Current Gas Metal Arc Welding Research Articles

An innovative pulsed current arc welding technology for armor steel: Processes, microstructure, and mechanical properties

This study presents a novel pulsed current arc welding technology, specifically pulsed current gas tungsten arc welding (PC-GTAW), single and double pulse gas metal arc welding (SP/DP-GMAW), and dual process welding (D-process). This study aims to investigate the effectiveness of these welding techniques for armor steel weldments. This research focused on investigating the welding processes, resulting microstructures, and mechanical properties of welded joints. Based on the macrography analysis, it was determined that the weldments exhibit no signs of porosity, inclusions, or inadequate penetration. This finding substantiates the optimum settings for the weldment production process. The weldment optical microstructure, fusion, and heat-affected zone were examined in the weld interface. The microstructural properties of the FZ include δ-ferrite, austenite, bainite, and acicular martensite. The HAZ has a bainite-untempered martensite microstructure. The chemical composition and variations across the weldment (base, weld and HAZ) were identified. The grain borders contained greater quantities of Cr, Ni, Mn, Si, and Mo than those of the grain cores. EBSD revealed average weld zone grain sizes of 17.7 µm, 32.6 µm, 30.8 µm, and 24.6 µm for PC-GTAW, SP-GMAW, DP-GMAW, and D-Process, respectively.Furthermore, the hardness measurements showed a progressive transition across different regions. Additionally, the D-Process-fabricated material exhibited a maximum ultimate tensile strength of 872 MPa and an elongation of 4%. The mechanical properties exhibited by this new process variant exceed those of other weldments, indicating its potential for fabricating armor steel. The impact toughness demonstrated superior performance in all the weldments. Within this context, the new use of pulsed current advanced welding methods has shown the ability to generate welded parts of exceptional quality.

Importance of Narrow Gap in Pulsed Current Gas Metal Arc Welding of Thick Wall Micro-alloyed Steel: Weld Appearance and Microstructure

Importance of Narrow Gap in Pulsed Current Gas Metal Arc Welding of Thick Wall Micro-alloyed Steel: Weld Appearance and Microstructure

Investigating microstructural evolution and wear resistance of AISI 316L stainless steel cladding deposited over mild steel using constant current GMAW and pulsed current GMAW processes

Abstract The main objective of this study is to investigate the microstructure and wear resistance of AISI 316L austenitic stainless steel (ASS) cladding deposited over mild steel (MS) of grade IS 2062 using constant current (CC-GMAW) and pulsed current gas metal arc welding (PC-GMAW) processes. The PC-GMAW process was employed to overcome the problems of wider heat affected zone (HAZ), coarse grained deposited weld metal microstructure, lower penetration depth, higher dilution and reinforcement height encountered in CC-GMAW used for cladding of AISI 316L steel over mild steel. The microstructural features of cladded region were analyzed using optical microscopy (OM). The wear rate of cladded specimens was studied using pin-on-disc method and the morphology of wear surfaces was studied using scanning electron microscopy (SEM). The microhardness distribution of cladded region was analyzed and correlated to the wear performance of cladded specimens. The results showed that PC-GMAW cladding exhibit greater hardness and wear resistance compared to CC-GMAW cladding. It is correlated to the grain refinement offered by current pulsing in weld region of PC-GMAW cladding. The PC-GMAW cladding showed 5.22% increases in weld metal deposition compared to CC-GMAW cladding. The, PC-GMAW cladding showed 23.72% reduction in dilution of weld compared to CC-GMAW cladding. The PC-GMAW cladding disclosed 15.83 improvement in weld overlay hardness compared to CC-GAMW cladding. The PC-GMAW showed 20.18% average reduction in wear rate compared to CC-GMAW cladding.

The influence of bypass current on arc energy density and metal transfer behaviour in bypass current compressed gas metal arc welding

A new welding method, bypass current compressed gas metal arc welding (BCC-GMAW), was developed to enhance the arc energy density and welding stability of GMAW. When the bypass current was applied, the arc energy density was increased with the constraining effect of the circumferential bypass electrode, which was studied by current density and arc pressure, resulting in an increase of 46% in weld depth and a decrease of 38% in weld width. As the coupled arc increased the melting speed of wire and forces of droplet downward transfer, the droplet transfer frequency increased by 185%, and the metal transfer mode was changed from short-circuit transfer to stable small globule transfer, obtaining a smooth and uniform weld appearance.

Wear properties and microstructural characteristics of mild steel cladded with AISI 316L stainless steel using constant current gas metal arc welding process

The main objective of this study is to investigate the microstructure and wear resistance of AISI 316L austenitic stainless steel (ASS) cladding deposited over mild steel (MS) of grade IS 2062 using constant current (CC-GMAW) gas metal arc welding process. The microstructural features of cladded region were analyzed using optical microscopy (OM). The wear rate of cladded specimens was studied using pin-on-disc method and the morphology of wear surfaces was studied using scanning electron microscopy (SEM). The microhardness distribution of cladded region was analyzed and correlated to the wear performance of cladded specimens. The results showed that CC-GMAW cladded surface exhibited greater hardness and wear resistance compared to mild steel substrate. The overlay region of CC-GMAW clad showed the evolution of dendritic structure and columnar grains. The CC-GMAW cladding showed martensite laths and widmanstätten ferrite plates microstructure in the HAZ region closer to interface. The wear rate of CC-GMAW cladding increases with increase in load from 1.5 kg to 5.5 kg. It showed 422.85% and 423.58% increase in material weight loss and wear rate at higher loads. The materials weight loss of CC-GMAW cladding increases from 0.0082 g to 0.0517 g with increase in speed from 150 rpm to 550 rpm. The wear rate of CC-GMAW cladding increases from 3.66 × 10-5 g/m to 10.94 × 10-5 g/m with increase in temperature from 27 °C to 200 °C.

Microstructural and wear properties of mild steel cladded with AISI 316L stainless steel using pulsed current gas metal arc welding process

The main objective of this study is to study the microstructure and wear resistance of mild steel (MS) of grade IS 2062 that has had an austenitic stainless steel (AISI 316L) coating applied utilizing the pulsed current gas metal arc welding (PC-GMAW) technique. The PC-GMAW method was used to overcome issues with the conventional gas metal arc welding (CC-GMAW) method used for cladding AISI 316L steel over mild steel, such as a larger heat affected zone (HAZ), coarse-grained deposited weld metal microstructure, less penetration depth and higher dilution and reinforcement height. Optical microscopy (OM) was used to examine the microstructural characteristics of the clad region. Using the pin-on-disc testing machine, the wear rate of cladded specimens was recorded, and scanning electron microscopy (SEM) was used to examine the morphology of wear surfaces. The microhardness distribution of the cladded region was examined, and the wear characteristics of the cladded specimens were correlated. According to the findings, PC-GMAW cladding is harder and more resistant to wear than a mild steel substrate. The PC-GMAW cladding exhibited higher weld metal deposition and lower dilution. Weld overlay hardness was 15.83% higher in the PC-GMAW cladding than in the mild steel substrate. The wear rate was decreased by an average of 20.18% as compared to the mild steel substrate with PC-GMAW cladding.

Characterization of the effects of high-intensity negative current pulses on metal transfer and melting rate in the AC-GMAW process

The use of variants of the gas metal arc welding (GMAW) process has become an affordable option in industry. Alternating current–gas metal arc welding (AC-GMAW) arises as one of them, providing additional degrees of freedom for process controllability and versatility. This study focused on the analysis of a complex waveform of the AC-GMAW process for welding stainless steel, employed in modern synergic programs, which has not been widely disseminated in the technical literature and assessed scientifically. The main objective was to characterize the effects of high-intensity pulses in negative polarity over the process and to discuss the potential of this strategy, since it has not been used in conventional AC synergic programs. In order to bring to light information on the phenomena involved, such as the arc climbing on the wire electrode, advanced techniques of high-speed videography were used, synchronized with the acquisition of electrical welding process signals, as well as infrared thermography, to verify the evolution of the cooling of the piece after welding. The results grounded discussions on different AC-GMAW waveforms. The process’ electrical data, along with images of the arc and analysis of the wire melting and workpiece thermal behavior, showed that there was a significant visible increase in wire melting during the negative pulse. In addition, it evidenced how the negative electrode increment contributed to the increase in wire melting even at lower power and also showed the thermal effects on the workpiece.

A study on tensile properties and microstructural characteristics of wire arc additive manufactured low carbon steel cylindrical components

Wire arc additive manufacturing (WAAM) is an additive manufacturing (AM) technology that uses a modified robotic arc welding machine to manufacture parts in a layer-by-layer pattern. Wire-based AM has many major advantages, including good fabrication flexibility and control, as well as easier automated manufacturing. This article compares the tensile proprieties of WAAM low carbon steel cylinders made by pulsed current gas metal arc welding (PGMAW) and pulsed current cold metal transfer (PCMT) arc welding techniques. The microhardness and tensile properties of the WAAM cylindrical parts were evaluated in the bottom and top zones. The PCMT-WAAM cylinder showed higher hardness, yield strength (YS), and ultimate tensile strength (UTS) than the PGMAW-WAAM cylinder. The microstructural characteristics of the produced low carbon steel cylinders varied from one process to another process. The inhomogeneity in tensile properties and hardness is caused by variations in microstructural characteristics.

A study on shrinkage residual stresses, microstructure and mechanical properties of ASS thick pipe welded by GMAW process

In this investigation, AISI 304LN austenitic stainless steel pipes having 25 mm thickness and 300 mm inner diameter with conventional and narrow groove were welded by continuous current gas metal arc welding (GMAW) and pulse current gas metal arc welding (P-GMAW) process. A gas tungsten arc welding (GTAW) process was used for the welding of the root pass. Microstructural study was carried out in fusion zone (FZ) and heat-affected zone (HAZ). A favourable microstructure characteristic was observed in the P-GMAW process. The study of transverse shrinkage and shrinkage stresses were done on the conventional groove with GMAW and P-GMAW process and narrow groove by P-GMAW process. It was found that narrow groove weld design with controlled welding parameters can reduce 45% shrinkage as compare to conventional groove, similarly 30% reduction in shrinkage stress can be achieved. The tensile properties were observed to increased, such as yield strength was improved from 260 MPa to 310 MPa and ultimate strength was improved from 510 MPa to 550 MPa in the case of narrow groove weld by the P-GMAW process.

Numerical analysis of the effect of heat loss by zinc evaporation on aluminum alloy to hot-dip galvanized steel joints by electrode negative polarity ratio varied AC pulse gas metal arc welding

In joining of aluminum alloy to hot-dip galvanized (GI) steel by arc welding-brazing process, evaporation of zinc (Zn) layer and formation of brittle Fe Al intermetallic compound (IMC) layer can affect the joint quality both thermally and metallurgically. At this point, the alternate current pulse gas metal arc welding (AC pulse GMAW) process is an excellent joining method because of its relatively low heat input to the base metal by controlling the electrode negative polarity (EN) ratio in its current waveform. In this study, a numerical analysis of joining 1.2 mm-thick GI steel to 1.2 mm-thick AA5052 aluminum alloy in the lap configuration using AC pulse GMAW was conducted to determine the effect of the EN ratio and Zn evaporation on joint quality. Based on the finite element method (FEM) 3D heat transfer model, the heat conduction analysis and the estimation of the IMC layer growth at the joint interface were carried out. The calculated results were validated with the corresponding experimental results and demonstrated a fair agreement. The results indicated that the temperature-dependent Zn mass evaporation and the increased EN ratio decrease the heat input to the joint interface. In particular, the heat loss caused by Zn evaporation with its latent heat restricts the growth of the brittle Fe Al IMC layer, which follows a function of temperature variation per unit length and time, by decreasing the heat from the arc to the joint interface. A 7.83 μm-thick IMC layer was obtained at a welding current of 55 A with an EN ratio of 20%, and a sound dissimilar material joint was achieved.

A Study on the Effect of Current Waveform on Intermetallics Formation and the Weldability of Dissimilar Materials Welded Joints (AA5052 Alloy—GI Steel) in AC Pulse GMAW

In joining aluminum alloy to galvanized (GI) steel, the huge gap of thermophysical properties, defects by zinc from the steel surface, and formation of excessive brittle Fe-Al intermetallics (IMC) are the main factors that deteriorate the joint quality. In this study, alternating current pulse gas metal arc welding (AC pulse GMAW) was suggested as a solution with a mix of electrode positive and negative modes. A 1.2 mm thick AA5052 aluminum alloy and GI steel plates were joined using 1.2 mm diameter AA4047 filler wire. A comparative study on the joint interface was conducted varying the welding current and electrode-negative (EN) ratio to investigate the effect of different welding parameters on the growth of the Fe-Al intermetallics (IMC) layer, the effect of zinc, and the mechanical characteristics of the joints. It was confirmed that the change of polarity affects the distribution of zinc element in the joints. An increase in the EN ratio suppressed the growth of the IMC layer to 3.59 μm with decreased heat input. The maximum tensile-shear strength of the welded joints was approximately 171 MPa (78% joint efficiency) at the welding current of 50 A with 20% EN ratio.

Effect of variants of gas metal arc welding process on tensile properties of AA6061-T6 aluminium alloy joints

This article describes the influence of gas metal arc welding (GMAW) variants on tensile properties of welded thin sheets of AA6061-T6 aluminium alloy. Single V butt joints were fabricated using the four variants of the GMAW process (constant current, pulsed current, cold metal transfer and pulsed cold metal transfer) under optimized conditions. Transverse tensile properties of the welded joints were evaluated, and a microhardness survey was done along the cross section of the joints. Higher hardness is recorded in the weld metal, i.e., 79 Hv for the pulsed cold metal transfer (PCMT) joint which is 14% higher than the continuous current GMAW joints. It is observed that a PCMT-welded joint exhibited the highest tensile strength of 227 MPa which is 16% higher than the continuous current GMAW joints. The fracture surface of the tensile specimens is highly dominated by the dimples with tearing ridges which suggests that the joints have experienced sufficient plastic deformation before failure irrespective of the welding process. The results demonstrated that the joints fabricated using the PCMT process exhibited superior tensile properties with controlled segregation of phases compared to the other variants of the GMAW process due to the pulsing effect associated with the retraction of the wire.

Three-dimensional particle simulation of buried space formation process during high current gas metal arc welding

A drop transfer mode and a rotating transfer mode in high current gas metal arc welding named buried arc welding were modeled using a particle method that was suitable for numerical simulations of a fluid behavior with phase changes and large deformations. Numerical simulations of the buried space and weld pool formation processes in both a drop transfer condition and a rotating transfer condition were conducted using computational models to clarify the effects of the arc pressure distribution and the transport position of the molten metal droplets on the buried space. Finally, numerical simulations using conditions combining these transfer modes to imitate low frequency modulated voltage control were also conducted. As a result, the computational model developed in this study clarified the roles of the drop transfer mode and the rotating transfer mode in the buried space formation process during buried arc welding. Moreover, the mechanisms of the experimental results obtained in a previous study, in which a deep penetration depth was obtained while preventing the collapse of the buried space by switching between the transfer modes, were qualitatively clarified.

PC-GMAW effect on the welding thermal cycle and weld metal geometry for high strength steels

Welding of medium carbon alloy steels used in the manufacture of special-purpose machinery imposes to solve two mutually exclusive problems – to increase the depth of penetration of the base metal and to reduce the width of the thermal impact zone of the welded joints. To successfully solve this problem, it is necessary to use arc welding processes with a concentrated heat source. One of these processes is pulsed current gas metal arc welding (PC-GMAW). The present researches have allowed estab-lishing, that with PC-GMAW change of welding current is a difficult character, namely: on high-frequency impulse signal (60 kHz), impulses of the current of low frequency (from 90–150 Hz) are imposed. The change in the values of the mean welding current at PC-GMAW is achieved by increasing the pause current and the frequency of high-amplitude current pulses. It is shown that the PCGMAW allows reducing the amount of metal splashing, to increase the depth of penetration (almost 2 times) in comparison with stationary welding. At the same time, the cooling rate of HAZ metal in the temper-ature range 600–500°C decreases almost 1.5 times, which allowed to reduce the width of HAZ by 40%.

Characterization of Mechanical and Metallurgical Notch Effects of DP980 Steel Weld Joints in Fatigue Performance

This work investigates the use of 980 MPa grade dual-phase (DP) steel joints with pulsed current gas metal arc welding (P-GMAW) for reliable weld performance by comparing actual welded joints with thermo-mechanical simulations. We focus on the weldment characteristics that can cause mechanical and metallurgical notch effects, which impact the fatigue performance of welds. For this purpose, we conduct experiments investigating the use of two types of filler metals and three heat inputs as variables. We find that HAZ regions in the actual weldments have varied microstructures caused by different phase transformations of martensite corresponding to various peak temperatures experienced. We confirm that improved weld geometry plays a key role in enhancing fatigue performance. We identify and discuss the degradation of mechanical properties arising from increasing heat input, in terms of transformation kinetics investigated by means of HAZ thermo-mechanical simulations and thermodynamic calculations. This study provides an overall understanding of the welded joints of DP steel and suggests a way to improve weldability by adjusting the mechanical and metallurgical parameters of various regions in the weldments.

Simulated Stress-Induced Sensitization Study for the Heat-Affected Zone of the 304LN Stainless Steel Weld Using a Thermomechanical Simulator

Stress-induced sensitization in the heat-affected zone (HAZ) of the 304LN austenitic stainless steel weld at 923 K (650 °C) was evaluated using a thermomechanical simulator (Gleeble 3800) at different stress levels. The simulated sensitization behavior of the HAZ was studied in close approximation of the stress and weld thermal cycle that is generally observed during pulse current gas metal arc welding of the 25-mm-thick section of the 304LN steel. The response to the degree of sensitization, as a function of the type and magnitude of stresses present in the matrix, was established through observations on changes in microstructure, electrochemical properties and hardness measurements. Transmission electron microscopy and selected area diffraction confirm that sensitization occurred and Cr23C6 precipitates formed at grain boundaries. The results indicate that the presence of tensile or compressive stresses, especially above the yield stress of the steel, enhances sensitization.

SMA, GTA and P-GMA dissimilar weld joints of 304LN stainless steel to HSLA steel; Part-2: hot corrosion kinetics

A study of hot corrosion kinetics of dissimilar weld joints of 304LN austenitic stainless steel and HSLA steel, which are welded by commonly used arc welding processessuch as P-GMAW (pulsed current gas metal arc welding), GTAW (tungsten inert gas welding), and SMAW (shielded metal arc welding), has been conducted. The joints were then exposed to a molten salt environment of K2SO4 + NaCl (50%) at 923 K (650 °C) under cyclic conditions, that is, 1 h of heating and subsequently 20 min of cooling. A gravimetric analysis was conducted and it was observed that salt-coated samples follow a parabolic rate law. SEM/EDAX, XRD, and line mapping were used to systematically characterize the resulting oxide scale in the dissimilar weld joints. The influence of the molten salt environment on the hot corrosion behavior of dissimilar welded specimens is also discussed. From the hot corrosion studies, it was concluded that the longer the duration of exposure to molten salt, the higher the weight gain by the weldment.

Assembling of thick-section HSLA steel with one seam per layer multi-pass PC-GMA welding producing superior quality

Assembling of 25-mm-thick HSLA steel plate with extra narrow gap between the plates is done with the help of multi-pass one seam per layer pulse current gas metal arc welding process maintaining vertical weld deposition. Assembling of thick plates is also made using conventional groove with commonly used procedure of multi-pass multi-seam per layer weld deposition. Distortion and shrinkage that developed in the weld joints have been suitably determined. The effects of welding parameters in reference to weld thermal behavior on shrinkage stress and bending stress have been studied. The observations show that the use of one seam per layer technique allowing extra narrow gap welding with properly selected parameters can improve quality of weld joint with respect to distortion and stresses. The effect of pulse parameters on weld quality is studied, correlated and discussed. Cost benefits of applying such a welding technique have been justified with respect to consumption of less filler material and time for preparation of weld joint.

Pulse Current Gas Metal Arc Welding : Characteristics, Control and Applications

This book is a part of the Materials Forming, Machining and Tribology book series. It has a total of 322 pages, and is primarily written for Masters and Ph.D. level students and for industries. Gas Metal Arc Welding Process is widely employed in industry at present. However, for some distinct reasons. Pulse Current Gas Metal Arc Welding Process is gaining focus nowadays. In this monograph, therefore, the author discusses the basic concept of this process, special aspects of this process and applicability of this process in different areas.

Numerical simulation of droplet transfer behavior in variable polarity gas metal arc welding

Gas metal arc welding (GMAW) using an alternating current waveform is usually termed as variable polarity GMAW (VP-GMAW), during which the electrode polarity switches between positive and negative periodically. The arc properties and the droplet transfer in VP-GMAW would be different from traditional direct current GMAW. In order to clarify the droplet transfer phenomena during a VP-GMAW process, a unified numerical model including the interaction between the arc plasma and the moving droplet is developed. The simulation results indicate that the arc plasma generated at electrode negative polarity shows a less constricted shape, a lower plasma temperature and velocity, compared to positive polarity. The resultant droplet is found to have a bigger size and a lower temperature than that of direct current gas metal arc welding with the same average welding current. Moreover, a quantitative analysis of the heat fluxes into the electrode is further conducted to explain the thermal mechanism for the differences in droplet properties between variable polarity and direct current gas metal arc welding. Finally, the simulated results are compared with the high-speed images, and the simulated and experiment results show good agreements.