Tungsten Inert Gas Research Articles

Microstructure evolution and corrosion behavior of TIG welded joint of a new Mg[sbnd]Gd[sbnd]Nd[sbnd]Zn[sbnd]Zr alloy during post-weld heat treatment

The corrosion behavior of the tungsten inert gas (TIG) welded Mg3Nd3Gd0.2Zn0.5Zr alloy with different post-weld heat treatments was systematically investigated. The results show that the corrosion resistance of the sand-cast base material (BM) was inferior to that of the fusion zone (FZ), which was attributed to the larger grain size and exacerbated galvanic corrosion caused by coarser Mg3(Nd, Gd) eutectic phases and numerous β precipitates. It is found that post-weld solid-solution (T4) treatment could significantly enhance the corrosion resistance of the joint due to the dissolution of the cathodic second phases and the denser protective film abundant in RE oxides generated in corrosive solution. The precipitation of nanosized phases and ZnZr clusters would slightly increase the susceptibility to localized corrosion of the peak-aged (T6) joint. As the main corrosion products, MgO and Mg(OH)2 are distributed throughout the whole corrosion film, while RE oxides and RE hydroxides are mainly distributed in the inner layer, which can be explained by inward oxidation and replacement reactions between RE elements and MgO/Mg(OH)2. Based on the composition and structure of the corrosion product film, a physical model has been proposed for depicting the microstructure evolution associated with the corresponding corrosion behavior of the joints. This work could promote the applications of welded MgRE alloy joint in some corrosion environments.

Influence of inconel interlayer on microstructural, mechanical and electrochemical characteristics in single-pass ATIG welding of dissimilar austenitic and duplex stainless steel

This study investigates the impact of Inconel 625 interlayer on dissimilar welded low nickel austenitic stainless steel (LNiASS) and super duplex stainless steel (S32760) using activated tungsten inert gas (ATIG) welding. Two weldments were prepared: with and without (autogenous) interlayer. Geometrical investigation of the weld cross sections revealed that interlayer-based welding significantly increased the depth of penetration and decreased weld width as compared to autogenous welding at the same welding current. The dual microstructure was observed in the weld zone (WZ) of autogenous weldment while fully austenitic structure with few intermetallics was observed in the WZ of interlayer-based weldment. Mechanical properties, particularly impact strength observed to be improved in the case of interlayer-based weldment (91 ± 2 J) compared to autogenous weldment (68 ± 2 J). Lower microhardness was noticed for the WZ of interlayer-based weldment (258 ± 3 HV0.2) than WZ of autogenous (279 ± 2 HV0.2) weldment due to the presence of higher content of Ni. However, UTS of interlayer-based weldment (654 MPa), falls short in comparison to the autogenous weldment (693 MPa), indicating a compromised joint efficiency of 5.96%. The corrosion resistance was observed to be higher for the WZ of interlayer-based weldment attributed to the higher content of Ni and Mo. The sensitization study revealed 47.33% degree of sensitization in the WZ of autogenous weldments due to dual microstructure, while interlayer-based weldments showed no sensitization.

Mechanical and micro-structural studies of pulsed and constant current TIG weldments of super duplex stainless steels and Austenitic stainless steels

Abstract In the present research work, the influence of heat input rates on microstructures, hot tensile properties, and weld surface hardness number of Super Duplex Stainless Steel 2507 super duplex steels and austenitic steels 316L plates were investigated. Pulsed current and constant current modes were used in Tungsten Inert Gas (TIG) welding to join the dissimilar metals using ER2205 as filler. Microstructural studies were revealed at different zones of pulsed and constant current TIG weldments using optical microscopy. The tensile test was conducted at two different temperature conditions (i.e., 27 and 350°C) to investigate the strength of dissimilar weldments. Hardness measurements were made on the weld surface along the transverse direction using Vicker’s hardness tester. The microstructures revealed the formation of inter-granular austenite at the fusion zone with grain boundaries with austenite structures. Due to the constant heat input, a significant microstructural development with high austenite fractions was observed in constant current (CC)-TIG weldment. In comparison to CC-TIG weldments (UTS at 27°C = 600 MPa UTS at 350°C = 456 MPa), higher tensile characteristics were noted in Pulsed Current (PC)-TIG weldments (UTS at 27°C = 695 MPa UTS at 350°C = 475 MPa). The UTS of PC-TIG weldment is improved by 15.8% when compared to CC-TIG weldment due to the controlled heat input rates. PC-TIG weldments exhibited improved hardness numbers in various zones with smaller HAZ widths than CC-TIG weldments.

Effects of Weld Heat Input on Mechanical Characteristics of Low Carbon Sheet Steels

This study focuses on examining the variation in mechanical characteristics of low-carbon sheet steels when they are subjected to heat input from Tungsten Inert Gas (TIG) welding. The weld heat input parameters, such as welding speed and current, were controlled through the TIG welding process. A finite element analysis was performed to evaluate the couple field thermomechanical effects of the weld heat line, using the Gauss heat flux approach for thermal heat variation across the weld heat-affected zone. The numerical study yielded results for weld heat-affected deflection, residual stress, and modal analysis through the finite element model. It was found that the ductility decreased and hardness increased in the fusion zone, as a function of weld current and speed. The residual stresses and their zone of influence, as determined by weld line parameters, were found to be key factors affecting deflection and natural frequencies in structural aspects of low carbon sheet steels.

Exceptional grain refinement induced by dispersed MgO particles in TIG-welded AZ31 alloy

Due to the low content of alloying elements and the lack of effective nucleation sites, the fusion zone (FZ) of tungsten inert gas (TIG) welded AZ31 alloy typically exhibits undesirable coarse columnar grains, which can result in solidification defects and reduced mechanical properties. In this work, a novel welding wire containing MgO particles has been developed to promote columnar-to-equiaxed transition (CET) in the FZ of TIG-welded AZ31 alloy. The results show the achievement of a fully equiaxed grain structure in the FZ, with a significant 71.9% reduction in grain size to 41 µm from the original coarse columnar dendrites. Furthermore, the combination of using MgO-containing welding wire and pulse current can further refine the grain size to 25.6 µm. Microstructural analyses reveal the homogeneous distribution of MgO particles in the FZ. The application of pulse current results in an increase in the number density of MgO (1-2 µm) from 5.16 × 104 m−3 to 6.18 × 104 m−3. The good crystallographic matching relationship between MgO and α-Mg matrix, characterized by the orientation relationship of [112‾0]α−Mg//[01‾1]MgO and (0002)α−Mg//(111)MgO, indicates that the MgO particles can act as effective nucleation sites for α-Mg to reduce nucleation undercooling. According to the Hunt criteria, the critical temperature gradient for CET is greatly enhanced due to the significantly increased number density of MgO nucleation sites. In addition, the correlation with the thermal simulation results reveals a transition in the solidification conditions within the welding pool from the columnar grain zone to the equiaxed grain zone in the CET map, leading to the realization of CET. The exceptional grain refinement has contributed to a simultaneous improvement in the strength and plasticity of welded joints. This study presents a novel strategy for controlling equiaxed microstructure and optimizing mechanical properties in fusion welding or wire and arc additive manufacturing of Mg alloy components.

In Situ Analysis of Stress and Microstructure Evolution during Welding of High-Alloy Steels Using Energy-Dispersive X-Ray Diffraction

Constrained thermal expansion and contraction during welding cause a compression-tension cycle and plastic deformation in the heat-affected zone, leading to work hardening. The nature of this hardening effect—isotropic or kinematic—determines the final local yield stress and thus affects the residual stress state. Therefore, mechanical hardening must be modeled correctly in welding simulations for accurately predicting welding residual stresses. Previous studies, relying on comparisons with experimental ex situ results, led to different recommendations regarding the choice of the hardening model and thus require clarification. In this work, the stress evolution in the heat-affected zone of a tungsten inert gas weld is studied in situ using energy-dispersive x-ray diffraction and a novel method of stress analysis based on crystallite anisotropy. Additionally, microstructural information is gathered through line profile analysis. Results are shown for both austenitic and ferritic high-alloy steels and compared to ex-situ results including a validation of the new method of stress analysis. Finally, conclusions on the nature of work hardening are drawn.

Thermal evaluation of aluminum welding: a comparative study of friction stir welding (FSW), plasma-fsw, and tungsten inert gas (TIG)-FSW techniques

Thermal evaluation of aluminum welding: a comparative study of friction stir welding (FSW), plasma-fsw, and tungsten inert gas (TIG)-FSW techniques

Investigation on dual wire TIG Arc additive manufacturing of IN625 and SS316L FGM for continuous gradient and sandwich structures

Fabrication of functionally graded material (FGM) has been studied using dual wire WAAM-TIG (wire arc additive manufacturing - tungsten inert gas) process. The experimental research aims to perform the feasibility study of different designs of FGMs, including continuous gradient (CG-FGM) and sandwich structures (SW-FGMs). The weight percentage of two wire materials, SS316L and IN625, was precisely controlled using individual wire feeding systems. Process parameters were identified to obtain the defect-free deposition for the desired combination of weight percentage. The governing elements, i.e., Ni and Fe, showed a gradual variation in the case of CG-FGM and alternate peaks for SW-FGMs while examined using energy-dispersive X-ray spectroscopy (EDS). The alternate material distinction was noticeable with the increase in the number of individual layers for each set of SW-FGMs. The microstructure evolution of CG-FGM showed a smooth transition from equiaxed to columnar dendrites along the build direction, while SW-FGM showed heterogeneous behaviour. The hardness was steadily increasing in CG-FGMs and formed a wavy pattern in SW-FGMs. X-ray diffraction (XRD) analysis confirmed the formation of the austenitic phase, and variation in peak heights correlates to the change in microstructure and hardness. The conducted tribological study showed the specific wear rate gradually decreased with an increase of Ni content in CG-FGM, whereas in SW-FGM, it showed a strong dependency on the adopted design. The alloying effect in SW-FGM with different design modalities and its comparison with equal weight percentages were also studied in detail and presented.

Comparative Analysis of Microstructure Evolution and Mechanical Properties of Dissimilar Welded Joints of AA7075/AA6061 via Friction Stir Welding, Tungsten Inert Gas Welding, and Tungsten Inert Gas + Friction Stir Processing

Comparative Analysis of Microstructure Evolution and Mechanical Properties of Dissimilar Welded Joints of AA7075/AA6061 via Friction Stir Welding, Tungsten Inert Gas Welding, and Tungsten Inert Gas + Friction Stir Processing

Corrosion Resistance and Mechanical Properties of Cr-Rich 316 Stainless Steel Coatings Fabricated by the TIG Process Using Flux-Cored Wires.

Arc welded 316 stainless steel coatings with flux-cored wires are very promising for marine service environments due to their low cost, high efficiency, and satisfactory performance, while they suffers from Cr dilution during the preparation process. Herein, based on the consideration of increasing the Cr content and ensuring the same value of the Cr/Ni equivalence ratio (Creq/Nieq), 316-modified flux-cored wires, 316F (19Cr-12Ni-3Mo) and 316G (22Cr-14Ni-3Mo), were designed under the guidance of a Schaeffler diagram for the improvement of the electrochemical and mechanical properties of 316 stainless steel coatings. The designed flux-cored wires were welded into a three-layer cladding by the tungsten inert gas welding (TIG) process, and the microstructure, corrosion resistance, and mechanical properties of the claddings were investigated. The results showed that 316F and 316G consist of γ-Fe (austenite) and a small portion of δ-Fe (ferrite) as the Creq/Nieq is approximately 1.5. However, due to the higher value of the equivalent Cr content (ECC), 316G has an additional intermetallic phase (σ), which precipitates as a strengthening phase at grain boundaries, significantly increasing the tensile and yield strength of 316G but reducing its plasticity. In addition, the corrosion current density (icorr) and pitting potential (Eb) for 316G are 0.20447 μA·cm-2 and 0.634 V, respectively, while the values for 316F are 0.32117 μA·cm-2 and 0.603 V, respectively, indicating that 316G has better anti-corrosion performance.

Fabrication of tungsten inert gas-welded dissimilar aluminium joints using different friction stir processing tools through response surface method

ABSTRACT AA6061-T6 and AA7075-T6 materials find wide application in manufacturing industries due to their excellent engineering properties. Fusion welding generates solidification cracks, high residual stresses, and brittle intermetallic compounds that degrade joint qualities. To solve these difficulties, friction stir processing (FSP) is frequently employed, which improves joint properties through local microstructural refinement. In this study, the combined effect of FSP parameters, namely tool pin profile (TPF), tool rotation speed (TRS), and travel speed (TS), on tungsten inert gas (TIG) weld properties was investigated. Response surface methodology (RSM)-based mathematical models were developed to predict responses, namely ultimate tensile strength (UTS), impact toughness (IT), microhardness (MH), and residual stress (RS). The optimal FSP parameters were determined through the desirability function technique. Post-FSP increased the UTS, IT, and MH of TIG welds by 71.51%, 95.40%, and 72.46%, respectively, and decreased the RS by 58.46%. ANOVA findings exhibited that TPF was the most influential parameter, followed by TRS and TS. The dissimilar aluminium TIG+FSP joints showed an optimal UTS of 282.08 MPa, an IT of 17.32 J, a MH of 121.48 HV, and an RS of 22.09 MPa when using a TRS of 1108.49 rpm and a TS of 37.74 mm/min with a THF pin.

Wear Behavior Assessment of New Wire-Arc Additively Manufactured Surfaces on AA6061 and AA5086 Alloys through Multi-Walled Carbon Nanotubes and Ni Particles Inducement

This study investigates the new surface development on AA6061 and AA5086 alloys considering the wire-arc additive manufacturing technique as a direct energy deposition (DED) process of wire. Two different quantities of MWCNTs, i.e., 0.01 (low) and 0.02 (high) g, with a constant nickel (Ni) weight (0.2 g) were pre-placed in the created square patterns. ER4043 filler was used as a wire for additive deposition, and an arc was generated through a tungsten inert gas (TIG) welding source. Furthermore, hardness and pin-on-disk wear-testing methods were employed to measure the changes at the surfaces with the abovementioned inducements. This work was designed to illustrate the hardness and the offered wear resistance in terms of mass loss of the AA6061 and AA5086 aluminum alloys with the function of nano-inducements. Two sliding distance values of 500 m and 600 m were selected for the wear analysis of mass loss from tracks. A maximum increase in hardness for AA6061 and AA5086 alloys was observed in the experiments, with average values of 70.76 HRB and 74.86 HRB, respectively, at a high mass content of MWCNTs. Moreover, the tribological performance of the modified surfaces improved with the addition of MWCNTs with Ni particles in a broader sense; the modified surfaces performed exceptionally well for AA5086 compared to AA6061 with 0.02 and 0.01 g additions, respectively. The system reported a maximum of 38.46% improvement in mass loss for the AA5086 alloy with 0.02 g of MWCNTs. Moreover, the morphological analysis of the developed wear tracks and the mechanism involved was carried out using scanning electron microscope (SEM) images.

EXPERIMENTAL STUDY ON MAG WELDED E350 HSLA STEEL JOINTS

Activated flux has been used successfully to improve the penetration of Tungsten Inert-Gas (TIG) welding, which is normally a welding process with low penetration. But the same activated flux when used for Metal Active Gas (MAG) welding showed a moderate improvement in penetration. Hence only a few research articles reported on activated flux MAG welding. TIG dressing is a post-weld treatment intended to improve the fatigue life of welded joints. The use of activated flux along with TIG dressing were not yet reported. In this work, an experimental study was conducted on the metallurgical changes and their effects on fatigue life in E350 steel welded by MAG welding with activated flux coating as well as toe TIG dressing. The metallurgical changes induced by various weld conditions and the effect on the fatigue life of welded joints were discussed. Welding conditions were categorised as: as weld (AW), weld with flux coating (FW), weld with TIG dressing (AWT), and flux weld with TIG dressing (FWT). Fatigue tests at stress ranges closer to the yield stress (80 % to 90 % of yield) were studied. In comparison with AW joints, the AWT and FWT showed a fatigue-life improvement of 60 % to 80 %, and 69 % to 103 % respectively. Whereas the FW joints showed 10 % to 17 % deterioration in fatigue life. Upon investigation with electron microscopy it was found that the variation in grain sizes and phase changes induced by the usage of flux and TIG dressing, as well as the changes in weld toe radius by TIG dressing and root strengthening due to extra penetration induced by the use of flux were the reasons behind these fatigue behaviours. In this work a novel effort is made to find a way to improve the fatigue life of a welded joint with a combination of two techniques. The activated flux is used to improve the penetration, whereas TIG dressing is performed to reduce the stress concentration. This new combination of techniques has improved the fatigue life of the weld significantly, which can lead to reduced maintenance costs of welded joints and a longer life.

Penetration identification of magnetic controlled Keyhole Tungsten inert gas horizontal welding based on OCR-SVM

Penetration identification of magnetic controlled Keyhole Tungsten inert gas horizontal welding based on OCR-SVM

Tungsten inert gas-assisted surface modification of 1045 steel with SiC particles

AISI 1045 steel is a medium-carbon steel with good strength, hardness, machinability, and weldability. However, it has poor wear and corrosion resistance. This study is an attempt to investigate the feasibility of creating a hard and wear-resistant composite layer on the surface of AISI 1045 steel using SiC particles through the tungsten inert gas (TIG) welding. The SiC powder was mixed with sodium silicate glue and polyvinyl alcohol and then applied to the samples using the TIG welding process. The welding voltage was kept constant at 15 V, and the welding current and welding speed were varied from 85 to 95 A and ∼ 0.5 to 1.8 mm/s, respectively. The powder percentage varied between 10 and 30 wt. %. The microstructural evolutions were studied using an optical microscope, a field emission scanning electron microscope (FESEM) equipped with an energy-dispersive spectroscope (EDS), and X-ray diffraction (XRD). It was observed that the microstructure of the surface-modified samples consisted of a dendritic Fe–Si matrix with carbon masses remaining from the partial dissolution of SiC particles. The effect of heat input on the microstructure was also investigated. The hardness of the surface-modified samples increased by about eight times compared to the base metal, and their wear resistance was notably improved. The results of the electrochemical corrosion tests showed an overall improvement in the corrosion resistance of the coated samples compared to the base metal.

Exploring the influence of pin geometry on metallurgical and mechanical characteristics of dissimilar aluminum TIG welds via friction stir processing

This study explored the effect of friction stir processing (FSP) on tungsten inert gas (TIG)-welded AA6061-T6 and AA7075-T6 joints by utilizing three different tool pin geometries, namely simple cylinder (SC), threaded cylinder with triflat faces (THF), and simple square (SS). The metallurgical aspects of unprocessed and processed weld regions were analyzed and correlated with the ultimate tensile strength, impact toughness, and microhardness properties. Results revealed that the post-FSP with a THF pin transformed the coarse dendritic structures (AGS of 34.55 µm) of the TIG weld into equiaxed fine structures (AGS of 3.51 µm) and increased the UTS, impact toughness, and microhardness by 71.51%, 95.40%, and 72.46%, respectively. The joint processed with the THF pin resulted in the highest ultimate tensile strength of 279 MPa, impact toughness of 15.02 J, and microhardness of 116.13 HV in the nugget region compared to the other two pin geometries. The highest joint properties of THF pin were attributed to the formation of fine grain structures in the nugget region, high effective strain and heat generation, improved material flow, and the decimation of intermetallic precipitates with their uniform dispersion in the nugget region. The tensile fractured surface of the TIG weldment had noticeable macro voids and coarse dimples with some rough cleavage facet in the fusion region, resulting in a brittle mode of failure. However, the tensile fractured surface of TIG + FSP weldments showed ductile failure due to the presence of fine and deep dimples with tear ridges without any void.

Void nucleation and growth behavior of TIG welded AA2219 deformed at cryogenic temperatures

This work investigates the failure behaviour of tungsten inert gas (TIG) welded 2219 aluminum alloy butt welds deformed over a range of cryogenic temperatures relevant to liquid hydrogen/oxygen propellent storage tanks. A novel in situ tensile testing machine, able to deform samples at temperatures down to 83 K, was designed to be accommodated on synchrotron computed tomography beamlines. In this way we were able to observe the accumulation of damage from void nucleation through growth to coalescence and ultimate failure by time-lapse X-ray microtomography during tensile straining at 293 K and 123 K. The results reveal that micro-void nucleation is triggered by θ (Al2Cu) precipitates and α-Al + θ (Al2Cu) eutectics in the form of particle fracture and interface decohesion. After nucleation, these freshly nucleated voids, along with pre-existing welding defects, extend with straining along the loading direction. This leads to void linkage, a very short void coalescence stage and subsequent catastrophic failure. The probability distribution function that describes the rate at which voids nucleate by interface decohesion considering the particle orientation was determined through the Eshelby inclusion theory. The evolution of void aspect ratio and void growth were modelled using the Gurson-Tvergaard-Needleman model and Le Roy model, respectively. This suggests that pre-existing defects grow faster, but that the numerous closely spaced nucleated voids play a significant role in failure.

Metallurgical and mechanical properties evaluation of the activated flux tungsten inert gas weldments

The activated flux tungsten inert gas welding process is an attractive joining technique to increase the depth of penetration in a single pass. In the last two decades, the research on activated flux tungsten inert gas welding increased drastically. Despite enhanced weld penetration, activated flux tungsten inert gas is not frequently implemented in industries because of a lack of information about the process. However, research on activated flux tungsten inert gas welding has significantly increased in the last decade due to the widespread information related to the advancements in weld penetration and mechanical properties of the activated flux tungsten inert gas process. The activated flux tungsten inert gas welding process provides a high single pass depth of penetration along with good mechanical properties compared to the tungsten inert gas welding process. The current work offers an in-depth analysis of the activated flux tungsten inert gas welding process mechanism, advancement in activated flux tungsten inert gas methodology to improve weld bead geometry, and mechanical and corrosion behaviour of the weldments. The current work also highlights recent progress made in the field of dissimilar metal joining using the activated flux tungsten inert gas welding process.

Fabrication of Titanium Aluminide Alloys by Twin-Wire Tungsten Inert Gas Welding Applied with High-Frequency Induction Heating Wire Technology: Processing, Microstructure, and Properties

Fabrication of Titanium Aluminide Alloys by Twin-Wire Tungsten Inert Gas Welding Applied with High-Frequency Induction Heating Wire Technology: Processing, Microstructure, and Properties

Stress corrosion effects on ADC12 Al alloy tungsten inert gas welding joint in 3.5 wt% NaCl solution

The stress corrosion behavior of ADC12 Al alloy tungsten inert gas (TIG) welding joint (WJ) outside its elastic deformation range was studied using electrochemical testing methods combined with surface analysis techniques in 3.5 wt% NaCl solution at 30 °C. The results showed that, with the enlargement of imparted stress, the corrosion potential of the TIG WJ shifted positively, the corrosion current density increased, and the polarization resistance decreased, indicating that the corrosion rate of the TIG WJ increased with the enlargement of imparted stress. With the prolongation of immersion time, the corrosion rate of the TIG WJ increased and then subsequently decreased. In addition, the plasticity and ductility of the TIG WJ decreased with the enlargement of imparted stress. When the imparted stress was 2100 N and 4200 N, the corrosion products on its surface were mainly composed of Al2O3 and Al(OH)3. This study provided a theoretical basis for the selection of structural materials and welding methods in the automotive, marine and aerospace fields.