Welding in the World最新文献

Friction Stir Processing (FSP) is an innovative and promising technique for microstructure refinement, material property enhancement, and surface composite production. The current study describes the fabrication of AA8090/boron carbide surface composites (SCs) by FSP. Experimental studies were conducted by varying the FSP parameters, specifically the rotational speed (800–1400 rpm), traverse speed (25–75 mm/min), and groove width (1–1.8 mm). Ultimate Tensile Strength (UTS), Surface Roughness (SR), and Percentage Elongation (El) were used as response measures. Experiments were planned based on the central composite design (CCD) of Response Surface Methodology (RSM) and a mathematical relationship between the input parameters and UTS, SR and El, and were obtained by RSM. The model adequacy was tested using analysis of variance (ANOVA). The models enabled the examination of individual and interaction effects of input parameters on the UTS, SR, and El of the produced SCs. AA8090/boron carbide SC strength was optimal of 366 MPa at 800 rpm, 75 mm/min, and 1.8 mm and optimal 21.13% elongation at 1400 rpm, 25 mm/min, and 1 mm. A smoother surface with 0.82-μm roughness was optimal at 1400 rpm, 25 mm/min, and 1.2 mm. The present study uses the FSP method to synthesize near-net-shaped SCs without further machining by systematically selecting process parameters. The study shows that the increase in rotational speed during AA8090/boron carbide SC fabrication produces composites with a good surface finish, lower UTS, and good ductility. However, the increase in the other two parameters, namely, traverse speed and groove width, produces low ductile composites with rougher surfaces and higher strengths.

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This paper examines the issue of wire deflection in wire and arc additive manufacturing (WAAM) and robotic welding, which leads to process instability and defects in printed geometry. The study focuses on the deflection of alloy 625, alloy 718, and 3Si1 welding wires during the deposition process. Measurements were taken to determine the relationship between wire deflection and the amount of wire used. Regression models were developed for each material to predict initial wire deflection and changes in deflection due to contact tip wear. The results showed that the deflection of alloy 625 and alloy 718 wires followed a nonlinear pattern for the first 500 m of wire, while the deflection of 3Si1 wire followed a nearly linear trend. The intensity of the contact tip wear is dependent on the normal contact load, which decreases as the wear increases. A generalized regression model of wire deflection was constructed based on the obtained regressions and the study of the wire’s deformed state. Based on these models, an algorithm was developed to correct the wire deflection by adjusting the tool center point coordinates. The effectiveness of the developed algorithm was verified in practice.

The weld of resistance projection welded joints is not visible from outside. Therefore, visual evaluation is restricted, and visual inspection is not possible at all. So far, the parameters of the welding process are monitored and controlled. In addition, the welds are periodically tested destructively to determine the quality of the welds. No industrial standard has yet been established in the field of non-destructive testing (NDT) for projection welded joints. This study focuses on NDT of projection welds using two different ultrasonic imaging inspection systems and the passive magnetic ux density testing (pMFT) method. The ultrasonic inspection systems commercially available and established in the field of NDT of spot welds. Both systems are originally designed for the NDT of spot welds and not for projection welds. Unlike the ultrasonic systems, the pMFT is still in laboratory status. The method has originally been developed to evaluate spot welds and is also used in this study to evaluate projection welds. The applicability of the investigated systems to projection welding is investigated in order to derive mandatory development steps to achieve reliable results. The pMFT method shows also good results for NDT of spot welds In this contribution, the measurement and evaluation concept of the three NDT systems for projection welded joints is presented. The NDT results are discussed in the context of the corresponding destructive results in terms of tensile forces and fracture areas. Advises for further development of all investigated systems are given.

A three-dimensional transient model of gas metal arc welding (GMAW) process including the arc plasma and droplet transfer was established to investigate the complex coupling mechanism of mass transfer, heat transfer, electromagnetism, and hydrodynamics. The arc shape, current density, temperature field, electromagnetic force, arc pressure and droplet behavior were analyzed. The results showed that the iron vapor generated on the droplet surface and diffused in the arc, which changed the plasma thermal-pressure distribution. The upward surface tension maintained the forming droplet at the wire tip. The electromagnetic force promoted necking, resulting in a decrease in surface tension. Gravity and plasma drag force accelerated the droplet. The behaviors of the inner arc layer varied periodically with the droplet transfer, while the arc periphery remained stable. Droplet transfer was the result of periodic changes in the resultant of all external forces over time, which also led to periodic changes in arc behavior. This study laid the foundation for further research on the influence of arc and droplet behaviors on the weld pool.

Graphical Abstract

In this study, solid-state diffusion welded joints of zirconium alloy (Zr-Alloy) and super duplex stainless steel (SS) were prepared at 875 °C with varying welding times of 30, 45, 60, 75, and 90 minutes using a welding pressure of 4-MPa in a vacuum. The interface microstructure was characterized using optical, scanning electron microscopy in backscattered electron mode, and electron probe micro-analyzer. With 30 minutes of welding time, no intermetallic compounds were observed at the weld interface due to the minimum diffusion activity of chemical elements across the joints. However, for 45 minutes and above welding time, a phase mixture of ZrFe₂ + ZrCr₂ was observed near the interface of the welded joint, and the width of the phase mixture gradually increased with a further increase in welding time. The maximum joint tensile strength of ~ 302 MPa along with ~ 5.9% elongation was achieved in the joint developed for 45 minutes of welding time due to the formation of finely widened reaction products at the diffusion interface. The electrochemical studies of the welded joints were also investigated and a comparison was drawn between the same base metals using different electrochemical measurement techniques such as open circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarization in 0.1 mol/L HCl solution. It was identified that the corrosion rate of the welded joint made with 90 minutes welding time is the highest and the corrosion of the welded joints occurred in micro-galvanic mode due to the presence of intermetallic compounds at the joint interface.

To control the formation and grain structural characteristics in the welding process, an alternating current (AC)-assisted double-wire feeding strategy was applied to a traditional gas tungsten arc welding (GTAW) process. During this process, two filler wires were connected to AC power and fed to the molten pool in a nonplanar and symmetric manner from one side. The influences of the AC, AC frequency, and arc current on various parameters, including the molten droplet size, droplet transition frequency, and deposited bead formation, were evaluated. The research revealed that this method could be implemented to effectively achieve a well-formed weld bead, especially at high ACs. Microstructural analysis indicated that the grain size decreased with increasing AC frequency. Finally, the underlying mechanism of grain refinement resulting from the addition of AC to the double filler wire was discussed.

Dissimilar metal welding (DMW) between titanium alloys and nickel-based superalloys can contribute to acquiring light, heat-resistant frameworks of enhanced efficiency. The current study constitutes an attempt to obtain joints between a Ni-superalloy and a Ti-alloy, investigating the beneficial impact of copper on the microstructure of the weld metal (WM), through precipitation of ternary Ti–Ni–Cu intermetallic compounds (IMCs), instead of Ni–Ti ones, previously reported in weldments between such alloys. Gas tungsten arc welding (GTAW) was performed between Ti–6Al–4V and Inconel® X-750, varying the welding current and using different copper filler wires (pure Cu and NiCu). The microstructural characterization of weldments was conducted by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), and a further nanoscale examination was performed using a transmission electron microscope (TEM). Identification of IMCs and precipitates was achieved by X-ray diffraction (XRD), while the mechanical properties were investigated through microhardness Vickers measurements. Crack-free joints were obtained, albeit with the presence of IMCs comprising Ti–Ni, Ti–Cu, and Ti–Ni–Cu, as well as titanium carbides (TiCs). Cu exhibited a positive influence on the joints’ microstructure. Elevating the welding current led to accelerated cooling and solidification rates, resulting in enhanced Vickers microhardness values. This phenomenon can be attributed to either the formation of finer microstructures or the precipitation of brittle IMCs, which were observed in specimens welded with higher currents. Especially near the Ti-alloy interface, it was found that a brazing-type bond took place instead of welding, while high hardness values (up to 800 HV) were also detected.