Welding in the World最新文献

This study investigates the ultrasonic-assisted activated tungsten inert gas (UA-TIG) welding process, a promising technique for advanced manufacturing. The objective was to model and optimize UA-TIG parameters to enhance weld geometry, specifically achieving a high depth-to-width (D/W) aspect ratio. Activated by SiO₂ nanoparticles as flux, the process employed central composite design (CCD) to examine the influence of welding current, travel speed, and ultrasonic vibration amplitude across five levels. Bead-on-plate welding tests on AISI 316L stainless steel were supported by simulations to identify optimal ultrasonic zones. Using analysis of variance (ANOVA) and response surface methodology (RSM) for optimization, results revealed robust regression modeling with an error margin below 6%. Compared to tungsten inert gas (TIG) and activated flux TIG (A-TIG) methods, UA-TIG welding achieved a substantial D/W improvement, enhancing the ratio by 320% and 56%, respectively. UA-TIG welding also demonstrated the highest microhardness (210 Vickers) among the tested samples and effectively minimized heat affected zone (HAZ) width, showcasing its superior thermal control and weld quality. This work demonstrates UA-TIG’s effectiveness in achieving superior weld geometry with optimized parameters, indicating its potential for widespread application in precision welding.

This work focuses on the preparation and heat treatment of Q345B low alloy steel produced by laser powder bed fusion (LPBF). An optimized process parameter (Eν = 94.28 J/mm³) was proposed for obtaining a high density and hardness of samples. It also evaluates the effect of the tempering temperature on the microstructure and mechanical properties of the LPBF-prepared samples. The results showed that the microstructure of the as-built sample was martensite and acicular ferrite. As the tempering temperature increased, martensite underwent decarburization and transformation into bainite and carbide. As the temperature continued to rise, the mesh-like carbide in the sample disappeared, and the microstructure transformed into ferrite and pearlite. The grain orientation in the as-built sample and the sample tempered at different temperatures were random. As the annealing temperature increased, the content of low-angle grain boundaries (LAGBs) in the sample decreased. When the annealing temperature was 250 °C, the tensile strength slightly decreased to 834.5 MPa, and the elongation increased to 12.5%. When the annealing temperature reached 850 °C, the maximum elongation of the sample reached 14.7%.

This work compares the welding of 5-mm-thick AA5052 H-32 butt welds using pulsed gas metal arc welding (P-GMAW) and cold wire pulsed GMAW (CW-P-GMAW). Welding metal transfer was studied using high-speed imaging in conjunction with synchronized current and voltage acquisition. After welding, the joints were characterized through radiographic examination and standard metallography. The results have successfully demonstrated the feasibility of CW-P-GMAW welding AA5052 H-32. Additionally, the results suggest that the introduction of cold wire feed with pulsed current affects the temperature distribution and reduces the cooling rate of the welding pool accounting for reduced hardness and coarser microstructure.

A new wrought FeMnAl steel contains high Mn content and high Al content. This steel has high strength. When it is compared to conventional steels with the similar strength, its density is lower. FeMnAl steels can be used in armor vehicle manufacturing, in which welding is a common practice to join the steel plates together. The welding of FeMnAl steels has not been sufficiently studied before. This work studied the weldability and weld microstructure of an FeMnAl steel and provided useful data for the welding practice of FeMnAl steels. The influences of weld filler metals and shielding gases were studied, using single-pass bead-on-plate gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) two processes. The optimal filler metals and shielding gases have been determined to achieve the better weldability. Autogenous GTAW and electron beam welding were also conducted. Cracks were found in the HAZ in the GMAW welds and electron beam welds. Fewer or no cracks were found in the HAZ of GTAW welds. SEM, SEM/EDX, TEM, TEM/EDX, and EBSD were used to analyze the grain boundaries in the HAZ and the cracks. The grain boundaries of FeMnAl base metal are mostly high angle grain boundaries (HAGBs), which attract impurity and solute atoms and cause intergranular cracking. The proposed cracking mechanisms are liquation cracking and ductility-dip cracking. It was found that GTAW provides much better weldability for the FeMnAl steel than GMAW and EBW.

Welded joints made of ductile materials exhibit a significant reduction in fatigue life under non-proportional multiaxial loading compared to proportional loading. Different methods to calculate multiaxial fatigue life are evaluated on a comprehensive database, which is created based on various fatigue tests showing ductile material behavior under uniaxial, proportional, and out-of-phase loading. This paper finds that well-known stress-based methods widely used in the literature to evaluate multiaxial fatigue of welded joints cannot accurately calculate fatigue life under both proportional and non-proportional loading for welded ductile materials. Two new methods providing reliable and accurate fatigue life predictions with little scatter under both constant and variable amplitude loading are developed, analyzed in detail, and compared to existing approaches. The new methods include an interaction equation derived from the criteria proposed in codes and standards, as well as a machine learning approach based on artificial neural networks, both developed and optimized or trained based on the created database. Using interpretable machine learning, the neural networks are found to have learned similar correlations between multiaxial loading and fatigue life as those represented by the new interaction equation.

Preload application techniques are often used to verify the structural integrity of mechanical systems. Generally, these procedures are performed after fabrication but before commissioning of such equipment, without any assessment of the impact of the preload on fatigue behaviour. These approaches are performed according to standards such as ASTM or DNV, which define applicable preload conditions, but neither technical justification nor quantification of the impacts is usually given. The aim of this study is to evaluate the effect of a preload on structural steel S355 or high-strength steel S700 cruciform joints for various levels of plastic strain. Fatigue tests were performed under tension (R = 0.1) without a preload as a reference and after two different levels of preload were applied: one corresponding to a local stress close to the weld toe equal to 1.25 times the yield stress and the other corresponding to a local stress equal to 1.56 times the yield stress. The fatigue results show an increase in the fatigue strength, depending on the configuration (load-bearing weld beads or non-load-bearing weld beads), of between two and seven fatigue (FAT) classes for the highest level of preload.

Electron beam welding uses high intensity beams that are generated by an electron emitting cathode under high vacuum conditions. The cathode, typically a ribbon or wire filament of refractory metal, must be heated to sufficiently high temperatures for electron emission to occur and must be carefully controlled to produce the desired beam current while at the same time optimizing filament lifetime. Traditional methods for doing this in commonly used triode gun assemblies consist of first finding the filament knee point in the filament current versus beam current relationship that produces the desired beam current for a given beam voltage. The filament current is then increased by some amount, typically 5–10%, per conventional wisdom to produce a peaked beam. This investigation studies and quantifies the beam and weld quality produced by underkneed and overpeaked filaments using electron beam diagnostics to measure the power density distribution of these beams. Underkneed filaments are shown to have power densities that drop off very quickly below the traditional knee, resulting in poor weld penetration. Kneed filaments do not reach the full beam intensity and also produce shallow welds. Increasing the filament current 10% above the traditional knee was shown to produce a circular Gaussian-like beam with peaked intensity optimized for welding and for filament lifetime. Further increases in the filament current that produce overpeaked beams do not significantly change the beam or weld quality and would only contribute to a reduced filament lifetime.

This study investigates the microstructure and mechanical properties of aluminum-steel explosive clad produced in both open-air and underwater environments. The clads obtained in open air exhibited porous, molten zones, while those obtained underwater displayed uniform and refined microstructures due to rapid quenching. Numerical simulations using the smoothed particle hydrodynamics (SPH) method in ANSYS AUTODYN revealed elevated temperature and pressure during the process. Although both conditions resulted in clads with increased interface hardness, the underwater clads demonstrated an 18% higher ram tensile strength. Additionally, an analytical welding window was developed, validating the optimal conditions for successful cladding.

Underwater welding (UW) has recently received attention due to technological advancements, leading to improved weld quality, efficiency, and automation. Its applications include nuclear, oil and gas, and marine structures. The present study aims to comprehensively review the advancements in UW, including various techniques and newly developed approaches. Additionally, corresponding process parameters that affect weld quality and material types involved in UW are discussed. Finally, the review concludes by addressing challenges, the capabilities of new approaches, and future research directions.

Sequential ultrasonic welding (USW) is a process at the heart of ultrasonic consolidation (USC) technology. In the presented study, this method was used to consolidate four 0.7-mm-thick high-strength nickel plates with an initial ultrafine-grained (UFG) structure obtained by high-pressure torsion. It was established that intensive grain growth occurred during USW of ultrafine-grained nickel. Normal grain growth in the bulk regions of plates led to the formation of a gradient microstructure along the sample height and width, with the average grain size varying from 4.6 to 0.7 μm. The origin of such a gradient microstructure was analyzed, basing on available data on the grain growth kinetics in UFG nickel. It was found that abnormal grain growth occurred in the vicinity of interfaces that resulted in an extremely heterogeneous microstructure. Abnormally large grains, with sizes of several tens of micrometers in the vibration direction and 5–15 µm in the normal direction, as well as areas with fine grains of 0.5–2 µm in size, were observed in the vicinity of interfaces. Thin gaps were visible along boundaries of abnormally large grains, and small voids were revealed between fine grains. The presence of discontinuities between the layers of the consolidated sample was associated with intense wear of the surfaces of high-strength plates during USW. In the defect-free regions, equiaxed grains with sizes of 3–7 µm were formed as a result of the migration of grain boundaries across the faying surfaces of the joined plates.