Welding in the World最新文献

This paper presents an experimental and numerical investigation of the fatigue crack growth behavior in different regions of metal inert gas (MIG) butt welded joints of 6005-T6 aluminum alloy. A series of experiments were carried out, including the compact tensile specimen crack growth rate, microstructure, and failure fracture analysis, which reveals the crack growth mechanism in different weld regions. A fracture mechanics numerical model considering geometric features and material inhomogeneity was developed, and the crack growth life results were obtained in agreement with the test. The results show that the microstructure and inhomogeneous material properties significantly affect their crack growth behavior and life distribution. The life distribution of different weld regions was quantified based on the Weibull distribution parameters to guide crack growth life assessment.

There is a growing demand in the industrial sector for the use of high-strength structural steels (HSSSs), which can achieve a significant weight reduction in structures. These structural steels are usually produced by quenching and tempering (Q + T) or thermomechanical treatment (TM), and their applications in welded structures pose several challenges for the users. In industrial practice, gas metal arc welding (GMAW) is basically the most commonly used fusion welding process, which has a relatively high heat input. However, at HSSSs, there is a need for low heat input but, at the same time, productive welding processes. High-energy density welding processes, e.g., electron beam welding (EBW), offer a unique opportunity to weld these steels. The widespread use of HSSSs is also hampered by the fact that the benefits of high strength can be exploited primarily under static loading. At the same time, different welded structures made of HSSSs are often subjected to cyclic loading, and possible weld defects and material discontinuities are major risks in this case. During our experiments, GMAW and autogenous EBW processes were applied to make welded joints from S960 Q + T and TM structural steels. The fatigue resistance of the welded joints was characterized by fatigue crack growth (FCG) tests, considering the increased crack sensitivity of HSSSs. A statistical approach was followed both in the design of the experiments and in the evaluation of their results. Based on the test results fatigue crack propagation design curves were determined for the investigated GMAW and EBW welded joints. The design curves were compared with each other, with design curves of lower strength material (S690QL) and with the recommended fatigue crack growth laws of BS 7910.

Controlling the growth of brittle intermetallic compounds (IMCs) and interfacial structure is crucial to obtaining desirable mechanical properties of the high-temperature brazing joints of titanium-zirconium-molybdenum (TZM) alloy. The effect of B addition on the mechanical properties of the joints and the microstructures in the brazing seam was investigated. The results show that the addition of 1%B enhances significantly the wettability of Mo-45Ni filler metal. The strength of the brazed joint with Mo-45Ni-1B filler metal is 30% higher than that of the joint with Mo-45Ni filler metal. The microstructure of the brazed joint with Mo-45Ni filler metal consisted of TZM/NiMo/eutectic (Mo + NiMo) + NiMo /NiMo/TZM. B addition led to the formation of Mo₂B intermetallic compounds at the interface between NiMo layer and TZM alloy during heating and the precipitation of faceted Mo₂B IMCs in the brazing seam during solidification, promoting the brittle-to-ductile fracture transition. This study provides a deep insight into the HT brazing of TZM alloy.

The final microstructure and mechanical properties of a welded joint are determined by the evolution and crystallization process of grain structure during welding. This study aims to improve the mechanical properties of the weak weld root zone in a G20Mn5 cast steel—Q345 low-alloy steel circular butt weld. The microstructure changes of the weld during the welding process were investigated using metallographic testing combined with Monte Carlo simulation, and suggestions for optimizing the welding process were provided. Firstly, the microstructural assessment of welded cast steel joints was conducted using metallographic and hardness tests. It was clarified that the heat-affected zone at the weld root on the Q345 steel side was the weak zone. Additionally, the relationship between grain size and mechanical properties of the joints was established. A Monte Carlo model was then used to simulate the dynamic recrystallization process and determine the final distribution of grain structure in the heat-affected zone. Finally, the calibrated model was utilized to analyze the impact of different welding processes on grain structure and mechanical properties. The findings indicate that employing a three-pass welding process, incorporating a V-shaped groove on the cast steel side, and dispersing the welding start and stop positions can effectively inhibit grain growth in the heat-affected zone, which provides valuable insights for optimizing the welding process of cast steel welded joints.

The U20Mn bainitic rail steel rods with a diameter of 15mm were joined by continuous drive friction welding (CDFW) below the A₁ temperature. The microstructure characteristics of the welded joints without post weld heat treatment (PWHT) were investigated by metallographic observation, scanning electron microscope investigation, and electron backscattered diffraction analysis. Their mechanical properties were evaluated through hardness, tensile, and impact tests. The results show that the welded joints are well-formed without metallurgical defects. They manifest a dense martensitic-bainitic composite phase structure with good mechanical properties attributed to fine-grain and second-phase strengthening effects. The maximum impact energy is 29.2J, with peak hardness increasing to about 124% compared to the base material (BM). Tensile strength reaches 1267±15.1 MPa (102% of BM), and elongation reaches 13.8±0.2% (97% of BM), realizing quasi-equal strength and toughness matching with the BM. These findings provide a basis for the realization of friction welding for bainitic steel rails and the future development of novel rail welding techniques and equipment.

The aim of this study was to investigate the influence of the discharge parameters on the initial spatial instability of arcs after their initiation by the non-contact method in single-pulse electrode-negative gas tungsten arc welding. The investigated parameters were the P_peak peak arc pressures, the T durations for achieving the peak arc pressure, and the P_final arc pressures at the end of current pulses. It was found that increasing the current amplitudes from 50 to 200 A enhanced mean both the P_peak values (from 0.25 to 4.00 kPa) and the P_final levels (from 0.16 to 1.72 kPa). Enhancing the electrode diameters from 1.0 to 2.4 mm increased these experimental output parameters from 1.85 to 1.99 kPa and from 0.57 to 1.23 kPa, respectively, while they were decreased from 2.32 to 1.47 kPa and from 1.19 to 0.62 kPa after changing the sharpening angle of their tips from 30° to 90°. The period of the spatial instability of arc discharges was shortened from 14.4 to 5.8 ms by increasing the current amplitudes from 50 to 200 A. However, enhancing the electrode diameters from 1.0 to 2.4 mm increased its duration from 9.2 to 12.0 ms. It was also prolonged from 6.2 to 16.8 ms after changing the sharpening angle of the electrode tips from 30° up to 90°. The shortest duration of the arc stabilization period of 5 ms was observed when using the WL15 non-consumable electrode, while it was the longest (35 ms) for the WP one.

The present study investigated the effect of bonding temperature on the dissimilar transient liquid phase (TLP)–bonded IN-625/Ti-6Al-4V dissimilar joints using a thin foil of pure copper as the interlayer. The samples were bonded in a vacuum chamber at 900, 930, and 960 °C for 60 min. The results indicated the occurrence of different intermetallic compounds such as Ti₂Cu, TiCu₂, TiCu, NiTi, and Ni₃Ti at different bonding temperatures, and it was concluded that in all the samples, isothermal solidification was accomplished. Maximum shear strength of 278 MPa was achieved at 930 °C. At lower bonding temperatures, the presence of porosities and cracks decreases the shear strength. At higher temperatures, a high-volume percentage of intermetallic compounds embrittled the specimen and reduced its shear strength. The results of scanning electron microscopy of the fracture surfaces revealed the formation of extensive cleavage fracture and river-like patterns in all samples, indicating a brittle failure mode.

Additive manufacturing (AM) has gained considerable interest due to its ability to produce lightweight parts with hierarchical microstructures. However, the current constraints on the build chamber size in powder-bed fusion type AM processes limit its industrial application. A hybrid welded joint, consisting of an AM-processed and a conventionally manufactured part, can be employed to produce larger components. Due to the varying processing conditions, these hybrid welded joints contain a wide range of microstructural heterogeneities, which influences the mechanical properties of the joint. Using a numerical model to predict the mechanical behavior of welded joints by considering the microstructural variations is essential for the safe and reliable implementation of hybrid welded joints. This study aims to predict the local tensile behavior of each region of a hybrid friction-stir welded joint of AlSi10Mg produced by laser-based powder bed fusion and casting using a microstructure-sensitive model as well as the global tensile behavior by considering the properties of each region using a joint macroscopic model. The results from this modeling approach agree well with the experimental results. Therefore, this method can predict the mechanical behavior of hybrid welded joints and can establish the structure–property relationship in each weld region.

To identify the microstructural factors effecting the electro gas welding (EGW) weld metal properties, this study investigated the influence of different prototype welding consumables and shielding gases on the microstructural composition and mechanical-technological properties. The aim was to adjust the weld metal properties as a trade-off between strength, ductility, and impact toughness to fulfill typical weld metal material specifications in cruise vessel shipbuilding under consideration of the manufacturing conditions at European shipyards. The microstructure is analyzed by quantitative metallography of the ferritic matrix, martensite-retained austenite (M/A) constituents, and non-metallic inclusions (NMI). The influence of the Ni content, the deoxidation concept by variation of Si and Ti contents, and different shielding gas activity by variation of the Ar proportions is discussed. The interaction of ferritic matrix with high acicular ferrite content of about 70 ± 10%, the existence of larger grain boundary ferrite formations, and the M/A morphology plus distribution are considered as the determining factors for the material properties.

The development of thermomechanically controlled processed (TMCP) high-strength steel (HSS) has significantly contributed to designing and developing the intricate structural components. It has broader applications in the cranes and lifting process industry (base frame, crane jibs, and crane columns), trailers, agricultural and forestry machinery, earth-moving equipment, etc. However, the development of new-grade steels with higher tensile strength led to higher requirements for welded joints, and the associated weldability issues have inspired detailed studies on electron beam welding (EBW) with different beam oscillations. Beam oscillation application with EBW processes improves the welding efficiency, weld quality, weld geometry, keyhole, etc., affecting the welded joints mechanical and microstructural properties. Thus, the present study investigates the impact and comparison of various beam oscillations on the microstructural and mechanical properties of EB-welded S1100M steel. The influence of welding parameters on the microstructure of welded joints was analyzed using a scanning electron microscope (SEM) and electron backscattered diffraction (EBSD). The analysis focused on evaluation of grain sizes, morphologies, distributions, and crystallographic orientations of different phase constituents in fusion zone (FZ) and heat-affected zone (HAZ). The mechanical properties were analyzed using hardness, tensile, and Charpy V-notch impact tests. The texture in the FZ is typically random, while the HAZ typically exhibits a strong rolling texture. In general, the cooling rate in EBW is very fast, possibly resulting in a fine-grained structure and reduced formation of coarse second-phase particles in the weld zone. The elliptical beam oscillation showed the highest hardness in HAZ 450 HV10. Elliptical beam oscillation slightly improves the welded joint’s tensile strength, and the impact test showed mixed fracture behavior.