Welding in the World最新文献

Galvanized DP590 steel plates were successfully welded using friction stir lap welding (FSLW), resulting in high-quality joints. The stir zone (SZ) of all joints consisted mainly of martensite, bainite, and ferrite, with a characteristic “hook-like”interface formed on the advancing side (AS). The distribution of Zn across three cross-sectional planes—near the tool shoulder, at the keyhole center, and in the final welded seam—was analyzed to understand the flowing behavior of Zn during welding. Various forms of Zn were detected along the interface, concentrated primarily along the “hook-like” interface near the keyhole center. Outside the heat-affected zone (HAZ), Zn layers on both the retreating side (RS) and AS remained stable, with Fe-Zn intermetallic compounds forming in the SZ center. A transitional layer of Fe₃Zn₁₀ was observed at the joint center in the final welded seam, increasing in thickness with higher welding speeds and accompanied by micro-void formation. It was revealed that the mechanical properties of the joints varied with welding speed. At 25 and 50 mm/min, HAZ softening led to reduced joint strength and failure within the HAZ. At 100 mm/min and 150 mm/min, the presence of Zn and numerous voids at the “hook-like” interface led to joint failure at the bonding interface between the two plates. The maximum shear tensile load observed at 50 mm/min was approximately 14.24 kN.

Graphical Abstract

A novel 7075/5356 aluminum alloy laminated composite was fabricated by alternately depositing a 7075 wire and a 5356 wire layer-by-layer using wire arc additive manufacturing (WAAM) process. The microstructure, mechanical properties, and fracture mechanism of the produced components under as-deposited and heat-treated conditions were systematically investigated. Results demonstrated that there was an interlayer formed between the 7075 layer and 5356 layer, which shows gradient changes in the number of second phases and microhardness. In comparison with single 7075 aluminum alloy components, the heat-treated 7075/5356 aluminum alloy laminated composite exhibited superior comprehensive mechanical properties. The elongation was 103.8%, 50.7% higher in vertical and horizontal directions, while the tensile strength was only 18.4% and 14.3% lower, respectively. The fracture modes of 7075 layer and 5356 layer show differences, which were intergranular fracture and intergranular-transgranular mixed fracture, respectively.

This study investigates the tungsten inert gas double-electrode (TIG-DE) welding process. The motivation for developing the TIG-DE process lies in its potential to significantly enhance productivity and versatility, especially for additive manufacturing applications. The focus is on the interaction between electrical parameters and geometric configurations to analyze the seam outcome. It is observed that increasing current and voltage broaden weld seams, with an elliptical penetration profile that reorients significantly at higher currents. Larger electrode angles, such as 50°, produced wider weld seams, enhancing base material fusion and overall weld robustness. Optimal electrode spacing proved crucial for arc stability and molten pool control. Tight electrode spacing results in lower arc pressures and a slightly elliptical arc shape, significantly lower compared to a single electrode process with the same total current. Larger spacings lead to arc separation and multiple arc pressure maxima. High welding speeds introduce instability, causing the arc to detach from the melt pool, a phenomenon exacerbated by directional dependencies in voltage profiles. The combined effects of torch inclination angle, electrode spacing, and arc length are visualized in welding range diagrams, which depict stable and unstable parameter ranges, arc separation conditions, and scenarios of insufficient energy input. These findings highlight the need for ongoing research and pave the way for developing advanced demonstrators to refine the TIG-DE welding process, particularly for additive manufacturing applications.

To this day, the structural strength of laser-welded joints of Al-Li alloys made with a fiber laser has not been thoroughly studied. In this research, high-strength laser-welded joints of Al-2.7Cu-1.8 alloy were obtained using a fiber laser followed by post-weld heat treatment. The laser-welding process parameters were optimized, including welding speed, radiation power, and location of the focal spot. In addition, the influence of these parameters on the microstructure of the welded joints has been studied. After welding, the welded joints were heat treated (PWHT) in two modes to achieve optimal mechanical properties. Changes in the structural and phase composition of the weld material before and after PWHT were examined using synchrotron diffraction and transmission electron microscopy. The obtained research results have shown that during laser welding, copper-containing phases formed at the boundary of dendrites in the weld material, which leads to a reduction in strength. The process of post-weld heat treatment (PWHT) has led to the restoration of the phase composition in the material of the weld. The cyclic (fatigue strength), dynamic (crack strength), and static (yield strength and ultimate tensile strength) properties of laser-welded joints after PWHT have been studied. It has been observed that PWHT using mode 1 allows to achieve maximum fatigue and dynamic properties, while PWHT using mode 2 results in achieving maximum static properties at various temperatures.

Galvanized steel has defects such as porosity and spatter during welding due to the presence of zinc coating. Currently, laser welding of galvanized steel mainly adopts plate gap to volatilize the zinc vapor. However, the zero-gap condition is desired for part component assemblies. The molten pool is the only way for zinc to escape in zero-gap condition. Oscillating laser has an inhibition effect on the defects. Consequently, it was applied to weld DP780 galvanized steel with zero-gap. The impact of various oscillation parameters on porosity and spatter was analyzed. The impact of various oscillation modes on defects primarily stems from their differing oscillation speeds. The experiment results showed that the spatter and porosity suppression under zig-zag oscillation was excellent, due to stabilized keyhole and slow solidification. The optimal parameters were 120 Hz and 1.2 mm, respectively. In addition, the solidification of the molten pool under the optimal oscillation parameter was 66.6% boost compared to that without oscillation.

The laser pre-heating (LPH) approach is a heating process performed with a laser by applying different amplitude and oscillation patterns without causing any deformation on the surface in order to reach the desired temperature at the joint line of the weld sheet before the joining process. At the beginning of the study, the ideal amplitude-laser power value for full penetration was determined using different circular oscillation path configurations for joining AA6005 sheets. In these processes, called laser beam oscillation welding (LBOW), longitudinal thermal cracks were found to form in the weld line due to high heat input generated by the increased amplitude-laser power. As a result of the analyses of the microstructure and mechanical properties of the LBOW processes, the ideal amplitude-laser power value (3.75 mm-3750 A) with the lowest weld defect was determined as a reference for use in the LPH process. In the other section of the study, using the laser power values calculated by the Rosenthal equation, temperatures of 200 °C, 300 °C and 400 °C were established separately on the sheet surfaces before welding for the LPH process and then the welding process was performed. As a result of the LPH treatment at 300 °C, although the hardness in the FZ region decreased by 20% compared to the reference treatment, the tensile lap strength was 15% higher and the elongation was 1.14% higher. In this context, the LPH process has been found to improve the weld quality in laser welding processes and has improvable properties.

A novel welding process that combines variable polarity pulsed gas metal arc welding (VP-GMAW) and high-frequency pulsed (HFP) welding is proposed to improve the weld quality of aluminum (Al) alloy. The effect of HFP frequency on the arc shape, stability, and weld formation of Al alloy in VP-GMAW is investigated. The arc shape at different HFP frequencies is analyzed using high-speed photography, and the arc profile is extracted by gray processing. It is found that the arc-projected diameter decreases gradually with increasing HFP frequency. The U-I characteristic curve is used to analyze the stability of the arc load. The curve before and after polarity switching is more compact after superimposing HFP, indicating that the superimposing HFP improves the stability of variable polarity arc. As the HFP frequency increases, weld penetration deepens, weld width narrows, and the penetration-to-width ratio (PW) increases. When 30 kHz HFP is superimposed, the PW reaches its maximum of 18.3%. When combined with the double circulation model of the weld pool, the HFP can improve the convergence circulation and penetration depth. The divergence circulation is weakened, and the width is reduced. In addition, high-frequency vibration can accelerate the flow of molten metal in the weld pool and help to deepen penetration.

One of the most promising solid-state methods for joining high-strength aluminum alloys, friction stir spot welding (FSSW), remains hindering due to formation of the keyhole defect. This paper presents its promising variation as a probeless-friction stir spot welding (P-FSSW) assisted by flat featureless shoulder. Based on the prior arguments on the feasibility of this method in joining aluminum alloys, present work provides in-depth study on the effect of rotational speed on microstructure, phase transformations, and final properties of dissimilar aluminum plates, studies using scanning electron microscopy (SEM), occupied by electron backscattered diffraction (EBSD) method and energy-dispersive X-ray spectroscopy (EDS) analysis. The resulting properties was examined through microhardness measurements and tensile-shear testing. Results showed that rotational speed plays a crucial role in determining the intensity of material softening, its flow, and mechanical properties. Uniform heating and circumferential material flow helped eliminate edge hook defects using a featureless tool during P-FSSW. The microstructure development followed progressive plastic deformation was accompanied by a gradual transition between continuous dynamic recrystallization (CDRX) and dynamic recovery (DRV) process. The re-precipitation of the Al₂CuMg phase restricted grain growth by pinning recrystallized grains within the stir zone (SZ). Mechanical tests indicated improved joint strength, suggesting that P-FSSW could produce high-quality, lightweight joints suitable for automotive and aerospace applications.

Prediction of temperature based on the process parameters in friction stir welding (FSW) of titanium alloys, particularly Ti6Al4V, underpins the production of defect-free welded joints at reduced levels of materials and energy wastages. This work proposes a new approach to model and validate the FSW process for Ti-6Al-4V based on the process variables using computational fluid dynamics (CFD). The work uses the sections welded by a newly developed low-cost single-use tool, to join 2-m long sections, to validate the model. The validation process was based on physical experimentation and microstructural measurements of micrographs produced using an Infinite Focus Microscope (IFM), which presented a simple technique when predicting thermomechanical parameters and properties including temperature distribution, torque, strain rate, and material flow properties. The developed model provides a predictive framework for a combined thermal and material flow response of Ti6Al4V under friction stir welding.

In this study, stirring tools, with pin diameters of 7 mm and 8 mm and sleeve diameters of 10 mm and 12 mm, were designed and manufactured to perform refill friction stir spot welding (RFSSW) on 3-mm thick 6061-T6 aluminum alloy. The spot welding was conducted under process parameters with rotation speeds of 1400 rpm and 1600 rpm and welding speeds ranging from 20 to 50 mm/min. We achieved well-formed spot welding zones and conducted performance tests on these zones. The test results indicate that the grains within the nugget zone are sufficiently refined and remain consistent regardless of changes in the diameter of the stirring pin. The grains in the thermal and mechanical affected zone (TMAZ) are smaller, reaching their smallest size with a stirring pin diameter of 8 mm. The presence of a “Hook” defect was observed, which serves as a crack initiation point for tension-shear fractures. The maximum tension-shear force was measured at 14.79 kN for an 8-mm stirring pin and 12.81 kN for a 7-mm pin, indicating a significant increase with the larger diameter. Thus, the increase in the diameter of the stirring tool not only impacts the maximum tensile and shear force in the spot welding zone but also contributes to considerable annealing.