Continuous Current Gas Tungsten Arc Welding Research Articles

Effect of constant current and pulsed current gas tungsten arc welding process on microstructure and mechanical properties of superalloy 59 joints

This research paper investigates the microstructure, microsegregation and mechanical behaviour of Ni-based superalloy 59 which is an important candidate in the pollution control application. The weld joints were produced with continuous current gas tungsten arc welding (CCGTAW) and pulsed current gas tungsten arc welding (PCGTAW) by applying both autogenous mode and filler wire ERNiCrMo-13. Weld flaws and weld aspect ratio of weld joints were identified using a macro analysis. An optical microscope (OM) and scanning electron microscope (SEM) were used to examine the microstructure of the welded joints. PCGTA weldments exposed refined grain structure, reduced heat-affected zone and narrow weld bead compared to CCGTAW. Microsegregation of the alloying elements at the weld center (WC) and weld interface (WI) was examined using Energy Dispersive x-ray spectroscopy (EDS). The findings of the metallurgical characterisation proved that the PCGTA weldments offer minimal microsegregation at the interdendritic region in comparison to CCGTA weldments. X-Ray Diffraction (XRD) examination reveals that there is a 16.7% enhancement in grain refinement in the autogenous mode and a 17.4% improvement in the filler wire ERNiCrMo-13 when switching from CCGTA to PCGTA welding. Tensile, Charpy impact and microhardness tests were used to assess the strength, toughness and hardness of the weld joints. Weld joints fabricated by PCGTAW offers higher tensile strength (∼1.4 to 1.6%), higher toughness (∼4.4 to 5.4%), and higher hardness (∼4.8 to 7.7%) than CCGTAW weld joints.

Improvement of hot corrosion resistance of dissimilar weldments by current pulsing in a simulated power plant environment

Hot corrosion studies are of utmost importance for welded components in the power plant industry as well as for industries which deal with exposure to the high-temperature corrosive environment. The failure of welded components at high temperatures has often led to the reduced service life of a component and catastrophic disasters. This has been a significant engineering challenge in the design of welded components. It is generally seen that the failure of the welded sections mostly occurs because of the deposition of molten salt over the weldments which accelerate the hot corrosion reactions. In this present research work, two dissimilar base materials, AISI 4340 and AISI 304L have been welded with two different welding processes namely continuous current gas tungsten arc welding (CCGTAW) and pulsed current gas tungsten arc welding (PCGTAW) while making use of ERNiCr-3 as filler material. A comparative study of the dissimilar welded plates was carried out by simulating a molten salt environment at 600°C involving hot corrosion behavior. By analyzing the microstructure and thermo-gravimetric data, it is concluded that the pulsed current gas tungsten arc welding process has superior corrosion resistance properties while using ERNiCr-3 as the filler material as compared to the continuous current gas tungsten arc welding process.

Influence of Filler Wires to Suppress the Microsegregation and to Improve Mechanical Properties of Conventional Arc-Welded Nickel-Based Superalloy Incoloy 20

Elemental segregation leads to hot fissuring in the Incoloy 20. The present investigation examines the possibility of lessening the elemental segregation in the conventional arc welding techniques. In the present investigation, Incoloy 20 plates were fused by continuous current gas tungsten arc welding (CCGTAW) and pulsed current gas tungsten arc welding (PCGTAW) with two different nickel-based filler wires (ERNiCrMo-2 and ERNiCrMo-3). The result of the macroexamination shows that steady fluid flow with crack-free welding was succeeded in all the weldments. Optical and scanning electron microscope proves the columnar and cellular structure in CCGTAW specimens and fine equiaxed dendritic structure in PCGTAW specimens. Energy-dispersive spectroscopy (EDS) and X-ray diffraction results exhibit that the weld joint produced by CCGTAW ERNiCrMo-2 shows Cr segregation that leads to the formation of M23C6 phases in the interdendritic regions, whereas ERNiCrMo-3 shows the presence of NbC instead of M23C6. The elemental segregation is suppressed when it comes to PCGTA weldments in both filler wires. Electron backscatter diffraction analysis shows that the CCGTA weldments show coarser grain structure in the heat-affected zone (HAZ). In all the cases, the formation of secondary phases affects the strength of the weld joints at HAZ. Refined microstructure obtained in the PCGTAW in both filler wires shows the marginally higher ultimate tensile strength and toughness compared to the corresponding CCGTA weldments. From the corrosion study, PCGTAW specimens exhibit higher corrosion resistance than the CCGTAW specimens for both filler wires.

Exploration of mechanical and metallurgical characterization of Incoloy 20 weldment using gas tungsten arc welding methods

In this paper, metallurgical and mechanical properties are assessed for Incoloy 20 weldment made using traditional arc welding methods with ERNiCrMo-4 filler metal. High magnification microscopes (optical and scanning electron microscopes) are utilized to observe the microstructure of welded specimens. Energy dispersive X-ray spectroscopy is utilized to explore the elemental segregation of welded specimens. Secondary precipitates formed during welding are identified through X-ray diffraction method. It is explored that crack-free weldments are achieved from both continuous current gas tungsten arc welding (CCGTAW) and pulsed current gas tungsten arc welding (PCGTAW) processes. Hardness, impact and tensile tests are conducted to identify the mechanical properties for welded specimens. Results of CCGTAW and PCGTAW specimens are compared and analyzed in detail. Comparatively, PCGTAW specimens offered better results than that of CCGTAW.

Studies on the effect of filler wires on micro level segregation of alloying elements in the alloy 617 weld fusion zone

Highly corrosion resistance nickel based superalloy 617 (UNS N06617) usually opts for high-temperature applications. This alloy is a constituent of alloying elements such as Cr, Co, and Mo, it also acts as solid solution strengtheners. The elements Mo and Cr segregation are prone to cracking tendency in this alloy. The current work investigates the mechanical and metallurgical behavior of the weldments produced by four different filler metals. The weldments were made by using Continuous current Gas Tungsten Arc Welding (CGTAW) technique with ERNiCrCoMo-1, ERNiCrMo-10, ERNiCrMo-4, and ERNiCrMo-14 filler metals. The existence of columnar and cellular structures in the weld zone was observed through microstructural inspection. Scanning Electron Microscope (SEM) confirmed the secondary phase existence in the subgrain boundaries region (SGBR) of all the weldments. Through Electron Dispersive Spectroscopy (EDS) examination Cr-rich phases were observed in ERNiCrCoMo-1 filler metal and Mo- rich phases in other filler metals (ERNiCrMo-10, ERNiCrMo-4, and ERNiCrMo-14). Weldment produced by ERNiCrCoMo-1 filler metal shows marginally higher tensile strength compared to the other weld joints. Ductile mode of failure was observed through SEM fractography for all the weldments. Results of bend test didn’t show any crack in the surface regions.

Effects of types of GTAW including superior GTAW-PC with superimposed HF current on mechanical and metallurgical properties of super duplex stainless steel weld joints

The manufacturing of a product with super duplex stainless steel generally involve joining using fusion welding techniques. The industries are continuously striving to produce better quality product through use of advanced techniques of welding. Investigation has been done to study the effects of types of GTAW including superior advanced GTAW-PC with superimposed HF current on mechanical and metallurgical properties of super duplex stainless steel weld joints. The weld joints of super-duplex stainless steel (UNS S32750) are prepared using continuous current gas tungsten arc welding (CCGTAW), CCGTAW with superimposed high frequency current, pulse current gas tungsten arc welding (GTAW-PC) and superior advanced GTAW-PC with superimposed high frequency current utilizing super duplex grade electrode over alloyed with 2%–3% nickel (ER2594). The association of high frequency either to CCGTAW or GTAW-PC is a novel technique being utilized in present research. The super imposed high frequency current restricts the arc with almost equal root and projected diameter. The weld joints are characterized with respect to quality of mechanical and metallurgical properties. Both these properties are found superior in case GTAW-PC with superimposed high frequency current as compared to all other types of CCGTAW. The association of high frequency with GTAW and GTAW-PC leads to reduction of weak section of weld joint of width of HAZ along with significantly improvement of associated properties. The superiority of properties due to involvement of high frequency current is explained and justified with the associated science involved.

Microstructural and Mechanical Characterization of Dissimilar Metal Welding of Inconel 625 and AISI 316L

This study investigated the microstructure of the dissimilar metal welding of Inconel 625 and AISI 316L using Continuous Current Gas Tungsten Arc Welding (CCGTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) processes with ERNiCr-3, TIG 316L and twisted (ERNiCr-3 and TIG 316L) fillers. Microstructure examinations were carried out using an optical microscope and Scanning Electron Microscopy (SEM)/Energy Dispersive X-Ray (EDAX). The results of the study showed the existence of a partially melted zone (PMZ) on the AISI 316L side. Weld zone (WZ) analysis showed the existence of a multi-directional grain growth on the 316L side in all specimens, although less growth was found on the Inconel 625 side. Grain growth almost disappeared using PCGTAW with twisted fillers. SEM/EDAX investigations indicated that secondary deleterious secondary phases were tiny and white in five experiments. However, a meager amount of precipitates occurred in PCGTA welding with twisted fillers. Moreover, these were particularly innocent precipitates, represented by black dots in images, whereas other tiny white secondary phases are known to be brittle. As a result, PCGTA welding with twisted fillers exhibited the best metallurgical properties.

Effect of Residual Stresses of GTA Welding for Dissimilar Materials

The purpose of the present work is to understand the evolution of residual stresses in weldments. The study made to weld the multipass dissimilar of Nickel-based superalloy Inconel 625 and stainless steel 316L using Continuous Current Gas Tungsten Arc Welding (CCGTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) process employing ERNiCrMo-3 and ERNiCr-3 fillers. The L4 orthogonal array was used in the present experimentation process. Analysis of Variance (ANOVA) is applied for the optimization and to identify the critical parameters. In welding process, the size of the lattice size will be stressed due to welding parameters; the lattice dimension is measured by non-destructive technique X-Ray diffraction to investigate residual stress in the weldment in the lateral surface of the plate. X-Ray Radiography test has evaluated the quality of welds. The results show that root gap is a critical parameter and filler wire and weld processes are not critical.

Comparison of pulsed and continuous current gas tungsten arc welding in dissimilar welding between UNS S32750 and AISI 321 in optimized condition

In this research, mechanical and corrosion properties of dissimilar joint between duplex stainless steel UNS S32750 duplex stainless steel and AISI 321 austenite stainless steel welded by pulsed current gas tungsten arc welding (PCGTAW) and continuous current gas tungsten arc welding (CCGTAW) were compared. The welding parameters and the filler metal were the same in both methods. Microstructural characterization of joint was determined by optical and scanning electron microscope. The pitting potential was evaluated by potentiodynamic polarization test in 3.5 wt.% NaCl solution at room temperature. Mechanical properties of optimal joint were investigated by impact test and vickers microhardness. Microstructural evaluation shows that the equal amounts of ferrite and austenite were obtained in PCGTAW weldment, while in CCGTAW weldment fraction of phases changed to 40% ferrite and 60% austenite. TiN precipitations were formed in fusion line of CCGTAW weldment on the side of AISI 321 austenite stainless steel. The average values of hardness in PCGTAW and CCGTAW weld zone were 241 and 225 HV0.2, respectively. The higher amount of ferrite in PCGTAW weldment in comparison with CCGTAW weldment was the reason of higher hardness average. The toughness of PCGTAW and CCGTAW was 106 and 102 J, respectively. Based on cyclic polarization test, pitting potential of weldment welded with PCGTAW and CCGTAW was 1.03 and 0.8 V, respectively, which is a proof of better pitting corrosion resistance of the weld zone in PCGTAW method.

Mechanical and microstructural evaluation of SAF 2507 and incoloy 825 dissimilar welds

This research work articulated a comparative study on Incoloy 825 Ni-based alloy and SAF 2507 super duplex stainless steel dissimilar joints. Welding was accomplished by ER2594 and ERNiFeCr-1 filler wires, pulsed current (PCGTAW) and continuous current gas tungsten arc welding (CCGTAW) techniques. Characterizations were conducted by optical microscopy, scanning electron microscopy equipped with an energy dispersive spectroscopy and X-ray diffraction. In order to investigate the evolution of mechanical properties of the weld joints’ micro-hardness, impact and tensile tests were employed. The results showed that Ti-rich phase was formed in weld zones employing ERNiFeCr-1 filler metal. On the other hand, Cr-rich phase was characterized in the weld zone of ER2594 sample employing CCGTAW. The welds of PCGTAW method displayed finer microstructure, lower ferrite contents and lack of Cr-rich phase formation. In tensile tests, fracture occurred at weaker base metals (Incoloy 825) in all cases. The use of ER2594 caused higher hardness and lower toughness than ERNiFeCr-1 filler metal. Based upon comparative investigations, ERNiFeCr-1 filler metal and PCGTAW technique were recommended to improve dissimilar joint efficiency.

Influence of filler metals and welding techniques on the structure–property relationships of Inconel 718 and AISI 316L dissimilar weldments

In the present investigation, an attempt has been made to weld the precipitation hardened Nickel based super alloy Inconel 718 and austenitic stainless steel AISI 316L using Continuous Current Gas Tungsten Arc Welding (CCGTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) process employing ER2553 and ERNiCu-7 fillers. Microstructure examination using optical and SEM analysis clearly witnessed the formation of unmixed zone at the Heat Affected Zone (HAZ) of Inconel 718 for all the joints. The studies showed the absence of deleterious phases in the CCGTA and PCGTA weldments employing ERNiCu-7. Tensile studies corroborated that the fracture occurred at the parent metal of AISI 316L in all the cases. It was inferred from the present study that PCGTA weldments employing ERNiCu-7 exhibited better metallurgical and mechanical properties. This study articulated the effect of filler metals on the structure–property relationships of the weldments.

Studies on Partially Melted Zone and Pitting Corrosion Resistance of A356 Aluminium-Silicon Alloy GTA Welds

Gas Tungsten Arc Welding (GTAW) of Pressure Die cast A356 Al-Si alloy with strontium modification was done both with and without filler. The microstructural changes in Weld metal zone (WM), Heat affected zone (HAZ) and Partially Melted Zone (PMZ) were studied. PMZ of aluminium alloy weld is an important region, as it is the weak link in the weldments. It is significantly affected by the welding parameters, filler metal and prior thermal condition. In the present work affect of welding techniques i.e. Continuous Current Gas Tungsten Arc Welding (CCGTAW) and pulsed Current Gas Tungsten Arc Welding (PCGTAW) on microstructure and pitting corrosion resistance of weld metal, Partially melted zone and Heat affected zone in the prior conditions of as cast and T6 conditions were studied. Susceptibility to liquation was found to be less in the weld made in as cast condition of pulsed current GTA welds compared to that of artificially aged condition (T6) of continuous current GTA welds. This was mainly attributed to the silicon enrichment of eutectics at the grain boundaries. Potentiodynamic polarization testing was carried out to study the pitting corrosion behavior of the welds. Pitting corrosion resistance of weld made with pulsed current GTAW of as cast alloy is better than the that of weld made with continuous current GTAW of T6 alloy. This is mainly attributed to the discontinuous eutectic formation at the grain boundary base metal and PMZ.

Microstructure and Corrosion Behavior of Cast A356 and Wrought AA6061 Aluminium Alloy Welds

In this work, it was intended to improve the corrosion resistance of welds of A356 and AA6061 by adopting mainly a special welding techniques, viz., pulsed current gas tungsten arc welding (PCGTAW), electron beam welding (EBW) and friction stir welding (FSW). It was found that the corrosion resistance of A356 and AA6061 welds could be improved by PCGTAW technique rather than continuous current gas tungsten arc welding (CCGTAW). It can be further improved by using electron beam welding. Improved corrosion resistance in A356 welds could be obtained by selecting T6 temper rather than as cast condition. In the case of AA6061, improved corrosion resistance was achieved by selecting T4 temper rather than T6 temper. As for as the welding techniques, friction stir welding (FSW) is useful than fusion welding techniques like CCGTAW,PCGTAW and EBW for improving the corrosion resistance of both the welds.

Effect of Autogenous Arc Welding Processes on Tensile and Impact Properties of Ferritic Stainless Steel Joints

The effect of autogeneous arc welding processes on tensile and impact properties of ferritic stainless steel conformed to AISI 409M grade is studied. Rolled plates of 4 mm thickness have been used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure, and fracture surface morphology of continuous current gas tungsten arc welding (CCGTAW), pulsed current gas tungsten arc welding (PCGTAW), and plasma arc welding (PAW) joints are evaluated and the results are compared. It is found that the PAW joints of ferritic stainless steel show superior tensile and impact properties when compared with CCGTAW and PCGTAW joints, and this is mainly due to lower heat input, finer fusion zone grain diameter, and higher fusion zone hardness.

Effect of Postweld Aging Treatment on Fatigue Behavior of Pulsed Current Welded AA7075 Aluminum Alloy Joints

This article reports the effect of postweld aging treatment on fatigue behavior of pulsed current welded AA 7075 aluminum alloy joints. AA7075 aluminum alloy (Al-Zn-Mg-Cu alloy) has gathered wide acceptance in the fabrication of light weight structures requiring high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers, and railway transport systems. The preferred welding processes of AA7075 aluminum alloy are frequently gas tungsten arc welding (GTAW) process and gas metal arc welding (GMAW) process due to their comparatively easier applicability and better economy. Weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often results inferior weld mechanical properties and poor resistance to hot cracking. In this investigation, an attempt has been made to refine the fusion zone grains by applying pulsed current welding technique. Rolled plates of 10 mm thickness have been used as the base material for preparing multipass 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. Four different welding techniques have been used to fabricate the joints and they are: (i) continuous current GTAW (CCGTAW), (ii) pulsed current GTAW (PCGTAW), (iii) continuous current GMAW (CCGMAW), and (iv) pulsed current GMAW (PCGMAW) processes. Argon (99.99% pure) has been used as the shielding gas. Rotary bending fatigue testing machine has been used to evaluate fatigue behavior of the welded joints. Current pulsing leads to relatively finer and more equi-axed grain structure in GTA and GMA welds. Grain refinement is accompanied by an increase in fatigue life and endurance limit. Simple postweld aging treatment applied to the joints is found to be beneficial to enhance the fatigue performance of the welded joints.

Influences of pulsed current welding and post weld aging treatment on fatigue crack growth behaviour of AA7075 aluminium alloy joints

This paper reports the influences of pulsed current welding and post weld aging treatment on fatigue crack growth behaviour of AA7075 aluminium alloy (Al–Zn–Mg–Cu alloy). The preferred welding processes for this alloy are frequently gas tungsten arc welding (GTAW) process and gas metal arc welding (GMAW) process due to their comparatively easier applicability and better economy. In this alloy, the weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often results inferior weld mechanical properties and poor resistance to hot cracking. In this investigation, an attempt has been made to refine the fusion zone grains by applying pulsed current welding technique. Rolled plates of 6 mm thickness have been used as the base material for preparing single pass butt welded joints. The filler metal used for joining the plates is AA5356 (Al–5Mg (wt.%)) grade aluminium alloy. Four different welding techniques have been used to fabricate the joints and they are: (i) continuous current GTAW (CCGTAW), (ii) pulsed current GTAW (PCGTAW), (iii) continuous current GMAW (CCGMAW) and (iv) pulsed current GMAW (PCGMAW) processes. Argon (99.99% pure) has been used as the shielding gas. Fatigue crack growth behaviour of the welded joints has been evaluated by conducting the test using servo hydraulic controlled fatigue testing machine. Current pulsing leads to relatively finer and equi-axed grain structure in GTA welds. Grain refinement is accompanied by an increase in fatigue crack growth resistance and fatigue life. Simple post weld aging treatment applied to the joints is found to be beneficial to enhance the fatigue crack growth resistance of the welded joints.

Effect of pulsed current and post weld aging treatment on tensile properties of argon arc welded high strength aluminium alloy

This paper reveals the effect of pulsed current and post weld aging treatment on tensile properties of argon arc welded AA7075 aluminium alloy. This alloy has gathered wide acceptance in the fabrication of light weight structures requiring high strength-to-weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding processes of high strength aluminium alloy are frequently gas tungsten arc welding (GTAW) process and gas metal arc welding (GMAW) process due to their comparatively easier applicability and better economy. Weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often results inferior weld mechanical properties and poor resistance to hot cracking. In this investigation, an attempt has been made to refine the fusion zone grains by applying pulsed current welding technique. Four different welding techniques have been used to fabricate the joints and they are: (i) continuous current GTAW (CCGTAW), (ii) pulsed current GTAW (PCGTAW), (iii) continuous current GMAW (CCGMAW) and (iv) pulsed current GMAW (PCGMAW) processes. As welded joint strength is much lower than the base metal strength and hence, a simple aging treatment has been given to improve the tensile strength of the joints. Current pulsing leads to relatively finer and more equi-axed grain structure in GTA and GMA welds. In contrast, conventional continuous current welding resulted in predominantly columnar grain structures. Post weld aging treatment is accompanied by an increase in tensile strength and tensile ductility.

Effect of pulsed current welding on fatigue behaviour of high strength aluminium alloy joints

High strength aluminium alloys (Al–Zn–Mg–Cu alloys) have gathered wide acceptance in the fabrication of light weight structures requiring high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding processes of high strength aluminium alloy are frequently gas tungsten arc welding (GTAW) process and gas metal arc welding (GMAW) process due to their comparatively easier applicability and better economy. Weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often results inferior weld mechanical properties and poor resistance to hot cracking. In this investigation, an attempt has been made to refine the fusion zone grains by applying pulsed current welding technique. Rolled 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 aluminium alloy. Four different welding techniques have been used to fabricate the joints and they are: (i) continuous current GTAW (CCGTAW), (ii) pulsed current GTAW (PCGTAW), (iii) continuous current GMAW (CCGMAW) and (iv) pulsed current GMAW (PCGMAW) processes. Argon (99.99% pure) has been used as the shielding gas. Fatigue properties of the welded joints have been evaluated by conducting fatigue test using rotary bending fatigue testing machine. Current pulsing leads to relatively finer and more equi-axed grain structure in gas tungsten arc (GTA) and gas metal arc (GMA) welds. In contrast, conventional continuous current welding resulted in predominantly columnar grain structures. Grain refinement is accompanied by an increase in fatigue life and endurance limit.

Effect of pulsed current welding on mechanical properties of high strength aluminum alloy

High strength aluminum alloys (Al-Zn-Mg-Cu alloys) have gathered wide acceptance in the fabrication of lightweight structures requiring high strength-to-weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding processes of high strength aluminum alloy are frequently the gas tungsten arc welding (GTAW) process and the gas metal arc welding (GMAW) process due to their comparatively easy applicability and better economy. Weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often results in inferior weld mechanical properties and poor resistance to hot cracking. In this investigation, an attempt has been made to refine the fusion zone grains by applying a pulsed current welding technique. Rolled plates of 6 mm thickness were used as the base material for preparing single pass welded joints. A single ‘V’ butt joint configuration was prepared for joining the plates. The filler metal used for joining the plates was AA 5356 (Al-5Mg (wt%)) grade aluminum alloy. Four different welding techniques were used to fabricate the joints: (1) continuous current GTAW (CCGTAW), (2) pulsed current GTAW (PCGTAW), (3) continuous current GMAW (CCGMAW) and (4) pulsed current GMAW (PCGMAW). Argon (99.99% pure) was used as the shielding gas. Tensile properties of the welded joints were evaluated by conducting tensile tests using a 100 kN electro-mechanical controlled universal testing machine. Current pulsing leads to relatively finer and more equi-axed grain structure in GTA and GMA welds. In contrast, conventional continuous current welding resulted in predominantly columnar grain structures. Grain refinement is accompanied by an increase in tensile strength and tensile ductility.

Vision based measuring system for both weld pool and root gap in continuous current GTAW

AbstractA low cost vision based measuring system is developed to detect both the weld pool geometry and root gap simultaneously. Efforts are made from both hardware and software aspects to decrease the strong interference from arc light during gas tungsten arc welding (GTAW) process with continuous current. A normal charge coupled device (CCD) camera is cooperated with specially made composite filter lens and the video signals before A/D conversion are adjusted according to the welding current. Clear images of both root gap and weld pool are captured under different welding parameters. The grey level distribution characteristics of root gap edges and weld pool edges in images are analysed and utilised for developing the algorithms for image processing. The continuum of weld pool edge and the linear features of root gap are also utilised in the algorithm. The results show that the algorithms can extract the weld pool edge and root gap edge effectively. A solid foundation for weld seam tracking and weld pen...