Welding in the World最新文献

Haynes 230 material is an important high-temperature alloy used in many significant applications. Electron beam welding (EBW) process is necessary for Haynes 230 to realize some complex structures. In this study, by combining three-dimensional finite element simulation with different experimental methods, the thermal behavior, residual stress, microstructure, and mechanical properties of Haynes 230 thin-walled weldment made by EBW were comprehensively investigated. The EBW process would induce an uneven temperature distribution in the weldment, which then results in a large amount of tensile residual stress. Sufficient amount of precipitates was generated to provide enough enhancement for the strength. The quality of the weldment was good to provide comparable strength to the base metal. This study could offer important information for the application of EBW welded Haynes 230 material, especially in the thin-walled workpieces that are used in hot-end components of combustion gas turbines.

The present work aimed to study the morphological, microstructural, and mechanical properties of Al sheet-Ti sheet-SS sheet composites produced by explosion welding. Trimetallic composites with sound structure and very good mechanical behaviour were obtained. The mechanical performance of the produced composites makes them very appropriate for applications requiring increased lightness, corrosion resistance, and mechanical properties at high and low temperature. Regarding the weldability of the material trio, the type of the explosive mixture was found to have a strong influence on the results. Better conditions were achieved by using a mixture with a lower detonation velocity, as high detonation velocities are not appropriate for welding low melting temperature flyers, like aluminium alloys. Although IMC-rich zones were formed at the Al-Ti and Ti-SS interfaces of the composites, these regions were encompassed/accommodated by ductile interfacial waves, which allowed to overcome the brittleness of the IMC regions and to achieve composites with an improved performance. An encompassing literature-based study also allowed to infer that, regardless of the material couples being joined by EXW, the matrix of the intermediate regions formed at the weld interface is always richer in the main element of the welded couple with lower melting temperature.

 This paper treats different fatigue (FAT)-scenarios for determining damage-equivalent stress ranges according to two methods for transforming a stress or load spectrum into a damage-equivalent constant amplitude loading, i.e., the Modified Equivalent Stress (MES) and the Required Fatigue Strength (RFS) concepts. The MES method is suggested by the IIW-recommendations for fatigue design and the RFS method is applied especially in the design of vehicle safety components. The resulting MES- and RFS-ranges are similar, but not equal. The MES-method delivers a damage-equivalent stress range that depends on the selected FAT-value, i.e., the position of the Woehler-curve is decisive. In contrast, the RFS-method results in a damage-equivalent fictitious Woehler-line that indicates the lowest necessary strength quality for a given stress spectrum. The allocation of the modified equivalent stress range to the appertaining bi-linear Woehler-curve does not result in the fatigue life caused by the spectrum. Only in the case of a linear Woehler-curve, the fatigue life is directly obtained. In the case of the RFS-application, the fatigue life is by definition equal to the spectrum length. For durability tests, the modified equivalent stress range (at ({L}_{S}) cycles) and the associated FAT-Woehler-curve should not be used. However, the Woehler-curve derived by the RFS-method allows experimental durability proofs for any amplitude-cycle combination along it. Furthermore, the required lowest necessary strength also enables the selection of the most cost-effective manufacturing technique and quality. The RFS-Woehler-curve also results in a FAT-value with a defined probability of failure depending on the required safety factor.

In this paper, the brazing of high-reliability C/C composite-metal joints for high-temperature application was studied. The surface of C/C composites was modified by the Cr metallization process and then brazed to Ni-based superalloy by AgPd braze. Alumina block was used as interlayer, and a zig-zag interfacial structure was constructed at the composites/braze interface. The results show that, after the metallization process, a strong adhesion reaction layer consisting of Cr carbides was coated on the C/C surface which in turn obviously improved the wettability of braze. The molted braze filled completely into the laser-machined holes in the C/C substrate and well-bonded interfaces and a homogeneous Ag(Pd) solution microstructure were obtained in the joint. The strength of the joint with C/C metalized at 1100 ℃ is higher than that of the joint with 1300 ℃. The joints exhibit very high bending strength of up to 82 MPa and shear strength of up to 54 MPa, respectively. The braze spikes increase the connection area and provide a strong pinning effect.

K417G superalloy is widely applied in gas turbine components such as blades, vanes, and nozzles. In this study, wide-gap brazing of K417G superalloy is investigated using BNi-5 filler alloy. The brazing experiment is conducted at 1150 °C for different holding times with the fixed gap of 0.2 mm. For the joints brazed for 15 min, the brazing seam mainly consists of γ/γ’ phase, Ni₂Si and TiC phase. The average tensile strength tested at 950 °C is 401 MPa. As the holding time increased, the excessive element diffusion phenomenon is observed. Hence, Ni₂Si intermetallic phases gradually become embedded in the additive alloy particles. The interfacial evolution and fracture behavior are discussed.

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.