Welding in the World最新文献

The development of suitable welding processes is required to meet the ever-increasing demands on joining processes, particularly for lightweight construction and increasing environmental awareness. Friction stir welding (FSW) represents a promising alternative to conventional fusion welding processes, particularly for the joining of low-melting-point materials such as aluminium and magnesium alloys, which present a number of challenges, including the formation of pores and the occurrence of hot cracks. The central element of the process is the friction stir welding tool, which consists of a shoulder and a probe. The rotation and the simultaneous application of pressure during the joining process create a friction-based heat input through the tool. The excellent mechanical properties resulting from dynamic recrystallisation during the welding process are a major advantage of the process. As a result, strengths comparable to those of the base material can be achieved. However, FSW is subject to process-specific challenges, including high process forces, which result in the fabrication of complex and robust devices. Additionally, high dynamic loads on the friction stir welding tools must be considered. In many cases, the design of friction stir welding tools is based on empirical data. However, these empirical values are machine-, component- and material-specific, which often results in under- or overmatching of friction stir welding tools. Sudden probe failure, component scrap, and low process reliability are the direct consequences of undermatching. Overmatching results in enlarged tools with limited accessibility, high heat input, and high process forces, leading to component deformation. The aim of this study is to determine the load on the probe by separating the forces and torque of the shoulder and the probe in order to be able to make statements about the load acting on the probe and the resulting stress state. The knowledge of the stress state can be employed to design friction stir welding tools, both statically and dynamically, for a specific welding task. A strategy was devised to distribute the load exerted on the shoulder and probe. To this end, the length of the probe was gradually reduced between the welding tests. The investigations were carried out with a force-controlled robotized welding setup in which AA 6060 T66 sheets with a thickness of 5 mm were welded. A Kistler multicomponent dynamometer type 9139AA allows to measure the Cartesian forces to be recorded in the x-, y-, and z-directions with a sampling rate of 80 kHz. The weld seam properties were determined by visual and metallographic inspections as well as tensile and bending tests in accordance with DIN EN ISO 25239–5.

An effect of distances between the flyer plate and the explosive (d = 30, 40, 50, and 60 mm) on the welded interfaces of tin (Sn)–aluminum (Al) plates is discussed. Sn (flyer) and Al (base) plates were welded by adopting an underwater explosive detonation system. The interfaces were characterized using a metallurgical microscope and scanning electron microscope (SEM). As the distance (d) was increased, a change in the wavy parameters (amplitude and wavelength) of the interfaces was observed. The experimental results for welded Sn/Al plates were investigated based on the welding window (WW) constructed using numerical software (AUTODYN-2D). Based on the data, window parameters (the collision point velocities, V_c, and the collision angles,β) for welded Sn and Al plates were found to be in agreement with numerical data, and plates welded at a water distance of 60 mm exhibited good quality of welding.

In this research, dissimilar friction stir welding of AZ31 magnesium alloy and St37 steel sheets was performed to investigate the effect of Zn, Cu, and brass interlayers on the microstructure and mechanical properties of the joint. After conducting microstructural and mechanical evaluations, welding with a Zn interlayer exhibited the best strength and bonding efficiency, achieving 161 MPa and 60%, respectively. Since mechanical and metallurgical bonding at the interface plays a complementary role in improving welding properties, the presence of the Zn interlayer, by deoxidizing and enhancing reactions at the interface, increases the thickness of the Fe-Al-based intermetallic compound layer from 110 nm in welding without an interlayer to 300 nm. This results in improved mechanical properties of the welds. Examination of the fracture surfaces from the tensile test samples shows that all samples exhibit brittle fracture, except for the sample with the Zn interlayer, which displays a combination of ductile and brittle fracture.

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.