The Inconel 690 alloy is widely used in the manufacturing of nuclear equipment, such as pipe welding for steam generators (SG) and pressure vessels, due to its excellent high-temperature strength, ...corrosion resistance, and thermal stability. However, coarse grains have been observed in the welded joint of Inconel 690. Considering its crucial role as a structural material under high pressure, temperature, and corrosive conditions, improvements should be made to the microstructure of the welded joint. The ultrasonic-assisted gas tungsten arc welding (UA-GTAW) was used in Inconel 690 welding. The influence of ultrasonic vibration on the microstructure and mechanical properties of welded joints was studied. The results show that the ultrasonic refined the microstructure further to improve the mechanical properties. The UA-GTAW sample performed superiorities over regular GTAW joint in multi perspective including refined solidification grains, less element segregation, higher tensile strength and hardness. The Yield strength, ultimate tensile strength, and elongation increased from 320 MPa, 591 MPa, and 25.1 % to 387 MPa, 672 MPa, and 31.6 %, respectively.
Automatic welding penetration recognition is a significant and challenging research direction to improve the manufacturing quality and intelligence level of gas tungsten arc welding (GTAW). In this ...paper, a data-driven deep learning approach based on vision transformer (ViT) is proposed to implement welding penetration recognition. To meet the requirement of the model training on data, a large weld pool image dataset composed of four penetration categories is constructed. Twelve ViT models with different architectures are constructed and trained from scratch to explore their feasibility for penetration recognition. Then, pretrained on ImageNet, a state-of-art ViT-B/16 model, is employed, which alleviates the issue of modeling complexity and data insufficiency and improves the validation accuracy by 4.45%. The transfer learning results demonstrate a 98.11% as the test accuracy for the ViT model. Compared with the other conventional recognition methods, the proposed model has fewer misclassifications and superior generalization performance due to self-attention. Furthermore, the attention rollout method is applied to visualize the image region of interest (ROI), confirming the reliability and effectiveness of the developed approach. This study expands the application scope of the ViT to penetration recognition and achieves remarkable effects, laying a reliable foundation for automated welding quality optimization in GTAW.
(a) Conventional GTAW, (b) U-GTAW, (c) PU-GTAW of 5 Hz and (d) PU-GTAW of 250 Hz.
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Pulsed ultrasonic assisted gas tungsten arc welding (PU-GTAW) is a newly developed welding method. In ...this work, the PU-GTAW and un-pulsed ultrasonic assisted gas tungsten arc welding (U-GTAW) was comparative investigated by analyzing the microstructure and mechanical properties of Q235 welded joints. The results showed that the improvement of PU-GTAW on microstructure was more efficient than that of the U-GTAW. The weld seam grain size in the U-TIG and PU-GTAW was refined compared with that of the conventional GTAW. Compared with the conventional GTAW, the change of texture type and the decrease of texture intensity were obtained in the U-TIG and PU-GTAW. The sizes of microstructures in the U-GTAW and PU-GTAW were reduced compared with that of the GTAW, which was caused by the refinement grain. Influence degree of the U-GTAW and PU-GTAW on the hardness of the weld seam was the same. The hardness was increased by about 30HV compared with that of the conventional GTAW.
304 stainless steel, which is widely used in the industrial field due to its excellent thermostability, corrosion resistance, and welding performance, was welded using local dry underwater pulse ...metal inert gas (LDU-PMIG) welding technology in this study. The effect of different pulse peak currents on droplet transfer behavior and weld formation was investigated. The results show that short circuit transfer, globular transfer, and projected transfer were observed in the LDU-PMIG process. With the peak current of 240 A, the droplet transfer modes were short-circuit transfer and globular transfer; the weld formation was irregular with large particle spatters around the weld. With the peak current increased to 260 A, the droplet transfer mode changed into the globular transfer, and the weld formation quality was improved. With the peak current of 280 A, the droplet transfer mode was projected transfer, the weld formation was satisfied with a few spatters, and the coefficient of weld formation was the largest, and projected transfer was the most stable mode. With the increase of the peak current from 300 to 320 A, the droplet transfer mode did not change, but the instability of the welding arc resulted in poor weld formation with serious spatters and undercuts.
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•Well-developed twinned dendrites are found in wire arc directed energy deposited aluminum alloys.•Formation causes of twinned dendrites are investigated via experiments and ...simulation.•Regular dendrites can grow epitaxially from lateral branch of twinned dendrites.•The evolution of twinned dendrites during deposition is sensitive to remelting depth.
Twinned dendrites have attracted worldwide attention in the past half century due to their unusual orientation and crystallographic symmetry. Successive research has established a basic understanding of them in relatively steady processes like direct chill casting and directional solidification. This work, for the first time, investigated the growth behaviors of twinned dendrites in the wire arc directed energy deposition. The crystallographic characteristics, formation, and evolution laws of the twinned dendrites in the unsteady localized solidification condition are explored via experiments and numerical simulations. Results show that stacking faults are vital in the longitudinal growth of twinned dendrites by adjusting intermittent twin boundaries. During deposition, Mg, Zn, and Cu, which have low stacking fault energy, can promote the growth of twinned dendrites. The molten pool tail has large temperature gradients, crystallization velocities, and sufficient convection, providing advantageous growth conditions for twinned dendrites. Competitive relationships form between twinned and regular dendrites at the molten pool center. However, the twinned dendrites also cooperate with regular dendrites in epitaxial growth via their 〈100〉 lateral branch. With the remelting depth increasing, the twinned dendrite morphology changes from lamellar to isolated unilateral feather shape, then to unchained islands, and finally disappear.
The traditional WE43 magnesium alloy (WE43-Mg) manufacturing process faces challenges in producing large and complex structures. The cold metal transfer wire arc additive manufacturing (CMT-WAAM) ...offers a promising solution due to its flexibility, high deposition efficiency and low heat put. However, energy transfer and mass transfer are highly coupled in the CMT additive manufacturing process. Under different working modes, the local thermal processes are quite different for the same transition metals, which can produce different microstructures and mechanical properties. Therefore, it is necessary to study the effect of working modes on microstructure and mechanical properties. This study successfully deposited single-pass multi-layer WE43-Mg components using four CMT processes: CMT, CMT-Pulse, CMT-Advance, and CMT-Pulse + Advance. The microstructure and mechanical properties of these deposited samples were compared. Results revealed equiaxed grains with uniform sizes in the top and middle regions, with fine-grain regions between layers in the four CMT modes. Compare the microstructure characterization results, the higher the line energy, the narrower the width of the remelted fine grain zone. Four CMT modes deposited components exhibited superior mechanical properties compared to as-cast WE43-Mg. The CMT pulse mode shows the best results due to its low porosity. The average yield strength is 149.0 MPa, tensile strength is 222.9 MPa, and elongation is 6.4 %.
Narrow gap TIG welding is a high efficiency and low-cost welding technique for heavy structures building. Due to the narrow groove’s constriction, the TIG arc characteristics are different from butt ...welding. Understanding the unique arc characteristics of narrow gap TIG welding is the foundation for investigating the heat and mass transfer, metallurgic process, as well as process design. This research conducted numerical simulation on the TIG arc plasma in the narrow groove. The effects of welding current and arc length on the arc characteristics are investigated. Results show that, with the welding current increasing, the global velocity magnitude of plasma rises. The evolution of axial velocity and radial velocity has different responses to the current changes. The arc pressure increases drastically, and the global temperature of arc plasma also goes up. With the arc length increasing, global axial velocity rises, but the axial velocity and its gradients decrease near the anode surface. Centripetal radial velocity near the cathode increases, while centrifugal radial velocity rises at the outside of arc plasma and drops near the central axis. The maximum arc pressure on the anode surface decreases. At the lower part of the arc, arc temperature decreases near the central axis and increases at the outside of the arc.
In narrow gap gas metal arc welding (GMAW), it is useful to understand the arc behaviors to ensure the weld quality. Arc behaviors are strongly affected by the shielding gas composition. In this ...study, a three-component shielding gas mixture was used in tandem narrow gap pulsed GMAW, and the effect of its composition on arc behaviors and weld formation were investigated. The shielding gas included argon, carbon dioxide, and helium. The arc behaviors and electrical characteristics were recorded by a high-speed camera and an electrical signal acquisition system. The results show that the arc behaviors in different shielding gas are different. The arc expands and the arc length decreases with the increase of CO
2
content or helium content. The arc is the widest when the shielding gas is 80%Ar10%CO
2
10%He. The weld shape was observed, and it was found that the weld width increases first and then decreases with increasing of the CO
2
content. When the helium content is below 15%, the weld width increases as the helium content increases, but when the helium is 15%, the weld width drops due to the decrease of arc length. When the helium content is above 15%, the weld width continues to increase as the helium content increases. The largest weld width can be obtained in 80%Ar10%CO
2
10%He.
The study focuses on investigating the relationship between the ultrasonic effect and microstructure of ultrasonic-assisted gas tungsten arc welding (UA-GTAW) Inconel690 alloy joints. The influence ...of ultrasonic vibrations on Inconel690 plates was examined, while also clarifying the distribution pattern of the ultrasonic effect across the plate. Furthermore, actual welding experiments were performed by varying the distance between the ultrasonic horn and the welding torch. The results revealed that there were changes in both grain growth direction within the weld zone and refinement effects achieved under different distances. The optimal refinement of primary and secondary dendrite arm spacing was observed at distances of 60 mm and 180 mm between the welding torch and ultrasonic horn. The hardness of weld zone reached 235HV1 when the distance between ultrasonic horn and welding torch is 180 mm.
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