Double-pulsed Gas Metal Arc Welding Research Articles

Analyzing microstructural, residual stress, and mechanical characteristics in dissimilar welds of Inconel 59 and AISI 904L through double-pulsed gas metal arc welding

In this research, dissimilar welding of the nickel-based superalloy Inconel 59 and austenitic stainless steel AISI 904L steel was successfully done with double-pulsed gas metal arc welding (DP-GMAW) using the filler ERNiCrMo-13. Macroscopic analysis showed a defect-free weld with an aspect ratio of 2.4, attributed to the efficient heat delivery (0.642 kJ/mm) in DP-GMAW. The microstructure of the weld joint was examined through both optical microscopy and scanning electron microscopy. Examination of the microstructure of the weld interface exposed grain coarsening near the heat-affected zone on the AISI 904L side. In contrast, the weld fusion zone contained fine equiaxed dendrites. Microsegregation and alloying element migration across the entire weld area were assessed through energy dispersive X-ray spectroscopy point analysis and line mapping, revealing controlled microsegregation across the region. X-ray diffraction (XRD) analysis was used to ascertain the average grain size (38.41 nm) and secondary phase composition. The XRD-cosα method was used to assess the residual stress of the weld joint, revealing tensile residual stress in the weld zone and compressive residual stress in other regions. Tensile, Charpy impact, and Vickers hardness tests were conducted in the study to evaluate the strength, toughness, and hardness of a dissimilar weld. The impact of two cryogenic treatments, namely shallow and deep, on tensile and toughness characteristics was investigated in this study. The cryogenic treatments significantly enhanced the mechanical properties of weld samples compared to their as-welded condition, leading to an 11.5% increase in tensile strength and a 10% improvement in toughness.

Process Optimization, Microstructure and Mechanical Properties of Wire Arc Additive Manufacturing of Aluminum Alloy by Using DP-GMAW Based on Response Surface Method.

Double-pulsed gas metal arc welding (DP-GMAW) is a high-performance welding method with low porosity and high frequency. Periodic shrinkage and expansion of the melt pool during DP-GMAW leads to unusual remelting, and the re-solidification behavior of the weld metal can significantly refine the weld structure. The advantages of DP-GMAW have been proven. In order to better apply DP-GMAW to aluminum alloy arc additive manufacturing, in this paper, the single-pass deposition layer parameters (double-pulse amplitude, double-pulse frequency and travel speed) of DP-GMAW will be optimized using the response surface method (RSM) with the width, height, and penetration of the deposition layer as the response values to find the superior process parameters applicable to the additive manufacturing of aluminum alloy DP-GMAW. The results show that the aluminum alloy components made by DP-GMAW additive are well formed. Due to the stirring of double-pulse arc and the abnormal remelting and solidification of metal, the microstructures in the middle and top areas show disordered growth. The average ultimate tensile strength of the transverse tensile specimen of the member can reach 175.2 MPa, and the elongation is 10.355%.

Development of a Novel Welding Technique With Reduced Heat-Input by Employing Double-Pulsed Gas Metal Arc Welding for Aerospace Grade 18% Ni Maraging Steel

Abstract Eighteen percent Ni maraging steels are high performance Fe–Ni martensite-based alloys with ultra-high strength and good toughness. They find applications in strategic sectors, joining of thick sections often coming into picture. Welding of thick section involves a longer processing time, more passes, and a higher heat-input. Double-pulsed gas metal arc welding (DP-GMAW) is an emerging welding technique, well suited for joining thick sections. DP-GMAW is capable of controlling the solidification parameters, weld pool geometry, and cooling rate at a reduced heat-input. The major concern regarding the welding of maraging steel is the formation of the reverted austenite (RA) phase in the fusion zone (FZ). The formation of RA deteriorates the mechanical performance of welded joints. The presence of RA can be supressed by the usage of suitable welding techniques and proper post-weld heat treatments (PWHTs). DP-GMAW process was employed to carry out the welding; studies on the joints produced are reported in this research paper. The studies also included the effect of various PWHTs on the metallurgical and mechanical properties of the maraging steel weldments. The research used three distinct PWHTs: direct aging (DA), solutionizing + aging (SA), and homogenizing + solutionizing + aging (HSA). The FZ microstructures under DA and SA conditions show that there is RA at the cell boundaries. However, there was no evidence of RA in FZ following HSA. The energy dispersive spectra (EDS) analysis of the as-welded FZ showed segregation along the grain boundaries (GBs). This led to the premature formation of RA upon subsequent aging. The SA treatments proved inadequate to totally eliminate RA in the microstructure. On the other hand, the HSA treatments were effective in evening out concentration differences and preventing formation of RA. This study demonstrates that DP-GMAW combined with HSA treatment has the best mechanical properties.

Mechanical, Metallurgical and Corrosion Properties of Dual Pulsed, Pulsed Gas and Shielded Metal Arc Welded AISI 310 Austenitic Stainless Steel

AISI 310 is a highly alloyed austenitic stainless steel used for high-temperature applications. The high chromium and nickel contents give this steel excellent oxidation resistance as well as high strength. In the present work, the material was welded using shielded metal arc welding (SMAW), Pulsed Gas Metal Arc welding (P-GMAW) and Double Pulsed Gas Metal Arc welding (DP-GMAW). A comparative study has been carried out on the basis of chemical, mechanical, metallurgical and corrosion properties of base metal and all other welded samples. SMAW process has high heat input and hence dilution effect is more prominent in this process. The mechanical properties evaluated in terms of maximum tensile strength, impact energy and hardness was obtained for DP-GMAW sample. This superior mechanical behaviour of DP-GMA welded sample was attributed to the better grain refinement occurred due to double pulsation effect. However, the DP-GMAW process showed highest corrosion rate when compared to other two welded samples.

Investigation of Double-Pulsed Gas Metal Arc Welding Technique to Preclude Carbide Precipitates in Aerospace Grade Hastelloy X

Investigation of Double-Pulsed Gas Metal Arc Welding Technique to Preclude Carbide Precipitates in Aerospace Grade Hastelloy X

Investigation on the Dynamic Behavior of Weld Pool and Weld Microstructure during DP-GMAW for Austenitic Stainless Steel

The influence of heat and droplet transfer into weld pool dynamic behavior and weld metal microstructure in double-pulsed gas metal arc welding (DP-GMAW) was investigated by the self-designed high-speed welding photography system. The heat input, the arc pressure, the droplet momentum and impingement pressure were measured and calculated. It was found that the arc pressure is far less than the droplet impingement pressure. The heat input and droplet impingement pressure per unit time acting on weld pool were proportional to the current pulse frequency, which fluctuated with thermal pulse. The size and oscillation amplitude of the weld pool had noticeable periodic changes synchronized with the process of heat input and droplet impingement. Compared to the microstructure of pulsed gas metal arc welding (P-GMAW) weld metal, that of DP-GMAW weld metal was significantly refined. High oscillation amplitude assisted the enhancement of weld pool convection, which leads to more constitutional supercooling. The heat input and shear force during the peak of thermal pulse causing dendrite fragmentation which provided sufficient crystal nucleus for the growth of equiaxed grains and the possibility of grain refinement. The effects of current parameters on welding behavior and weld metal grain size are investigated for further understanding of DP-GMAW.

Exploration of Weld Bead Forming Rule during Double-Pulsed GMAW Process Based on Grey Relational Analysis.

Weld bead forming rule is very important during double-pulsed gas metal arc welding (DP-GMAW) process, and this process has more advantages than that of conventional arc welding process. This work employed grey rational analysis to explore the weld bead forming rule. Since the latest twinpulse XT DP control process was employed, the parameters adjustment was easier than that of conventional operation. The grey relational analyses between five main process parameters, which were average welding current, welding speed, twin pulse relation, twin pulse frequency together with twin pulse current change in percent, and three key characteristic parameters, which were bead width, bead height and penetration, were conducted to explore the weld bead forming rule. To accurately calculate the grey relational degree, the negative relevancies were transformed to positive ones. According to calculations and corresponding analyses, it can be concluded that the effects of average welding current and welding speed on the weld bead forming and key characteristic parameters of the weld bead were higher than that of other process parameters. Moreover, the relevancies between key characteristic parameters of the weld bead, and process parameters which included twin pulse relation, average welding current and twin pulse current change in percent were positive, while the relevancies between key characteristic parameters and other two process parameters were negative. The work can supply a new method to evaluate the effects of process parameters during the DP-GMAW process on the weld bead forming or other process characteristics, and references for parameters selection and process optimization.

Process and Parameter Optimization of the Double-Pulsed GMAW Process

The double pulsed gas metal arc welding (DP-GMAW) process has been effectively employed to realize joining of steel plates and obtain weld bead surfaces with high quality fish scale ripples. In this work, a DP-GMAW process based on robot operation using the latest twinpulse XT DP control technology was employed to join the stainless-steel base plates. Four key operational parameters, which were robot welding speed, twin pulse frequency, twin pulse relation and twin pulse current change in percent, were selected to be input elements of orthogonal experimental design, which included nine experiments with three levels. To accurately understand the performance and process of weld bead obtained from DP-GMAW operation based on robot operation, the appearance observation and key shape parameters measurement, microstructure analysis, tensile and hardness testing, as well as stability analysis of the electrical signals, were conducted. Correlation analysis showed that the grain size was significantly correlative to the toughness and hardness. Then, to obtain quantitative evaluation results, fuzzy comprehensive evaluation (FCE) was employed to provide quality evaluation of weld beads from the above experiments. The influential levels of the key operational parameters on the appearance, grain size and FCE scores, and corresponding physical analyses, were respectively presented. In addition, optimal parameters combinations for obtaining weld beads with optimal appearance, grain size, and the highest FCE scores of weld bead quality were respectively provided according to the range analysis of the results from orthogonal experimental design. This work can provide an effective analysis method of influential levels of key operational parameters on the performance of the weld bead, optimal operational parameters combination seeking method, and quantitative quality evaluation method for the DP-GMAW process, which can improve the process optimization and increase the production efficiency, both in academic research and actual industrial production.

Effects of Operational Parameters on the Characteristics of Ripples in Double-Pulsed GMAW Process.

This study focuses on the characteristics of the ripples of the weld bead formed during the double-pulsed gas metal arc welding (DP-GMAW) process. As a special output of the process, ripples include many useful information and can reflect the quality of the welding process. The work analyzed the operational characteristics of the DP-GMAW process based on robot operation which used the latest twinpulse XT DP control process, and then selected five key operational parameters, such as average current, welding speed, twin pulse frequency, twin pulse relation, and twin pulse current change in percent, to explore their effects on the formation and characteristics of ripples. A reliable method of measuring the distance of the ripples was used to provide convincing data. According to a series of experimental observations and analyses, the distance of ripples and appearance under different conditions were obtained. Also, curve fitting equations between each operational parameter and corresponding distances of ripples was obtained. To testify the effectiveness of the curve fitting equations, corresponding verifying experiments were conducted, and the results showed that all the errors were below 10%. In addition, the different levels of the operational parameters on the formation and characteristics of ripples were provided. This work can be a reference for the process and quality control improvement for the DP-GMAW process.

Analysis of current phase influence on weld seam formation in double-wire DP-GMAW

Double-wire double-pulsed gas metal arc welding (DP-GMAW) experiments were conducted in the double pulse synchronous (DPS), alternating (DPA), and independent (DPI) phases. The effects of current phase on weld seam formation were analyzed. Experimental results showed that a stable welding process was achieved in all three current phases and the derived weld seams demonstrated little spatter, no hump, or undercut. Different current phases had little influence on weld reinforcement and width, but had a significant influence on weld penetration and toe angle. The fish-scale ripples of weld seams were prominent; specifically, the fish-scale ripples in the DPA phase were more prominent than those in other current phases. The penetration and penetration shape factor (PSF) in the DPA phase were at their highest while those in the DPS phase were at their lowest. In the DPS phase, the ferrite was coarse and in higher quantity, while the pearlite was relatively in lower quantity. In the DPA phase, the ferrite was finer and in lower quantity, while the pearlite was relatively in higher quantity and the microstructure was more uniform. Last, in the DPI phase, the microstructure appeared in a state between the DPS and DPA phases.

Effects of single and double pulses on microstructure and mechanical properties of weld joints during high-power double-wire GMAW

High-power double-wire gas metal arc welding (GMAW) experiments were conducted with the single and double pulses technology. The effects of single and double pulses on the weld bead formation, microstructure and mechanical properties of the weld joints were investigated. The experimental results demonstrated that through the high-power double-wire single and double pulsed GMAW stable welding could be achieved. Also, the high quality weld beads were acquired with slight spatter, without undercut or hump. Double-wire double pulsed GMAW was more stable, producing more perfect weld shape and higher microhardness compared to double-wire single pulsed GMAW. The stirring effect of alternating strong and weak pulses on the weld pool during the double-wire double pulsed GMAW could produce significant fish-scale ripples and refine the grains, resulting in finer grain microstructure with higher hardness. The results proved that the low-frequency pulse cycle controlled the formation of each weld pool precisely. This meant that a weld pool was formed in a low-frequency pulse cycle.

Effect of Droplet Impingement on the Weld Profile and Grain Morphology in the Welding of Aluminum Alloys

To achieve a better understanding of the effect of droplet impingement on the weld profile and grain morphology, welding with vertical and inclined torches in the double pulsed-gas metal arc welding of aluminum alloy were compared. When using vertical welding, the grains along the wall of the finger-like penetration (FLP) were refined by a more violent flow driven by droplet impingement running in the confined space created by FLP. When using inclined welding, the sharp inflection point disappeared and the curved columnar grains emerged on the non-impact action side, which was attributed to the gradually weakened impingement at that location. Moreover, when the penetration became shallower due to a low mean current, the droplets impinged alternately along split trajectories, causing significant changes in the grain morphology, such as creating grains which were sharply shortened by the direct impact of droplet impingement at impact point. The change of trajectory was ascribed to the variation of the width/depth ratio of FLP, which changed the magnitude of the contradiction between the room required by the fluid flow driven by droplet impingement and the space supplied for that by FLP.

Effects of Thermal Frequency on Microstructures, Mechanical and Corrosion Properties of AA6061 Joints

Three thermal frequencies that were designated as 3, 4, and 5 Hz were used to reveal the microstructural evolution, mechanical, and corrosion properties of AA6061-T6 sheets that were welded by double pulsed gas metal arc welding (DP-GMAW) using microstructural observations, microhardness tests, tensile tests, bend tests, impact tests, and corrosion tests. A self-developed welding system consisted of a digital multifunctional welder and an arc dynamic waveform wavelet analyzer was chosen to perform welding operations and to record electrical signal waveforms during the welding process. The results show that the process of DP-GMAW was stable, and the weld beads exhibited aesthetic ripples. The ripple distance, the grain size, and porosity of the fusion zone decreased with an increasing thermal frequency. Microhardness and corrosion properties of the weld joint improved when the thermal frequency increased. In addition, all of the joints exhibited excellent bending properties. However, the impact property of the weld joint was lower than that of the BM. It indicated that the low impact energy results of the welded AA6061-T6 sheet were mainly due to the formation of micro-cracks in the fusion zone.

Effect of double-pulsed gas metal arc welding (DP-GMAW) process variables on microstructural constituents and hardness of low carbon steel weld deposits

In this study, a bead on plate welding on a low carbon steel plate at different parameter combinations in double-pulsed gas metal arc welding (DP-GMAW) process has been carried out. The effect of heat input, pulse frequency and thermal pulse frequency on solidification variables and microstructure of the weld metal have been thoroughly studied. Formation of inclusion and acicular ferrite during solidification has been calculated to observe the effect of process parameters on the microstructural constituents. Furthermore, the microhardness analysis of the weld metals has been carried out to evaluate the effect of microstructural variations on the property. Several linear and non-linear equations have also been developed to predict the responses as a function of different process variables. The results indicate that decrease in heat input, pulse frequency and thermal pulse frequency increases the volume fraction of inclusion and acicular ferrite in the weld metals. The higher volume fraction of acicular ferrite ultimately results in fine grain microstructure with the higher hardness of weld metals. On the other hand, the grain size of coarse grain heat affected zone (CGHAZ) at lower heat input was finer which ultimately increases the heat affected zone hardness.

Double arc interference and dynamic behavior characteristics of double wire double-pulsed GMAW

The double wire gas metal arc welding (GMAW) technology combined with double pulse low-frequency modulation offers the benefits of the higher efficiency of double wire GMAW combined with superior weld joint quality offered by double pulse low-frequency modulation. However, the potential for severe double arc interference of double wire double-pulsed GMAW affects the stability of the welding process and has thus far limited its widespread use. In this study, high-speed photography was used to record the arc profiles and arc interference of double wire double-pulsed GMAW in the synchronous and alternant phases, while the voltage and current waveforms were simultaneously recorded. Experimental results demonstrated that the double arc deflection of the strong pulse was more severe than that of the weak pulse due to the high current associated with a strong pulse. It was also discovered that the trailing arc stiffness was lower than the leading arc stiffness. Moreover, the deflection of trailing arc was greater under the influence of the leading arc’s electromagnetic attraction. Whereas, the arc deflection of the pulse stage in the alternant phase was small, less than that of the pulse stage in the synchronous phase, the arc deflection of the background stage was much greater. Furthermore, the arc deflections of the pulse and background stages in the synchronous phase were smaller than the arc deflection of the background stage in the alternant phase. Finally, the leading and in the synchronous phase maintained their stiffness and demonstrated weaker magnetic arc blow, fewer spatters, a more refined fish-scale appearance, and weld beads with better uniformity.

Perspective on Double Pulsed Gas Metal Arc Welding

Aluminum alloy welding suffers from problems such as solidification cracking and hydrogen-induced porosity, which are sufficiently severe to limit its potential applications. Because mitigated porosity incidence and solidification cracking are observed in aluminum welds using double pulsed gas metal arc welding (DP-GMAW), a comprehensive review of the mechanism is necessary, but absent from the literature. The oscillation of arc force and droplet pressure causes a weld pool stir effect. The expansion and shrinkage of the weld pool cause unusual remelting and resolidification of the previously solidified metal. DP-GMAW has an increased solidification growth rate and cooling rate, compared with conventional pulsed welding at same heat input. Both numerical and experimental results reveal the remarkable concept that refined microstructure in the fusion zone is obtained by using DP-GMAW. The mechanism of microstructural refinement is revealed as a weld pool stir effect and increased cooling rate. Hydrogen bubbles easily float out and then release from the weld pool originated from the weld pool stir effect. Reduced solidification cracking is achieved due to the refined solidification structure that originated from the increased cooling rate. The advantages, evolution process, and future trend of DP-GMAW are discussed.

Influence of shielding gas on the mechanical and metallurgical properties of DP-GMA-welded 5083-H321 aluminum alloy

In the present research, 6-mm-thick 5083-H321 aluminum alloy was joined by the double-pulsed gas metal arc welding (DP-GMAW) process. The objective was to investigate the influence of the shielding gas composition on the microstructure and properties of GMA welds. A macrostructural study indicated that the addition of nitrogen and oxygen to the argon shielding gas resulted in better weld penetration. Furthermore, the tensile strength and bending strength of the welds were improved when oxygen and nitrogen (at concentrations as high as approximately 0.1vol%) were added to the shielding gas; however, these properties were adversely affected when the oxygen and nitrogen contents were increased further. This behavior was attributed to the formation of excessive brown and black oxide films on the bead surface, the formation of intermetallic compounds in the weld metal, and the formation of thicker oxide layers on the bead surface with increasing nitrogen and oxygen contents in the argon-based shielding gas. Analysis by energy-dispersive X-ray spectroscopy revealed that most of these compounds are nitrides or oxides.

Methods and results regarding sinusoid modulated pulse gas metal arc welding

In this investigation, a sinusoid modulated pulse gas metal arc welding (SP-GMAW) method based on a current waveform control method and on the welding mechanism of pulsed gas metal arc welding (P-GMAW) was proposed. This method achieved smooth control over the welding current. The process formulas were simplified. Then, the control parameters were discussed and optimized. Finally, three comparison experiments were conducted. The results indicated that the SP-GMAW method, as an improved double-pulsed gas metal arc welding (DP-GMAW) method, had the following features: The SP-GMAW minimized porosity rate and generated palpable weld ripples in contrast with the P-GMAW. The SP-GMAW produced the finest fusion zone grain, highest fusion zone microhardness, and highest tensile strength among three welding methods. The feasibility and superiority of the method for welding aluminum sheet were verified.

Microstructures and mechanical properties of 30Cr-4Mo ferritic stainless steel joints produced by double-pulsed gas metal arc welding

Joining of medium-thick ferritic stainless steel (FSS) traditionally follows the protocol of multi-layer and multi-pass welding to avoid massive grain coarsening in the heat-affected zone (HAZ). In this study, an attempt has been made to join 5-mm-thick 30Cr-4Mo FSS with single pass using double-pulsed gas metal arc welding (DP-GMAW) process employing ERNiCr-3 Ni-based filler. Defect-free joints were made under optimized welding parameters. Microstructural examination elucidated that mean grain size number of HAZ was successfully controlled above 3 due to the relatively low heat input of DP-GMAW. A linear relation between width of HAZ and heat input was found and given. In HAZ, no sigma (σ) phase, chi (χ) phase, or Laves phase was detected, and even-distributed (Ti, Nb)(C, N) precipitates presented mostly inside grains, which significantly kept the integrity of grain boundaries to preserve ductility. Ni-based filler greatly improved the ductility of welds as well. In the fusion zone (FZ), some dispersed white Nb-rich carbides have been observed and columnar dendrites turned into equiaxed dendrites near the centerline of FZ. All specimens qualified the bending test indicating favorable ductility of welded joints.

Study on welding process and prosperities of AA5754 Al-alloy welded by double pulsed gas metal arc welding

In this paper, the effect of double pulsed gas metal arc welding (DP-GMAW) on metal droplet transfer, weld pool profile, weld bead geometry and weld joint mechanical properties of Al alloy AA5754 are presented. A high speed camera was utilized to reveal the metal transfer behavior and weld pool profile. A self-developed electrical signal acquire system was adopted to record the current waveform during welding process. The results indicated that the metal transfer, weld pool profile and weld bead geometry in DP-GMAW significantly differ with P-GMAW. The microstructure showed that grain size of the weld bead decreased with increasing of thermal pulse frequency, and the eutectic precipitates Mg2Si were homogeneously distributed at fusion zone. The mechanical properties of welded joints were improved.