Welding in the World最新文献

Beryllium-aluminum (BeAl) alloys are widely used in the aerospace industry for their low density, high stiffness, and excellent thermal stability. However, the significant physical and metallurgical differences between Be and Al render conventional fusion welding methods ineffective for achieving high-quality joints. This study applied both conventional FSW and heat-assisted FSW to weld as-cast BeAl alloys. Comparative analysis reveals that the heat-assisted FSW process, which involves preheating both the base material and the backing plate, significantly enhances the plastic flowability of the material during welding and effectively prevents the formation of tunnel defects and surface cracks. The elevated temperature during welding promotes dynamic recrystallization, resulting in notable grain refinement in the weld nugget and an increase in microhardness to approximately 330 HV, about 2.3 times that of the base material. However, local microstructural inhomogeneity and microcracks within the Be particles still reduce the tensile strength of the joint to some extent. This study demonstrates the promising potential of heat-assisted FSW for addressing the welding challenges of BeAl alloys and provides valuable insights for future process optimization.

This study investigates the influence of martensitic start temperature on residual stress and distortion. A double-sided fully welded T-joint was fabricated by welding a high-alloy base material (1.4318) with two different filler wire combinations (G19 9, G4Si1). The temperature distribution and distortion were measured during the welding process using thermocouples and displacement transducers. The thermo-metallurgical-mechanical effect was considered when computing a numerical simulation model for a T-joint geometry. A phase transformation model was incorporated to predict martensite formation during welding, with the martensite start temperature varied as a parameter. Further, the mechanical model was developed by integrating the thermal strains, phase strains, and mechanical strains. Results from numerical simulations and experimental measurements are compared and analyzed to assess the impact of martensite start temperature on residual stresses and distortion. From the findings, it was found that, at a reduced martensitic start temperature, there was a significant reduction in residual stresses and distortion.

Twin wire arc additive manufacturing (T-WAAM) offers the capability to fabricate functionally graded material (FGM) tailoring in a variation of compositional elements and the related properties. In this context, two feedstocks, SS 316L (SS) and ER-70S6 (LCS), were used to fabricate a FGM structure using a T-WAAM setup integrated with gas-tungsten-arc-welding (GTAW) power source. The variation of elemental compositions of the fabricated structure was obtained by controlling the feed rate of the two different feedstock materials. The two extreme ends of the fabricated wall were made of pure SS and LCS, whereas the intermediate zones were fabricated by mixing 75% SS+25% LCS, 50% SS+50% LCS, and 25% SS+75% LCS. The intermixed zones exhibited complex microstructural, mechanical, and tribological phenomena. It showed duplex phase formation, i.e., austenite (FCC) and ferrite (BCC), where the microstructure varied from austenite+martensite to bainite+pearlite to polygonal ferrite. The average hardness and wear behaviour of these zones is better than that of pure SS and LCS. Maximum hardness value of 398 HV is observed at 50–50 SS and LCS mixing zone. This SS-LCS combination shows a remarkable surface durability and excellent wear resistance. The coefficient of friction, specific wear rate, and wear depth in this zone are 0.128, 0.01 × 10³ mm³/Nm and 2.687 µm, respectively. This research offers a feasible and flexible approach to fabricating FGM, tailored design, and renovation of components, where hardness and wear interaction are more prominent.

Friction stir welding (FSW) technology was employed for joining the selective laser melted (SLM) AlSi7Mg specimens, and the microstructures and mechanical properties of welded joints were elucidated. During FSW, the material underwent severe thermo-mechanical coupling effect, resulting in features of the welded zone completely distinct from the SLM base material: pore size and number were significantly reduced, the eutectic Si-rich phase transformed from a continuous network into discrete blocky particles (2–8 μm), and grain coarsening occurred in the heat-affected zone. Notably, the heat-affected zone became a weak position for fracture failure. Based on comprehensive experimental investigations and microstructural analyses, FSW was found to (i) reduce porosity in SLM AlSi7Mg welds by 83.6% and (ii) achieve 81.5% of SLM base material’s tensile strength alongside enhanced microhardness and density—outperforming traditional fusion welds such as argon arc welding. These results confirm the significant potential of FSW for joining SLM aluminum alloy components.

Graphical abstract

The age-hardenable aluminum alloy AW6082 combines high strength with good formability, but its weldability is limited due to precipitation dissolution and softening, as well as a high susceptibility to hot cracking. Conventional approaches often use dissimilar filler materials from the 4000 and 5000 series, which can result in reduced strength and limited hot cracking resistance. These challenges are addressed by the heat-treatable filler material AlMg0.7SiTiB. The alloyed TiB nanoparticles are expected to minimize the grain size, reduce the tendency to hot cracking, and improve strength values. Therefore, the aim of the investigations is to validate the welding of the aluminum wrought (AW) alloy AW6082 using the novel filler material AlMg0.7SiTiB in comparison to the standard filler alloy (AlSi5). Based on a process development, test specimens were manufactured in accordance with DIN EN ISO 15614-2:2005. Microstructural and mechanical properties were assessed through optical microscopy (OM), energy dispersive spectroscopy (EDS), tensile and 3-point bending test, and hardness testing. The evaluation was carried out for each filler material for both the as-welded and the artificially aged condition. Additionally, hot cracking resistance was evaluated using the self-restraint Houldcroft-Test. The results show a significant grain refinement of approximately 65% on average, along with a reduced susceptibility to hot cracking compared to the standard filler material. The evaluation of the mechanical-technological properties showed comparable values between the two filler materials. In summary, welding AW6082 with the TiB₂-modified filler material shows improved grain refinement and hot cracking resistance, indicating enhanced weldability compared to the standard filler material.

The influence of a post-weld heat treatment (PWHT) on the microstructure and mechanical behaviour of a 2.25Cr1Mo0.25 V weld was investigated. The study focused on three distinct regions: the base metal, the heat-affected zone (HAZ), and the weld metal. Due to the limitations in conducting standard mechanical tests on all the weld regions, particularly the HAZ, Small Punch Tests (SPT) were performed across all regions, while standard mechanical tests were conducted only when sufficient material was available. Microstructural characterisation involved microstructure identification, hardness profiling, X-ray diffraction measurements, and fractographic examination. The results demonstrate that the SPT method effectively characterises the mechanical behaviour of all weld regions. Furthermore, PWHT significantly enhances microstructural homogeneity and improves the mechanical performance of both the HAZ and weld metal. The treatment leads to relaxation of residual stresses and microstructural refinement, thereby increasing the resistance of welded components to mechanical failure.

The powder-feed underwater laser metal deposition (ULMD) of Ti6Al4V alloy was carried out in a local dry cavity generated by a special drainage nozzle, and the influence of laser power and scanning speed on the deposition appearance and geometry characteristics of a single track was investigated. The results show that as the laser power increases, the aspect ratio and dilution rate increase. With the scanning speed increasing, the aspect ratio increases, but the dilution rate and the deposition angle decrease. A high-quality ULMD single track with a uniform appearance and no metallurgical defects is obtained at the laser power of 2.2 kW and scanning speed of 14 mm/s. In addition, a thin wall part was fabricated using the optimal process parameters. The microstructure of the deposited metal is composed of acicular martensitic α′ phase, and the sizes of the martensitic in the top region are finer than those of the martensitic in the middle region and bottom region.

Internal defects in friction stir welded (FSW) joints can undermine weld integrity, while the release of ultrafine particulates (UFPs) during welding presents significant occupational health concerns. This study evaluates the effectiveness of induction preheating-assisted FSW for marine-grade AA6082 aluminium alloy by comparing preheated (250 °C) and non-preheated conditions, using identical welding parameters (58 mm/min traverse speed; tool rotation speeds of 636, 900, and 1224 rpm). UFP emissions were measured with a scanning mobility particle sizer (SMPS), while internal defects were assessed via phased array ultrasonic non-destructive testing. Additionally, the study also examines the microstructural evolution of the joints using field-emission scanning electron microscopy (FE-SEM) and optical microscopy, alongside comprehensive assessments of mechanical properties through tensile and microhardness testing. The results showed that induction preheating reduced UFP emissions by 41% to 59% across all tool rotation speeds, highlighting its potential to lower health risks for workers. Internal weld defects were successfully mitigated in joints produced with induction preheating. Microstructural analysis showed the formation of finer grains (~ 4–6 μm) in the stir zone of preheated joints. Mechanically, the highest transverse tensile strength of 161.94 MPa, representing 97.06% of the work material’s strength, was achieved in preheated joints, along with notable improvements in hardness compared to conventional FSW joints. These findings demonstrate that induction preheating-assisted FSW offers substantial benefits for both weld quality and environmental safety, providing a promising approach for the fabrication of high-performance aluminium joints.

In this study, original welds of 12 mm thick S355J2G4 steel used for railway vehicles were repaired through Metal Active Gas (MAG) welding to determine influence of repair welding numbers on microstructure and mechanical properties of welded joints. The results indicated that the weld macrostructure did not significantly change with increasing repair welding numbers, the phase composition of the microstructure in the heat affected zone were the same while the grain size slightly increased. The microhardness values on upper weld surface between the repaired and original weld fusion lines gradually reduced as repair welding number increased. Both the average yield and tensile strengths reduced with increasing repair welding numbers, while the average elongations remained nearly constant. The tensile specimens all fractured in base metal. There were no visible cracks appeared on surface of the bending test specimen. The average impact energy and median fatigue strength both presented gradual downward trends as repair welding number increased. The fatigue specimens of the 0R (original), 1R (repaired once), and 2R (repaired twice) welded joints all fractured in weld metal, while the fatigue specimens of the 3R (repaired thrice) welded joints fractured near fusion line, this change was primarily due to the serious joint softening as repair welding number increased. The above results indicated that the microstructure and mechanical properties of the repair-welded joints still could meet the application requirements even the repair welding number reached up to three, which could provide practical guidance for developing repair strategies in industrial applications.

Hydrogen is the energy carrier for a sustainable future without fossil fuels. As this requires a reliable transportation infrastructure, the conversion of existing natural gas (NG) grids is an essential part of the worldwide individual national hydrogen strategies, in addition to newly erected pipelines. In view of the known effect of hydrogen embrittlement, the compatibility of the materials already in use (typically low-alloy steels in a wide range of strengths and thicknesses) must be investigated. Initial comprehensive studies on the hydrogen compatibility of pipeline materials indicate that these materials can be used to a certain extent. Nevertheless, the material compatibility for hydrogen service is currently of great importance. However, pipelines require frequent maintenance and repair work. In some cases, it is necessary to carry out welding work on pipelines while they are under pressure, e.g., the well-known tapping of NG grids. This in-service welding brings additional challenges for hydrogen operations in terms of additional hydrogen absorption during welding and material compatibility. The challenge can be roughly divided into two parts: (1) the possible austenitization of the inner piping material exposed to hydrogen, which can lead to additional hydrogen absorption, and (2) the welding itself causes an increased temperature range. Both lead to a significantly increased hydrogen solubility in the respective materials compared to room temperature. In that connection, the knowledge on hot tapping on hydrogen pipelines is rare so far due to the missing service experiences. Fundamental experimental investigations are required to investigate the possible transferability of the state-of-the-art concepts from NG to hydrogen pipeline grids. This is necessary to ensure that no critical material degradation occurs due to the potentially increased hydrogen uptake. For this reason, the paper introduces the state of the art in pipeline hot tapping, encompassing current research projects and their individual solution strategies for the problems that may arise for future hydrogen service. Methods of material testing, their limitations, and possible solutions will be presented and discussed.