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Activating flux is made up of inorganic material mixed with a volatile medium. The objective of this study is to identify and review the literature in activating flux, and different type of welding techniques. For that purpose, a structured review method is adopted and the Scopus database is used as a primary source for the selection of papers. The papers were identified using the string term of “Activating flux” OR “Activated flux” in the title of papers. And a total of 238 papers were identified for the study. Besides the above few other papers were also reviewed and the materials used, the type of flux used, and the findings of different combinations were highlighted in the form of tables. The findings of the study provide a comprehensive understanding of the different type of welding techniques focusing on TIG welding, and the different combination of flux used and their impact was summarized.

Inconel 718 alloy is widely used in applications that require advanced strength properties especially at high temperature conditions. Combust room walls, exhaust parts, jet tribune blades and gas tribune equipment are the most known using areas. This alloy can be welded with various fusion welding methods, but TIG (Tungsten Inert Gas) welding is preferred since, it provides simply application, mobility and low cost. This study was aimed to clarify that how adjusting the welding parameters and welding automatically can help to achieve promising mechanical properties before heat treatments. The welding experiments were conducted on three different welding current values and attention was paid to provide full penetration for each condition. The results showed that the highest welding current value which did not cause welding defects lead to decrease heat input due to the high transverse speed usage. Moreover, by automatically welding, the heat input was decreased to a minimum level that provided excellent tensile strength and elongation properties. Dendrites turned to cellular from colon. Hazardous zones, such as HAZ and PMZ, narrowed down. The Laves phase ratio and grain size also decreased. Microhardness results confirmed these microstructure observations. The crack observations after tensile tests showed that failures were near HAZ in high-heat input conditions. However, failures were observed in FZ for low-heat input conditions. Additionally, ductile fracture and fracture similar to cleavage mechanisms were observed together due to adjusting the parameters and automatization.

В роботі розглядаються питання отримання мінімальної хвилястості поверхонь, що формуються аддитивним процесом аргонно-дугового зварювання. Відомо, що геометричні параметри валика розплаву, що пошарово формує відтво-рювану заготовку, визначаються як енергетичними, так і кінематичними характеристиками процесу. При цьому викладання валиків відбувається з оптимальним перекриттям, завдяки чому вдається досягти максимальної щільності моделі, однак з одночасним виникненням певної хвилястості, обумовленої термодинамічними явищами у ванні розплаву. Запропонована модель формування валику наплаву, завдяки якій встановлено раціональні умови викладання шарів. Наведено експериментальні дослідження процесу аргонно-дугового відтворення моделей заданої форми, отримано регресійні рівняння для визначення контрольованого параметру хвилястості. Показано, що на параметр хвилястості випливають динамічні явища та хвильові процеси, які розвиваються під дією системи сил під час формування валику наплаву. Покращення якості виробів вбачається в оптимізації способів формування валиків, забезпеченням динамічної сталості руху робочої головки, забезпеченням відповідного перекриття траєкторій руху по шарам викладання на величину 0,5 е, забезпеченням динамічної сталості руху робочої головки, встановленням раціональної довжини дуги, а також підтриманням режиму динамічної сталості горіння дуги Побудовано поверхні відгуків цільових функцій в площинах параметрів впливу, які дозволяються наглядно проілюструвати залежність контрольованих геометричних параметрів шва від окремих параметрів впливу. The paper deals with the issues of obtaining the minimum waviness of surfaces formed by additive processes of TIG welding. It is known that the geometric parameters of the melt bead, which form a reproducible workpiece layer by layer, are determined by both the energy and kinematic characteristics of the process. In this case, the laying of the rollers occurs with optimal overlap, as a result of which it is possible to achieve the maximum density of the model, however, with the simultaneous appearance of a certain waviness due to thermodynamic phenomena in the melt bath. The proposed model of the formation of a bead of melt, the use of which made it possible to establish the rational conditions for laying out the layers. Experimental studies of the process of argon-arc surfacing of models of a given, regression equations for determining the controlled waviness parameter are obtained. It is shown that the waviness parameter is influenced by dynamic phenomena and wave processes that develop under the action of a system of forces during the formation of a melt bead. An improvement in the quality of products is seen in the optimization of the methods of forming the rollers, in ensuring the dynamic stability of the movement of the working head, ensuring the appropriate overlap of the trajectories of movement along the layers of the layout by an amount of 0.5e, establishing a rational arc length, and maintaining the dynamic stability of the arc burning. The response surfaces of the objective functions in the planes of the process parameters are constructed, which provide a clear illus-tration of the dependence of the controlled geometric parameters on the welding modes. В работе рассматриваются вопросы получения минимальной волнистости поверхностей, формируемой аддитивными процессами аргонно-дуговой сварки. Известно, что геометрические параметры валика расплава, которыми послойно формируется воспроизводимая заготовка, определяются как энергетическими, так и кинематическими характеристиками процесса. При этом выкладка валиков происходит с оптимальным перекрытием, в следствие чего удается достичь максимальной плотности модели, однако с одновременным возникновением определенной волнистости, обусловленной термодинамическими явлениями в ванне расплава. Предложенная модель формирования валика расплава, использование которой позволило установить рациональны условия выкладки слоев. Приведены экспериментальные исследования процесса аргонно-дуговой наплавки моделей заданной формы, получены регрессионные уравнения для определения контролируемого параметра волнистости. Показано, что на параметр волнистости влияют динамические явления и волновые процессы, которые развиваются под действием системы сил при формировании валика расплава. Улучшение качества изделий видится в оптимизации способов формирования валиков, в обеспечении динамической устойчивости движения рабочей головки, обеспечением соответствующего перекрытия траекторий движения по слоям выкладки на величину 0,5е, установлением рациональной длины дуги, а также поддержанием режима динамической устойчивости горения дуги. Построено поверхности отклика целевых функций в плоскостях параметров процесса, которые дают наглядную иллюстрацию зависимости контролируемых геометрических параметров от режимов сварки.

The titanium (Ti) and its alloys are taken into interest for commercial purpose due to its low density, high yield strength and high corrosion resistance properties. The present work deals with microstructural observation and mechanical property analysis of tungsten inert gas (TIG) welded Ti-6Al-4V alloys joints. For the purpose, two different set of plates were welded at same current and voltage, i.e., 190 A and 24 V, by TIG welding technique. A critical analysis into microstructure and mechanical properties like tensile strength and hardness of the welded Ti-6Al-4V plates was carried out in this work. It was found that both the plates showed different behavior during tension test. Plate 1 possessed 464.54 MPa of tensile stress and it had broken at the welded joint. Plate 2 was unaffected at welded zone but was broken at the base metal zone. The second plate consisted 501.83 MPa tensile strength. According to hardness test, both the welded plates possessed the highest hardness at the welded zone. However, plate 2 showed approximately 10% higher hardness than that of plate 2. A proper inter-relationship was observed between mechanical behavior and microstructural appearance. The microscopic view of the welded joints revealed the presence of α, β and martensitic-α phases.

Aluminium alloys are widely used in the fields of electric module packaging, electronic technology, automotive body structure, wind and solar energy management, due to the advantages of high specific strength, high processability, predominantly anti-erosion, increased conductivity, eco-friendly nature and recoverability. The objective of the study is to review the previous papers on aluminium usages, application, and workability parameters. The methodology adopted for the study is to use the structure literature review technique, and the time period selected for the study is 2008–2019 from the Scopus database. The findings of the study concluded that there are various types of aluminium alloys has been used by the previous researchers, and only 6061 is least explored aluminium alloy among all of them. The future scope of the study is to investigate using distinct activating fluxes for raising penetration & to understand consequences on mechanical components & rust behaviour of TIG-welded aluminium metal welds.

The effect of sensitization on the intergranular corrosion (IGC) of TIG welded AlMg6Mn was investigated by means of scanning electron microscopy (SEM) and corrosion NAMLT tests. The as-received hot rolled AlMg6Mn alloy plates with a thickness of 8 mm were welded by TIG welding with S-AlMg5 as a filler material. Specimens were sensitized at 100°C for 7 days. It was found that welded specimens are sensitive to IGC. The. mass loss in NAML test was 106.7 mg/cm². The welding increases the susceptibility to IGC, since the mass loss of the base metal at the same test was 70.7 mg/cm². The increase of susceptibility to IGC is attributed to significant continually precipitated Mg-rich phase along the grain boundaries during the sensitization treatment.

International audience; In this paper we address the question of the influence of cathode tip geometry on the physical quantities relevant to Tungsten Inert Gas (TIG) arc welding. Although cathode geometry is known to influence arc-plasmas, a thorough quantification of the Lorentz phenomenon, which is the dominant source of momentum in the fluid flow of TIG arcs has not been strongly investigated. Therefore, we have performed a numerical parametric study at a constant inlet electric current and arc height, for different cathode sizes and shapes (pointed, chamfered and rounded tips), parameterised by the truncation angle and tip radius. To this end, we developed a coupled steady-state magneto-hydrodynamic finite element model in a 2D axi-symmetric configuration, implemented in the Cast ε M toolbox. The paper characterises, quantifies and analyses the influence of tip geometry on TIG arcs and the workpiece. The model reveals that tip size and truncation angle similarly influence the magnitude of the transported quantities of the arcs. We find that the imparted momentum and transferred heat flux to the workpiece vary about 4 and 2-fold between the bluntest and sharpest cathodes, respectively. This signifies the importance of the choice of cathode tips in numerical TIG welding simulations. Agreement between the literature and the current work is analysed and discussed and the importance of coupling the cathode and arc domains is highlighted.

Titanium and titanium alloys can be welded by gas tungsten arc, gas metal arc, plasma arc and electron beam welding processes. Titanium material is a reactive metal and is sensitive to embrittlement by oxygen, nitrogen, and hydrogen gas at elevated temperatures. Consequently, the metal must be protected from atmospheric contamination. This can be provided by shielding the metal with welding grade inert gas. The present work describes the application of TIG arc welding to titanium and investigated the effect of welding parameters like weld current, weld gap and gas flow rate on mechanical properties of welded joints of unalloyed commercially pure titanium Gr-2 materials. Taguchi optimization method has been used to find out optimal setting of parameters for weld joints characterization. The welded joints showed maximum ultimate tensile strength of about 429MPa with percentage elongation of 23.33%. A significant grain coarsening has noticed in the fusion zone consisting of a-phase in different direction bounded by -phase. The hardness value at fusion zone and base metal are typically observed to be 235HV and 145HV respectively.

Welding is an important process in terms of manufacturing components for various types of machines and structures. One of the vital and still unsolved issues is determining the quality and properties welded joint in an online manner. In this paper, a technique for prediction of joint hardness based on the sequence of thermogram acquired during welding process is proposed. First, the correspondence between temperature, welding linear energy and hardness was revealed and confirmed using correlation analysis. Using a linear regression model, relations between temperature and hardness were described. According to obtained results in the joint area, prediction error was as low as 1.25%, while for HAZ it exceeded 15%. Future work on optimizing model and input data for HAZ hardness prediction are planned.

Automated in-process Non-Destructive Testing (NDT) systems are rapidly gaining traction within the manufacturing industry as they reduce manufacturing time and costs. When considering calibration and verification of such systems, creating defects of known geometry and nature during the deposition of a weld can: (I) help examine the capability of the automated system to detect and characterise defects, (II) be used to form a database of signals associated with different defect types to train intelligent defect classification algorithms, and (III) act as a basis for in-process gain calibration during weld inspection at high temperatures, where the ultrasound beam can be skewed as a result of velocity gradients. In view of this, this paper investigates two unique methodologies for introducing: (a) lack of fusion weld defects by embedding tungsten in the weld and (b) creating artificial weld cracks by quenching to imitate the real cracking scenarios. According to the results of Phased Array Ultrasound Testing (PAUT) inspections, the methodologies used for embedding the artificial defects were successful. The validity of inspections was also verified by extracting micrographs from the defective sections of the welds, and model-based simulations were carried out to gain a better understanding of the wave propagation path and interaction with the generated defects.

This article is focused on an analysis of factors negatively affecting the tube production process of tubes made from austenitic stainless steel with a very small diameter of 0.34 mm. The analysis was concentrated on factors that affect the drawing process stability of the seam tubes where the desired final dimensions&mdash, a diameter of 0.34 mm and a wall thickness of 0.057 mm&mdash, are limiting factors. Seam tubes made from steel 1.4306 and 1.4301, from producers KT and EW with a longitudinal weld line made by tungsten inert gas (TIG) welding, were used as blanks for constituent drawing operations. It is desirable to provide sufficient inert gas flow and cooling during the formation of a weld joint in a protective atmosphere chamber. A significant temperature gradient prevents the formation of undesirable Cr23C6 carbides in the heat-affected zone (HAZ) which negatively affects the plasticity and formability of the steel and is the cause of technological fractures.

In this article, the mechanical properties and microstructure of 304L austenitic stainless steel/Incoloy 800HT nickel alloy dissimilar welded joints are investigated. The joints were made of 21.3 mm × 7.47 mm tubes using the TIG process with the use of S Ni 6082 nickel filler metal. No welding imperfections were found and high strength properties of joints were obtained, meeting the assumed acceptance criteria of the product’s standards. The tensile strength of the welded joints was higher than for the joined materials (Incoloy 800HT). Macro- and microscopic metallographic tests revealed the correct morphology of the joints and the appropriate structures in their critical zones. However, differences were found in the morphologies of the zones between the weld and the base materials. In fusion boundary from the side of the Incoloy 800HT alloy, no clear outline of the fusion line was observed (type A fusion boundary), while increased grain size and an epitaxial structure were observed. In turn, in the zone: weld–304L steel, a distinct fusion line was observed with areas with an increased amount of high-temperature δ ferrite (type B fusion boundary). No precipitates were found that could reduce the resistance of the joints to intergranular corrosion. A hardness decrease (approximately 30 HV0.1) in the transition zone: austenitic steel–weld and an increase of hardness (approximately 10 HV0.1) on the opposite side of the welded joint were observed.

Recent developments in artificial intelligence (AI) modeling tools allows for envisaging that AI will remove elements of human mechanical effort from welding operations. This paper contributes to this development by proposing an AI tungsten inert gas (TIG) welding algorithm that can assist human welders to select desirable end factors to achieve good weld quality in the welding process. To demonstrate its feasibility, the proposed model has been tested with data from 27 experiments using current, arc length and welding speed as control parameters to predict weld bead width. A fuzzy deep neural network, which is a combination of fuzzy logic and deep neural network approaches, is applied in the algorithm. Simulations were carried out on an experimental test dataset with the AI TIG welding algorithm. The results showed 92.59% predictive accuracy (25 out of 27 correct answers) as compared to the results from the experiment. The performance of the algorithm at this nascent stage demonstrates the feasibility of the proposed method. This performance shows that in future work, if its predictive accuracy is improved with human input and more data, it could achieve the level of accuracy that could support the human welder in the field to enhance efficiency in the welding process. The findings are useful for industries that are in the welding trade and serve as an educational tool.

In this research work, Inconel 718 specimens are fabricated by Direct Metal Laser Sintering process in the closed chamber which is filled with argon gas environment from a pre-alloyed powder. The process contains the high intensity of the laser source to melt the powder material, and the segment is placed on the top of the previous layer. Plates were vertically fabricated systematically (i.e., z-axis) and columnar grains are exhibited perpendicular to the build direction (i.e., x-axis). Test specimens are stress-relieved at 980°C for 2 hours and the recrystallized zone are found to be spheroid structure precipitates. The Ni-Cr matrix in the recrystallized interface and grain boundaries is observed in the samples, the micro hardness of the as-fabricated material is found as 340-350 VHN. Also, correspondingly mechanical properties are comparable with the wrought inco-718 alloy material. Further, the as build condition specimens are used for making butt joint configuration using Tungsten Inert Gas (TIG) welding process and Mechanical and microstructural properties are studied. The studies on welding of additive manufactured component will ensure the weldability of the AM material for the research community and industry.

Weld quality mainly depends on the weld bead geometry and mechanical-metallurgical characteristics of the welded joint which has a direct relationship with the type of welding process being used and its input process parameters i.e. welding current, arc voltage, travel speed etc. In the present study, determination of tungsten inert gas (TIG) welding input parameters for achieving maximum tensile strength of 316L austenitic stainless steel is investigated. Box-Behnken design of response surface methodology has been employed to formulate the experimental plan to identify the effect of process parameters on tensile strength. Square butt joint configuration has been made using three factors - three levels of welding input parameters. Joint strength has been evaluated by notch tensile strength (NTS) and Unnotch tensile strength (UTS) method and correlated with microstructure and micro hardness of the weld. The results indicate that gas flow rate has greater influence on both NTS and UTS followed by welding current.

For a low cost, there are industrial infrared monitoring systems used for imperfection detection and identification in welded joints. The key drawback that impedes real life industrial applications is the low spatial resolution, as well as the temporal resolution of low-cost infrared (IR) cameras. This is also the case in tungsten inert gas (TIG) welding. Taking into consideration the influence of voltage on the arc energy and heat input, high frequency sampled voltage was used to evaluate the interpolated temporal resolution of IR sequences. Additionally, a reflected temperature correction method was proposed to reduce the uncertainty of absolute temperature measurement with a thermographic camera. The proposed method was applied to detect several imperfection types, such as lack of or incomplete penetration as well as incorrect weld shape and size (including burnouts). Results obtained for different interpolation factors were compared. The obtained results emphasize the validity of reflected temperature correction method. For the weld defects detection task, the smallest detectable defect was found for various interpolation factors. Moreover, the correspondence of arc voltage and the joint temperature was checked. Additionally, a set of decision rules was elaborated on and applied to distinguish between various joint conditions. It was found that defects that do not have symmetrical temperature distribution with respect to the joint axis are harder to identify.

The present work develops a multi-region dynamic coupling model for fluid flow, heat transfer and arc–melt interaction in tungsten inert gas (TIG) welding using the dynamic mesh technique. The arc–weld pool unified model is developed on basis of magnetohydrodynamic (MHD) equations and the interface is tracked using the dynamic mesh method. The numerical model for arc is firstly validated by comparing the calculated temperature profiles and essential results with the former experimental data. For weld pool convection solution, the drag, Marangoni, buoyancy and electromagnetic forces are separately validated, and then taken into account. Moreover, the model considering interface deformation is adopted in a stationary TIG welding process with SUS304 stainless steel and the effect of interface deformation is investigated. The depression of weld pool center and the lifting of pool periphery are both predicted. The results show that the weld pool shape calculated with considering the interface deformation is more accurate.

5th International Conference on Material Science and Engineering Technology, ICMSET 2016 -- 29 October 2016 through 31 October 2016 -- -- 190139, In this work, Charpy notch pendulum impact test was performed on non-welded and TIG (Tungsten Inert Gas) welded Inconel 718 specimens at three different temperatures as 20°C, 500°C and 700°C. After the completion of tests, SEM (Scanning Electron Microscopy) inspection and EDX (Energy-Dispersive X-Ray Spectroscopy) analysis were performed for the microstructural examination of the specimens. Hardness measurements on the rupture zone of selected welded and non-welded specimens were also performed to make a better approach to interpretation of the impact behavior of material. Inspections indicated that hardness values in the heat affected zone of welded specimens dramatically decreased and they displayed higher ductility during fracture than non-welded samples due to partial softening of structure. The reason of further decrease in impact resistance of welded specimens was explained as the precipitation and coarsening of ?'' and carbide phases in the interdendritic regions with increasing temperature

After several years of service under high temperatures and high pressure, the Ti-6Al-4V aero-engine components may need to be repaired by Tungsten Inert Gas (TIG) welding to prevent crack growth. However, the material properties tend to worsen after TIG welding due to residual stresses developed adjacent to the fusion zone (FZ) and the heat affected zone (HAZ). It can lead to premature failure of the repair area resulting in a shortened service life of the components. Post weld heat treatment (PWHT) is generally adopted to reduce the residual stresses and to improve the mechanical properties. A comprehensive study of the effects of PWHT on the mechanical properties of Ti-6Al-4V was conducted in this paper. The residual stresses, micro-hardness, tensile strength and low cycle tensile fatigue life of as-welded Ti-6Al-4V before and after PWHT were compared and analyzed. The results indicate that the PWHT at 700 °C for 1 hour increases the yield strength of weld metal around 2.1% and improves the low cycle tensile fatigue life significantly under fatigue loads from 750 MPa to 950MPa by reducing residual stresses to close to 0 MPa. NRF (Natl Research Foundation, S’pore) Published version

The main purpose of this work was to investigate the microstructure and mechanical properties of spray-formed 2195-T6 Al-Li alloy welding joints produced by tungsten inert gas (TIG) with Al-Cu and Al-Si-Cu filler wires, so that they can be better used in space vehicle tanks. The porosity analysis indicates that the porosity area of the weld seam with the Al-Si-Cu filler wire is approximately 7.989 times larger than that of the Al-Cu filler wire. Furthermore, the microstructure and microhardness results indicate that the Al/Cu eutectic near the fusion line distributes more at the grain boundaries, while more dispersed Al2Cu phase is found inside the grain, which improves the strength of the joint when using Al-Cu filler wire. However, when using the Al-Si-Cu filler wire, more Si, Cu, and Ti elements are segregated at the grain boundaries, forming a brittle-hard network Al/Cu/Ti eutectic, which reduces the performance of the joint. Additionally, the tensile strength and elongation of the weld joint are about 68.6% and 89.9% of the base metal (BM) when using the Al-Cu filler wire, and can approach the level of friction stir welding (FSW). However, the tensile strength and elongation are only about 56.8% and 39.9%, respectively, of the BM in the weld joint when using the Al-Si-Cu filler wire. Lastly, the fractures both occur on the fusion line and the fracture morphology of the weld joint shows that it is a mixed fracture mode dominated by plastic fracture when using Al-Cu filler wire, while it is mainly a quasi-cleavage fracture mode when using Al-Si-Cu filler wire. Therefore, the joint strength when using Al-Si-Cu filler wire with high strength matching is not as good as that of Al-Cu filler wire with low strength matching.

The paper presents the influence of pulsation frequency on the results of pulsed current TIG welding based on two criteria: geometric parameters of weld and changes in microstructure. The investigations were carried out for 301L austenitic stainless steel with constant current parameters, constant welding speed, 50% duty cycle ratio and constant heat input. The results were referred to the commonly used methods for measuring the amount of heat input.

A semi-solid stir casting mixed multi-pass rolling process was successfully employed to manufacture TiCp/Al-5Mg composite filler wires with different contents of TiC particles. The 5083-H116 aluminum alloys were joined by tungsten inert gas (TIG) using TiCp/Al-5Mg composite weld wires. The microstructure, mechanical properties, fractography and corrosion behavior of the welds were evaluated. The results revealed that TiC particles were distributed in the welds uniformly and effectively refined the primary &alpha, Al grains. The hardness and tensile strength of the welds were improved by increasing the TiC particle content, which could be attributed to the homogeneous distribution of TiC particles and the microstructure in the weld joints. Potentiodynamic polarization testing revealed that the corrosion resistance of the welds also increased with the addition of TiC particle contents. In addition, the stress corrosion cracking (SCC) susceptibility of the welds decreased as micro-TiC particles were introduced into the welds. The electronic structure of the Al/TiC interface was investigated by first principle calculation. The calculation showed that valence electrons tended to be localized in the region of the TiC-Al interface, corresponding to an addition of the overall work function, which hinders the participation of electrons in the composite in corrosion reactions.

Besides a wide application in corrosion protection, wear resistance increase, providing thermal properties and power conversion, oxide coatings have found an alternative application in welding technology as catalysts of the tungsten inert gas (TIG) welding process. In this paper, the novel approach of fabricating a coating containing nanoparticles based on nanosized SiO2 and TiO2 and their mixtures was applied to the austenitic stainless-steel base metal. It was found that coatings increased depths of penetration, enabling a consumable-free welding. Using this method, the use of several critical and near-critical raw materials (e.g., Si and Cr), as well as the relatively expensive Ni can be completely avoided. The most effective coating in terms of weld penetration consisted of a mixture of nanoparticles, rather than unary oxide coatings based on nanoparticles. A model for liquid weld metal flow is proposed based on the metallographic examination of recrystallized grains and microhardnesses measured near the weld metal, supporting the reversed Marangoni convection theory.

In this study, AA 6063 aluminum was joined using Tungsten Inert Gas (TIG) welding with a butt joint. The ER-5356 filler metal feeding method is used intermittently to find its effect on weld geometry, mechanical properties, microstructure, and chemical composition. The dimensions of the specimens used in this study were 120 mm × 50 mm, with a thickness of 3 mm. The ratio used is the configuration of the feed time and delay time. The length ratio of wire filler is varied from a ratio of 4 to 6. The top bead width and back bead width decreased by 17.66% and 40.33%, respectively. At a ratio of 6, it has the largest cross-sectional area of 295.37 ± 27.60 mm2. The results show that the general tensile strength was proportional to the ratio, but the difference was not significant, only around ±8 MPa. The microstructure formed in each weld has different characteristics, conversely, grains with a relatively coarse structure have decreased hardness values. The chemical composition test shows that the length ratio of filler metal feed directly correlates with magnesium’s average weight content, where the weight content of magnesium value tends to be homogeneous in all areas of weld metal (WM).

The influence of different welding processes on the mechanical properties and the corresponding variation in the microstructural features have been investigated for the dissimilar weldments of 18% Ni maraging steel 250 and AISI 4130 steel. The weld joints are realized through two different fusion welding processes, tungsten inert arc welding (TIG) and laser beam welding (LBW), in this study. The dissimilar steel welds were characterized through optical microstructures, microhardness survey across the weldment and evaluation of tensile properties. The fiber laser beam welds have demonstrated superior mechanical properties and reduced heat affected zone as compared to the TIG weldments.

This paper deals with the effects of weld parameters on residual stress developed during TIG welding of pipes. Circumferential TIG welding is widely used in industries such as piping, oil refineries, power stations, etc. The 3D numerical simulation ANSYS code is used to predict the residual stress distribution developed during circumferential TIG welding. Due to non-uniform distribution of plastic and thermal strains in and around the weld pool, large amounts of residual stresses and deformations are present in all welded structures. The simulated results are validated using experimental results available in the literature. The effects of welding current and pipe thickness on residual stress and temperature fields at different locations were assessed.

In this paper, Tungsten Inert Gas Welding (TIG) and single-sided welding and double-sided forming have been used to weld the 7A05-T6/5A06-O dissimilar aluminum alloy circular welded joint of a ring-stiffened closed cylindrical sandwich shell. Microstructural characterization and mechanical properties of welded joints were investigated by use of scanning electron microscopy (SEM), backscatter electron diffraction (EBSD) and transmission electron microscopy (TEM), respectively. Hardness distribution and tensile properties of the welded joints were examined. The results showed the failure of the welded joints produced in the fusion zone (FZ). The tensile strength and yield strength of the welded joints were, respectively, 78.87% and 97.24% of the 5A06-O base metal (BM), and the elongation reached 84.29% of 7A05-T6 base metal. Welding high heat input led to the coarse grain size in the fusion zone, and the long-term similar quenching effect can lead to the full dissolution of the strengthening zone of the fusion zone resulting in the reductions of strength and hardness. Around 7A05 heat-affected zone (HAZ), there is an obvious hardening zone and softening zone, the solid solution precipitates into the Rayleigh brilliant &eta, &prime, (MgZn2) phase, which results in natural aging strengthening, thus obtaining high hardness. &eta, (MgZn2) enhanced phase dissolved fully and the dislocation density decreased rapidly in the HAZ region resulted in a softening zone with a lower hardness at about (10&ndash, 18) mm from the center of the weld center.

Structural integrity assessment of welded joints requires characterising the residual stresses generated during the process. Although measurements can provide a quantitative estimation of the residual stresses, a reliable numerical model offers greater advantages in terms of cost, time and versatility. A validated model can be used to optimise the measurement procedure and thereby aiding in further refinement of the model itself. In the current work, a three-pass tungsten-inert gas welding in an austenitic stainless-steel plate is simulated using a three-dimensional sequentially coupled thermo-mechanical analysis for the purpose of predicting the transient thermal profiles and the final residual stresses as a part of NeT programme. Block-dumped heat transfer analysis was conducted with element activation and deactivation to represent the physical deposition of the weld beads for each pass, followed by a mechanical analysis to predict the stresses. Incremental deep-hole drilling and neutron diffraction techniques at ILL and HZB facilities in Grenoble and Berlin respectively, were employed to measure the residual stresses through the thickness of the sample plate at the center. The predicted thermal history and the residual stresses are verified with the measured thermocouple recordings and the stresses respectively.

Visual inspection through image processing of welding and shot-peened surfaces is necessary to overcome equipment limitations, avoid measurement errors, and accelerate processing to gain certain surface properties such as surface roughness. Therefore, it is important to design an algorithm to quantify surface properties, which enables us to overcome the aforementioned limitations. In this study, a proposed systematic algorithm is utilized to generate and compare the surface roughness of Tungsten Inert Gas (TIG) welded aluminum 6061-T6 alloy treated by two levels of shot-peening, high-intensity and low-intensity. This project is industrial in nature, and the proposed solution was originally requested by local industry to overcome equipment capabilities and limitations. In particular, surface roughness measurements are usually only possible on flat surfaces but not on other areas treated by shot-peening after welding, as in the heat-affected zone and weld beads. Therefore, those critical areas are outside of the measurement limitations. Using the proposed technique, the surface roughness measurements were possible to obtain for weld beads, high-intensity and low-intensity shot-peened surfaces. In addition, a 3D surface topography was generated and dimple size distributions were calculated for the three tested scenarios: control sample (TIG-welded only), high-intensity shot-peened, and low-intensity shot-peened TIG-welded Al6065-T6 samples. Finally, cross-sectional hardness profiles were measured for the three scenarios; in all scenarios, lower hardness measurements were obtained compared to the base metal alloy in the heat-affected zone and in the weld beads even after shot-peening treatments.

Basyigit, Aziz Baris/0000-0003-1544-3747 WOS: 000434882800029 Duplex stainless steels are gaining greater interest due to their increasing amounts of application fields. Accordingly, there is a need for awareness of problems associated with improper microstructural distributions such as delta-ferrite (delta-ferrite), austenite and other important intermetallic phases that may form in these steel weldments. Since delta-ferrite versus austenite ratio profoundly influences corrosion and mechanical properties, optimum delta-ferrite ratios must be kept approximately within 35-65 vol % and balance austenite to maintain satisfactory corrosion and mechanical properties on welding of these steels. Cooling rates of welds and alloying elements in base metal are the major factors that determine the final microstructure of these steels. In this work, 3 mm thickness of 2205 duplex stainless-steel plates were TIG (Tungsten Inert Gas) welded with various amounts of nitrogen gas added to argon shielding gas. Specimens were joined within the same welding parameters and cooling conditions. As nitrogen is a potential austenite stabilizer and an interstitial solid solution hardener, the effects of nitrogen on mechanical properties such as hardness profiles, grain sizes and microstructural modifications are investigated thoroughly by changing the welding shielding gas compositions. Increasing the nitrogen content in argon shielding gas also increases the amount of austenitic phase while delta-ferrite ratios decreases. Nitrogen spherodized the grains of austenitic structure much more than observed in delta-ferrite. The strength values of specimens that welded with the addition of nitrogen gas into the argon shielding gas are increased more in both austenitic and delta-ferritic structure as compared to specimens that welded with plain argon shielding gas. The addition of 1 vol % of nitrogen gas into argon shielding gas provided the optimum phase balance of austenite and delta-ferrite in S32205 duplex stainless-steel TIG-welded specimens. Gazi University Scientific Research Projects DepartmentGazi University [07/2011-50] Authors would like to thank for the financial supports to the Gazi University Scientific Research Projects Department. (Project Code: 07/2011-50)

Split anode calorimetry investigations of tungsten inert gas (TIG) arcs were conducted using a large-diameter shielding gas nozzle. Some conditions displayed arc symmetry whilst others proved distinctly asymmetric. The variation of welding current and electrode tip to workpiece distance (ETWD) was studied. Decreasing the ETWD was found to increase the current density towards the arc axis but similar to a previous study of the authors, Gaussian distributions were not observed. The gas nozzle was designed to produce laminar gas flow and sound shielding behaviour; however, anode surface oxidation was found after welding, presumably caused by shielding gas contaminated with oxygen through the welding sequence. Therefore, axial arc symmetry was influenced by random effects. The conditions and reasons for the observed phenomena are explored within this paper.

The paper reports the three-point bending test results of welded joints. The joints were made of chromium-molybdenum cast steel designed for the use at elevated temperatures. TIG (tungsten inert gas) welding technique was used. The fracture energy for particular joint zones and the stretch zone width (SZW) under the notch bottom were determined in a qualitative fracture toughness assessment. Fracture surface morphology was analyzed. The stretch zone measurement indicated a qualitative relationship between its width and the values of fracture energy. The results confirmed the influence of the modification on the character of fracture and the portions of brittle and ductile fracture in particular areas of welded joints.

This paper describes the welding technology applied for mixed joints of tubes made of austenitic steels in the X10NiCrAlTi32-21 and X6CrNiMoTi17-12-2 grades. One made a butt joint and a multi-run joint, with the inert gas welding method and a non-consumable electrode. The mechanical properties were tested in the following scope: static tensile test, bending test from the side of the face and from the side of the root, impact test of the joint and hardness measurements. The tests were supplemented by the assessment of the macrostructure and microstructure of the joint. The performed non-destructive and structural tests did not reveal any welding imperfections, and the mechanical test results confirmed high properties of the welded joint. On this basis, the joint was classified into the “B” quality level according to PN EN ISO 5817. The mechanical and structural test results constitute the basis for qualification of the welding technology according to PN EN ISO 15614.

Metallic materials have received special attention in the aerospace and defense areas. A few decades ago, Brazil was faced with technological challenges concerning the production and processing of ultra-high strength steels, such as AISI 4340 and SAE 300 M steels. The AISI 4130 steel had been also considered, since it is applied in landing gears, small aircrafts engine cradles, and besides general industries. In this work, as a comparative welding process, Laser Beam Welding (LBW) was used as an alternative to the traditional TIG (Tungsten Inert Gas) welding. For the mechanical characterization of laser and TIG welds, tensile and hardness tests were performed. Microstructural characterization through optical microscopy was realized as well, in the fusion zone (FZ) and heat-affected zone (HAZ). Martensite was found in the fusion zone for both processes. However the average grain sizes were different due to different heating and cooling rates. In the present study, the weld was autogenous and a post weld heat treatment was conducted to evaluate its influence on mechanical properties. This treatment proved to improve the ductility of the steel and reducing the embrittlement in the welded region. It was observed that the thicknesses of the FZ and HAZ in the TIG welds were ten times larger than in the laser. The hardness values observed in FZ and HAZ were similar in both cases. Tensile strength after heat treatment remained at levels similar to the base material. After the heat treatment, there was a recover in the material ductility, particularly after the laser welding, demonstrating the usefulness of the process.

Ultrasonic‐assisted tungsten inert gas welding was carried out on a thin plate of 2195 Al‐Li alloy, and the characteristics of the weld pores were analyzed in terms of their size and porosity. The effects of welding speed and ultrasonic power on the porosity and size of the pores were investigated. The pores were found to occur primarily adjacent to the surface of the weld. The porosity decreased and the size increased with a decrease in welding speed. The effect of ultrasonic power on the characteristics of the pores was different from that of the welding speed. The porosity and size of the pores decreased and then increased with an increase in ultrasonic power. A relationship was found between the transient cavitation intensity and the characteristics of pores. An increasing transient cavitation intensity results in a decrease in the porosity and size of pores when the transient cavitation intensity is lower. However, it can result in an increase in the porosity and pore size when the transient cavitation intensity further increases. Finally, the influencing mechanism of cavitation on welding pores was discussed.

Fatigue crack usually initiates at welded joints of structural elements. For a high-responsibility aeronautic component, called “Motor-Cradle” - critical to the flight safety -, successive weld repairs are carried out toward restoring the original condition of the aircraft and extending the in-service life of them. Motivated by the high fracture incidence on this particular component an extensive research program to evaluate the effects of maintenance weld repairs on the structural integrity, mechanical properties and microstructural changes has been developed. In this research-work, a maintenance weld repair procedures widely employed along the useful life of aircrafts, characterized by overlapping the weld bead by gas tungsten arc welding with filler metal was investigated. From the data obtained with fatigue crack growth laboratorial tests in base material (BM), heat affected zone (HAZ) and weld metal (WM) the effects of successive TIG welding repairs on the structural integrity of AISI 4130 aeronautical steel were analysed. After TIG welding and re-welding processes, specimens were prepared in accordance with ASTM 647 standard and fatigue tested with constant amplitude (R=0,1) at 10 Hz frequency and room temperature. The obtained results were associated to the micro hardness and microstructure variations, as well as to the residual stresses field generated by the successive weld cycles. Key-conclusion is that welding repair increase the fatigue crack growth resistance in the weld metal and in the HAZ.

Welding is widely used in all the fabrication processes for the development of structural components. An accurate and physically suitable heat flux simulation model is to be given as input for analysis of welding processes. The outcome of the heat input is structural deformation and residual stress formation. The temperature and residual stress modelling is one of the complex process which utilise the weld parameters and material properties at higher temperatures. A representation of heat flux model is developed using heat source with constant and uniformly applied condition. Present work is done with cylindrical heat flux model further a realistic model is possible by combining present with other heat flux models, such as Gaussian. The temperature distribution and stress analysis has been carried out with developed model by using the temperature dependent material properties for Stainless steel SS304. This work can be used for selecting process parameters for reducing structural distortion and residual stresses by simulation process. In this paper temperature and residual stresses are discussed.

In this research work, Finite Element Modeling (FEM) using SYSWELD was carried out to predict thermal cycles, residual stresses and distortion in type 316 LN stainless steel weld joint made by TIG welding process. The numerically predicted thermal cycles and temperature distribution were validated using Infrared (IR) Thermography. The model predictions of the surface and bulk residual stress profiles were validated using X-ray Diffraction (XRD) and Ultrasonic Testing (UT) respectively. Distortion analysis was also performed and validated using digital height gauge measurement. IR thermography was found to be a good tool for validating the model predictions of the temperature distribution in the weld joint. There was good agreement between the model predictions and the experimentally observed values of temperature, residual stresses and distortion. Therefore, the numerical modeling in combination with non-destructive methods provides an efficient approach for predicting the effect of welding process on the weld attributes.

This paper aims to develop a novel tungsten inner gas (TIG) welding torch in order to join thin sheets efficiently. Using a narrowing nozzle (constricted nozzle) inside a conventional TIG torch can critically improve the position accuracy of the tungsten electrode and also the arc plasma characteristics and heat input density. In order to evaluate the efficiency of this new torch, weld bead appearance and cross-section images were examined by an optical microscope, scanning electron microscope (SEM), and electron back scatter diffraction patterns (EBSD). The results showed that in all cases, the weld bead profile was stable without undercut and burn-through. Full penetration weld was seen. The width of weld bead on the bottom surface was increased much in comparison to conventional TIG welding. However, the results from SEM and EBSD images indicated that in the case of low welding current, the blowholes were found out on the side of the thinner material (SS400). The penetration of SUS430 material to SS400 material was not good. It seems that no fusion of SUS430 material to SS400 at the bottom surface can be seen. Meanwhile, no blowholes were seen in the case of high welding current. The penetration was better, and the fusion was reached on the bottom surface.

Tungsten usually exhibits poor weldability and marked brittleness at room temperature. This causes tungsten welds to be affected by the evolution of cracks along the weld bead, which can be eliminated by using a pre-heating step to reduce thermal straining. In this study, based on the tungsten inert gas welding process, a working envelope, focussed on varying welding speed and five different shielding gas mixtures of argon and helium, has been defined with the view of producing crack-free autogenous welds. The bead appearance and the microstructure of the different welds were correlated to the welding parameters, whose main effects have been analysed. Welding defects such as humping occurred when using gas mixtures with relatively low content of helium, and when using relatively high welding speeds. Crack-free autogenous welds have been produced without pre-heating when using a high content of helium and relatively low welding speeds. Thus, this study has demonstrated that a helium-rich shielding gas is required for welding thick tungsten plates. Moreover, the low thermal shock induced by the process, coupled with the purity of the tungsten plates used, strongly contributed to avoid the occurrence of any crack.

Finite element (FE) analysis of welding residual stress and deformation is one of the essential stages in the manufacturing process of mechanical structures and parts. It aids in reducing the production cost, minimizing errors, and optimizing the manufactured component. This paper presents a numerical prediction of residual stress and deformation induced by two-pass TIG welding of Al 2219 plates. The FE model was developed using ABAQUS and FORTRAN packages, Goldak&rsquo, s heat source model was implemented by coding the nonuniform distributed flux (DFLUX) in user subroutine to represent the ellipsoidal moving weld torch, having front and rear power density distribution. Radiation and convection heat losses were taken into account. The mechanical boundary condition was applied to prevent the model from rotation and displacement in all directions while allowing material deformation. The FE model was experimentally validated and the compared results show good agreement with average variations of 18.8% and 17.4% in residual stresses and deformation, respectively.

This work provides a comprehensive investigation of multi-walled carbon nanotubes (MWCNTs) inducement in weldment and their apparent effect on the microstructure, %elongation and ultimate fracture behavior of Al-Mg-Si alloy referring modified tungsten inert gas (TIG) welding joints. Serious experimental work is carried out at 1 wt%, 1.5 wt%, and 2 wt% of MWCNTs to provide a gradually increasing heterogeneous nucleation. The behavior of grain morphology showed the pure field of epitaxial growth without MWCNTs, and the forestry type morphology for 1 wt% MWCNTs at low welding currents (160 A), though there was a noticeable conversion into equiaxed (EQZ) grains filled with inter-dendritic particles at high welding currents (180 A and 200 A) for 1.5 wt% and 2 wt% of MWCNTs. Moreover, the formation of a cellular type network above the fusion line predominated initially at all parameters. Conversely, fine EQZ grains were formed as they moved upward into the welded zone (WZ) explicitly at a high heat input. A conceptual pictorial model is presented in the study which summarized the behavior of morphological changes at the utilized parameters. The welded joints have demonstrated an increasing trend of strength and %elongation in contrast to joints without added MWCNTs. Comparative results have shown an exceptional increment of 71 to 76% and 67 to 75% of elongation up to ultimate tensile strength (UTS), and a fracture point that was clinched for 1 wt% and 1.5 wt% MWCNTs at 180A. From macro to micro-examination of the fracture surfaces, pure ductile modes constituting elliptical cup and cone type isotropic flow was evident in all specimens. Detailed confirmation of the pull-out fracture mode of MWCNTs has highlighted in the scanning electron microscope (SEM) images that intimated a methodical contribution in load-transfer from matrix to the fiber under axial load. Overall, a concise en-route for MWCNTs inducement is well-appointed through tube fillers along with an activating facilitator (TiO2) in contrast to stereotype fillers for improved behavior termed as modified TIG welding joint process in study.

In this work the influence of main parameters that take part during TIG welding process are analyzed. Some of these parameters belong to the welding process, as for example the welding speed, intensity and voltage while others are from the material and tooling features, as for example foaming material and tooling design. The result of this work shows a strong dependence on these parameters of the TIG welding process for metallic foams.En este trabajo se analiza la influencia de los principales parámetros que intervienen en el proceso de soldadura TIG. Algunos de estos parámetros pertenecen al proceso de soldadura, velocidad de soldadura, intensidad y tensión, mientras otros son propios de las características del material y el utillaje, material precursor y forma de implementar la instalación de ensayo. El resultado de este trabajo muestra una fuerte dependencia de estos parámetros con el proceso de soldadura TIG para las espumas metálicas de aluminio.

Made available in DSpace on 2013-09-27T14:53:59Z (GMT). No. of bitstreams: 1 WOS000278762900202.pdf: 1417958 bytes, checksum: 0b370ce282da31aaf78c0bb00d4e5e26 (MD5) Previous issue date: 2010-01-01 Made available in DSpace on 2013-09-30T18:11:48Z (GMT). No. of bitstreams: 1 WOS000278762900202.pdf: 1417958 bytes, checksum: 0b370ce282da31aaf78c0bb00d4e5e26 (MD5) Previous issue date: 2010-01-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T13:28:25Z No. of bitstreams: 1 WOS000278762900202.pdf: 1417958 bytes, checksum: 0b370ce282da31aaf78c0bb00d4e5e26 (MD5) Made available in DSpace on 2014-05-20T13:28:25Z (GMT). No. of bitstreams: 1 WOS000278762900202.pdf: 1417958 bytes, checksum: 0b370ce282da31aaf78c0bb00d4e5e26 (MD5) Previous issue date: 2010-01-01 Structures critical to the flight-safety are commonly submitted to several maintenance repairs at the welded joints in order to prolong the in-service life of aircrafts. The aim of this study is to analyze the effects of Tungsten Inert Gas (TIG) welding repair on the structural integrity of the AISI 4130 aeronautical steel by means of experimental fatigue crack growth tests in base-material, heat-affected zone (HAZ) and weld metal. The tests were performed on hot-rolled steel plate specimens, 0.89 mm thick, with load ratio R = 0.1, constant amplitude, at 10 Hz frequency and room temperature. Increase of the fracture resistance was observed in the weld metal but decreasing in the HAZ after repair. The results were associated to microhardness and microstructural changes with the welding sequence. (C) 2010 Published by Elsevier Ltd. UNESP Univ Estadual Paulista, Dept Mat & Technol FEG DMT, BR-12516410 Guaratingueta, SP, Brazil UNESP Univ Estadual Paulista, Dept Mat & Technol FEG DMT, BR-12516410 Guaratingueta, SP, Brazil

In this study, we focus on the determination of the heat transfer properties in Tungsten-Inert-Gas welding (TIG) problem combining an experimental and a three-dimensional simulation approaches. Optimal conditions are used to weld stainless steel (304L) sheets in butt configuration. Both instrumental monitoring and metallographic investigation of the welded material are carried out. The modelling of the heat source is performed by a mobile Gaussian surface source exhibiting a bi-elliptical shape. This source is implemented in a three-dimensional finite element model to compute heat flux and temperature fields. The comparison between the experimental and numerical thermal cycles shows a fair agreement. Predicted temperature fields and heat flux distributions are discussed. Conversion of isotherms into microstructural information shows that the size of the fusion zone is four times smaller than the heat affected zone dimension. The metallographic analysis confirms the expected microstructural evolutions but highlights differences between observed and predicted extents of the heat affected zone.

International audience; The present work deals with the estimation of the time evolution of the weld fusion boundary. This moving boundary is the result of a spot GTA welding process on a 316L stainless steel disk. The estimation is based on the iterative regularization method. Indeed, the three problems: direct, in variation and adjoint, classically associated with this method, are solved by the finite element method in a twodimensional axisymmetric domain. The originality of this work is to treat an experimental estimation of a front motion using a model with a geometry including only the solid phase. In this model, the evolution of this solid domain during the fusion is set with the ALE moving mesh method (Arbitrary Lagrangian Eulerian). The numerical developments are realized with the commercial code COMSOL MULTIPHYSICS coupled with the software MATLAB . The estimation method has been validated in a previous work using theoretical data ([1]). The experimental data, used here for this identification are, temperatures measured by thermocouples in the solid phase, the temporal evolution of the melt pool boundary observed at the surface by a fast camera and the maximal dimensions of the melted zone measured on macrographs. These experimental data are also compared with numerical results obtained from a heat and fluid flow model taking into account surface tension effects, Lorentz forces and the deformation of the melt pool surface under arc pressure.

Made available in DSpace on 2013-08-12T19:22:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-11-01 Made available in DSpace on 2013-09-30T18:33:57Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-11-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T13:47:19Z No. of bitstreams: 0 Made available in DSpace on 2014-05-20T13:47:19Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-11-01 This study compared the tensile strength and fracture mechanism of tungsten inert gas (TIG) welds in cylindrical rods of commercially pure titanium (cp Ti) with those of laser welds and intact samples. Thirty dumbbell-shaped samples were developed by using brass rods as patterns. The samples were invested in casings, subjected to thermal cycles, and positioned in a plasma arc welding machine under argon atmosphere and vacuum, and titanium was injected under vacuum/pressure. The samples were X-rayed to detect possible welding flaws and randomly assigned to three groups to test the tensile strength and the fracture mechanism: intact, laser welding, and TIG welding. The tensile test results were investigated using ANOVA, which indicated that the samples were statistically similar. The fracture analysis showed that the cpTi samples subjected to laser welding exhibited brittle fracture and those subjected to TIG welding exhibited mixed brittle/ductile fracture with a predominance of ductile fracture with the presence of microcavities and cleavage areas. Intact samples presented the characteristic straightening in the fracture areas, indicating the ductility of the material. São Paulo State Univ UNESP, Dept Social Dent, Sch Dent, Araraquara, SP, Brazil São Paulo State Univ UNESP, Dept Social Dent, Sch Dent, Araraquara, SP, Brazil

Defects control such as hot cracking or solidification cracking, in aluminum alloys welding is an important industrial issue and must be carefully examined. This phenomenon is a complex problem involving process, material and mechanical loading due to clamping. Several tests have been previously developed in order to characterize the material propensity to hot cracking. The purpose of the present work is to study, using a new hot cracking test and numerical simulation, the relationship between mechanical and metallurgical factors in order to better identify the parameters leading to hot tearing during welding. The originality of the test presented here is that an external stress is applied on the test specimen parallel to the welding direction. The advantage of this test, compared to others like Varestraint test, is its simplicity and therefore its possible for an industrial use. A weld seam is made with a Tungsten Inert Gas (TIG) arc welding on a thin sheet of aluminum alloy (6061). The crack initiation occurs once steady state thermal conditions are reached. The present test enables to distinguish between the structural effects on a global scale and the microstructural effects on a local scale. Microstructure control is made possible by adjusting welding power, welding speed and sample geometries. The grain structure which is characterized by the shape, size and the growth direction and which depends on welding current and speed plays a crucial role in the crack initiation. Microstructural features are observed using high speed camera recording and post mortem micrographs. Mechanical factors are varied by adjusting the welding parameters and the applied initial stress. The relationship between welding parameters, grain morphology, and sensitivity to hot cracking are discussed. Experimental measurements and numerical results will help to better determine global and local conditions at the onset of hot tearing and to compare those conditions using existing hot tearing criteria.

The paper treats studies of TIG gas-shielded arc welding using pure nitrogen, N2+ 5-20 % Ar gas mixtures and N2 + 2-10 % H2 gas mixtures. A weld root shielding was provided by nitrogen gas. Welding in N2 requires by 40 % lower welding current than welding in argon. The study showed that porosity was an issue due to overalloying of N2 in the weld pool; it can, however, be avoided with adequate welding parameters, particularly sufficiently high welding speed and controlled low heat input. The microstructure of all-weld metal is fully austenitic (γ). Hydrogen reduces nitrogen solubility in the weld pool and produces an austenitic-ferritic (γ+δ) microstructure. Titanium increases nitrogen solubility in the weld pool and strongly reacts with nitrogen. Consequently, there is a high fraction of TiN inclusions in the weld metal.Hemos efectuado las investigaciones de la soldadura TIG en nitrógeno puro, las mezclas de gas N2 + 5 hasta un 20 % Ar, así como también N2 + 2 hasta un 10 % H2. Para la protección se utilizó nitrógeno. Para la soldadura se necesitan aproximadamente un 40 % menos de corriente de soldadura, comparado con la soldadura de argón. La investigación ha mostrado que la porosidad es un problema de absorción excesiva de la fundición con nitrógeno y que es posible suprimir la porosidad mediante parámetros adecuados de soldadura, sobre todo con una suficiente velocidad de soldadura y, con ella, una pequeña emisión controlada de calor. El hidrógeno reduce la solubilidad del nitrógeno en la fundición y acciona la segregación de ferrita. El titanio aumenta la solubilidad del nitrógeno en la fundición y reacciona fuertemente con el nitrógeno, de tal modo que en la soldadura hay una gran parte de inclusiones TiN.