Pulsed Tungsten Inert Gas Welding Research Articles

Study on Fatigue Performance of Pulsed Tungsten Inert Gas Welding Joint of Duplex Stainless Steel Thin Tube.

To solve the shortage of austenite phase precipitation caused by nitrogen loss in the welding process of UNS S2205 duplex stainless steel (DSS), shielding gas nitriding was investigated by adding different N2 contents in Ar shielding gas during the welding process. A good thin-walled pipe butt joint was formed using the pulsed tungsten inert gas (P-TIG) welding method with Ar-N2 shielding gas. High cycle fatigue tests of the weld joints were conducted to study the effect of shielding gas nitriding on the fatigue properties. Fatigue tests at three stress levels of 225 MPa, 270 MPa, and 360 MPa were carried out on the weld joints with different N2 contents, and the fatigue samples were all fractured in the high temperature heat-affected zone (H-HAZ). Within the current process parameters, the fatigue life of the 4 vol.% N2 welded joints was optimal. Fatigue striations appeared in the fatigue crack propagation zone, and the transient fracture zone was similar to the tensile fracture. Under the low-stress level, the area of the crack propagation zone under 4 vol.% N2 was the highest, the tear ridges all expanded around the crack source area, and the fatigue crack propagation zone presented a radial distribution. The proliferation and expansion of dislocations were mainly carried out in the austenite grains, and the dislocation density of the fatigue specimens under 4 vol.% N2 was smaller than that of the Ar specimens. Shielding gas nitriding effectively improved the balance of the two-phase ratio and the hardness of austenite phase, optimized the internal slip system, inhibited the proliferation of dislocations in the austenite phase, and improved the fatigue life of weld joints.

Optimization on the mechanical parameters and impact of welding parameters of pulsed TIG welding of Aluminium-Zinc-Magnesium alloy

As a function of pulsed Tungsten Inert Gas (TIG) weld processing factor, authors have studied the relationship between dilution and mechanical qualities including impact toughness, notch tensile strength, hardness in the as-welded condition. Welds made with a pulsed TIG torch have a minimum notch tensile strength and impact toughness than the base metal (BM) because of the grains of the inter-dendritic network formed during the welding process. Weldments made from heat-treatable (Al-Zn-Mg) Aluminium alloys have their process parameters for pulsed TIG welding optimized employing the Taguchi analysis to get the best possible mechanical qualities. Notch tensile strength is shown to be inversely proportional to impact toughness.

Ultrasonic-assisted Pulsed TIG Welding (U-P-TIG) of Inconel 690 for Nuclear Power Plants

Inconel 690 has been extensively used in steam generator tubing materials for pressurized water reactors. In order to improve the weld quality of Inconel 690, ultrasonic-assisted pulsed tungsten inert gas (TIG) welding is studied. In this study, the macrostructure, microstructure, and mechanical properties of Inconel 690 weldments welded by TIG welding with and without ultrasonic assistance were investigated. The microstructures of the fusion zone (FZ) and heat-affected zones (HAZ) were examined by an optical microscope and the Electron Backscatter Diffraction (EBSD) technique, and weldment properties were compared through tensile and impact tests. Experimental results indicate that the base metal (BM) was composed of equiaxed crystalline austenite, and the austenite grains in the heat-affected zone were obviously grown; the fusion zone (FZ) was composed of columnar austenite. Besides, the ultrasonic assistance was effective in refining the structure and improving the strength and toughness of weld metal.

Strengthening of Al/Cu dissimilar joint due to complicated interface produced by pulsed TIG welding with a constricted nozzle

Al/Cu dissimilar welding is a key technology for weight reduction in fabricating high-functional products, however, conventional tungsten inert gas (TIG) welding is difficult to be applied due to a large fusion area. The constricted nozzle equipped inside the conventional TIG torch has been developed and can improve the position accuracy of tungsten electrode and arc plasma characteristics, moreover increase the heat input density. In this study, 0.5 mm-thick Al and Cu dissimilar sheets were butt welded using pulsed TIG welding with the constricted nozzle under two welding speed-current combinations of 50 mm/s-85 A and 100 mm/s-105 A. The 50 mm/s-85 A joint exhibited that Al and Cu mixed each other in the entire weld metal, containing two intermetallic compounds (IMC) of Al2Cu and Al4Cu9 mainly in the Al side. In contrast, both elements hardly mixed each other in the 100 mm/s-105 A weld metal and the interface exhibited hook-like shape at a nearly constant pitch, depending on the welding speed and pulse frequency. Consequently, the formation of IMC layers was limited. Based on the three-dimensional images reconstructed using a serial sectioning technique, the hook-shaped Al/Cu interface was also formed inside the weld metal. The mixed-zone volume per unit weld length of the 100 mm/s-105 A joint was estimated to be about 0.12 mm3/mm, and is much smaller than that of the 50 mm/s-85 A joint (0.97 mm3/mm). The average tensile strength of the 100 mm/s-105 A joint were higher than those of the 50 mm/s-85 A joint, suggesting that the hook-shaped Al/Cu interface together with the reduced mixed zone seems to increase the joint strength.

Refining microstructures and enhancing mechanical properties of Inconel 718 weldment via fast-frequency double pulsed waveforms adopting in FFP-TIG

Raising the frequency of pulsed welding current in conventional tungsten inert gas (TIG) welding would stimulate the arc to stir the molten metal and thus refine microstructures and enhance mechanical properties of Inconel 718 (IN-718) weldment. In the high-frequency pulsed welding waveform, scholars are usually focused on the high-frequency pulses distributing above the low-frequency pulses while seldom considering the large space inside the low-frequency pulses to accommodate the high-frequency pulses. A fast-frequency double pulsed (FFDP) waveform is proposed to apply in fast-frequency pulsed TIG (FFP-TIG) welding. The effect of FFDP waveform modulation on the stirring of the molten pool and grain refinement was studied. The electromagnetic effect of FFDP waveform concentrated the welding energy and caused the increasing depth and decreasing width of IN-718 weldments, which enhanced the cooling rate during the solidification and formation of the weldments. Besides, the melt IN-718 within molten pool would be stirred due to the Marangoni effect induced by FFDP waveform. The increasing cooling rate and inducing stirring effect synergistically acted and thus refined the microstructures of IN-718 weldments, with the minimum size being 35.15 and 0.59 µm for irregular polygonal equiaxed grain and strip Laves phase, respectively. The tensile strength and the corresponding elongation of IN-718 weldments at high temperature (700 ℃) achieved 91% and 209% of the base metal. Current work provides an important direction towards the fabrication and development of high-reliability IN-718 weldment with good mechanical performance in high-temperature.

Influence of pulsed TIG welding process parameters on the mechanical characteristics of AA5083 with AA6082 weldments

Aluminium alloys have been widely accepted in manufacturing lightweight materials with high strength. Therefore, welding aluminium alloys is essential in industrial applications to attain complex shapes. In the present work, AA5083 and AA6082 dissimilar alloys were welded using pulsed tungsten inert gas (PTIG) welding since PTIG reduces welding defects more than TIG welding. But to get better mechanical strength on the weld joints, PTIG welding process parameters must be optimized. During PTIG welding, peak current, pulse frequency, and welding speed were chosen as the input parameters, and ultimate tensile strength (UTS) and microhardness were measured as output responses in the current investigation. The UTS of the welded AA5083-AA6082 alloys was predicted using an empirical relationship. For the design of experimental trials, a three-variable, five-stage central composite design is adopted. The findings indicate that the welding speed impacts tensile strength the most, followed by the peak current and the pulse frequency has the least impact. Therefore, the peak current of 197 A, pulse frequency of 4.9 Hz, and welding speed of 181 mm min−1 was identified as the optimal welding parameters to weld AA5083 and AA6082 alloys with high UTS values. The hardness analysis on the optimized welded samples showed that the lowest hardness values of 40 to 50 Hv0.5 and the highest value of 90 to 100 Hv0.5 were observed on the HAZ of the AA6082 side of the weldment.

Strengthening of Al/Cu dissimilar joint due to complicated interface produced by pulsed TIG welding with a constricted nozzle

Al/Cu dissimilar joining is a key technology for weight reduction in fabricating high-functional products, however, conventional tungsten inert gas (TIG) welding is difficult to be applied due to a large fusion area. The constricted nozzle equipped inside the conventional TIG torch has been developed and can improve the position accuracy of tungsten electrode and arc plasma characteristics, moreover increase the heat input density. In this study, 0.5 mm-thick Al and Cu dissimilar sheets were butt welded using pulsed TIG welding with the constricted nozzle under two welding speed-current combinations of 50 mm/s-85 A and 100 mm/s-105 A. The 50 mm/s-85 A joint exhibited that Al and Cu mixed each other in the entire weld metal, containing two intermetallic compounds (IMC) of Al2Cu and Al4Cu9 mainly in the Al side. In contrast, both elements hardly mixed each other in the 100 mm/s-105 A weld metal and the interface exhibited hook-like shape at a nearly constant pitch, depending on the welding speed and pulse frequency. Consequently, the formation of IMC layers was limited. Based on the three-dimensional images reconstructed using a serial sectioning technique, the hook-shaped Al/Cu interface was also formed inside the weld metal. The mixed-zone volume per unit weld length of the 100 mm/s-105 A joint was estimated to be about 0.12 mm3/mm, and is much smaller than that of the 50 mm/s-85 A joint (0.97 mm3/mm). The average tensile strength of the 100 mm/s-105 A joint were higher than those of the 50 mm/s-85 A joint, suggesting that the hook-shaped Al/Cu interface together with the reduced mixed zone seems to increase the joint strength.

Assessment of intelligent CMT with TIG welding on stacked thin sheets of CRNGO electrical steel

TIG (Tungsten Inert Gas) is the widely utilized welding process in industrial operations till date. TIG welding is commonly adopted for ease of use and economic reasons. The industries are recently dealing with the issues associated with higher losses in equipments occurred due to the welding process. Stators, which are utilized in electric motors (EM) and hybrid electric vehicles (HEV), are one among such industrial products. The advanced pulse operated cold metal transfer welding technology offers a workable substitute for traditional and pulsed TIG welding, because of its characteristic features. The study's primary objective is to combine stacks of CRNGO (Cold rolled non-oriented) electrical steel, which are prime materials for stators of HEV and EM and join them using welding process. After choosing the GMAW CMT technique over the conventional TIG welding procedure, which was predominantly employed to join the electrical steel sheets, a systematic strategy is used to emphasize the studied investigations. The GMAW CMT welding samples revealed improved performance with around 15 HV reductions in micro-hardness variations (mechanical property), about 25% reduced geometry (D/W ratio) of weld seam (macroscopic features), and around 50 µm reduced grain sizes (microscopic characteristics) of the weld CRNGO thin sheet samples compared to conventional TIG welding. The research work can be considered as a reference to utilize GMAW CMT technology for joining stacks of CRNGO sheets.

Interfacial evolution of titanium/steel clad plates during pulsed tungsten inert gas welding

Joining titanium alloy with steel has important applications in the shipbuilding and aerospace industries. Successful titanium/steel joints fabricated by explosive welding have been reported recently. However, explosive welding is not ideal for welded structures with complex geometry. Here, pulsed tungsten inert gas (TIG) welding is introduced to promote the application of explosively welded transition joints. In this work, pulsed TIG of commercially pure titanium to mild steel with an explosively welded titanium/steel transition joint was carried out. The results showed that at peak current (Ip) ≤ 260 A, the TiC layer hampered the generation of FeTi and Fe2Ti. However, at Ip = 300 A, the TiC layer broke up, which resulted in the thickness of FeTi and Fe2Ti increasing sharply to 0.8 μm.

Weld Strength and Cracking Susceptibility Analysis of Pulsed TIG Welded Al-Mg-Si Alloy by Experimental Approach

Aluminium is a non ferrous corrosive resistance metal mainly used in automotive coolers, inter coolers and radiators. They are the part of automobile vehicles and made from aluminium alloys. The joints in this application are created by fusion welding process specifically Tungsten Inert Gas (TIG) and Pulsed current TIG (PCTIG) welding process. The working temperature range of different coolers, radiators are 20° C to 300° C and pressure ranges from 2.5 bar to 3.5 bar. During actual working of coolers, the weld joint experiences sudden high level and low level temperature changes. These will create high thermal stresses in the joints. It leads to cracking in the weld region and create failure of the weld joints. Various factors such as mechanical, metallurgical and thermal are responsible for cracking in the weld joints. Range of solidification temperature is one of metallurgical factor, stress generation is mechanical factor and cooling rate of weld metal is thermal factor for cracking. Houldcroft weldability test is employed to identify the cracking susceptibility (CS) of the weld. The current investigation is intended to discover the effect of pulse TIG welding process parameters on the mechanical properties and cracking susceptibility of precipitated aluminium Al-Mg-Si alloy. Diverse pulsed TIG welding process parameters such as peak current (Ip), base current (Ib) and frequency (f) were investigated with the objective of identify the tensile strength, yield strength and cracking susceptibility. The corresponding findings of optimum parameters are 180 peak current (Ip), 60 A base current (Ib) and at 6 Hz frequency (f) with tensile strength of 185.55 MP, yield strength 156.62 MPa. The significant of each parameter for tensile strength are Ip, Ib, Ip*Ib, Ip*f and Ib*f. The corresponding contributions in % are 14.56, 49.49, 12.26, 5.44, 12.15, 5.04, and 1.05 respectively. The statistical method such as Taguchi was employed for experiment design. Weldability test (Fishbone test) was performed on standard specimen and the cracking susceptibility index was identified. The cracking susceptibility index 5.26 % were observed with the value of 180 A of Ip, 80 A of Ib & 2 Hz of frequency (f).The results give an idea about the effect of pulsed TIG welding parameters on mechanical properties and cracking susceptibility.

Dissimilar P-TIG welding between Inconel 718 and commercially pure Titanium using niobium interlayer

The formation of brittle intermetallics is a challenge for the direct joining of commercially pure titanium (CpTi) and Inconel 718 (IN718) alloy. In the present work, dissimilar weldments using the P-TIG (Pulsed-Tungsten Inert Gas) welding technique were produced, with elemental Niobium (Nb) as an interlayer. The insertion of Nb acted as a barrier and suppressed the interdiffusion of Ti and Ni across the interlayer resulting in no TixNiy intermetallic compounds (IMCs) at the CpTi/IN718 dissimilar joint. Titanium (Ti) and Nb on CpTi side joined by solid solution (Ti, Nb) strengthening mechanism. Nickel (Ni) joined with Nb at IN718 side via eutectic reaction, where a diffused layer comprising of NbNi3, and Nb7Ni6 IMCs was found. Owing to the formation of brittle IMCs (NbNi3, Nb7Ni6), the diffused layer at Nb/IN718 interface exhibited the microhardness of ∼782 HV, which is ∼64% higher than the Nb/CpTi interface and considered highest in comparison to the other regions of the joint. The maximum tensile strength of the weldment was 150 MPa, which is significantly less than CpTi (360 MPa) and IN718 (850 MPa) base alloys possibly due to the presence of cracks in the diffused layer and the welded joint.

Improvement in Depth of Weld Penetration During TIG, Activated-TIG, and Pulsed TIG Welding

Joining of dissimilar materials has gained a lot of interest in the recent years due to the increased demand of high strength and light weight designs. Fusion welding plays a vital role in repairing and manufacturing industries like automobile, construction, ship building, and energy sector. Tungsten inert gas (TIG) welding is more advantageous over other welding processes as it produces high precision welds with aesthetic appearance. The limitation of the process is shallow penetration, distorted and weaker joint formation, and low productivity. In the present work, a critical review and analysis has been done on weld penetration and its enhancement during TIG, activated flux TIG, and pulsed current TIG welding of steels. The purpose of this review is to raise an insight about using the variants of TIG, minimising the energy consumption and heat affected zone while increasing the weld penetration and productivity. Proper selection of welding parameters along with welding speed, electrode diameter, shielding gas, electrode tip angle, arc gap, and flux greatly increase the weld penetration.

Pulsed TIG Welding – A Review

GTAW (Gas Tungsten Arc Welding) or TIG (Tungsten Inert Gas) Welding is one of prime welding process which plays a vital role in most of the fabrication industries to weld various metals grades with various parameters. This TIG welding is most preferred because of the better joint which is produced during the process. Recent days new hybrid TIG like pulsed TIG, pulsed synergic TIG etc, comes into practice based on the applications. These TIG Welding variations comes into play because it increases the quality of weld furthermore by changing the various parameters like background current, voltage and control the heat that is generated over the process. In this paper, Pulse TIG is discussed to create an overall idea.

Investigation on the Pulsed TIG Welding of Nickel-Base Alloy for Improved Microstructure and Weld Penetration

In this study, a novel pulsed tungsten inert gas (TIG) welding technique that is capable of effectively improving the weldabilities of nickel-based alloys was developed.  The correlation between process parameters and material properties was studied. The effects of ratios of pulse to background welding currents on hardness and penetration in welds and heat-affected zones (HAZs) of Inconel 718 alloy were investigated experimentally by using the pulsed TIG welding technique. It is found that with an increasing ratio of the pulse to background welding current, the hardness in welds increased from 2% to 3.5%, compared to that in constant current TIG welding at the same level of heat input. When the ratio of pulse to background welding current is higher than 6, the penetration in weld was improved significantly by up to 61%. Research work has demonstrated that the pulsed TIG welding technique is an effective approach to control the microstructure and reduce cracking susceptibilities.

Investigation of numerical modelling of TIG welding of austenitic stainless steel (304L)

Welding is one of the most commonly joining processes used in industry at widespread. Austenitic stainless steel are application in fabrication pressure vessels. Thin sheets of 304L can be welded by pulsed Tungsten Inert Gas (TIG) joining process. The current study investigates the numerical modelling of pulsed TIG welding of austenitic stainless steel using ANSY APDL. Double ellipsoidal heat source have been used for modelling the pulsed TIG welding. The objective of the present investigation is to study the effect of varying welding current on the temperature distribution curve. Temperature profile affects the microstructure, mechanical properties and the residual stresses developed in the welded joint during TIG welding. It has been observed that the peak temperature increases with increasing welding current.

Effect of TIG, pulsed TIG and Interpulse TIG welding techniques on weld strength of dissimilar joints between Monel 400 and AISI 316

Abstract Dissimilar welds of Monel 400 and AISI 316 are extensively used in boiler feedwater heat exchanges, petrochemical industries, nuclear industries where moderate weld strength and high corrosion resistance are required. In this paper, dissimilar welded joint between Monel 400 and AISI 316 have been developed by employing Tungsten Inert Gas (TIG), pulsed TIG and Interpulse TIG welding techniques. The heat input rates and filler wire for joining the base metals were same for three welding techniques. The developed weldments have been inspected by employing X-ray Radiography Test (XRT) to determine the macro/micro defects. The tensile properties of weldments have been evaluated. The ultimate strength of TIG, pulsed TIG and Interpulse TIG weldments were observed to be 528 MPa, 542 MPa and 588 MPa, respectively. The tensile properties of Interpulse TIG weldments are superior to that of welds made of other two welding techniques.

Effect of filler wires on weld strength of dissimilar pulse GTA Monel 400 and AISI 304 weldments

Abstract Dissimilar welds of Monel 400 and AISI 304 are extensively used in feedwater heat exchanges, petrochemical industries, nuclear industries where moderate weld strength and high corrosion resistance are required. In this paper, dissimilar weldments of AISI 304 and Monel 400 have been developed by employing pulsed tungsten inert gas welding. Three filler wires, namely, ERNiCrMo-3, ERNiCrMo-4 and ER304 were used to study the effect of fillers on these weldments. The tensile properties of weldments have been evaluated for three filler weldments and compared. The tensile properties of ERNiCrMo-3 filler are superior to that of welds made of other two filler welds.

Integration of RSM with Grey based Taguchi Method for optimization of pulsed TIG welding process parameters

Abstract This research paper focused on process parameters optimization of Tungsten Inert Gas (TIG). Taguchi method is very effective and efficient to solve the process parameter optimization problem to the find optimum processing parameter, but it is found that the traditional Taguchi method is not sufficient to solve the problem with multi response problem to get optimum results and to meet the global challenges of the manufacturer as it is impractical to obtain more than one optimal processing parameter through Taguchi. In order to survive in the global market it is necessary to used advanced and modified optimization techniques. To intensify the efficiency of Taguchi method, it is absolutely necessary to integrate it with the other optimization approach. However, it is important to integrated Taguchi method with Grey Retion Analysis (GRA) to solve multi response optimizaton promblem futher Taguchi method is integrated with Response Surface Methodology (RSM) to determine optimum value of each parameters. Using orthogonal array L9 experiments were performed. Experimental data are used to obtain signal to noise ratio by using Minitab18 and then response surface plot is developed to obtain optimum level for every input parameter. Further, the process is integrated with RSM to developed mathematical model by using design expert 11 statistical software through full-factorial central composite design (CCD). RSM is a useful statistical tool for process optimization to obtain the required quality of weld. The Surface plot obtained from Design Expert Software 11 represent that the actual value of response i.e. depth of penetration (DOP) and width of penetration (WOP) versus the predicted value of response are close to each other. The higher value of DOP and WOP represents higher strength; analysis of variance (ANOVA) gives the highest value of F-ratio of welding speed in DOP and WOP, this result obtained from RSM showed that welding speed is the most influencing parameter which affects response characteristics.

Microstructure, mechanical properties and residual stress distribution in pulsed tungsten inert gas welding of Ti–5Al–2.5Sn alloy

Pulsed tungsten inert gas welding with full penetration was performed on 1.6 mm thick Ti–5Al–2.5Sn alloy sheet. Hole-drill strain measurement method was employed to measure the distribution of residual stresses across the weld line. Tensile tests were performed on the specimens sectioned in transverse direction of the welded sample. The evolved microstructure in the welded zone was investigated by metallography and X-ray diffraction. Transverse residual stresses of tensile nature were present at different depths below the surface and decreased the yield strength and ultimate tensile strength. However, this decrease was not dependent on the maximum value of transverse residual stress. Fracture location was found to be dependent on the micro-hardness profile and fracture took place in base metal where micro-hardness was the lowest. Furthermore, the presence of tensile residual stresses in the welded sample had no influence on the fractured surface morphology. Peak current and background current had a significant influence on the fusion zone width, heat-affected zone width, and fusion zone grain size.

Response surface approach to minimize the residual stresses in full penetration pulsed TIG weldments of Ti-5Al-2.5Sn alloy

Pulsation of current in tungsten inert gas (TIG) welding is employed to obtain good quality weldments. Peak current, background current, and welding speed in TIG welding are important parameters and their effects on the induced residual stresses are studied using Box–Behnken design methodology. The location of maximum residual stress was found to be close to the weld centerline. Longitudinal and transverse residual stresses at this location were found to be dependent on the pulsed TIG welding input parameters. However, using design of experiment approach, welding speed was found to have the most dominant influence on the stress values. In order to minimize the residual stresses, a reduction in heat input also led to reduction of weld pool penetration. The results of multiresponse optimization showed that in order to achieve a full penetration weldment, a minimum value of 235 MPa for longitudinal and 84 MPa for transverse residual stress will be attained. A weldment with these features can be obtained by using a high value of peak current and a high value of welding speed.