Welding in the World最新文献

The present study evaluates the effect of beam oscillation on the mechanical and electrochemical properties of electron beam welded commercially pure aluminium. The circular beam oscillation diameters of 1 mm and 2 mm have been used while keeping all the other welding parameters constant. The churning effect of beam oscillation led to the formation of a broader fusion zone compared to static beam joint. The fusion zone of a static beam weld consists of equiaxed and columnar structures, while the fusion zone of an oscillated beam weld mainly consists of equiaxed structures. The joints produced using beam oscillation have less porosity (0.01%) than static beam joint (0.02%). Also, the pores were more evenly distributed in the oscillated beam joints. The application of circular beam oscillation of diameters 1 mm and 2 mm increased the microhardness (56 VHN and 58 VHN) as compared to the static beam joint (52 VHN) and base metal (45 VHN). The tensile strength of aluminium (102 MPa) decreased slightly after electron beam welding (99 to 91 MPa). Beam oscillation reduced the tensile strength further (91 MPa and 93 MPa) as compared to the static beam joint (99 MPa), whereas the percentage elongation increased (9 to 17%) due to beam oscillation. Beam oscillation has reduced the corrosion rate from 0.02 mm/year (base metal) to 0.001 mm/year (oscillated beam weld). The mechanism of variation in mechanical and electrochemical properties of electron beam welded aluminium with the application of beam oscillation has been established.

Microalloying elements such as Nb and Ti are essential to increase the strength of quenched and tempered high-strength low alloy (HSLA) structural steels with nominal yield strength ≥ 690 MPa and their welded joints. Standards such as EN 10025–6 only specify limits or ranges for chemical composition, which leads to variations in specific compositions between steel manufacturers. These standards do not address the mechanical properties of the material, and even small variations in alloy content can significantly affect these properties. This makes it difficult to predict the weldability and integrity of welded joints, with potential problems such as softening or excessive hardening of the heat-affected zone (HAZ). To understand these metallurgical effects, previous studies have investigated different microalloying routes with varying Ti and Nb contents using test alloys. The high-strength quenched and tempered fine-grained structural steel S690QL is the basic grade regarding chemical composition and heat treatment. To evaluate weldability, three-layer welds were made using high-performance MAG welding. HAZ formation was investigated, and critical microstructural areas were identified, focusing on phase transformations during cooling and metallurgical precipitation behavior. Isothermal thermodynamic calculations for different precipitations were also carried out. Mechanical properties, especially Charpy notch impact toughness, were evaluated to understand the influence of different microalloys on the microstructure of the HAZ and mechanical properties.

MIG welding still had a lot of potential in the titanium alloy industry with many advantages. How to achieve stable process and forming was still a hard nut to crack for titanium alloy MIG welding. The conventional MIG welding torch had a small coverage of shielding gas which causes an obvious insufficient capability of isolating air. Therefore, this study introduced the fluid field composite MIG process, proposed a novel strategy of titanium alloy MIG welding process under the synergistic effect of coaxial dual channel gas path, and had explored the impact of the synergistic effect of internal gas flow(Q) and external gas flow(q) on the welding process from three aspects: droplet transfer characteristics and weld surface morphology, weld cross-section. The results showed that the form of “one large droplet + several small droplets” was always maintained during transition process. Q mainly impacted on the variation law of the droplet transition; however, the length of transition period was mainly affected by q. In addition, the arc length was reduced meanwhile the geometric parameters of welds’ cross-section had more regular changes after adding q. The surface morphology was the worst when Q acted solely; however, it was straight and uniform after adding q. When q = 40L/min and Q = 15L/min, the coverage and protective effect of shielding gas was excellent, no turbulence was generated, and no pores generated in the cross-section of the weld. It was easier to obtain a more stable forming of titanium alloy MIG welding when Q and q worked together.

Welding parameters play a crucial role in determining the quality of welds. In this study, we investigated the motion characteristics of aluminum pipes under underwater explosion loads using theoretical calculations and experimental measurements to obtain welding parameters. We conducted contrasting experiments with varied welding parameters to examine their effect on the aluminum/steel composite pipe interface. Subsequently, we thoroughly analyzed the microstructures and mechanical properties of the joints. The velocity histories predicted by theoretical calculations closely matched our experimental findings, validating the use of these calculations for predicting welding parameters in underwater explosive welding processes. Notably, our observations revealed that at an impact velocity of 510 m/s and a dynamic collision angle of 10.4°, no visible melted layer was detected at the welding interface. However, at lower impact velocities (340 m/s) and smaller dynamic collision angles (6.9°), some interfaces exhibited melted layers, contrary to theoretical predictions of kinetic energy loss. This discrepancy underscores the significant influence of collision angle on the formation of interfacial microstructures, a factor often overlooked in similar studies. Furthermore, the melted layer identified at the welding interface was identified as an intermetallic compound, which resulted in a 10.75% reduction in the bonding strength of the aluminum/steel interface. These findings contribute valuable insights for optimizing the design of underwater explosive welding processes for metal pipes, offering a practical tool for industry applications.

Due to electronics miniaturization, the size of voids is becoming comparable to that of solder joints, thereby increasing the risk of reduced reliability. This work presents a novel method of achieving void reduction through preliminary characterization of the flux and, consequently, the proper flux selection and adjustment of the temperature profile during soldering. To validate this approach, five SAC305 solder pastes differing in flux composition were subjected to testing. The flux components were characterized by a gas chromatograph combined with a mass spectrometer (GC–MS) and thermogravimetric analysis (TGA). Subsequently, four temperature profiles differing in the heating rate were employed for reflow soldering of the test boards with components while maintaining the same peak temperature for all profiles. The results of the X-ray computed tomography (XCT) analysis indicated that as the temperature gradient decreased, the number of voids decreased by up to 36%. The decrease in the number of flux residues detected by TGA present at the peak process temperature was also accompanied by a decrease in the void area within the solder joint. Moreover, a comparison between the GC–MS and XCT results revealed that certain flux compounds, such as butylated hydroxytoluene, were found to have a greater impact on void formation than others. The proposed method combining flux characterization by GC–MS and TGA and adjustment of temperature gradient during the soldering process can be an efficient way to reduce voids in solder joints. Additionally, it appears that a lower temperature gradient is generally associated with a lower incidence of voids.

Nonuniform temperature field upsetting is prone to oxide inclusions, and the temperature field of rail flash butt welding (FBW) is primarily formed because of the Joule heat generated by the end-face current. The current distribution at the end face largely determines the heat distribution; thus, the current distribution and heat production at the end face of an alternating-current (AC) FBW must be investigated. This study combined finite element simulation and experimental validation to establish an AC rail FBW electric–magnetic–thermal coupling model to explore the influence of current parameters, end-face temperature, and feed mode on the distribution of the end-face current. The results show that a reduction in the welding current, current frequency, and time in low- and medium-temperature stages can improve the uniformity of the temperature field. The electrode clamping method determines the shape of the temperature field, whereas the proposed hybrid clamping method is the most conducive to uniform heat generation at the end face. Moreover, electrode clamping at 210 mm near the end face yielded uniform temperature fields. The experimental validation results were consistent with the calculated results, indicating that the proposed model is reasonable and reliable. In practical welding operations, it is advisable to optimize current and frequency to achieve an end face temperature > 1000 °C swiftly. This study provides a direction for enhancing the uniformity of the temperature field and improving the expulsion capability of impurities during the upsetting process, thereby optimizing the flash butt welding process for rails.

This study addresses the effects of alloying elements and radius curvature of the electrode on the degradation behavior during resistance spot welding (RSW) of A6451-T4. The importance of electrode characteristics is emphasised according to changes in hardness and electrical conductivity by electrode composition and radius curvature. The electrodes that were alloyed with Ag, Cr, and Be with varied radii were used in this study. The endurance limit of electrode was investigated by producing 100 welds with the optimised welding parameters. In addition to mechanical characterisation of the weld samples, comprehensive analyses of the electrode surfaces were carried out by carbon imprint, 3D digital microscope profiling, and electron microscopy. A computational analysis using the commercialised SORPAS software was also conducted to analyse heat generation according to the electrode characteristics. The results demonstrate that the electrode degradation proceeds by four discrete stages: aluminum pick-up and alloying, contact area increase, pitting, and cavitation. It was confirmed that load-bearing capacity and nugget diameter also change in proportion to the generated heat between the electrode and welded sheet. Among the physical properties of the electrode, the hardness and electrical conductivity most influence the electrode wearing behavior.

Proper parameter selection is crucial for obtaining the required shape of the beads and reducing defects like uneven welds, cracks, porosity, and irregularities while creating wire arc additive manufacturing (WAAM) samples. This study aims to investigate the impact of three input process parameters (current, welding speed, and gas flow rate) at three different levels on the properties (weld bead width, bead height, and dilution) of samples made from aluminum 4047 using the CMT-WAAM process. The study will analyze the data using response surface methodology (RSM). A central composite design (CCD) matrix was employed to develop a design of experiment incorporating three process factors. The appropriateness of the design was assessed by ANOVA analysis. The upper limits for the height and penetration of the weld bead were 2.83 mm and 3.12 mm, respectively. The lowest level of width measured was 9.44 mm. The forecasted ideal input parameters were a current of 150 A, a welding speed of 50 cm/min, and a shielding gas flow rate of 15 l/min. The findings demonstrated that the current exerted the most significant impact on determining the various responses, with welding speed and gas flow rate being the subsequent influential factors. The microstructures were analyzed using optical microscopy, revealing that the microstructure of the wall region comprised columnar and equiaxed grains. This study has considerable potential for manufacturing aluminum items utilizing a CMT-based arc welding technique.

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In this paper, the results of microstructural analyses, including optical microscopy, scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction analysis, of the Ni-based self-fluxing alloys NiCrBSi, NiCrBSi–WC, and NiBSi–WC deposited on a previously quenched and tempered (QT) steel substrate 42CrMo4 by flame spraying with simultaneous fusing and plasma transferred arc (PTA) process are presented. The aforementioned microstructural analysis was carried out to determine the microstructural characteristics of the investigated coatings, especially at the coating/substrate interface, and the influences of the spraying and welding technology on the steel substrate. The analysis revealed a change in the microstructure of the coating/substrate interface. Specifically, the diffusion characteristics of certain chemical elements (carbon and iron) from the coating to the substrate and from the substrate to the coating were observed. Additionally, the analysis established the existence of new phases within the coating that arose as a result of the aforementioned diffusion and reaction with chemical elements from the coating. The diffusion of chemical elements was most pronounced in the area of the coating/substrate interface, while it decreased away from this area.