Gas Tungsten Arc Welding Joints Research Articles

Evolution of microstructure and mechanical properties of GTAW joint for magnesium alloy thin plate by post-weld reinforcement compression treatment

Gas tungsten arc welding (GTAW) joints of magnesium alloy thin plates generally exhibit low welding coefficients. Therefore, post-weld reinforcement compression treatment is utilized to improve mechanical properties of the joints in this experiment. The study shows that the grain shapes and sizes in various zones of the treated welded joints alter significantly, and the presence of twins is also detected especially in the base material (BM) and heat-affected zone (HAZ). The strength of the welded joints progressively rises with the increase in the compression reduction. The welding coefficient of the C3-joint reaches 91.6% when the compression reduction is 1 mm. The ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) are 271 MPa,173 MPa and 7.2% respectively. The post-weld reinforcement compression treatment introduces abundant dislocations in the fusion zone (FZ), contributing significantly to the increase in joint strength. In addition, solid solution strengthening and texture strengthening also exert a role.

Evaluation of microstructure, corrosion resistance performance, and mechanical properties of 316L austenitic stainless steel FCAW welded joints: a comparative study

ABSTRACT This research aims to not only examine the effect of different mixtures of Ar and CO2 on microstructural features and corrosion behavior of double-pass FCAW of 316L SS but also compare these characteristics with gas tungsten arc welding (GTAW) and self-shielded FCAW. Different shielding gas mixtures, namely 100%Ar, 100%CO2, 82%Ar+18%CO2 were used to make the specimens. All specimens represent biphasic microstructures containing austenite (Ɣ) and delta-ferrite (δ-ferrite). Based on the potentiodynamic (PD) test results, the anti-corrosion protection performance of the welded region was enhanced when using GTAW compared to self-shielded FCAW. Additionally, the impedance value of the GTAW joint was higher than that of the FCAW-welded specimens. The ductility of welded joints was ranked as GTAW > CO2 +Ar shielded FCAW > self-shielded FCAW > CO2 shielded FCAW. The ranking of transverse tensile strength was as follows: CO2 shielded FCAW> self-shielded FCAW > CO2+ Ar shielded FCAW> GTAW.

Evaluation of Residual Stresses and Distortion of Ti-5Al-2.5Sn and SS 304 Gas Tungsten Arc Welded Joints under Hybrid Thermal Tensioning Technique: Transient Thermal Tensioning and Trailing Intensive Cooling

Evaluation of Residual Stresses and Distortion of Ti-5Al-2.5Sn and SS 304 Gas Tungsten Arc Welded Joints under Hybrid Thermal Tensioning Technique: Transient Thermal Tensioning and Trailing Intensive Cooling

Study on high-cycle fatigue properties of 9 %Ni steel joints welded by GTAW and SAW using nickel-based alloy

Welding of 9 %Ni steel was conducted using gas tungsten arc welding (GTAW) and submerged arc welding (SAW). High-cycle fatigue (HCF) tests were performed at 297 K and 77 K to investigate the effect of welding process on fatigue properties of the joints. The results showed that GTAW joint (GJ) exhibited a longer fatigue life than SAW joint (SJ) under similar situation. At 297 K, the fatigue limit for GJ and SJ was measured as 231.3 MPa and 202.5 MPa respectively. All the fracture locations were at weld metal (WM), with cracks initiating from Mo-enriched precipitates in GJ and non-metallic inclusions in SJ. The microstructure of GJ and SJ was similar. However, WM of GJ had fewer inclusions and a finer grain size than that of SJ, enhancing the HCF performance of the joints.

Study on the Effect of Hydrogen in Argon-Nitrogen Shielding Gas on Pitting Corrosion for Austenitic Stainless Steel by GTA Welding Process

The addition of hydrogen in shielding gas has been found to contribute to increasing the productivity of gas tungsten arc (GTA) welding compared to the processes using argon-nitrogen shielding gas. In this report, the GTA welding joints of AISI 304 stainless steel with Ar-N2 and Ar-N2-H2 addition were fabricated. The microstructure and pitting corrosion resistance were studied in this work. The corrosion characterisation of welds metal was investigated by a potentiodynamic method in NaCl solution. It was found that H2 addition also had effects on delta-ferrite microstructures and corrosion behaviour. Increasing hydrogen in argon-nitrogen shielding gas increased the delta-ferrite content and improved pitting corrosion resistance.

High-Temperature Tensile Behaviour of GTAW Joints of P92 Steel and Alloy 617 for Two Different Fillers.

This study explores the high-temperature (HT) tensile rupture characteristics of a dissimilar gas-tungsten-arc-welded (GTAW) joint between P92 steel and Alloy 617, fabricated using ER62S-B9 and ERNiCrCoMo-1 fillers. The high-temperature tensile tests were performed at elevated temperatures of 550 °C and 650 °C. An optical microscope (OM) and a field emission scanning electron microscope (FESEM) were utilized to characterize the joint. The high-temperature test results indicated that the specimen failed at the P92 base metal/intercritical heat-affected zone (ICHAZ) rather than the weld metal for the ERNiCrCoMo-1(IN617) filler. This finding confirmed the suitability of the joint for use in the Indian advanced ultra-supercritical (A-USC) program. The fracture surface morphology and presence of precipitates were analysed using an SEM equipped with energy dispersive spectroscopy (EDS). The appearance of the dimples and voids confirmed that both welded fillers underwent ductile-dominant fracture. EDS analysis revealed the presence of Cr-rich M23C6 phases, which was confirmed on the fracture surface of the ER62S-B9 weld (P92-weld). The hardness plot was analysed both in the as-welded condition and after the fracture.

Enhancement of mechanical properties of GTAW joints for ZC63 magnesium alloy by post-weld heat treatment

To further improve the microstructure and mechanical properties of gas tungsten arc welded (GTAW) welded joints for ZC63 magnesium alloy, post-weld heat treatment is carried out. It is found that the majority of the MgZnCu phase in the fusion zone (FZ) is dissolved in the α-Mg matrix under suitable heat treatment conditions. The remainder is diffusely distributed as rods or granules at the grain boundaries. The excessive heat treatment temperature (460 °C) leads to abnormal grain growth (AGG) in the FZ. The substructure gradient between the abnormally grown grains and the surrounding small grains provides the driving force for AGG. Meanwhile, the dissolution of the MgZnCu phase weakens the hindering effect of the second phase on grain boundary migration, setting the stage for AGG. In addition, the detrimental impact of the continuous MgZnCu phase on the mechanical properties of the welded joint is also lessened by its dissolution. The ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) of the welded joints are 255 MPa,119 MPa and 27.0%, respectively, under the post-weld heat treatment process of 440 °C × 12 h. The welding coefficient of the welded joint reaches 97.0%, satisfying the service criteria set forth by the mechanical properties of the welded joints.

Contrasting the mechanical and metallurgical properties of laser welded and gas tungsten arc welded S500MC steel

S500MC steel is a grade of high-strength low-alloy steel (HSLA) which is widely used in the automotive industry and for agricultural machinery and equipment. Considering properties of this alloy, selection of the welding process and parameters becomes essential to ensure that HSLA assemblies meet specific service requirements. In this work, mechanical and metallurgical properties of S500MC steel produced by autogenous laser beam welding (LBW) and automatic gas tungsten arc welding (GTAW) were compared. Tensile testing, metallography, hardness testing, and fractographic analysis were performed on the welded specimens, revealing that the heat input by these welding processes caused significant microstructural changes within the joints. In LBW samples, the heat input about 10 times lower than that in GTAW produced a finer microstructure, narrower fusion zone width, and smaller heat-affected zone. All fractures of the GTAW specimens occurred in the base metal, while all fractures of the LBW specimens occurred in the weld zone, both regardless of the heat input. GTAW joints exhibited higher mechanical properties (even higher than those obtained in the base metal) as compared to LBW joints.

Minimizing intermetallic Laves phase evolution and enhancing precipitation strengthening of Superalloy-718 joints using InterPulse magnetic arc constriction and high frequency pulsation

The techniques of InterPulse magnetic constriction and high frequency pulsation of arc in gas tungsten arc welding (GTAW) were deployed to minimize the detrimental intermetallic laves phase evolution in fusion zone (FZ) of Superalloy-718 welds and enhance the precipitation strengthening of joints. The Superalloy-718 joints were developed by using an advanced variant of GTAW popularly known as InterPulse gas tungsten constricted arc welding (IP-GTCAW). The joints were subjected to the post weld heat treatment (PWHT) cycles of direct aging (DA), solution annealing at 980 °C and 1065 °C followed by aging (980STA and 1065STA) respectively. The tensile properties and hardness of joints were evaluated. The microstructures of joints were analyzed using optical (OM) and scanning electron microscopy (SEM). The elemental analysis of Laves phase and dendrite core of FZ of joints was performed by using energy dispersive spectroscopy (EDS). The tensile fractured surfaces were analyzed using SEM. Results showed that the Superalloy-718 joints developed using IP-GTCAW showed better response to PWHT than GTAW joints because of the greater refinement of FZ microstructure and evolution of finer and discrete Laves phases in FZ. The 980STA joints exhibited superior tensile properties than DA and 1065STA joints. It is correlated to the greater dissolution of Laves phases in nickel austenitic (γ) matrix of FZ resulting in more niobium (Nb) accessible for the precipitation strengthening of FZ. The 1065STA joints showed slightly higher hardness of FZ than 980STA joints because of the almost complete dissolution of Laves phases in FZ. However, the tensile properties of 1065STA joints are lower than 980STA joints because of severe grain growth in FZ and BM. The evolution of microvoids at the interface of Laves phase/weld matrix leading to the development and coalescence of microcracks in FZ on tensile loading is the main mechanism responsible for the premature fracture of joints.

Effect of welding current and Laves phase on the microstructures and mechanical properties of GTAW joints for ZC63 magnesium alloy

Gas tungsten arc welding (GTAW) is used to successfully join ZC63 magnesium alloy extruded plates. The effect of welding current and Laves phase on the microstructures and mechanical properties of the welded joints were studied. It was found that when the welding heat input is low, the grains in the heat affected zone (HAZ) of the welded joints of ZC63 alloy with low recrystallization fraction will not grow significantly. This is due to the fact that the heat energy of the HAZ in the welding process is mostly consumed in the process of recrystallization nucleation and growth of new grains. Besides, compared to base metal (BM), The HAZ and fusion zone (FZ) present greater randomness of grain orientation and weaker crystallographic texture. With the increase of welding current, the mechanical properties of the welded joints decrease. The welded joints exhibit the most excellent properties when the welding current is 90 A (the UTS is 229 MPa, the YS is 100 MPa, and the EL is 12.6%). The FZ is the weakest position of the welded joints. The Laves phases are distributed in a continuous network at the grain boundaries in the FZ. Under the stress, the Laves phases are the initiation of crack, which eventually causes intergranular fracture of the welded joints.

Evaluation of microstructure and mechanical behavior of Aluminum 2024 and Stainless steel 304 GTAW joints

This study aims to evaluate the microstructure and mechanical behavior of aluminum 2024 and stainless steel 304 dissimilar joints. The gas tungsten arc welding (GTAW) process has been employed to weld base metals by inserting copper-nickel-based (Cu-10%Ni) filler metal. The effects of GTAW parameters such as welding current, welding speed, and gas flow on microstructure and tensile strength have been analyzed through the Taguchi method. Results revealed that tensile strength is primarily influenced by welding current, followed by speed and gas flow rate. The excellent joint strength of 138 MPa has been achieved by using Cu-10%Ni filler metal. The optimal combination of parameters, i.e., welding current of level 2 (80 A), welding speed of level 1 (100 mm/min), and gas flow rate of level 3 (10 l/min), has been obtained through SN ratio optimization. Microstructure and EDS analysis depicted that the weld zone of a high-strength joint contained fine dendrites and CuAl and NiAl solid solutions, while the weld zone of a low-strength joint featured coarse dendrites and brittle FeAl phases.

A Survey on Post-Weld Modification of Microstructural and Mechanical Properties of GTAWed Aluminum Butt Joints Through FSP and T6 Heat Treatment

Ergitme kaynağı ile birleştirme endüstrinin her alanında yaygın olarak uygulanan imalat yöntemlerindendir. Özellikle yüksek ısıl iletim ve genleşme katsayısına sahip, sıvı halde hidrojen çözünürlüğü yüksek olan ve yüzeyinde rijit oksit tabakası bulunan alüminyum alaşımlarının ergitme kaynağıyla imalatında iri tane oluşumu, mekanik özelliklerde düşüş vb. olumsuzluklar gerçekleşebilmektedir. Bu nedenle ergitme kaynaklı birleştirmelerin ömürleri ve mukavemetleri açısından kaynak sonrası işlem ile kaynak bölgesinin iç yapı ve mekanik özelliklerinin iyileştirilmesi çoğu uygulama için önemli rol oynamaktadır. Çalışmamızda, tungsten inert gaz (TIG) kaynağı ile birleştirilen AA6082-T6 plakaların kaynak bölgesi özelliklerine kaynak sonrası işlem olarak uygulanan sürtünme karıştırma prosesi (SKP) ve T6 ısıl işleminin etkileri araştırılmıştır. SKP ve T6 ısıl işleminin mekanik özelliklere ve iç yapıya etkileri çekme testi, mikrosertlik testi ve mikroyapı incelemeleri ile araştırılmıştır. SKP ile kaynak dolgusunun işlem gören bölgesindeki (karıştırma bölgesi) dendritik tanelerin parçalanarak ince taneli iç yapının elde edildiği tespit edilmiştir. Bununla birlikte, SKP’nin malzemede oluşturduğu ısıl girdi ile ısıdan etkilenen bölgenin (IEB) genişlemesine ve sertliğin daha geniş bölgede düşmesine sebep olduğu gözlemlenmiştir. Kaynak sonrası uygulanan T6 ısıl işlemi ile kaynaklı birleştirmenin mekanik özelliklerin arttırıldığı ancak tokluğunun azaldığı gözlemlenmiştir.

Microstructural and mechanical characterization of pre-used SA 335 P91 super-heater pipe weldment used in 70 MW CFBC boilers

The enhanced SA 335 P91 steels are specially designed to be used in the super-heaters in thermal power plants which are commonly operated at an elevated temperature. The present study involves an analysis of microstructure and the tensile property of the used P91 tubular steel of such heat exchanger in as-received conditions. The joints were fabricated by gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) by employing ErNiCrMo-3 and E9018 B9 fillers. The microstructure showed the presence of flakes of martensite, formation of Nb-rich phases with an unmixed zone in the interface of the weld followed by the columnar and equiaxed dendrites in the centre of the weld zone, while employing the ERNiCrMo-3 filler in GTAW. Whereas in SMA welding, no such unmixed zone was observed while employing E9018 B9 filler except the precipitation of carbides. The metallurgical and mechanical characterization of welded joints was performed by optical microscope, scanning electron microscopy with energy dispersive spectroscopy (EDS), hardness, toughness and tensile tests. From the SEM/EDS analysis in the fusion zone of joints inferred the uniform distribution of the element with Nb phases and oxide formation in the pre used P91 steel for both the weldments irrespective of the fillers employed. Alongside the hardness of the SMA weld zone showed a higher hardness by the precipitation of M23C6 and martensitic structure compared to the GTAW weld zone which is found to be lower owing to the presence of elements such as Mo, Nb, Al and C. In both the joints, the tensile failure occurred away from the fusion zone in the parent metal and SMAW joints imparted better strength than GTAW joints. The GTAW joints showed better toughness by ensuring the ductile mode of failure in fractography studies.

Influence of PWHT Parameters on the Mechanical Properties and Microstructural Behavior of Multi-Pass GTAW Joints of P92 Steel.

The 9% Cr steels were developed for ultra-supercritical (USC) power plants to meet the requirements of high operating temperature and pressure. These steels are produced to operate at high temperatures where impact toughness is not a concern; however, it becomes important for the welded joints to have good impact toughness at room temperature for manufacturing. The present work investigates the effect of the post-weld heat treatment (PWHT) parameters, i.e., temperature and time, on the impact toughness of multi-pass gas tungsten arc welded (GTAW) joints of ferritic/martensitic grade P92 steel. The microstructural evolution in welded joints given varying post-weld temperatures and times was studied. The lath martensitic structure of the weld metal for the as-welded joints resulted in high hardness and low impact toughness. The weld fusion zone toughness was 12 J, which was lower than the minimum specified values of 41 J (ASME standards) and 47 J (EN ISO 3580:2017). The PWHT temperature and time were found to have a significant effect on the impact toughness of the weld metal. A drastic increase in the impact toughness of the weld metal was noticed, which was attributed to lath break-up, reduction in dislocation density and reduction in solid solution hardening. The maximum impact toughness of 124 J was measured for PWHT temperature and time of 760 °C and 120 min, respectively. The effect of PWHT parameters on tensile strength was also investigated, and test results showed that the joint was safe for USC boiler application as it failed from the region of the P92 base metal. The variation in microstructural evolution along the weldments resulted in hardness variation. PWHT led to homogeneity in microstructure and, ultimately, reduction in hardness value. According to the study, the optimum temperature and time for PWHT of a GTAW joint of P92 steel were found to be 760 °C and 120 min, respectively.

Liquation Cracking Susceptibility and Mechanical Properties of 7075 Aluminum Alloy GTAW Joints.

In this work, aluminum alloy 7075-T651 was welded by using customized Al-Cu-Si and Al-Cu-Mg-Zn filler wire during gas tungsten arc welding. The liquation cracking susceptibility of the joints was tested under a circular-patch welding experiment. Besides, the temperature vs. solid fraction curves (T-fS) was calculated for different samples to reveal the formation mechanism of liquation cracking. The joint was susceptible to liquation cracking if (fS)weld > (fS)workpiece during the cooling stage. The results of the circular-patch welding experiment show that the liquation cracking susceptibility of the joint by using ER5356, Al-Cu1.5-Si4.5, Al-Cu3.0-Si2.5, Al-Cu4.5-Si1.5, Al-Cu2.3-Mg2.3-Zn6.6 and Al-Cu2.2-Mg2.0-Zn7.8 filler metal is 22.8%, 8.3%, 2.8%, 2.8%, 3.3% and 1.4%, respectively. The mechanical test shows that the data dispersion of the 7075 gas tungsten arc welding joint can be decreased by eliminating the liquation crack.

Friction Stir Welding of 2205 Duplex Stainless Steel: Feasibility of Butt Joint Groove Filling in Comparison to Gas Tungsten Arc Welding.

This work investigates the feasibility of using friction stir welding (FSW) process as a groove filling welding technique to weld duplex stainless steel (DSS) that is extensively used by petroleum service companies and marine industries. For the FSW experiments, three different groove geometries without root gap were designed and machined in a DSS plates 6.5 mm thick. FSW were carried out to produce butt-joints at a constant tool rotation rate of 300 rpm, traverse welding speed of 25 mm/min, and tilt angle of 3o using tungsten carbide (WC) tool. For comparison, the same DSS plates were welded using gas tungsten arc welding (GTAW). The produced joints were evaluated and characterized using radiographic inspection, optical microscopy, and hardness and tensile testing. Electron back scattering diffraction (EBSD) was used to examine the grain structure and phases before and after FSW. The initial results indicate that FSW were used successfully to weld DSS joints with different groove designs with defect-free joints produced using the 60° V-shape groove with a 2 mm root face without root gap. This friction stir welded (FSWed) joint was further investigated and compared with the GTAW joint. The FSWed joint microstructure mainly consists of α and γ with significant grain refining; the GTWA weld contains different austenitic-phase (γ) morphologies such as grain boundary austenite (GBA), intragranular austenite precipitates (IGA), and Widmanstätten austenite (WA) besides the ferrite phase (α) in the weld zone (WZ) due to the used high heat input and 2209 filler rod. The yield strength, ultimate tensile strength, and elongation of the FSWed joint are enhanced over the GTAW weldment by 21%, 41%, and 66% and over the BM by 65%, 33%, and 54%, respectively. EBSD investigation showed a significant grain refining after FSW with grain size average of 1.88 µm for austenite and 2.2 µm for ferrite.

Fatigue crack growth behavior and fracture model of the hydrogenated Ti-0.3Mo-0.8Ni alloy gas tungsten arc welded joints

Fatigue crack growth behavior of the hydrogenated Ti-0.3Mo-0.8Ni alloy gas tungsten arc welded (GTAW) joints was investigated. Fracture model of hydrogen-induced GTAW joint was revealed in details. The results show that as hydrogen level increased, crack growth rate in Paris and instability growth zones increased, the more the hydride, the more crack growth channels, the faster crack growth rate, and brittle fracture was intensified. There was the mutation of dislocation density on both sides of the hydride, and dislocation tangles and dislocation lines were concentrated in the vicinity of the hydride. Dislocation weakening caused by solute hydrogen and internal stress generated by hydrogen-rich clusters respectively promoted crack initiation. Evolution of hydride morphology and distribution caused by the interaction between the hydride and persistent slip bands (PSB) significantly reduced crack initiation resistance. Hydride inside the PSB as a hardening phase accelerated to separate from the matrix or itself fracture, which further promoted crack initiation. Cracks in Paris zone rapidly propagated along grain boundary of coarse size “cluster”, alpha / beta phase boundary and the hydride, or cut through alternating lamellar alpha and fine needle beta grains and the hydride.

Microstructure and Mechanical Properties of Hydrogenated Ti-0.3Mo-0.8Ni Alloy Gas Tungsten Arc Welding Joints

Microstructure, tensile property, microhardness and fracture behavior of the hydrogenated Ti-0.3Mo-0.8Ni alloy gas tungsten arc welding (GTAW) joints were investigated. The results show that the microstructure of the hydrogenated 0.21 wt.% H weld zone were composed of alternating lamellar alpha/needle-like transformed beta and the hydride. Transformed beta was secondary decomposed into the short rod-shaped secondary alpha and lamellar residual beta. The “Pinning” effect of the hydride and more difficult dislocations cross slip directly led to the increased ultimate tensile and yield strength. Average hardness of weld zone, heat affected zone and base metal for the hydrogenated specimens were 196, 177 and 169 HV respectively. Hardness of the former was greater than that of the latter two, hydrogen-induced hardness of the welded joint was significantly increased. Fracture mode of the hydrogenated welded joints changed from the single ductile fracture to mainly brittle fracture with a few dimples fracture. Main cracks that propagated alternately to the original beta grain boundary resulted in local fracture of the microstructure, the interconnected local fractures finally led to the overall fracture of the hydrogenated welded joint.

Effect of inclusions on microstructure and mechanical behavior of multi-pass welded naval grade steel

This paper assesses the metallurgical characteristics and mechanical properties of multi-pass gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) of micro-alloyed steel DMR 249-A. The prime objective was to carry out a comparative study of the microstructure and mechanical properties of the joints produced by the two types of welding. A high volume of larger sized inclusions in GMAW contributed to inferior mechanical properties. The coarse-grained part of the heat-affected zone (CGHAZ) showed a lower microhardness. Fracture always occurred in the heat-affected zone, and it is believed that it is associated with CGHAZ. GTAW joints showed low tensile residual stress, higher hardness, and tensile strength. GTA weldment also showed superior impact toughness at sub-zero temperature (–60 °C). Mn-containing inclusions were seen in GTA weldments; it is believed that they promote the formation of acicular ferrite. This is believed to be responsible for the superior mechanical properties of GTA weldments. The microstructural analysis of the two weldments revealed the presence of a higher volume fraction of acicular ferrite in the GTAW. All in all, GTAW joint was found to perform better than GMAW joint.

Mechanical and micro structural behaviour of flux coated GTAW and FSW joined AA6061 aluminium alloy

In the present paper, an attempt was made to experimentally investigate the mechanical properties of flux coated weld butt Joints of AA6061 aluminium alloy by considering two different welding processes namely GTAW and FSW. Gas Tungsten arc welding (GTAW) is preferred due to its comparatively simpler applicability and better economy. And the revolutionary solid-state welding technique, friction stir welding (FSW) is used due to its defect-free welds with good mechanical properties. Rolled plates of 3 mm thickness have been used as the base material for preparing single pass butt welded joints. The filler metal used to join the plates is AA4043 aluminium alloy. In this the investigation, tensile properties, Micro hardness, Microstructure and fracture surface morphology of the GTAW and FSW joints have been evaluated and the findings are contrasted. FSW Joint of Aluminium alloy AA6061 has shown superior mechanical properties compared to the GTAW Joint, this is mainly due to the formation of very fine, fully equally axed grain microstructures in the weld zone.