. current, travel speed, and gas flow rate, on the tensile strength of the composite’s weld joint using response surface methodology (RSM). Also, a dedicated study of the microstructure and mechanical properties of weld joints at optimal parameters has been conducted. Results indicate that current significantly affects tensile strength, followed by travel speed and gas flow rate. The optimal parameters identified are 142 A current, 9 mm/s travel speed, and 14 L/min gas flow rate for maximizing tensile strength. Welds at optimal parameters displayed no solidification cracking and minimum porosity. The microstructural analysis confirmed the presence of reinforcements in the composite with the formation of finer grains in the fusion zone (FZ) compared to the heat-affected zone (HAZ). Microhardness tests showed the highest values in the FZ and the lowest in the HAZ, while tensile tests showed reduced strength at HAZ compared to the FZ and base composite, with dominant brittle behaviour. Post-weld heat treatment improved ductility, as indicated by deeper dimples and tear ridges with fewer cleavage facets in fracture analysis.

Dissimilar metal welding (DMW) between titanium alloys and nickel-based superalloys can contribute to acquiring light, heat-resistant frameworks of enhanced efficiency. The current study constitutes an attempt to obtain joints between a Ni-superalloy and a Ti-alloy, investigating the beneficial impact of copper on the microstructure of the weld metal (WM), through precipitation of ternary Ti–Ni–Cu intermetallic compounds (IMCs), instead of Ni–Ti ones, previously reported in weldments between such alloys. Gas tungsten arc welding (GTAW) was performed between Ti–6Al–4V and Inconel® X-750, varying the welding current and using different copper filler wires (pure Cu and NiCu). The microstructural characterization of weldments was conducted by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), and a further nanoscale examination was performed using a transmission electron microscope (TEM). Identification of IMCs and precipitates was achieved by X-ray diffraction (XRD), while the mechanical properties were investigated through microhardness Vickers measurements. Crack-free joints were obtained, albeit with the presence of IMCs comprising Ti–Ni, Ti–Cu, and Ti–Ni–Cu, as well as titanium carbides (TiCs). Cu exhibited a positive influence on the joints’ microstructure. Elevating the welding current led to accelerated cooling and solidification rates, resulting in enhanced Vickers microhardness values. This phenomenon can be attributed to either the formation of finer microstructures or the precipitation of brittle IMCs, which were observed in specimens welded with higher currents. Especially near the Ti-alloy interface, it was found that a brazing-type bond took place instead of welding, while high hardness values (up to 800 HV) were also detected.

Dissimilar metal joints, particularly those involving aluminum and iron (Al–Fe), are widely employed in engineering due to their exceptional mechanical properties and unique microstructures. The purpose of this literature review is to assess the extent and depth of research related to dissimilar metal joint research, with a specific focus on microstructure analysis and the reported findings. The review identified three key themes for improving the quality of these joints: welding techniques, parametric optimization, and material treatment. Three themes were identified, namely, the welding techniques (i.e., Friction Stir Welding, TIG-MIG Hybrid welding, etc.), parameter optimization (e.g., Taguchi method, Response Surface Method etc.), and the material treatment (pre-heating, Backing Plate, etc.). This systematic and comprehensive literature review highlights the importance of microstructural analysis in Dissimilar Metal Joint research, providing a foundation for understanding the nuances of different welding methods and their effects on joint quality. Additionally, strategies to mitigate the challenges posed by thick Fe2Al5 formation are discussed, ultimately contributing to advancements in dissimilar material joint technology and joint strength enhancement.

This paper aims to investigate the combined effect of circular beam wobbling and varying laser power on crack formation, weld geometry, microstructure and hardness during remote laser welding of AA6082 alloy. AA6082 sheets of 2 mm thickness were joined in overlap weld configuration using wobbling mode remote laser welding at 4 kW, 3 kW and 2.5 kW. Full penetration was achieved in the joints made at 4 kW and 3 kW, with severe crack formation. Welds at 2.5 kW showed partial penetration and no cracks; however, porosity formation was observed. While no significant change was observed in the dendritic structure and compound contents in fusion zones with full penetration, compound clusters dominated by Cu and Si elements were revealed in the seam root region at 2.5 kW (partial penetration). In full penetration welds (4 and 3 kW), the hardness decreased in the center of the fusion zone but increased from the surface to the root zone. However, for the partial penetration weld (2.5 kW), a limited change in the hardness values determined in the same direction was observed.

The use of multi-material components offers customization of physical properties, weight reduction, effective thermal management, and the creation of material-compatible buffer components to join two material with ease. These features surpass the capabilities of single-material compositions. When the multiple materials are used with sharp interfaces, failure often occurs at the interfaces due to the presence of sharp stress concentration gradients under service loading conditions. Failure can be delayed, if the multi-material compositions across the interface can be varied smoothly. To prevent this, functionally graded materials with diffuse interfaces can be employed. Functionally graded materials (FGM) possess preferred spatial variation of properties aligned in specific directions. However, producing complex FGM components through conventional methods is challenging, as the conventional manufacturing methods are part and tool-specific. Components made using additive manufacturing, such as powder bed fusion (PBF), can create FGM with intricate geometric features and precision at the micron scale. This opens up new avenues for innovative design possibilities with FGM components. The methodologies developed to create FGM by PBF are still in their infancy and require further attention to realize defect-free components. By employing high-fidelity mathematical models, new methodologies can be developed and minimize expensive trial-and-error experimental development strategies. The discrete element method (DEM) is a suitable numerical approach for modelling discontinuous media, such as powder particles in PBF. In this study, a spreading procedure in a powder bed fusion process is developed so that the desired distribution of material composition can be obtained before laser melting. A partition-based approach is adapted to achieve functional gradation along the spreading direction. The role of recoater speed on the evolution of the distribution of the material was studied through a parameter called gradation index (GI). A unique experimental setup was developed to analyze the prediction of the developed model. Results show that an angular partition at the dispenser can generate a customized functionally graded spreading in the build platform, and the obtained graded spreading is found to vary as a function of the recoater speed, partition angle, and spread layer thickness.

In this study, a WC-10Ni + AgCuTi/Cu composite coating was applied to a copper substrate using vacuum brazing. The initiation and propagation of thermal fatigue cracks in the composite coating were investigated under various upper limit temperatures of thermal fatigue, and the law governing crack initiation was explored. Additionally, the mechanism of thermal fatigue behaviour was also analysed. The findings reveal that no cracks are observed in the composite coating when the upper limit temperature of the thermal fatigue test is set at 400 °C and subjected to 50 cycles. However, as the upper limit temperature and the number of cycles increase, the rate of crack initiation and propagation significantly accelerates, eventually leading to macroscopic cracking and coating failure. The behaviour of thermal fatigue cracks in composite coatings is characterized by the coating undergoing alternating tensile and compressive stresses during the thermal fatigue process. This stress cycle causes the hard layer to develop longitudinal cracks that propagate inward. Moreover, transverse cracks initiate near the interface layer of the hard layer and extend along the interface direction. The study identifies four primary modes of crack propagation.

The dissimilar Al/Ti joints were tentatively welded under different welding tools via dynamic support friction stir welding (FSW). The joint formation, intermetallic compounds (IMCs) layer, and mechanical properties of Al/Ti joint were investigated. The results showed that a Co-based alloy welding tool with a 15-mm shoulder diameter achieved the good external appearance and internal tissue. A diffusion layer with ~ 4 μm existed at the upper interface, while the diffusion layer at the lower layer was ~ 3 μm. Detrimental and continuous IMC layers were not generated at the Al/Ti interface, and root defects were avoided. This joint had the largest tensile strength of 189 MPa and fractured at the heat-affected zone (HAZ). The interface bonding, Ti fragments and hole defects in stirring zone, and the HAZ softening determined the ultimate fracture location. The dynamic support FSW offered a novel approach to achieve high-quality joining of Al/Ti dissimilar metals.

The ultrasonic metal welding technology is widely promoted as a new connection approach in the field of current energy vehicle wiring harness connection. In the present investigation, low-temperature mechanical properties of slotted and normal terminals were studied. The EVR 25 mm² copper wires are selected for welding using ultrasonic wire harness welding with two different structures of T2 copper terminals. Then, a more stable joint structure under the same welding parameters is investigated through tensile tests at − 30 °C and 25 °C. The results showed that the ST joint has higher static mechanical properties than the NT joint at 25 °C and the peak load of the joint is increased. In addition, the results investigated that the performance and welded interface texture of ST joints is reliable than NT joints under 25 °C, the maximum joint load is increased by 12.93% under − 30 °C, the joint energy absorption is increased by 87.58%, and ST joint stability is better and safer in actual production applications. At the same welding parameters, the ST joints have less neck contraction at 25 °C and the ligamentous sockets are smaller and densely welded surfaces. The failures of ST joints and NT joints are investigated under the same welding parameters. The energy loss during the ST joint welding process is smaller and the welding effect is better and advantageous. The SEM findings showed that the failure of the ST joint and the NT joint is different and the tensile strength of the ST joint is greater under the same low-temperature conditions.

Welding of dissimilar polymers is becoming more common. While joining of dissimilar polymers is traditionally accomplished via the use of adhesives or mechanical methods such as fasteners, snap fits, and staking, these approaches cannot always be effectively applied. For these applications, where adhesives and mechanical bonding cannot be used, it may be possible to directly weld or bond polymers that are miscible but have different material properties via welding techniques. In this work, infrared welding was used to join acrylonitrile butadiene styrene (ABS) to polyphenylene oxide (PPO), and hot plate welding was used to join ABS to polyvinyl chloride (PVC), and polystyrene (PS) to polycarbonate (PC) as an initial investigation into a new approach to bonding dissimilar polymers. Through the use of targeted heating to match the polymer viscosities to each other, the weld strength was improved by up to three times and, when optimized, the strength of the dissimilar bond as equivalent to that of the similar material weld.