Current TIG Research Articles

Residual stress analysis, mechanical and metallurgical properties of dissimilar weldments of Monel 400 and AISI 316

Abstract This research manuscript explores the residual stress analysis, mechanical and metallurgical aspects of dissimilar welded joints between AISI 316 and Monel 400 developed by constant, pulse and Interpulse current TIG welding processes. The induced residual stresses have been measured experimentally by employing X-ray diffraction. The mechanical properties of welded joints have been determined by conducting tensile and Vickers hardness testing. The metallurgical properties of weldments have been analyzed by employing optical and scanning electron microscopy. From the experimental results, lower residual stresses have been observed in Interpulse current TIG weldment than the other two weldments. The tensile properties of the Interpulse current TIG weldment were observed to be higher than the other two weldments. In Interpulse TIG weldments, grain refinement and reduced heat affected zone near the fusion zone have been observed.

Residual stress analysis, mechanical and metallurgical properties of dissimilar weldments of Monel 400 and AISI 316

Abstract This research manuscript explores the residual stress analysis, mechanical and metallurgical aspects of dissimilar welded joints between AISI 316 and Monel 400 developed by constant, pulse and Interpulse current TIG welding processes. The induced residual stresses have been measured experimentally by employing X-ray diffraction. The mechanical properties of welded joints have been determined by conducting tensile and Vickers hardness testing. The metallurgical properties of weldments have been analyzed by employing optical and scanning electron microscopy. From the experimental results, lower residual stresses have been observed in Interpulse current TIG weldment than the other two weldments. The tensile properties of the Interpulse current TIG weldment were observed to be higher than the other two weldments. In Interpulse TIG weldments, grain refinement and reduced heat affected zone near the fusion zone have been observed.

Study of metallurgical changes and mechanical properties of dissimilar weldments developed by interpulse current TIG welding technique

This research manuscript compares the metallurgical changes and mechanical behavior of AISI 316 and Monel 400 dissimilar weldments developed by Interpulse TIG welding process with ERNiCrMo-3 and ER316 filler wires. Metallurgical aspects are envisioned by using optical and scanning electron microscopes. Mechanical behavior of welded joints were studied by conducting tensile and microhardness tests. Metallurgical study has shown that the ERNiCrMo-3 filler weldment divulged completely with austenitic phase structure at the weld zone. Also, at the HAZ of Monel 400 clear grain boundaries with fine grains were observed. The mechanical properties corroborated that the weld strength of ERNiCrMo-3 weldment was found better than the ER316 weldment. Microhardness on the weldment made of ERNiCrMo-3 filler has shown higher values than that of base metals. Weldment made by ER316 was observed to fail near the interface of Monel 400 under tensile test due to the existence of micro-pores and partially melted zones. Further, the metallurgical and mechanical properties are compared with that of the weldment developed by TIG welding process.

The effect of the current pulsation frequency on heat supply results during pulsed current TIG welding in 301L stainless steel

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.

Observation and analysis of metal transfer phenomena for high-current super-TIG welding process

ABSTRACTSuper-TIG welding is a newly developed TIG welding process using C-type filler metal in TIG welding. In Super-TIG welding, C-filler can prevent the molten pool depression, which is caused by high pressure in the center of the arc during high current TIG welding. In this study, metal transfer modes for C-type filler metal were observed. During these observations, feeding heights were varied for the current of 430 A. It was observed that the stable and continuous bridging transfer along with the arc blow on filler at zero gap feeding height. An intermittent bridging transfer of bridging and separating was repeated at 2 and 4mm height. The arc and filler voltages were low at bridging and high at separating.

A comparison of TIG-MIG hybrid welding with conventional MIG welding in the behaviors of arc, droplet and weld pool

The influence of electrode relative position and TIG current variation on arc stability and weld formation of TIG-MIG hybrid welding were studied comparing with that of conventional MIG welding. The welding current-voltage waveform was analyzed to characterize the arc stability. When TIG arc was leading, the hybrid arc was more stable than conventional MIG welding even when the TIG current was as low as 50 A, while the TIG current should be higher than 100 A to avoid spatters when TIG arc was trailing. The arc shape and droplet transfer were investigated to describe the heat and force distribution in weld pool. When TIG arc was leading, the backward arc force and droplet impingement could not decrease the backward flow of molten metal. The increment of MIG arc length dispersed MIG arc heat and resulted in narrower weld width, compared with conventional MIG welding, which was the main factor to suppress undercut defect. When TIG arc was trailing, the forward arc force and droplet impingement significantly decreased the backward flow velocity and gave molten metal more time to spread transversely to suppress undercut defect. Regardless the relative position of TIG and MIG arcs, the hybrid welding speed could reach up to at least 1.5 m/min.

Enhancement of weld quality of AISI 304L austenitic stainless steel using a direct current pulsed TIG arc

In welding processes, the quality of weldment usually refers to the desired weld bead geometry and its microstructural characteristics, which affect the mechanical properties of the welded components. The present paper aims to investigate the influences of the main process input factors on weld geometry, metallurgical characteristics, and mechanical properties of weldments of 3.8-mm-thick plates of austenitic stainless steel type 304L using tungsten inert gas welding with pulsed/non-pulsed current processes. This research paper investigates the effects on the arc pressure of pulse frequencies at levels of 6 and 1,000 Hz, and thereby their effects on the aspect ratio and morphology of the weld metal. The key outcomes of this work are that the frequency of arc pulsation has a strong effect on the breaking of the dendritic arms during the welding process. The obtained microstructure results reveal that the structure of the high pulse frequency current welded specimens are thus generally finer grained, with higher levels of residual ferrite and an absence of columnar grains; such pulse frequencies thus strongly influence the tensile strength and microhardness of affected weldments as compared to those seen in continuous current welded specimens. Additionally, the most important factor affecting the bead geometry and aspect ratio is identified as the pulse frequency, with a contribution of 64%.

An Experimental Study on Mechanical Behaviour of Pulsed Current Welding on Aluminum Alloy Joints

Aluminum alloys (Al–Si–Mg alloys) have gathered wide acceptance in the fabrication of light weight structures requiring high strength-to weight ratio, such as transportable bridge girders. An improvised method is Pulsed current tungsten inert gas (PCTIG) welding (Developed in 1950s). The pulse current is more frequently used in manual welding because it has a lot of advantages in comparison to direct current. The main advantages are improved bead contour, greater tolerance to heat sink variations, lower heat input requirements, reduced residual stresses and distortion. In the present work to study the effect of PCTIG welding over continuous current TIG welding, work plates of 6 mm thickness have been used as the base material for preparing single pass welded joints. Single V butt joint configuration has been prepared for joining the plates. The filler metal used for joining the plates is AA 5356 (Al–5Mg (wt%)) grade aluminum alloy The preferred welding processes of moderately high strength aluminum alloy are frequently tungsten inert gas welding (TIGW) process. Two different welding techniques are used to fabricate the joints and they are: (i) continuous current TIG welding (CCGTAW) (ii) pulse current TIG welding (PCGTAW) processes. Argon (99.99% pure) has to use as the shielding gas. This report presents the effect of pulsed current TIG welding on mechanical behavior of high strength aluminum alloy joints, and studying about the grain refinement of weld bead, conducting the mechanical tests such as tensile test, impact test, and hardness test. Pulsed current welded joints have given superior mechanical properties comparative to continue current welded joints. PCTIG welded joints given high tensile strength, hardness and impact strength values. Current pulsing leads to relatively finer structure.

Study the correlation between Microhardness, Microstructure & In-situ thermal analysis of PCATIG weldedments of Al-SiC composite

Activated TIG welding has been performed on Al – 8% SiC composite 5mm plate with various fluxes such as Al2O3, MnO2, CaO, MgO, SiO2 & TiO2. Microstructure, Micro hardness and cooling rate are observed. Correlation between micro hardness, microstructure and cooling rate of Pulsed Current TIG welding and Pulsed Current Activated TIG welding on Al-SiC composite has been studied. Combining the pulsed current TIG and activated TIG welding (PC-A-TIG) on Al-SiC composite showed very fine superior weld microstructure on PCATIG – SiO2 & PCATIG – TiO2 which resulted in higher micro hardness values around 70 – 75 Hv. Micro hardness are observed in different locations of weld surface such as 1mm, 2mm & 3mm below the weld surface and it also observed along the weld zone to heat affected zone upto 12mm for the profiling the micro hardness value around the weldment. Microstructure observed in weld centre for observed on weld zone & heat affected zone. Minimum micro hardness value between 63 – 65 Hv found in PCATIG – MnO2, PCATIG – CaO & PCATIG – MgO due to intermediate micro structure between coarse and fine. PCATIG – Al2O3 weld zone & heat affected zone and heat affected zone of PCATIG – MnO2, PCATIG – CaO & PCATIG – MgO shows coarse microstructure. This resulted in reduced micro hardness around 55 – 60 Hv. Coarse micro structure in weld zone and heat affected zone have least cooling rate. Fine micro structure in weld zone is due to higher cooling rate. Heat affected zone directly depends on temperature gradient between the weld centre and weldment heat affected zone.

Optimization of Process Parameters of Pulsed Current TIG Welding for Ferrite Content of DSS Joints

Optimization of Process Parameters of Pulsed Current TIG Welding for Ferrite Content of DSS Joints

Mechanical properties, thermal profiles, and microstructural characteristics of Al-8 %SiC composite welded using pulsed current TIG welding

This experimental study on Al-SiC composite investigated the temperature distribution and microstructural characterization during pulsed current tungsten inert gas (PCTIG) welding. The parameters considered for PCTIG welding were peak current, base current, pulse frequency, and pulse on time. Experiments were designed and conducted using L9 orthogonal array technique. Regression model was developed to predict the ultimate tensile strength, bending load, cooling rate, and peak temperature. Statistical software was used to obtain the optimal PCTIG welding parameters, such as peak current of 160 A, base current of 60 A, pulse on time of 50 %, and pulse frequency of 5 Hz to attain desired result, including increased peak temperature of 446 °C, increased ultimate tensile strength of 138 MPa, and high cooling rate of 20 °C/s. Fine grain structures were also observed in weld region. Additionally, SEM fractography showed the difference in fracture surface between the PCTIG welding effects of different welding conditions. Statistical software was also used in identifying significant factors that caused improvement in weld strength, grain refinement in weld zone, and high cooling rate during PCTIG welding of Al-SiC composite.

Suppression Mechanism of Low Current Auxiliary TIG Arc on High Speed TIG-MIG Hybrid Welding and Process Optimization

Suppression Mechanism of Low Current Auxiliary TIG Arc on High Speed TIG-MIG Hybrid Welding and Process Optimization

Behaviors of Cathode Spot in Alternative Current Helium TIG Welding of Aluminum

Behaviors of Cathode Spot in Alternative Current Helium TIG Welding of Aluminum

Investigation of Micro Hardness, Cooling Rate and Microstructure of ATIG Welded samples of Al-SiC composite

Activated TIG welding has been performed on Al – 8% SiC composite 5mm plate with various fluxes such as Al2O3, MnO2, CaO, MgO, SiO2 & TiO2, to study & analyze the Microstructure, Micro hardness and cooling rate. Correlation study between micro hardness, microstructure and cooling rate for Constant Current TIG welding and Activated TIG welding on Al-SiC composite are also carried out to analyze the relation between the effect of cooling rate on microstructure & the effect of microstructure on micro hardness. The experimental results of ATIG welding on Al-SiC composite shows fine grain weld microstructure on ATIG – SiO2 & ATIG – TiO2, which results in higher micro hardness. Micro hardness values are taken in different locations of weld surface at 1mm, 2mm & 3mm below the weld surface and the same is also observed along the weld zone to heat affected zone upto 12mm for the center of the weldment. Minimum micro hardness values found in ATIG – MnO2, ATIG – CaO & ATIG – MgO are due to intermediate micro structure between coarse and fine in heat affected zone. ATIG – Al2O3 weld zone & heat affected zone and heat affected zone of ATIG – MnO2, ATIG – CaO & ATIG – MgO shows coarse microstructure leading to reduction in micro hardness value. Cooling rate for the different CCTIG & ATIG welding are recorded and correlation between the micro structures are studied. Coarse micro structure in weld zone and heat affected zone have least cooling rate whereas fine micro structure in weld zone resulted at higher cooling rate. Heat affected zone strongly depends on temperature gradient between the weld center and weldment’s heat affected zone.

Effect of TIG current on microstructural and mechanical properties of 6061-T6 aluminium alloy joints by TIG–CMT hybrid welding

In order to expand the direct current-cold metal transfer (DC-CMT) method to include large-thickness plate welding, a tungsten inert gas–CMT (TIG–CMT) hybrid welding process was employed in this work. Adding a stable TIG arc can increase the total heat input on the workpiece and the penetration capacity of the DC-CMT welding process. Al6061 plates 4mm thick were welded successfully by this method. As the TIG current increased, the heat input of the welding process increased. The effect of TIG current on the microstructure and mechanical properties of the joints was investigated. The hardening phase in Al6061 was sensitive to the heat input provided by the welding process. Because of microstructural transformation, a decrease in the mechanical properties (softening phenomenon) invariably appeared in the heat-affected zone (HAZ). With increasing TIG current, the microstructures of the joints coarsened, and the width of the partially melted zone (PMZ) and HAZ of the joints broadened. A precipitation strengthening phase of Mg2Si appeared in HAZ. The hardness curve of the joint presented roughly W-type distribution. The hardness obtained in the softened zone was approximately 50% that of the base metal (BM). The joints demonstrated good deformation capability before fracture. As compared to the base material, the strength and the elongation of the joints decreased approximately 40% and 50%, respectively.

Assessing the effect of TIG alternating current time cycle on aluminium wire + arc additive manufacture

The effect of electrode positive time cycle (% EP) of the alternating current TIG process has been investigated for aluminium wire+arc additive manufacture of linear walls. The study considered the effect on oxide removal, linear wall dimensions, microstructure, mechanical properties as well as the effect on electrode wear. The results showed that the effective wall width was minimum at 20%EP with a corresponding maximum in layer height. It was also observed that increasing the% EP increased the electrode wear rate, which in turn affected the arc stability. Microstructure analysis showed a noticeable increase in the grain size for higher% EP. The study also showed that% EP had no significant effect on mechanical properties. From a heat input analysis, a direct correlation was observed between the arc voltage and the% EP. The study also indicated that there could be other contributing factors to wall dimensions. For aluminium wire+arc additive manufacture of linear walls, minimum cleaning ranged between 10%EP and 20%EP.

Study on butt joining 5052 aluminum alloy/Q235 mild steel by MIG-TIG double-sided arc welding-brazing process

MIG-TIG double-sided arc welding-brazing (DSAWB) was introduced to join 5052 aluminum alloy and Q235 mild steel of 3 mm thickness without groove. Variations of weld appearance, interfacial intermetallic compounds (IMCs), and mechanical properties with the increase of TIG current were studied under same MIG heat input. The comparison of DSAWB and single-side MIG welding-brazing process with same heat input was carried out. The results showed that DSAWB can significantly benefit the weld appearance, especially the back weld appearance, due to the heat and gas shielding provided by TIG source at the back. The weld appearance gradually became better before getting poor with the increase of the TIG current. Optimal DSAWB joint, which possessed excellent weld appearance and crack-free IMC layer with an average thickness of 3.1 μm, was achieved at a heat input of 858 J/cm. Under the same welding heat input, however, the single-side MIG welding-brazing process cannot achieve back weld appearance and the IMC layer was thicker near the top of the weld, indicating that the DSAWB process decreased the welding heat input needed for the sound joint. Average tensile strength of the optimal joints obtained by DSAWB process reached 148.1 MPa while the single-side MIG joint cracked after welding.

Combined effects of MIG and TIG arcs on weld appearance and interface properties in Al/steel double-sided butt welding-brazing

AA5052 aluminum alloy and Q235 low-carbon steel of 3.0mm thickness were butt joined without groove. The combined effects of the MIG-TIG double-sided arc on the weld appearance and interface properties were investigated in three aspects: weld appearance, interfacial properties and joint tensile strength. Form efficiency was defined to evaluate the quality of the weld appearance. The strength of the whole joint and the brazed interface were examined in the tensile tests of joints with and without excess weld metal, respectively. The weld appearance can be well characterized by the form efficiency. The form efficiency is found to be most sensitive to TIG current. Sensibility of the form efficiency to MIG voltage and welding speed is relatively low, indicating that the TIG arc at the back of the weld is the key factor for the double-sided weld appearance. Double-sided weld appearance can be achieved at a maximum welding speed of 2.2cm/s because a part of welding energy is input by TIG arc directly to the back weld. The interfacial properties of the joints are closely tied to the heat input ratio of MIG and TIG. Proper input ratio (1.35–1.64) leads to uniform deformation of the base metals and suppresses the initiation of the cracks in interfacial IMC layer. The differences between the interfacial strength and the whole joint strength indicate that the optimum weld appearance with desirable excess weld metal provides extra 20MPa strength for the whole joint. Benefitting from combined effects of the best weld appearance and toughest interfacial IMC layer, the highest tensile strength of the joint exceeds 70% the tensile strength of 5052 alloy.

Optimization of hybrid laser–TIG welding of 316LN stainless steel using genetic algorithm

ABSTRACTDetermination of optimum hybrid laser–TIG welding process variables for achieving the maximum depth of penetration (DOP) in type 316LN stainless steel has been carried out using a genetic algorithm (GA). Nd:YAG pulsed laser and the TIG heat source were coupled at the weld pool to carry out hybrid welding. Design of experiments approach was used to generate the experimental design matrix. Bead-on-plate welds were carried out based on the design matrix. The input variables considered were laser power, pulse frequency, pulse duration, and TIG current. The response variable considered was the DOP. Multiple-regression model was developed correlating the process variables with the DOP using the generated data. The regression model was used for evaluating the objective function in GA. GA-based model was developed and it produced a set of solutions. Tournament and roulette wheel selection methods were used during the execution of GA. It was found that both the selection methods identified similar welding process parameters for achieving the maximum DOP. Excellent agreement was observed between the target DOP and the DOP values obtained in the validation experiments during hybrid laser–TIG welding.

Optimization of hybrid laser – TIG welding of 316LN steel using response surface methodology (RSM)

In the present study, the hybrid laser – TIG welding parameters for welding of 316LN austenitic stainless steel have been investigated by combining a pulsed laser beam with a TIG welding heat source at the weld pool. Laser power, pulse frequency, pulse duration, TIG current were presumed as the welding process parameters whereas weld bead width, weld cross-sectional area and depth of penetration (DOP) were considered as the process responses. Central composite design was used to complete the design matrix and welding experiments were conducted based on the design matrix. Weld bead measurements were then carried out to generate the dataset. Multiple regression models correlating the process parameters with the responses have been developed. The accuracy of the models were found to be good. Then, the desirability approach optimization technique was employed for determining the optimum process parameters to obtain the desired weld bead profile. Validation experiments were then carried out from the determined optimum process parameters. There was good agreement between the predicted and measured values.