Welding in the World最新文献

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.

Directed energy deposition-arc (DED-arc) provides a process with high deposition rates for the additive manufacturing of metal components. Due to the close coupling of material and energy input, especially in gas metal arc welding (GMAW) process variants, different deposition rates lead to varying thermal conditions during material deposition, which in turn influence the resulting properties of the final component. For steels, high thermal cycles can lead to a degradation of the mechanical properties. This study presents the influences of energy input and interpass temperature on the mechanical properties in DED-arc manufacturing of AISI 316L stainless steel. Thin-walled structures were additively manufactured under variation of energy input and interpass temperature, from which specimens for metallographic investigations and tensile tests were subsequently extracted. Regarding possible material anisotropies, the tensile tests were carried out in three different loading directions in relation to the build-up direction. The results show pronounced grain growth and associated softening zones in the build-up direction, the extent of which depends on the process parameters. At moderate energy inputs and interlayer temperatures, this leads to distinct anisotropic properties with beneficial mechanical properties diagonal to the build-up direction. Higher thermal cycles result in increased softening zones and thus less anisotropic material behavior with slightly lower yield limit and elongation.

In this study, the optimization of welding parameters, pore defects, microstructure, and mechanical properties of Ti6Al4V welded joints subjected to ultrasonic-assisted laser welding was studied. The optimal parameter combination and the most significant factor influencing the tensile strength of the joint were determined by three-factor and three-level Taguchi experiments with range and variance analysis methods. A control experiment was set up under the optimal parameters to reveal the reason for ultrasonic influence on joint strength from the pore defects and microstructure. The control test showed that the cavitation effect and acoustic streaming effect of ultrasound could significantly improve the weld defects and microstructure. Compared with no ultrasound, the porosity of the welded joint decreased from 3.06 to 0.08%, and the average grain size of prior-β and α′ martensite was refined by 15.1% and 6.7%, respectively, under an ultrasonic power of 1000 W. Ultrasonic vibration improved the grain orientation of α phase and β phase and promoted the transition from LAGBs to HAGBs. When the ultrasonic power increased from 0 to 1000 W, the tensile strength of the joint increased from 920.1 to 997.2 MPa, which increased by 8.38%.

This study focuses on the estimation of the fatigue life of welded joints, considering elastic–plastic notch strains. Various finite element modelling approaches such as idealized geometries or measured geometries of weld toes will be discussed. By means of Monte Carlo simulations, partial safety factors are derived, which provide the possibility to account for the geometrical variability of the weld toe geometry. For computational efficiency, neural networks are employed to estimate notch stresses rapidly, revealing the influence of geometry parameters, like the notch radius or the flank angle at the weld toe and the weld throat thickness, but also variations of the wall thickness and angular misalignment. In addition, fatigue life evaluation using damage parameters applicable to low cycle, high cycle, and very high cycle fatigue will be presented.New experimental constant amplitude fatigue data from 84 tests on T- and butt joints made of X6CrNiTi18-10 stainless steel, including different sheet thicknesses, weld dimensions, weld types and weld seam variations, are used for validation of the proposed approach. Additionally, 144 tests from literature on materials S960M and X6CrNiTi18-10 are employed to validate the approach. For practical applications on component type specimen, 36 rectangular hollow section joints are used for additional validation. In summary, the study demonstrates that idealized weld modelling, following IIW-recommendations, coupled with an expanded effective notch stress approach, can enhance agreement between model predictions and experimental results. The derived partial safety factors facilitate the safe design of welded joints based on notch strains.

Over the past decades, vehicle manufacturers have been striving to reduce vehicle weight to minimize energy consumption and emissions in line with key priorities of the environmental objectives of the European Union. These goals can be met by using high strength steels, but their application raises numerous challenges in welding. In general, the railway vehicle body consists of ribs-stiffened shell structure which bears the load together with chassis. By substituting mild steel with high strength steel in these structural elements, joined by resistance spot welding (RSW), significant weight reduction can be achieved. It is possible to use thermomechanically rolled high strength steels with relatively low carbon equivalent which can be ideal for the RSW of railway vehicles. In this paper, the results of tensile shear (TST) and cross-tension (CTS) tests of resistance spot-welded joints made of 3-mm thick S700M thermomechanically rolled high strength steel are presented. The main research scope was to develop a resistance welding technology including the determination of optimal welding parameters based on TST and CTS tests. The optimal technological parameters were nearly the same for the two loading circumstances; however, a bit shorter cycle was justified during the optimization for the cross-tension strength. The value of the tensile shear force exceeded the minimum value specified by the AWS recommendation D8.1M by more than 22% with an electrode indentation depth of 5.56% in average.

To satisfy recent demands for reducing NVH (noise, vibration, harshness), vehicle weight, and improving collision safety, the development of reliable processes for dissimilar joining of lightweight vibration-damping aluminum to ultra-high strength steels is required. The resistance element welding (REW) process to join the dissimilar material involves a two-step process of pre-drilling a hole in the aluminum to insert the element and then welding to join the element to steel. Consequently, this increases cycle time and makes it challenging to ensure joint quality due to potential robot teaching errors. To overcome these limitations, an innovative one-step REW process was proposed to shorten the two-step REW process into a single process. However, the thermoplastic resin layer at the interface of the vibration-damping aluminum limits current conduction, posing challenges for REW. The current study introduces stainless-steel clips to bypass the thermoplastic resin layer between the vibration-damping aluminum, which limits the current conduction during the one-step REW process. The adjacent REW joint ensures further bypass of the current and acts as an initial weld point (shunt weld) for continuous one-step REW. Optimization of the welding variables was carried out to achieve excellent joint performance in terms of joint formation. Subsequently, the quality evaluation of the joint was done based on the evaluation of microstructure and mechanical properties. This process significantly enhances productivity with one-step REW instead of the traditional two-step welding. It surpasses the difficulty of welding the vibration-damping aluminum to HPF (hot press forming) steel.

Hybrid ultrasonic welding experiments on Inconel 625 alloy were carried out to address the challenges of refining microstructure. The welding process phenomena and resulting microstructures were systematically analyzed. Four distinct welding methods—conventional tungsten inert gas (C-TIG), ultrasonic-frequency pulsed TIG (UFP-TIG), ultrasonic vibration-assisted TIG (UV-TIG), and hybrid ultrasonic TIG (HU-TIG)—were compared in terms of grain morphology, grain size distribution, and overall refinement. In the weld zone adjacent to the fusion line, hybrid ultrasonic treatment demonstrated a superior effect on grain morphology adjustment. The results show that HU-TIG effectively suppresses columnar growth and increases the proportion of equiaxed grains, yielding a finer microstructure than the other methods. The synergy of ultrasonic-frequency pulsing and mechanical ultrasonic vibration enhances cavitation activity in the molten pool, promoting dendrite fragmentation and homogenizing elemental distribution. Moreover, ultrasonic-frequency pulsed arcs alter the physical properties of the molten pool, enabling the melt to respond more effectively to ultrasonic cavitation.

In this study, thin-walled parts of ER 4043 Al-5Si alloys were deposited using the cold metal transfer (CMT)-wire arc additive manufacturing (WAAM) process. The effects of variation of process parameters of wire feed speed (WFS), interlayer time interval (ITI), and travel speed (TS) on the microstructure and mechanical properties of thin-walled parts were investigated. The results showed that the microstructures of the thin-walled parts were composed of the α-Al phase and Al-Si eutectic phase. The samples deposited by WAAM consisted mainly of a large number of columnar grains and a few equiaxial grains. As WFS increased, heat input increased and reduced the temperature gradient; the average grain size of thin-walled parts increased significantly from 90 μm to 135 μm. The maximum texture intensity of the thin-walled parts is also increased. The ultimate tensile strength (UTS) of the samples decreased from 134 to 101 MPa. As ITI increased, the average grain size of thin-walled parts decreased from 122 to 85 μm due to higher subcooling and temperature gradient. This resulted in an increase in UTS from 104 to 130 MPa. Although the increased TS enhances the solidification rate, the average grain size of the thin-walled parts only decreases from 145 to 129 μm. The UTS of thin-walled parts was increased from 123 to 146 MPa. The tensile fractures of the samples were plastic fractures; therefore, the samples maintained high elongation (EL). In addition, the anisotropy in the mechanical properties results from differences in grain size, directional growth and inhomogeneous grain structure, eutectic microstructure, and texture.

Stiffened panels are common structural units in marine vessels, civil and aerospace structures. Production via welding can lead to excessive distortion of their plates, which negatively affects structural integrity and dimensional accuracy. Conventional practical approaches for distortion control are costly, making simulation models attractive tools to mitigate distortions. Prediction of welding distortions using finite element (FE) simulations is computationally intensive, especially when used repeatedly in design and optimization. Effective surrogate models in the form of deep learning could alleviate this issue, but the selection and construction of deep neural networks for this purpose are presently unclear. This study focuses on predicting welding-induced distortions in a T-joint. Two neural networks—a multilayer perceptron (MLP) and a convolutional neural network (CNN)—are employed to predict distortions. Two case studies are conducted for each model, exploring variations in geometry and welding sequences. The database is generated from FE simulations of the gas metal arc welding (GMAW) process. The effects of welding order and direction on distortions are studied, concluding that an appropriate selection of welding sequence and direction can reduce distortion by up to 40%. This data is then used to train the neural networks. The MLP and CNN models are designed and trained to predict distortion fields by tuning their architecture and other hyperparameters. Results demonstrate that both models are effective; however, the CNN achieves higher accuracy for complex distortion patterns, highlighting its suitability for more intricate scenarios. 

Controlling prior-β grain morphology is crucial for achieving specific isotropic properties in Wire Arc Additive Manufacturing (WAAM). Arc oscillation has been proven effective in refining grain size during aluminum welding, primarily due to the dendrite fragmentation mechanism. However, its impact on the grain structure of Ti-6Al-4 V remains underexplored. In this study, various arc oscillation amplitudes were applied to assess grain morphology evolution. In the stringer method (without oscillation), 100% equiaxed grains were observed in both the transverse and longitudinal directions due to lower heat input. As oscillation amplitude increased, the grain structure gradually transformed from equiaxed to columnar. At an amplitude of 6 mm, 80% columnar grains were obtained. To understand these findings, numerical simulations were conducted to quantitatively analyze the thermal history. SYSWELD calculations showed that a larger oscillation amplitude (6 mm) significantly influenced the weld pool shape (height and width), amplifying the temperature gradient (G) to nearly twice that of the specimen without oscillation during solidification. Furthermore, the dendrite fragmentation mechanism suggests that although thermal fluctuations caused by oscillation were observed in the molten region, they gradually dissipated after one or two remelting cycles. Controlling the frequency of these thermal fluctuations and the weld geometry presents a potential approach to modifying prior-β in Ti-6Al-4 V using arc oscillation.