Papers by Keyword: Welding

Abstract: Optimizing the performance and reliability of welding techniques for dissimilar aluminum (Al) to titanium (Ti) is a promising way to establish new applications in aerospace industry. Due to structural weight reduction, lightweight materials can help to minimize fuel consumption and save emissions. Solid-state welding technologies allow short joining cycles and metallurgical changes, residual stresses and severe intermetallic compound formation can be reduced by limited thermal exposure. Besides temperature and plastic deformation, intimate contact plays an important role for diffusion. In this work, AlMgSi alloys with systematic variations of Mg and Si alloying elements, were welded to Ti6Al4V (Ti64) by refill Friction Stir Spot Welding. The focus lays on the effect of Ti64 sheet surface roughness, varied by different surface preparations. Additionally, the influence of the plunge depth, the distance between the tool and the Ti64 sheet surface is analyzed. It was found that a reduced tool to interface spacing has a beneficial influence on joint integrity. Grinding trenches allowed better bonding compared to the pit-like surface structure generated by sandblasting, which led to an increase in mechanical lap-shear properties. Knurling the grinded surfaces resulted in high standard deviation, as most likely not the whole interface area was bonded. However, the partially outstanding properties showed that a beneficial effect can be expected due to mechanical interlocking mechanisms, when sufficient diffusion is ensured.

Abstract: High-performance thermoplastic polymers paved the way for new fast manufacturing pro-cesses, including welding. In order to obtain optimal bonding of the substrates, an adhesion step isrequired, governed by two main phenomena : intimate contact and healing. While healing has beenvastly explored, theorized and starts to be understood, prediction and characterization of the degree ofintimate contact is still a challenge. After a review of squeeze flow models for intimate contact, alongwith the expressions of the analytical solutions for a Newtonian and a shear-thinning fluid modeled bypower law, a finite element model is presented in order to observe the influence of asperity geometry,fluid behavior, and other assumptions on the evolution of the degree of intimate contact.

Abstract: One of the main problems with the use of steels for elevated temperatures is their limited weldability. This is mainly due to the fact that these materials may contain in their chemical composition. Due to the susceptibility to cold cracking, PWHT is necessary, especially in high-stiffness welded structures. In addition, depending on the condition after heat treatment or in the absence of heat treatment, precipitates may appear in the microstructure of the steel, affecting its mechanical properties. It is important in this case to ensure the high quality of welded joints, which means that the manufacturer has to demonstrate a very high technical culture. Currently, thin-walled pipe butt joints are welded manually using a tungsten electrode with solid wire material (TIG method). One of the solutions that can significantly speed up the welding process of components for work at elevated temperatures is the use of an electron beam welding. In addition, the ability to make welded joints without the use of filler material and to achieve narrow heat-affected zones may find application in the welding of modern materials used in the power industry. This paper presents the welding experience of materials assigned for the power industry (TEMPALOY AA1 and T92) by use of electron beam. In this article authors present the results of tests gained during first steps of welding welded joints. The article also includes preliminary results on the service life of the fabricated joints.

Abstract: Non-metallic inclusions in weld metals often have a role inducing the formation of acicular ferrite, which is known to improve the toughness and other properties of the weld metal. The ability of the inclusions to promote the acicular ferrite formation depends on various factors such as chemical composition, morphology and size of the inclusions. In multipass welding, additional thermal cycles affect the inclusions in the pre-existing weld passes, potentially causing compositional and morphological changes in the inclusions. These changes may influence the inclusions’ ability to promote the formation of acicular ferrite. In the current study, the thermal cycles of multipass welding were produced on a single pass weld by physical simulation. Coarse-grained heat-affected zones (CGHAZ-W) in weld metal were simulated using three different cooling times from 800 °C to 500 °C (t_8/5). Inclusions in the heat-affected zones of the weld were analyzed using field emission scanning electron microscope equipped with energy dispersive spectroscope (FESEM-EDS), after which they were classified according to their chemical composition. The results showed that the inclusion content in the weld metal was affected by the thermal cycles. In the CGHAZ-W simulation the number of Mn-bearing inclusions increased compared to the unaffected single-pass weld metal. Increasing cooling time was observed to increase the area fraction of MnS in CGHAZ-W. The increase of these inclusions was expected to affect the microstructure by increasing the acicular ferrite fraction.

Abstract: This study investigates the effects of different welding and heat treatment sequences on the mechanical and microstructural properties of laser powder bed fusion (PBF-LB) fabricated Inconel 718. Three conditions were examined: laser welding of as-built material (LW-built), welding after heat treatment (HT-LW), and welding followed by post-weld heat treatment (LW-HT). Tensile testing, microscopy, fractography, and finite element simulations were used to evaluate performance. The LW-HT condition exhibited the highest strength (UTS ~1430 MPa) and the most uniform stress distribution, attributed to the re-precipitation of laves/δ phases during post-weld aging. In contrast, the HT-LW condition showed localized softening and early failure due to precipitate dissolution in the fusion zone. Fracture surface analysis confirmed enhanced ductility in LW-built and refined microstructural features in LW-HT. These findings demonstrate that post-weld heat treatment (LW-HT) is the most effective route for optimizing strength and structural stability in welded PBF-LB Inconel 718, with some trade-off in ductility.

Abstract: Nowadays, the application of hydrogen as an energy carrier has become important as a result of decreasing availability of oil and gas fields as well as increasing demands on sustainable energy carriers. Providing an adequate hydrogen transportation infrastructure is a key step. During transportation, many different materials can interact with hydrogen, but in order to transport high quantities of hydrogen at higher pressures, the use of steels is preferred. However, hydrogen has many negative effects on steel, thus extensive research needs to be performed before hydrogen can be transported safely. Solubility of hydrogen in steel depends on the temperature, pressure, and the crystal structure of steel, so welding is also an important subject. Since most of the steel structures are welded, welded joints should also be examined for exposure to hydrogen. In the case of welding, a number of factors can decrease the hydrogen resistance of the welded joint and thus increase the risk of degradation by hydrogen. In this research work, hydrogen damage, and hydrogen traps will be reviewed. Possible ways to reduce the diffusible hydrogen content will also be summarized, as well as aspects of the filler material and shielding gas selection. In addition, an overview will be provided on welding technology aspects of carbon steels related to hydrogen, such as heat input, preheating, t_8/5 cooling time, heat-affected zone size, number of weld runs, effect of discontinuities, etc. In general, filler material with the lowest possible diffusible hydrogen content should be used; for electrode coatings and fluxes, special care should be taken to ensure proper baking; for wire electrodes, care should be taken to ensure surface cleanliness; in case of shielding gas the use of the purest possible shielding gas is recommended, and the use of shielding gas containing hydrogen is prohibited; and strict attention must also be paid to the purity of the base material. In addition, other important considerations for welding technology development will be outlined for carbon steels. Such as pipelines, where the most important technological aspects of welding will also be discussed, e.g. low heat input, multi-pass weld design, etc.

Abstract: Magnesium alloys are used more and more in automotive industry due to specific strength (ratio between tensile strength and density) of 158kNm/kg versus 46kNm/kg in case of structural steel [1]. Another advantage of magnesium alloys is machinability, aspect and automated caste/extrusion. With this last procedure is possible to achieve high rate of productivity for complicate pieces, needed in automotive sector. Technologically, a big issue of magnesium alloy is its reactivity in contact with carbon steel, accentuated by high temperature and pressure from extrusion chambers.

Abstract: Titanium is widely used in aerospace and medical industries for its high strength-to-weight ratio and corrosion resistance, while Inconel 718 is favored in aerospace and power generation for its exceptional mechanical strength and oxidation resistance at high temperatures. It’s challenging to directly combine the Inconel 718 and the titanium, so the interlayer of vanadium is used which causes the strengthening of the bond by the formation of inter-metallics (TiaNib, NixVy). In this study, the RVE model was developed in order to examine the mechanical properties (i.e. Modulus, Poisson ratio) of the inter-metallics, by examining their microstructures. Furthermore, nanoindentation techniques are employed across different zones of the weldment to determine the modulus and hardness values. At the vanadium-Inconel interface, hardness and modulus values were observed to range from 2 to 8.5GPa and 130 to 205GPa respectively. The maximum error in hardness between the experimental and simulation was 3.75%. The pile up behavior was also examined in the simulation setup to determine the amount of plastic zone in the indent.

Abstract: The study investigates the kinetics of plastic deformation propagation in a welded joint of 10G2FB steel after submerged arc welding. A metallographic analysis of the microstructure of the weld seam, fusion zone, and heat-affected zone was performed. Tensile testing and electron microscopy studies were conducted to determine the mechanisms of plastic deformation and crack initiation. It was found that the fusion zone is the most vulnerable to the formation of deformation defects, which can affect the durability of the structure. Recommendations for optimizing welding parameters to improve the mechanical properties of welded joints are proposed.

Abstract: Welding in general is a production process of joining metals that is carried out in a hot state. One of the welding developments in additive manufacturing is hardfacing. Hardfacing is one of the efforts that can be made to improve the mechanical properties and wear resistance of materials that allow them to be used in all conditions. Some of the problems found in ship companies, especially on ship hulls, are a decrease in mechanical properties and wear due to external factors such as damage to the hull due to waves. This research was conducted to determine the amount of mechanical properties produced in welding using the hardfacing process. In this study, the hardfacing method is used as the addition of weld metal to ASTM A36 plates using the SMAW welding method with angle variations. Furthermore, it will be analyzed by tensile testing to determine the tensile strength of the test specimen. In the process, material with a thickness of 5 mm is then welded by the SMAW method to the hardfacing process steel plate using a 3.2 mm E7018 electrode with the addition of 5 mm weld metal. The results obtained from tensile testing with high mechanical properties are found at the highest angle variation with good tensile test results and continue to increase from the lowest angle variation. This research can produce materials that can be used in companies as new materials with high mechanical properties.