Welding in the World最新文献

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.

The reduction of CO₂ emissions is closely linked to the development of highly efficient and economical steel components in plant and process engineering. To withstand the high combined corrosive, tribological, thermal, and mechanical stresses, wear-resistant coatings tailored to the application and steel grade are used. In addition to the increasing demand to substitute conventional cobalt alloys with nickel alloys, there is also a growing need for defined or functional surfaces of high integrity. Due to high tool wear, milling operations required to produce the complex geometries of the components are often not economically feasible for SMEs. By means of alloy modification of the filler metals for nickel-based plasma build-up welded wear-resistant coatings and by the use of innovative ultrasonic-assisted milling processes more favourable machinability shall be achieved without reducing the wear protection potential. In this paper, the influence of the microstructure and precipitation morphology adjusted by means of alloy modification on the machinability is investigated. This is done based on a wear protection alloy NiCrMoSiFeB (trade name: Colmonoy 56 PTA) typically used for screw machines, which substitutes conventional CoCr alloys (Stellite). Metallurgical investigations and in-situ measurements of occurring process forces and temperatures at the tool cutting edge during milling as well as subsequent investigations of tool wear and surface integrity allow a detailed analysis and correlation between microstructural properties and machinability. For the cast samples, a clear change in the microstructure and hardness can be seen through the addition of Al, Ti, or Nb. These differences lead to an improvement in the machining process for Nb. Al and Ti cause long-needled or star-shaped precipitations and hardness increases, which lead to higher cutting forces and increased tool wear.

In the welded joints, fatigue failures typically originate from defects or notch-like geometries under cyclic loading. This study investigates the impact of stress relief grooves (SRG) on the fatigue performance of butt-welded cast steel to ultra-high-strength steel components using experimental fatigue tests and finite element method. The experiments examined the fatigue properties of hybrid joints between G26CrMo4 cast steel (t = 20 mm) and S960 steel plate (t = 6 mm) with and without SRG. Gas metal arc welding process was used to weld the butt joints that had a permanent root backing machined on the cast steel part, causing a crack-like defect to the weld root. Additionally, the top surfaces of the welded parts were aligned, resulting in a significant axial misalignment in the butt joint. The SRG, positioned close to the weld root, was found to have a beneficial influence on the joint’s fatigue performance by a factor of 1.2 when using the nominal stress criterion. However, the fatigue capacity was still roughly 35% lower compared to the symmetrical equivalent due to the secondary bending stress, caused by axial misalignment. The finite element analyses indicated that the SRG reduces the amount of secondary stresses at the weld root leading to lower total structural stress. The study recommends using the FAT80 (m = 3) design curve in the structural stress method, for similar butt-welds having a crack-like defect, parallel to the loading direction, at the weld root. However, for welded joints with crack-like defects, it is advisable to use linear elastic fracture mechanics rather than relying solely on stress-based local approaches.

Duplex stainless steels (DSS) in wire and arc additive manufacturing (WAAM) have attracted significant research attention due to their mechanical properties and corrosion resistance. This study uses conventional and nanomechanical testing methods to compare the mechanical and microstructural behaviors at macroscopic and microscopic length scales. Macro hardness (HV10) testing yielded 259 and 249 in low and high heat input (HI) samples, respectively, while ferrite content averaged 52.7 and 48.5%. However, these results fail to provide conclusive insight into the potential influence of microstructural variations at the macroscopic level, likely due to the composite response of the material. To overcome this limitation, the mechanical response of the DSS samples is assessed at the grain level via high throughput nanoindentation mapping with image processing to track the location of each indent. This approach enabled differentiating the indents landing on ferrite and austenite phases as well as those landing on the interfaces. The results showed that the austenite phase had higher hardness (4.30 and 4.35 GPa) than the ferrite phase (3.89 GPa and 4.03 GPa) for high and low HI samples, respectively. The observed differences in hardness between the phases can be attributed to higher nitrogen content in the austenitic phase.