Welding in the World最新文献

This study investigates the microstructural evolution and cryogenic fracture behavior of friction stir welded (FSW) 2195 aluminum–lithium (Al–Li) alloy joints, with emphasis on grain boundary transformation and precipitate instability. The results reveal a progressive increase in the fraction of high-angle grain boundaries and a pronounced weakening of crystallographic texture from the base material to the weld nugget zone, driven by dynamic recrystallization. Strengthening precipitates undergo significant transformation, with T₁ (Al₂CuLi) phases in the base material degraded in the thermo-mechanically affected zone and replaced by θ′ (Al₂Cu) in the weld nugget zone. A distinct softening zone with minimum hardness (~ 92 HV) was identified at the TMAZ/HAZ interface, where tensile fractures consistently initiated under cryogenic conditions. The joints exhibited a mixed ductile–brittle fracture mode, dominated by microvoid coalescence and quasi-cleavage. These findings clarify the mechanism of cryogenic failure in Al–Li alloy FSW joints and provide guidance for enhancing the reliability of aerospace cryogenic structures.

High‑strength steels (HSS) are increasingly used in modern structural engineering due to their improved strength‑to‑weight efficiency and sustainability benefits. This study presents an extended formulation of the regular inclined shell element model (RISEM) through the incorporation of a Eurocode‑compatible plastic strain limit for predicting the resistance of fillet welded connections. The enhanced model employs equivalent plastic strain (PEEQ) as the ductile failure indicator, aligned with EN 1993‑1‑5 Annex C, enabling strain‑based verification without dependence on fracture calibrations. A comprehensive mesh sensitivity study and strain‑limit evaluation demonstrate that RISEM achieves stable predictions using mesh sizes between a/15 and a/20, with weld resistance variations remaining below 8% for the full 2–6.4% strain‑limit range. Verification against analytical design resistances confirms that the strain‑limited RISEM is accurate, computationally efficient, and suitable for design applications. The study delivers practical design recommendations for engineers using HSS welded connections under ULS verification conditions.

The challenging problem of quantitatively regulating friction rolling additive manufacturing (FRAM) process parameters to optimize forming quality and morphology is addressed in this study. A quadratic regression orthogonal combination method is employed to establish the relationship between process parameters, deposition height, and forming quality, thereby constructing a theoretical model of single-pass cross-section deposition. The results indicate that during FRAM multilayer deposition, the deposition height tends to stabilize as the number of layers increases. Among the process parameters, tool head speed has the most significant impact on deposition height. Additionally, the lift-off amount should be smaller than the deposition height to effectively prevent the formation of interlayer defects. This research facilitates stable control of FRAM deposition morphology and layer height and provides valuable guidance for selecting process parameters.

Ultrasonic metal welding (USMW) is a widely used solid-state welding process for electrical components. Since the joining zone remains largely hidden during the welding process and high-frequency oscillations are used to form the joint, there is only a limited range of technologies available for process monitoring. The strategies and sensor technologies used so far are not always able to detect process disturbances or defective welds. Consequently, intensive research is currently being carried out to obtain significant process information through additional sensor technology. One solution is to install sensors on the tools (horn and anvil) in the closest distance to the joining zone. Due to their flexibility and contactless measurement, laser vibrometers are frequently used in USMW research to determine the working and interfering frequencies and their amplitudes. However, the integration of such systems into production is limited by the high system costs, the lack of installation space, and the failure of sensors due to contamination. An alternative solution for determining amplitudes and frequencies is the use of piezoelectric shear force sensors in the anvil. This overcomes the challenges of limited installation space and contamination. At the same time, however, sensor integration poses new challenges such as reduced anvil stiffness and possible resonant excitation of the sensor, resulting in a sensor defect. In this study, we demonstrate a design process for a shear force sensor system for USMW, including calibration and validation, which provides high-frequency process information on the anvil side. It is shown in detail that piezo-based force sensors can be used as a cost-effective and integrable alternative to laser-based sensors in USMW processes. The correlation of the measurement data from 175 welding tests results in a mean coefficient of determination R² ~ 0.986 with an error measure nRMSE of ~ 0.032 between signals of the shear force sensors and a vibrometer as a reference sensor.

The directed energy deposition-arc (DED-Arc) process, using high-strength low-alloy (HSLA) feedstock wire, presents a promising solution for fabricating large-scale steel connectors in civil engineering. Due to the use of carbon steel feedstock wire, corrosion protection of the 3D-printed components is necessary. Therefore, this study investigates low-pressure cold spray (LPCS) as a method for applying zinc-based coatings. Two sets of thin walls were 3D-printed: one set uncoated and one set coated with LPCS Zn + Al₂O₃ coating. This LPCS coating was successfully deposited on untreated and on grit-blasted DED-Arc surfaces. Coating thicknesses exceeding 300 µm as well as electrochemical polarisation analysis confirmed sufficient corrosion resistance of the coated as-built specimens. To evaluate the influence of the surface condition and the coating process on the mechanical behaviour, dog-bone tensile specimens were extracted from the walls, 3D-scanned, and subsequently mechanically tested. Structured-light scanning of the geometry revealed different scatter of the specimens’ thickness based on their orientation with respect to the build direction. Uniaxial quasi-static tensile tests, combined with a four-camera digital image correlation (DIC) system, were performed both on specimens with machined surfaces and with LPCS Zn + Al₂O₃ coating on the as-built surface. While the machined specimens exhibited nearly isotropic behaviour, the coated as-built specimens showed pronounced anisotropy with comparable mechanical properties to uncoated as-built specimens from literature when excluding the coating thickness from the load-bearing cross-section. The LPCS Zn + Al₂O₃ coating led to a reduction of the corrosion rate by two thirds compared to uncoated HSLA DED-Arc.

FeCoNiCrAl high-entropy alloy (HEA) coatings were fabricated on the surface of 9Cr18 bearing steel using laser cladding technology. A total of nine experiments were conducted based on an L9(3⁴) orthogonal array with three selected factors at three levels. Range analysis and signal-to-noise (S/N) ratio analysis were employed to investigate the effects of laser power, scanning speed, and powder feed rate on microhardness and dilution rate. Cross-sectional defects were observed using a super-depth-of-field microscope. The microstructure, crystallographic orientation, and elemental distribution of the cladding layers were systematically characterized by metallographic analysis, electron backscatter diffraction (EBSD), and energy-dispersive spectroscopy (EDS). The results showed that the powder feed rate had the most significant effect on microhardness. The maximum microhardness of 597.86 HV was achieved under the condition of 1.3 r/min powder feed rate, 6 mm/s scanning speed, and 2100 W laser power. Scanning speed was the dominant factor affecting dilution rate, which reached a minimum of 28% at 1.3 r/min powder feed rate, 5 mm/s scanning speed, and 1800 W laser power. The cladding layer exhibited a gradient microstructure, with equiaxed grains in the upper region, mixed grains in the middle, and fine columnar grains near the substrate. EBSD analysis revealed that the cladding layer was mainly composed of a BCC phase, while the heat-affected zone (HAZ) consisted primarily of an FCC phase. A local BCC/FCC mixed-phase region was also observed, which may increase the risk of stress concentration.

To address the challenges of irregular geometry, significant curvature variations, and disordered normal vector distribution in aviation Invar steel S-type molds, this paper proposes a welding trajectory generation method based on multi-level trajectory fitting and adaptive connection. To address issues such as high trajectory fitting error rates and trajectory gaps caused by irregular geometric shapes and significant curvature variations, the model point cloud is first segmented into regions. Subsequently, trajectory points are extracted using slicing operations and domain searches, and trajectory fitting is performed via Euclidean clustering. After obtaining a simple trajectory, an adaptive connection mechanism is introduced to enhance the algorithm’s practicality, thereby translating the algorithm’s intended outcomes into actual results. The proposed algorithm achieves a fitting accuracy exceeding 90%, with smoothness and average Z-direction values below 0.1, objectively demonstrating the high accuracy and stability of the trajectory fitting method presented herein. This study provides a feasible solution for automated welding of aviation Invar steel molds and offers new insights for the development of robotic welding trajectory planning.