Tungsten Inert Gas Arc Welding Research Articles

Studies on remelting of tungsten carbide and rare earth modified nickel base alloy composite coating

The Ni base alloy (EWAC 1004EN) was used to develop coatings on the mild steel substrate by flame spraying process. The Ni base alloy powder was modified by adding tungsten carbide (10 and 20 wt-%) and CeO2 to study their effects on the microstructure, microhardness and abrasive wear behaviour of unmodified and modified coatings. All the coatings were subjected to remelting using tungsten inert gas arc welding. The abrasive wear behaviour of all the coatings in different conditions was studied using different normal loads (5, 10, 15 and 20 N) against 120 and 600 grit size abrasive medium. Scanning electron microscopy analysis of the worn out surfaces was carried out to understand the wear mechanisms. It was observed that the remelting of the coatings increased the hardness of WC and CeO2 modified flame sprayed coatings by ∼35%, while the abrasive wear resistance increased by 1·5- to threefold.

Prediction and Optimization of TIG Weldment Macrostructure Zones Using Response Surface Methodology

The present work discusses the modeling and optimization of tungsten inert gas arc welding (TIG) and graphical representation of weldment macrostructure zones' shape profiles based on full factorial design of experiments and response surface modeling. To accomplish the task, an in-house developed low cost arc image magnifying system was used. The welds were produced based on a full factorial design matrix of TIG process parameters such as welding current, arc length and traverse speed. Interaction effect plots of control factors indicated weld width is affected more by the welding arc length and current. Similar effects were also observed for depth of penetration and heat affected zone (HAZ). The full factorial experimental data was further analyzed for response surface regression modeling and the response surface regression equations were tested for a number of test case data for their adequacy. The response surface regression relations were further used to optimize the TIG welding process parameters using multi response optimization technique. A mapping scheme was also developed to map the TIG weldment cross-sections' macrostructure zones including that of HAZ. The responses predicted by the surface response regression equations for the test cases were further utilized for graphical representation of the welment shape profiles including that of HAZ. The modeling methodology, regression relations and weldment mapping scheme used in the present investigation were found to be adequate for the estimation of fusion and heat affected zone boundaries.

Study on Fast-Convert Ultrasonic Frequency Pulse TIG Welding Arc Characteristic

Based on ultrasonic frequency pulse tungsten inert-gas (TIG) welding for 0Cr18Ni9Ti austenitic stainless steel, the influence of pulse level parameters was investigated on the field of arc characteristic and arc force. The experimental results show that the pulse level parameters could have huge impact to arc characteristic and arc force. With the increased frequency of pulse level, arc plasma has a more obvious pinch effect, which causes the enhance of arc voltage. Similarly, the arc force can be improved obviously compared with that during conventional direct current (DC) TIG welding. By contrast, the sensitivity of welding characteristic to pulse current level frequency would reduce while the duty of pulse peak current increased.

TZM Alloy TIG Welding Process and Microstructure of Welded Joints

In this paper, the effect of welding current of the tungsten inert gas arc (TIG) welding process on weld quality of TZM alloy was investigated and the fracture microstructure and mechanical properties of the welding joints of TZM alloy was analyzed by x-ray flaw detection, metallographic microscopic analysis, scanning electron microscopy and mechanical properties test. The results indicate that the weld bead with excellent mechanical properties can be obtained using the welding process parameter with the welding current of 210A, welding speed of 4 mm/s and the argon gas flow rate of 8~12 L/min. The microstructure of weld presents the large columnar grains in the center of the weld bead and the equiaxed grains in heat-affected zone instead of the lamellar fiber texture of the TZM alloy matrix, which resulted in the weakened strength of the matrix and the improved plasticity of it.

A study of crack and fracture on the welding joint of Fe 3Al and Cr18–Ni8 stainless steel

Fe 3Al and Cr18–Ni8 steel dissimilar materials were welded by tungsten inert gas arc welding (TIG) with filler metal in this paper. The micro-crack and the fracture in the welding zone were analyzed by means of scanning electron microscope (SEM) and electron probe micro-analyzer (EPMA), the morphology of the dislocation was analyzed by means of the transmission electron microscopy (TEM). The results indicated that the cracks of the Fe 3Al/Cr18–Ni8 welding zone were produced in the fusion zone of Fe 3Al side, the trans-granular cleavage crack was the main form of the fracture, and the river pattern distributed in the cleavage face which was composed of the cleavage steps. The dislocations with the different density distributed in the fusion zone, which was the potential crack origin of the Fe 3Al/Cr18–Ni8 joint. The micro-crack propagated to the heat-affected zone of Fe 3Al side until rupture when the local stress was larger than critical stress.

Weld pool formation and flowing behaviors of aluminum alloy during TIG welding process with a longitudinal electromagnetic field

The Tungsten Inert Gas Arc Welding (TIG) hybrid an electromagnetic field (abbr. FM-TIG) is an effective method to improve the welding quality of steel, and it is also an accepted joining technique in a wide range of non-ferrous metal manufacturing application. In order to study the forming inception of welding pool in TIG hybrid longitudinal electromagnetic field (abbr. LMF-TIG), the process of breeding, growing and developing of LMF-TIG welding pool is simulated by finite element method (abbr. FEM). Our study shows that LMF-TIG is significantly different from TIG welding in the welding pool formation process. The molten liquid metal flowing actions have these characteristics in LMF-TIG welding pool: the incubation stage has the step type unsteady flowing property, the growth stage shows the double loop flowing pattern, and a unique stirring movement mode occurs in the whole developing process. The experimental results indicate that the FEM simulation is effective and reliable.

Effects of TIG Welding Parameters on Morphology and Mechanical Properties of Welded Joint of Ni-base Superalloy

The influences of parameters of tungsten inert gas arc welding on the morphology, microstructure, tensile property and fracture of welded joints of Ni-base superalloy have been studied. Results show that the increase of welding current and the decrease of welding speed bring about the large amount of heat input in the welding pool and the enlargement of width and deepness of the welding pool. The increase of impulse frequency has the same effect on the microstructure compared with the increase of welding current. The effect of welding parameters on the tensile strength and fracture was analyzed. It is found that the root of welding joint is unwelded when the welding current is lower, so that the strength and elongation of welded joint are inferior. And the more welding defects in the welding zone and the more hard and brittle phase precipitates in the overheated zone when the welding current is too high. Consequently, the strength and plasticity go up first and then go down, i.e. they have a peak value with welding current increasing. In addition, the decrease of impulse frequency is beneficial to the strength of the welded joint.

FEM prediction of welding residual stresses in a SUS304 girth-welded pipe with emphasis on stress distribution near weld start/end location

A finite element approach based on Quick Welder software is developed to simulate welding temperature field and welding residual stress distribution in a 3D multi-pass girth-welded pipe model. The characteristics of welding residual stress distributions in a SUS304 stainless steel pipe induced by heating with a tungsten inert gas arc welding torch are investigated numerically. Meanwhile, an emphasis is focused on examining the welding residual stress distributions in and near the weld start/end location. Moreover, the residual stresses predicted by the present computational approach are compared with the measured data; and the comparison suggests that the numerical simulation method has basically captured the feature of welding residual stress distribution near the weld start/end region. The numerical simulation results show that both the hoop and the axial residual stresses near the weld start/end region have sharp gradients and are significantly different from those in the steady range.

Characterization of microstructure, mechanical properties and corrosion resistance of dissimilar welded joint between 2205 duplex stainless steel and 16MnR

The joint of dissimilar metals between 2205 duplex stainless steel and 16MnR low alloy high strength steel are welded by tungsten inert gas arc welding (GTAW) and shielded metal arc welding (SMAW) respectively. The microstructures of welded joints are investigated using scanning electron microscope, optical microscope and transmission electron microscopy respectively. The relationship between mechanical properties, corrosion resistance and microstructure of welded joints is evaluated. Results indicate that there are a decarburized layer and an unmixed zone close to the fusion line. It is also indicated that, austenite and acicular ferrite structures distribute uniformly in the weld metal, which is advantageous for better toughness and ductility of joints. Mechanical properties of joints welded by the two kinds of welding technology are satisfied. However, the corrosion resistance of the weldment produced by GTAW is superior to that by SMAW in chloride solution. Based on the present work, it is concluded that GTAW is the suitable welding procedure for joining dissimilar metals between 2205 duplex stainless steel and 16MnR.

The influence of Sc addition on the welding microstructure of Zr-based bulk metallic glass: The stability of the amorphous phase

Pulsed direct current autogeneous tungsten inert gas arc welding was conducted on rods of bulk metallic glasses (BMGs) Zr55Cu30Ni5Al10 and (Zr55Cu30Ni5Al10)99.98Sc0.02 under two different cooling conditions. The crystalline precipitates in the fusion zone of BMG Zr55Cu30Ni5Al10 were confirmed by microfocused x-ray diffraction pattern analysis as Zr2Ni and Zr2(Cu,Al) intermetallic compounds. In contrast, BMG with Sc addition (Zr55Cu30Ni5Al10)99.98Sc0.02 shows an excellent stable glass forming ability. The fusion zone of BMG (Zr55Cu30Ni5Al10)99.98Sc0.02 remains in the same amorphous state as that of the amorphous base metal when the weld is cooled with accelerated cooling.

Microstructure performance on TIG welding zone of Fe3Al and 18–8 dissimilar materials

Fe3Al intermetallic and 18–8 stainless steel were welded by means of tungsten inert gas (TIG) arc welding. The microstructure performance of the welding zone was analysed using a metalloscope and a scanning electron microscope. The test results indicated that microstructure of the welded metals consists of austenite, proeutectoid ferrite, acicular ferrite, carbide free bainite and lath martensite distributed on the austenitic boundaries as well as grains inside. The microhardness of the fusion zone was lower than that of Fe3Al base metal. The NiAl in the fusion zone was favourable to improve toughness and avoid the welding cracks.

Analysis of the microstructure of Cr–Ni surface layers deposited on Fe 3Al by TIG

A series of Cr–Ni alloys were overlaid on a Fe 3Al surface by tungsten inert gas arc welding (TIG) technology. The microstructure of the Cr–Ni surface layers were analysed by means of optical metallography, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated that when the appropriate TIG parameters were used and Cr25–Ni13 and Cr25–Ni20 alloys were used for the overlaid materials, the Cr–Ni surface layers were crack-free. The matrix of the surface layer was austenite (A), pro-eutectoid ferrite (PF), acicular ferrite (AF), carbide-free bainite (CFB) and lath martensite (LM), distributed on the austenitic grain boundaries as well as inside the grains. The phase constituents of the Cr25–Ni13 surface layer were γ-Fe, Fe 3Al, FeAl, NiAl, an Fe–C compound and an Fe–C–Cr compound. The microhardness of the fusion zone was lower than that of the Fe 3Al base metal and Cr25–Ni13 surface layer.

Pulsed laser focusing for triggering arc discharge in an arc welding system

In tungsten inert gas (TIG) arc welding systems, arc plasma is generated between the cathode (tungsten rod) and anode (workpiece).1 Availability of a dependable technique for triggering arc discharge is indispensable for production processes using arc welding. Typical conventional triggering techniques include the high-frequency, high-voltage and touch-start methods. The high-frequency and high-voltage methods involve arc discharge being triggered through ionization of the gas present between the electrodes by means of a conventional high-frequency generator or high-voltage DC generator.2 The high-frequency method, however, may possibly disrupt operation of peripheral computer systems, whereas the high-voltage method involves suitable electric circuits being arranged inside the power source to prevent high voltage-related accidents.2, 3 After the rod is lowered to make contact with the workpiece in the touch-start method, it is quickly withdrawn to trigger the arc. This method obviates the need for any power source other than the arc welding power source. An important advantage of the touch-start method therefore is its simplicity. When the rod is withdrawn, however, part of it (tungsten) may sustain melt-through to the workpiece in a way that adversely affects weld quality. This is a disadvantage of the touch-start method.3

Influence of Specimen Configuration and TIG Welding on Fracture Toughness of RAFs (JLF-1)

In order to apply a reduced activation ferritic (JLF-1) steel to the blanket/first-wall structure of a fusion reactor, its fracture toughness is very important for the strict estimation of material life. Fracture toughness testing of irradiated materials requires the use of miniaturised specimens and evaluation of TIG welding (tungsten inert gas arc welding) weldment properties is an important issue because necessary for production of nuclear fusion reactors. In this study, the fracture toughness tests were carried out according to the ASTM E1820-99. It was performed on various sizes (ligament and thickness) and various side-grooves of specimens and the TIG welding joint of JLF-1. The test results showed the standard specimen with side-groove of 40% represented valid fracture toughness. Fracture resistance curve (R-curve) increased with increasing specimen ligament and decreased with increasing specimen thickness. However, the R-curve of half size specimen was similar to that of the standard (1inch thickness) specimen. The fracture toughness test results of the TIG welded specimen showed a slight increase in the TIG welded specimen compared with JLF-1 base metal specimen.

Microstructure and bend strength of WC–Co and steel joints

Tungsten inert gas arc welding of WC–30 wt-%Co cemented carbide and steel was carried out using a variety of filler alloys. Precipitation of Fe3W3C occurred at the joint interface and this reduced the bend strength and toughness of the welded joint. The problem could be alleviated by adjusting the carbon concentration of the filler metal.

アーク溶接システムにおける放電誘発のためのパルスレーザフォーカシング

New methods of triggering arc discharge using a plume and a plasma channel in a tungsten inert gas (TIG) arc welding system were demonstrated. The plume and the plasma channel were produced by pulsed laser focusing on an aluminum alloy plate (anode) under a tungsten rod (cathode). The plume was ejected from the laser focusing spot. The plasma channel was generated by gas breakdown in laser beam path. To avoid oxidation, argon (Ar) or helium (He) gas is usually used to shield the rod and molten metal of the workpiece from air. Therefore, formation of the plume and the plasma channel was performed in Ar or He gas. The disadvantages of the conventional triggering methods that require high-frequency generation, high-voltage pulse, or may cause sticking of the rod to the plate are removed in the new methods. The minimum laser energy required for the triggering using the plume and the plasma channel was investigated. Results in this study indicated that laser energy required for the triggering using the plume in Ar gas was lower than that in He gas and that laser energy required for the triggering using the plasma channel in Ar gas was lower than that using the plume in Ar gas. It was found that plasma channel formed by pulsed laser focusing in Ar gas is preferable for triggering arc discharge in the TIG arc welding system.

Plasma channel formation for triggering arc welding

A method of starting arc welding using a plasma channel formed between electrodes in a tungsten inert gas arc welding system was demonstrated. The plasma channel was generated by gas breakdown in the laser beam path. In a previous study by the present authors, the arc welding could be started using a laser produced plume. Results in the present study indicated that the laser energy required to start the process using the plasma channel was lower than that using the plume.

Fatigue of Welded Magnesium Alloy Joints

Magnesium alloys have attracted special attention of researchers working in transportation industries because they are the best lightweight structural materials with a relatively high-strength to weight ratio and excellent technological properties. Enhancement of structural application of such a structural material depends on the ability of construction by welding. The welding of magnesium alloys has been investigated widely. Results indicate that FSW (friction stir welding) and TIG (tungsten inert gas arc welding) are successful welding methods for magnesium alloys and aluminum alloys. 1–4) Reliability is their salient attribute, especially for use in the transportation industry. Therefore, the clarification of fatigue properties must precede application of joining by welding. 5) This study investigated the factors which affect the fatigue strength of the welded commercial magnesium alloy joints as welded surface. Investigated alloys were extruded or rolled AZ31 and AZ61. The welding processes used in this investigation were TIG and FSW. Joint efficiencies (%)

Thorium-232 exposure during tungsten inert gas arc welding and electrode sharpening.

To assess the exposure of welders to thorium-232 (232Th) during tungsten inert gas arc (TIG) welding, airborne concentrations of 232Th in the breathing zone of the welder and background levels were measured. The radioactive concentrations were 1.11 x 10(-2) Bq/m3 during TIG welding of aluminum (TIG/Al), 1.78 x 10(-4) Bq/m3 during TIG welding of stainless steel (TIG/SS), and 1.93 x 10(-1) Bq/m3 during electrode sharpening, with 5.82 x 10(-5) Bq/m3 background concentration. Although the annual intake of 232Th estimated using these values did not exceed the annual limit intake (ALI, 1.6 x 10(2) Bq), we recommend reducing 232Th exposure by substituting thoriated electrodes with a thorium-free electrodes, setting up local ventilation systems, and by using respiratory protective equipment. It is also necessary to inform workers that thoriated tungsten electrodes contain radioactive material.

Pulsed Laser Irradiation for Triggered Discharge in Arc Welding System

We propose a new method that uses a plume produced by a pulsed laser for triggering arc discharge in a tungsten inert gas (TIG) arc welding system. When a pulsed laser is focused onto an aluminum alloy plate (anode) placed under a tungsten rod (cathode), an arc is discharged between the electrodes through a plume generated from the laser focusing spot. The disadvantages of the conventional triggering methods that require high-frequency generation, high-voltage pulse, or may cause sticking of the rod to the plate are removed in the new method. We also investigate the minimum laser energy required for triggering, and find that laser irradiation in Ar gas is preferable for triggering arc discharge in the TIG arc welding system.