Gas Tungsten Arc Welding Process Research Articles

Laser-assisted removal of weld heat tints from stainless steel surface

The heat generated during the welding of stainless steel results in the oxidation of the surface that, apart from aesthetics, adversely affects its corrosion property too. This communication reports the successful removal of heat tint generated by the gas tungsten arc welding process off a stainless steel surface in addition to an improvement in its pitting corrosion resistance by exposure to the emission of a nanosecond pulsed fiber laser. The laser cleaning experiments, conducted with six different laser pulses having different temporal shapes and duration that varied from 20 to 1020 ns, revealed that removal of the weld heat tint was possible in all conditions provided the effective laser fluence exceeded a definite threshold value. This threshold value, in turn, was found to increase with an increase in pulse duration. The laser cleaned specimens were subsequently analyzed for surface morphology, roughness, and pitting corrosion resistance. The pitting corrosion resistance of the laser-treated specimens was compared with the as-welded specimens and welded specimens with heat tint removed using conventional methods like wire brush cleaning and chemical pickling. The superior quality of tint removal, improved pitting corrosion resistance, and the ease of noncontact operation indicates the significant potential of the fiber laser-based weld tint removal method to substitute the conventional mechanical or chemical cleaning methods currently in use in the manufacturing industry.

Residual stresses in gas tungsten arc welding: a novel phase-field thermo-elastoplasticity modeling and parameter treatment framework

The fusion welding process of metallic components, such as using gas tungsten arc welding (GTAW), is often accompanied by detrimental deformations and residual stresses, which affect the strength and functionality of these components. In this work, a phase-field model, usually used to track the states of phase-change materials, is embedded in a thermo-elastoplastic finite element model to simulate the GTAW process and estimate the residual stresses. This embedment allows to track the moving melting front of the metallic material induced by the welding heat source and, thus, splits the domain into soft and hard solid regions with a diffusive interface between them. Additionally, temperature- and phase-field-dependent material properties are considered. The J2 plasticity model with isotropic hardening is considered. The coupled system of equations is solved in the FE package FEniCS, whereas two- and three-dimensional initial-boundary-value problems are introduced and the results are compared with reference data from the literature.

Study on Microstructural Characterization, Mechanical Properties and Residual Stress of GTAW Dissimilar Joints of P91 and P22 Steels.

This article deals with the dissimilar joining of two different grade Cr-Mo steel (2.25Cr-1Mo: P22 and modified 9Cr-1Mo: P91) for power plant application. The dissimilar butt-welded joint was produced for conventional V groove design by using the gas tungsten arc welding (GTAW) process with the application of an ERNiCrMo-3 Ni-based super alloy filler. A microstructure characterization was performed to measure the inhomogeneity in the microstructure and element diffusion across the interface in a welded joint. The experiments were also performed to evaluate the mechanical properties of the dissimilar welded joint in as-welded (AW) and post-weld heat treatment (PWHT) conditions. An acceptable level of the mechanical properties was obtained for the AW joint. After PWHT, a significant level of the element diffusion across the interface of the weld metal and P22 steel was observed, resulting in heterogeneity in microstructure near the interface, which was also supported by the hardness variation. Inhomogeneity in mechanical properties (impact strength and hardness) was measured across the weldments for the AW joint and was reduced after the PWHT. The tensile test results indicate an acceptable level of tensile properties for the welded joint in both AW and PWHT conditions and failure was noticed in the weak region of the P22 steel instead of the weld metal.

A study on shrinkage residual stresses, microstructure and mechanical properties of ASS thick pipe welded by GMAW process

In this investigation, AISI 304LN austenitic stainless steel pipes having 25 mm thickness and 300 mm inner diameter with conventional and narrow groove were welded by continuous current gas metal arc welding (GMAW) and pulse current gas metal arc welding (P-GMAW) process. A gas tungsten arc welding (GTAW) process was used for the welding of the root pass. Microstructural study was carried out in fusion zone (FZ) and heat-affected zone (HAZ). A favourable microstructure characteristic was observed in the P-GMAW process. The study of transverse shrinkage and shrinkage stresses were done on the conventional groove with GMAW and P-GMAW process and narrow groove by P-GMAW process. It was found that narrow groove weld design with controlled welding parameters can reduce 45% shrinkage as compare to conventional groove, similarly 30% reduction in shrinkage stress can be achieved. The tensile properties were observed to increased, such as yield strength was improved from 260 MPa to 310 MPa and ultimate strength was improved from 510 MPa to 550 MPa in the case of narrow groove weld by the P-GMAW process.

Comparing the effect of continuous and pulsed current in the GTAW process of AISI 316L stainless steel welded joint: microstructural evolution, phase equilibrium, mechanical properties and fracture mode

In this paper, the effect of continuous and pulsed current in the gas tungsten arc welding (GTAW) on the various properties of an AISI 316L stainless steel joints was investigated. 316L austenitic stainless steel sheets with a thickness of 10 mm were used together with ER309L filler. The sheets were welded together by the GTAW technique in two modes of continuous and pulsed currents. Microstructural characterization and phase equilibria were done using optical microscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) equipped with electron backscatter diffraction (EBSD) detector, techniques. Charpy impact, uniaxial tensile, and microhardness tests were used to investigate the effect of the type of the welding current on mechanical properties of the joints. The fracture surfaces were evaluated by FE-SEM after tensile and Charpy impact tests. Results showed that the weld metal (WM) microstructure is austenitic-ferritic (AF). It was also consisted of columnar and coaxial structures, in a way that varying the welding current from continuous to the pulsed mode changed the morphology of the grains from elongated columnar to a fine coaxial morphology. In addition, such a change in the welding current reduced the size of the grains in the WM, and the width of the unmixed zone (UMZ) as well. XRD analysis showed that the predominant phase and the preferred crystal plane of the WM are austenite, and (111), respectively. Both joints were broken from the base metal (BM) during the tensile test. Also, the above change of the welding current mode increased hardness and fracture toughness of the WM. Finally, fractography of the joints indicated that both joints experienced a completely ductile fracture.

Reduction of the Backing Gas Sequence as a Facile Method to Improve Corrosion Resistance in Duplex Stainless Steel (DSS) Weldment

Duplex stainless steel (DSS) is an important material used for corrosion resistance in various harsh environment plants such as petrochemical, offshore subsea component, and other chemical industries. An approximately equal amount of austenite and ferrite (A/F) ratio grants good mechanical properties and rust protection on. The detrimental intermetallic phase frequently occurs due to an unbalanced A/F ratio caused by the welding’s thermal cycle. Backing gas is commonly applicable in the field combined Gas Tungsten Arc Welding (GTAW) process. However, the use of backing gas to complete a single weld from root to cap joint required huge additional costs for consumables. Maintaining the thermal cycle in the welding parameter and GTAW process with ER2209 filler metal for DSS below 10 mm thick can reduce the backing gas sequence. The research aims to efficiently substitute full backing gas consumption, which meets a desirable quality in terms of corrosion resistance. The effect of backing gas reduction was studied. All specimens were tested by visua Vickers microhardness, metallography, ferrite content measurement, and electrochemical corrosion test. The visual test shows no defects beyond the range of the ASME IX acceptance and criteria. The evaluation comes from the ferrite scope and electrochemical corrosion test. The backing gas on the root weld shows a balance A/F ratio of around 38% ferrite content accepted in various standards. The backing gas sequence on the root until filler-pass obtained 0.04 mm/year, which is the desirable corrosion resistance and met the requirement of ASTM A932.

Long-term oxidation behaviour and thermal stability of heat-resistant stainless steel claddings deposited on AISI 316 stainless steel by the GTAW process

In the present study, the microstructure, oxidation behaviour, and thermal stability of the ER310 and ER446 weld overlay claddings deposited on AISI 316 stainless steel by the gas tungsten arc welding (GTAW) process were investigated. In this regard, the chemical composition, microstructure, and phase composition of the weld metals were characterized by optical microscopy (OM), field-emission scanning electron microscopy (FESEM-EDS), and X-ray diffraction (XRD) analysis. The oxidation behaviour and the bonding state of the clad plates were evaluated and compared after 1500 h of oxidation at 1000 °C using the isothermal oxidation and shear strength tests. Cross-sectional microstructural observations revealed that the substrates and weld overlay claddings were well bonded, and dense and uniform cladding layers without pores, cracks, or discontinuities were achieved. The weld metal produced by ER310 filler wire exhibited a completely austenitic microstructure, while the weld overlay produced by ER446 filler wire showed a ferritic-martensitic two-phase microstructure. The shear strength test results indicated that the bond strength of the ER446/AISI 316 and ER310/AISI 316 interfaces in the as-welded and oxidized conditions was higher than the minimum value (140 MPa) stated in the ASTM A264 standard. It was found that the oxidation process did not significantly reduce the bond strength of the interfaces. The weight gain data showed that both weld overlay claddings follow the parabolic rate law of oxidation, improving the oxidation behaviour of the AISI 316. The ER446 weld overlay had a lower parabolic rate constant (k p ) than the ER310 weld overlay. The SEM images showed that the oxide scales formed on the weld overlay claddings mainly consisted of three layers; Si-rich oxide at the innermost layer, Cr-rich oxide in the middle layer, and spinel oxide at the outer part of the scale. The oxidation behaviour of the clad samples was explained by the diffusion coefficients of elements, thermal stresses, and growth stresses, which are all associated with the matrix structure. • Heat-resistant stainless steel claddings were deposited on the surface of AISI 316 stainless steel using the GTAW process. • Thermal stability and oxidation behavior of the claddings after 1500 h of isothermal oxidation at 1000 °C were investigated. • The ER446 overlay displayed a ferritic-martensitic, while the ER310 overlay exhibited a fully austenitic microstructure. • The clad plates in the as-welded and oxidized conditions had a strength higher than the minimum value stated in ASTM A264. • Both ER446 and ER310 weld overlay claddings were improved the oxidation behaviour of the substrate.

Effect of electromagnetic arc constriction applied in GTAW-based wire arc additive manufacturing on walls' geometry and microstructure

New technologies for the additive manufacturing process applied to metallic materials have created a great outlook for complex geometries, cycle time and waste reduction. However, advances in efficiency and productivity are still needed for this process to be consolidated as a reliable manufacturing process. Wire arc additive manufacturing (WAAM) uses metallic materials to deposit a series of layers through melting and solidification, and that have proved to be an attractive process for the manufacturing of medium to large size components due its high deposition rate and potentially unlimited building size. Among the available heat sources is the GTAW (Gas tungsten arc welding) process with feed wire, where the heat source comes from an electric arc. The electric arc cross section is bell shaped and forms a round shape when it touches the weld pool. This study presents a device to electromagnetically constrict the electric arc in the GTAW process, capable of changing the cross section from round to elliptical (elongated), and the result of its application in additive manufacturing. The results show that the application of this arc constriction in wire arc additive manufacturing increases the height of the deposited walls by 10%, produces more regular geometry walls, in addition to increasing the process efficiency and promoting a microstructural grain refining effect. The results were statistically supported by the t-student test with 95% reliability, enabling the applicability of this device to increase the height of the deposited walls.

Hot corrosion performance of bare and pulsed current welded Fe-based A-286 alloy in chlorine and sulphur environment

This present research work focuses on the hot corrosion performance of the base metal, weldment, and weld metal of A-286 alloy in sodium sulphate (Na2SO4)–5% sodium chloride (NaCl)–7.5% sodium metavanadate (NaVO3) (3SM) atmosphere at 700 °C. A pulsed current gas tungsten arc welding process is employed to make a similar joining of A-286 alloy using the filler material ERNiCrMo-3. The corrosion kinetics of the specimens has been determined using the thermo-gravimetric technique. The phase compositions of the reaction products are studied by X-ray diffraction, and the surface morphology of the scales is explored by scanning electron microscope analysis. The corroded samples are subjected to a cross-sectional study to ensure the corrosion attack and scales thickness using a SEM with elemental mapping technique. The result indicates that weldment showed better corrosion resistance than bare metal. A thick oxide scale could be found in the bare metal specimen than the weld metal. In the case of base metal, the formation of non-adherent and porous iron (III) oxide (Fe2O3) leads to rapid corrosion. The weight gain of weldment is about 1.96 and 1.13 times less than bare alloy and weld metal.

Effect of filler and autogenous welding on microstructure, mechanical and corrosion properties of low nickel Cr-Mn ASS

ABSTRACT This experimental study investigates the effects of welding low nickel Cr-Mn austenitic stainless steel with gas tungsten arc welding process with and without filler (autogenous) weld by varying the welding currents (120A, 130A and 140A). The microstructural examination of weld has been carried out with optical microscope and mechanical properties with Vickers microhardness and tensile tester. The corrosion behaviour of the welded joints are analysed by double loop electrochemical potentio-kinetic reactivation test to obtain degree of sensitisation. The microstructural examination of welded joints revealed that, as the welding current increases, the inter-dendritic spacing as well as the dendrite size increases. The tensile strength and hardness decrease with increasing welding current for 308 L filler and autogenous weld. The degree of sensitisation increases with increasing welding current for both the welds. The results reveal that the autogenous welds have higher tensile strength, higher hardness and lower degree of sensitisation as compared to welds with 308 L filler.

Experimental investigation on microstructure, mechanical properties, and residual stresses of dissimilar welded joint of martensitic P92 and AISI 304L austenitic stainless steel

In this study, microstructural characteristics and mechanical properties of martensitic steel P92 and AISI 304L austenitic stainless steel (ASS) dissimilar metal weld (DMW) have been examined. The welding was performed using the multipass gas tungsten arc welding (GTAW) process. The ERNiCrMo-3 (Inconel 625) filler metal was used due to its excellent compatibility with the P92 and AISI 304L ASS metals. The microstructure characterization performed with an optical microscope and scanning electron microscope revealed the presence of an unmixed zone in the form of beach, peninsula, and island at the base metal and weld fusion zone interface. Secondary phases enriched with Nb and Mo, and migrated grain boundaries (MGBs) were also observed at the weld fusion zone. The microstructural characterization at the P92 side revealed the presence of a soft ferrite zone and delta ferrite at the weld and P92 interface. The different peak temperature experienced by the P92 metal during the welding process results into the formation of three distinct zones with diverse mechanical and microstructural properties namely coarse grain heat affected zone (CGHAZ), fine grain heat affected zone (FGHAZ), and inter-critical heat affected zone (ICHAZ). The post weld heat treatment (PWHT) at 760 °C for 2 h followed by air cooling was performed to homogenize this heterogeneous microstructure formed toward the P92 side. It was observed that this PWHT does not have any significant effect on weld fusion zone and 304L SS heat affected zone (HAZ) microstructure. But, PWHT modifies the microstructure of P92 side HAZ. The tensile test, Vickers micro-hardness test, and charpy impact test were carried out to determine the mechanical properties of the DMW. The tensile strength was found as 587.709 MPa in the as-welded condition and 594.515 MPa in PWHT condition. The tensile test results indicated that specimens were failed from 304L stainless steel (SS) base metal (BM) in as-welded and PWHT condition. The charpy impact toughness test results showed that the toughness of the weld joint was very low in as-welded and PWHT condition (47J) compared to the P92 (190J) and SS 304L (285J) BM. From the microhardness examination, it was observed that the ICHAZ was the weakest zone among all the other regions due to its lower micro-hardness value compared to the other regions. After welding process, residual stresses were measured in as-welded and after PWHT condition at the center of the weld and at the HAZ of P92 and SS 304L (through the thickness of the plate) using experimental-based deep hole-drilling (DHD) strain-gauge method. The results showed that both circumferential (hoop stress) and axial (longitudinal stress) welding residual stresses were decreased after PWHT.

Modeling and optimization of A-GTAW process using back propagation neural network and heuristic algorithms

Apart from different merits of using conventional gas tungsten arc welding (C-GTAW) process, some demerits have been introduced among which shallow penetration is the most important ones. In order to cope with the mentioned disadvantage, some procedures have been proposed among which using a paste like coating of activating flux during welding process known as activated-GTAW (A-GTAW) is the most extensively used ones. In this study effect of the most important process variables (welding current (C), welding speed (S)) and percentage of activating fluxes (TiO2 and SiO2) combination (F) on the most important quality characteristics (depth of penetration (DOP), weld bead width (WBW), and consequently aspect ratio (ASR)) in welding of AISI316L austenite stainless steel parts have been considered. To gather the required data for modeling and optimization purposes, box-behnken design (BBD) in design of experiments (DOE) approach has been used. In order to establish a relation between process input variables and output characteristics, back propagation neural network (BPNN) has been employed results of which have been compared with regression modeling outputs. Particle swarm optimization (PSO) algorithm has been used for determination of BPNN architecture (number of hidden layers and neurons/nodes in each hidden layer). Dragonfly (DFA) and PSO algorithms have been employed for process optimization in such a way that desired AR, minimum WBW, and maximum DOP achieved simultaneously. Finally, confirmation experimental tests have been carried out to evaluate the performance of the proposed method. Based on the results, the proposed procedure is efficient in modeling and optimization (with less than 3% error) of A-GTAW process.

Corrosion resistance of the dissimilar alloy AL6XN-Inconel 718 in 0.5 M NaCl

In the present work, the corrosion resistance of the dissimilar alloy AL6XN-Inconel 718 bound by the Gas Tungsten Arc Welding (GTAW) method was studied. Different alloy zones were analyzed: base materials (BMs), heat affected zones (HAZs) and welds. The effect exerted by the GTAW method on the corrosion resistance displayed by such dissimilar alloy in 0.5 M NaCl was established by means of corrosion studies employing potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests. The electrochemical results revealed that the alloy HAZs are more susceptible to corrosion due to microstructure changes caused mainly by elements such as Ni, Cr and Mo during the GTAW process.

Metallographic, Structural, and Mechanical Characterization of Weld Nuggets in Fe–Mn–Al–C Low‐Density Steels Microalloyed with Ti/B and Ce/La by Gas Tungsten Arc Welding Process

The use of low‐density (LD) steels has become increasingly important due to the advantages they offer, such as high strength, high ductility, and principally weight reduction. However, there are few studies regarding their weldability by conventional processes due to the metallurgical complexity of these alloys, including kappa carbides precipitation and hot‐cracking associated with the high contents of Mn, Al, and C. Herein, the main objective is the characterization of the fusion zone and different heat‐affected zones of austenitic Fe–Mn–Al–C LD steels microalloyed with Ti/B and Ce/La. For this purpose, weld nuggets were prepared by autogenous gas tungsten arc welding process using heat inputs of 660 and 975 J. The weld nuggets were characterized metallographic, structural, and mechanically by light optical microscopy, scanning electron microscopy, X‐ray diffraction, and Vickers microhardness. In general, weld nuggets shows three well‐defined zones where γ‐austenite is the main phase and AlN and MnS particles act as nuclei of complex precipitated particles of microalloying elements such as TiC and (Ce, La)O. A considerable decrease in hot‐cracking was noticed in the microalloyed grades. A modulated structure of kappa‐carbide particles was responsible of the largest hardness values (≈450 Vickers microhardness) in the second heat‐affected zone.

Dissimilar Welding of Nickel Based Superalloy with Stainless Steel: Influence of Post Weld Heat Treatment

ABSTRACT Dissimilar welding potentially has great importance for many industries. Joining of two different alloys is very challenging. In this paper, an attempt was made to produce a reliable joint between Nickel-based superalloy with stainless steel using the gas tungsten arc welding process with nickel-based filler wire. Post-weld heat treatment was executed at 700°C for 2 h. A critical comparison was made between the post-weld heat-treated samples and as-welded samples. The tensile test indicates that the strength of the joint is higher than the weaker base metal (Stainless Steel). The macrostructure and microstructure show proper fusion and bonding among the parent metals and filler wire. There is a formation of the partially melted zone at fusion boundary and secondary phase (Niobium-rich phase) at a region adjacent to the fusion boundary on heat-affected zone of Inconel side. It was also observed that the post-weld heat-treated samples have a significant reduction in the secondary phase. Vickers’ microhardness value indicates that the secondary phase has a higher value of hardness both in as-weld condition and post-weld heat treatment condition. Thus, Nickel-based filler wire is a compatible filler wire for the dissimilar joint.

Effects of W and Ce micro addition in filler metal on microstructure and creep strength of Cr35Ni45NbM alloy weld joint

The effect of the filler metal chemical composition on the performance of Cr35Ni45NbM alloy weld joint is studied in this paper. The Cr35Ni45NbM alloy weld joints with two type filler metals are produced through manual gas tungsten arc welding (GTAW) process. The number of carbide in weld metal is more than that of base metal, and the size of carbide is smaller. The carbide size in the fusion zone of the weld joint with addition Ce and W elements in filler metal is smaller than that without Ce and W elements. The micro addition of W and Ce in filler metal could improve the high temperature creep strength of weld joint, and has no evident effect on the tensile properties at room temperature. After high temperature creep test, the creep test specimens break at fusion zone, which indicates that the weak part of the weld joint is the fusion zone during service. In the creep process, the cracks first nucleate at the interface between carbide and γ matrix, and then propagate along the carbide, finally the weld joint fractures along the dendrite boundary.

Prediction of distortions and residual stresses in narrow gap weld joints prepared by hot wire GTAW and its validation with experiments

The present paper aims to predict distortions and residual stresses in thick plate weld joints of austenitic stainless steel material prepared by automatic hot wire gas tungsten arc welding (GTAW) process and narrow gap technique using finite element analysis (FEA). The prediction has been validated by carrying out experiments. The variables considered in welding of plate joints are narrow groove configuration, high deposition rate leading to lower heat input (hot wire GTAW), and stress relieving treatment. A suitable stress-relieving treatment has been proposed for relaxing residual stresses and preventing sensitization of the heat-affected zone (HAZ) of the ASS weld joint. Predicted and experimental results of temperature distribution, distortions, and residual stresses were found to be in good agreement. The applicability of prediction of residual stresses for higher weld thicknesses has also been verified. The nature of residual stresses across thickness has also been compared with that given in Structural Integrity Assessment Procedures for European Industry (SINTAP) and BS 7910 standards. Details of the above finding are discussed in this paper.

Role of the Ni-based filler composition on microstructure and mechanical behavior of the dissimilar welded joint of P22 and P91 steel

The manuscript described the effect of Ni-based filler on microstructure and mechanical properties of the dissimilar welded ASTM A335 grade P22 and P91 alloy steel plate. The dissimilar welds joint (DWJ) was produced using the Gas Tungsten Arc Welding (GTAW) process. The DWJ was characterized for metallographic and mechanical testing for as-welded and post-weld heat treatment (PWHT) conditions. For mechanical properties, microhardness, tensile test and Charpy impact test were performed. The DWJ showed the heterogeneity in microstructure and mechanical properties (microhardness, impact toughness) along the welded joint. The weld metal showed the formation of the austenitic microstructure consisted of the equiaxed dendrite along with segregation of the alloying elements like Cr, Mo, and Ti at the inter-dendritic boundaries, while P91 and P22 HAZ showed the formation of coarse-grained, fine-grained, and inter-critical heat-affected region depends on the temperature experienced during the welding cycle. The region of P91 HAZ was characterized by untempered and tempered martensite, while P22 HAZ was characterized by coarse and fine bainitic microstructure. The PWHT showed a negligible effect on the microstructure of the weld metal, while a significant change in microstructure of P91 HAZ and P22 HAZ was observed. PWHT also led to the formation of the soft and hard zone along the interface of the P22 steel due to the carbon diffusion. At the interface of the weld metal and base material, a sharp gradient was observed for the elements Cr, Fe, Ni and Mo. The weld metal near the interface showed the columnar dendritic structure having segregation of the alloying elements Mo, Ti and Cr along the inter-dendrite boundaries. A variation in hardness was measured along the weldments for as-welded and PWHT conditions. The peak hardness was measured in P91 coarse-grained heat-affected zone (CGHAZ) for both as-welded and PWHT, while the poor hardness of 202 HV and 195 HV was measured for weld metal in as-welded and PWHT conditions. The strength of the welded joint was measured higher than the strength of P22 steel for both conditions; however, the fracture was observed in P22 base metal for the as-welded joint, while in PWHT, it was in P22 HAZ near the interface. A variation in Charpy impact toughness was observed along the weldment for both as-welded and PWHT conditions. In as-welded, the minimum Charpy impact toughness (CIT) of 95.8 J was measured in weld metal, while the maximum was 152 J in P91 HAZ. After the PWHT HAZ region of P22 and P91 steel showed a drastic increase in CIT, however reduction in CIT of the weld metal was measured.

Non-equilibrium modeling of arc plasmas in the gas–metal arc–welding process

In recent years, the thermal and chemical non-equilibrium properties of arc plasmas have been among the most critical topics in the modeling of welding arcs. Non-equilibrium phenomena can be observed in the near-electrode regions, where the characteristics of the arc are determined. Although non-equilibrium modeling should contribute to a deeper understanding of the gas–metal arc-welding (GMAW) process, no non-equilibrium model has been reported for GMAW processes, while several models have been reported for gas–tungsten arc-welding processes. In this study, we attempted to elucidate the non-equilibrium phenomena in the GMAW process. In addition, as a first step, we developed a non-equilibrium model of the arc plasma in the GMAW process. The influence of the iron vapor was successfully determined by our model. We then inferred that the concentration of iron vapor affects the number density of electrons and, consequently, the thermal equilibrium of the arc in the GMAW process.

Experimental investigation on temperature profiles and residual stresses in GTAW dissimilar weldments of AA5052 and AA7075

ABSTRACT In this research, the dissimilar metals of AA5052 and AA7075 were joined by employing gas tungsten arc welding process using ER4043 as filler metal. During welding, the temperature distribution over the weld surface was measured using Infrared thermography. Using X-ray diffraction technique, residual stresses were measured in each welding pass on different weld zones. From thermography results, the peak temperature of 712, 789 and 816 °C was recorded in pass-1, pass-2 and pass-3, respectively. Higher temperature values were recorded at the HAZ of AA5052 than at the HAZ of AA7075. Peak residual stress of 66, 28 and 45 MPa was observed in pass-1, 2 and 3, respectively. Minimum residual stresses were observed at the HAZ of AA5052 than HAZ of AA7075.