Pulsed Current Gas Metal Arc Welding Research Articles

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.

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.

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.

Influence of Metal Transfer Modes and Postweld Heat Treatment on Tensile Properties of Gas Metal Arc–Welded AA6061-T6 Aluminum Alloy Joints

Abstract The issues of dissolution or overaging of precipitates in the weld metal or heat-affected zone of aluminum alloy joints welded by conventional or constant-current gas metal arc welding (CC-GMAW) process are the key factors responsible for the formation of softening region, which leads to the degradation of the mechanical properties of the joint. In order to prevent the precipitate dissolution, a low heat input welding process is required. Further, to improve the mechanical properties of the welded joints, reprecipitation is necessary, and this can be achieved by postweld heat treatment (PWHT). The main aim of this investigation is to study the combined effect of metal transfer modes (i.e., CC-GMAW, pulsed-current gas metal arc welding [PC-GMAW], and cold metal transfer gas metal arc welding [CMT-GMAW]) and heat treatment on the tensile properties of gas metal arc–welded AA6061 aluminum alloy joints. This investigation effectively implements the low heat input GMAW variants like PC-GMAW and CMT-GMAW to control the dissolution of precipitates. Moreover, PWHT procedure (solutionizing at 530°C for 1 h, followed by quenching in water and then artificial aging at 170°C for 19 h, and finally cooling in air at an ambient temperature) was imposed on the specimens in order to recover the mechanical properties of the welded joints. It is observed from the tensile properties that PWHT joints exhibited improved mechanical properties compared with the as-welded joints. But the joint welded by CC-GMAW process has shown no improvement in the tensile properties because of the segregation of alloying elements that are observed along the grain boundary. The PWHT CMT-GMAW joint showed huge improvement in tensile properties (i.e., 13 % higher than the CC-GMAW joint and 9 % higher than the PC-GMAW joint) because of the controlled segregation of alloying elements with nucleation of β″ precipitates.

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.

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.

Critical aspects of pulse current GMA welding of stainless steel influencing metallurgical characteristics

Metallurgical characteristics of the weld of austenitic stainless steel (ASS) has been studied as a function of pulse parameters, heat input and heat transferred to the weld pool in pulsed current gas metal arc welding (P-GMAW) process. The combined influence of these three aspects on microstructure and hardness of weld bead and the heat affected zone has been thoroughly investigated. Intergranular corrosion susceptibility of heat affected zone of different weld has also been investigated. The characteristics of pulse current gas metal arc weld have been compared with conventional gas metal arc welds at similar heat inputs. The pulse parameters are suggested which will produce superior quality relative to gas metal arc welding (GMAW) as a research goal. The superiority of pulse current gas metal arc weld has been justified.

Advancement in narrow gap GMA weld joint of thick section of austenitic stainless steel to HSLA steel

In current welding research the development of new procedure to join thick section of dissimilar metal between austenitic stainless steel (γ-SS) and high strength low-alloy (HSLA) steel which are extensively used in elevated temperature applications like petrochemical plants and power stations is required to improve the quality of weld joint. In this paper the development and advanced study of narrowest possible gap GMA weld joint of thick (more than 25mm) γ-SS and HSLA steel and thermal behaviour of weld pool has been discussed for production of multipass single bead per layer narrow gap pulse current gas metal arc (P-GMA) weld joint of thick dissimilar plates free from any lack of fusion to the side wall. This advance procedure is simulated in ANSYS for production of a sound weld joint and the role of pulse current gas metal arc welding (P-GMAW) and its effect on shrinkage behaviour has been also discussed. The study of weld pool isotherm is very convenient to select the pulse parameter to produce the sound weld joint. The measurement of weld pool isotherm clearly indicate the proper selection of pulse parameter to produce sound fusion to the both side of groove wall specially in dissimilar weld joint.

Metallurgical Characteristics on PGMA Welding of Dissimilar 304 Austenitic Stainless Steel and HSLA Steel

Welding of dissimilar metal between austenitic stainless steel (γ-SS) and, high strength low-alloy (HSLA) steel are widely used in high-temperature applications in power station and petrochemical plants. Fusion welding is one of the most widely used methods for joining of dissimilar metal. Therefore, continuous efforts are made to apply this method for joining of dissimilar metal of various combinations and despite many difficulties encountered. These difficulties include problems associated with microstructure of the weld metal and heat-affected zone (HAZ). Considering the lack of such knowledge some understanding in this regard has been presented in reference to dissimilar Austenitic stainless steel (γ-SS) and high strength low alloy (HSLA) steel under controlled pulsed current GMAW. This paper focus on effect of grain size, microstructure and the width of the heat affected zone by pulsed current gas metal arc welding (PGMAW) of dissimilar γ-SS and HSLA steel. The observations show that in PGMA welds, the decrease in grain size at heat affected zone and lower HAZ Width in both HSLA steel and γ-SS especially with the lowering of summarized influence of pulse parameters factor () at similar heat input per unit length of weld (Ω) has been observed.

Influence of thermal characteristics on microstructure of pulse current GMA weld bead of HSLA steel

The influence of pulse parameters of pulse current gas metal arc welding (P-GMAW) on thermal behavior of weld has been studied considering summarized influence of pulse parameters defined by a dimensionless factor ϕ = [(I b/I p)f. t b], mean current (I m), and heat input (Ω) during weld bead deposition on high-strength low-alloy steel plate using low-alloy steel filler wire. The thermal behavior of the weld has been estimated with the help of appropriate expressions. The validity of those estimations has been confirmed by comparing them with measured values and found that they are well in agreement to each other with a deviation lying in the range of 7 to 8 %. It is observed that variation in thermal characteristics of weld is maintaining good correlation with ϕ, I m, and Ω of the welding process. The thermal characteristics of the weld are correlated to microstructure.

Thermal Modeling of Multipass Narrow Gap Pulse Current GMA Welding by Single Seam per Layer Deposition Technique

A thermal model has been developed for production of multipass single seam per layer narrow gap pulse current gas metal arc (GMA) weld joint of thick plates free from lack of groove wall fusion under no angle of attack to groove wall. The model considers the fusion of groove wall as well as a part of earlier deposited weld based on the geometrical aspects and temperature of weld pool, which primarily arises out of initial arc heating and heating by droplets of superheated filler metal transferred to the weld pool. The geometrical aspects of weld pool are considered as its width and height appeared under narrow weld groove. For prduction of a sound weld joint, the favorable role of pulse current gas metal arc welding (P-GMAW) has been amply justified. But the selection of pulse parameter is quite complex due to involvement of relatively large number of pulse parameters simultaneously interactive in nature, which has been solved by considering a summarized influence of pulse parameters defined by a dimensionless hypothetical factor . The model is able to help in proper selection of pulse parameters prior to carrying out welding with appropriate groove wall fusion. The model is experimentally verified by preparing weld joints of high strength low alloy high-strength low-alloy (HSLA) steel using different combinations of pulse parameters.

Thermal Characteristics of Weld and HAZ during Pulse Current Gas Metal Arc Weld Bead Deposition on HSLA Steel Plate

The criticality of pulse current gas metal arc welding (P-GMAW) due to simultaneous influence of its pulse parameters on thermal characteristics of weld and heat-affected zone HAZ) has been studied as a function of summarized influence of pulse parameters defined by a dimensionless factor φ = [(I b /I p )f·t b ], mean current (I m ), and heat input (Ω) during weld bead deposition on high strength low alloy (HSLA) steel plate using low alloy steel filler wire. The thermal characteristics have been estimated with the help of suitable expressions and in consideration of relevant geometrical features of the ripples formed at the surface of weld bead. The validity of those estimations has been confirmed by comparing them with measured values and found that they are well in agreement with each other with a deviation lying in the range of 8 to 10%. It is observed that the trends of variation in thermal characteristics of weld and HAZ are maintaining good correlations with the φ, I m , and Ω of the welding process.

Modern Engineering of Arc Welding Provides Wider Scope in Thermomechanical Weld Simulation for Fabrication of Advanced Structural Steels

The weldability and formability of advanced structural steels largely dominate their use in fabrication of various components of modern applications in automobile industries dealing with sheet metal to heavy engineering employing thick sections. With respect to their chemical compositions often these steels maintain good weldability due to low carbon and alloying content. But consideration of weldability of these steels becomes a delicate issue when their unique combination of superior properties primarily results from the presence of some specific morphological characteristics of the matrix. Control of deterioration of such microstructures during weld fabrication requires thorough knowledge of with and without strain induced transformations of these steels at nonconventional heat treatment of weld thermal cycle. The advances in welding engineering especially with respect to development of new arc welding processes and procedures introduces wide possibilities of control of thermal and mechanical behavior of weld joint. Certain extraordinary aspects of thermal and mechanical behavior of weld of advanced welding process have been discussed considering the versatile pulsed current gas metal arc welding (P-GMAW) process. In reference to the opportunities further prospect of more critical consideration of thermomechanical weld simulation which may facilitate more appropriate handling of delicate microstructure for desired joint properties of varied section of advanced structural steels has been discussed.

Pulsed Current Gas Metal Arc Welding under Different Shielding and Pulse Parameters; Part 2: Behaviour of Metal Transfer

The behaviour of metal transfer and arc stiffness understood in terms of arc pressure (Pa) of pulsed current gas metal arc welding (P-GMAW) using mild steel filler wire have been studied with respect to change in pulse parameters under different gas shieldings of Ar+2%CO2 and Ar+18%CO2. The arc environment revealing the droplet transfer from electrode to weld pool in bead on plate weld deposition has been studied by high speed video graphy. Effect of pulse parameters has been considered by their hypothetically proposed summarized influence defined by a dimensionless factor φ, mean current (Im) and arc voltage. The droplet diameter and velocity of droplet at the time of detachment are found to vary significantly with the variation of φ. At a given φ the experimentally measured behaviour of metal transfer is found well in agreement to their corresponding theoretical estimates. The average droplet diameter transferred per pulse predominantly reduces but, the velocity of metal transfer at the time of detachment enhances with the increase of φ under both the shielding gases. In general a higher values of φ, Im and arc voltage enhances the Pa depending upon type of gas shielding. The use of Ar+2%CO2 shielding gas reduces the droplet diameter and enhances the arc pressure than that observed under Ar+18%CO2 gas shielding.

Arc characteristics and behaviour of metal transfer in pulsed current GMA welding of stainless steel

The variation in arc characteristics, stability in shielding of arc environment and behaviour of metal transfer with a change in pulse parameters have been studied by high speed video-photography during pulsed current gas metal arc (P-GMA) weld deposition using austenitic stainless steel filler wire. A comparative study of similar nature has also been carried out during gas metal arc (GMA) weld deposition in globular and spray transfer modes. The effect of pulse parameters has been studied by considering their hypothetically proposed summarized influence defined by a dimensionless factor ϕ = [( I b/ I p) ft b], mean current and arc voltage and correlation between welding parameters and arc characteristics have been established. The arc characteristics studied by its root diameter, projected diameter, length and stiffness measured in terms of arc pressure and the behaviour of metal transfer noted by the droplet diameter and velocity of droplet at the time of detachment have been found to vary significantly with the variation in ϕ. At a given ϕ the experimentally measured values of the behaviour of metal transfer are found well in agreement to their corresponding theoretical values estimated through mathematical expressions reported earlier. The increase of ϕ and the ratio of ( I b/ I p) have been found to adversely affect the stability of shielding jacket and arc profile especially at high arc voltage.

Analytical studies on thermal behaviour and geometry of weld pool in pulsed current gas metal arc welding

In view of the criticality of pulsed current gas metal arc welding (P-GMAW) due to simultaneous influence of the pulse parameters on thermal and metal transfer behaviour of the process an analytical model has been developed for predicting the temperature and geometry of the weld pool by appropriately considering two types of heat sources of different nature. The model considers the impact of heat in droplets of filler metal depositing in the weld pool in addition to initial arc heating. The model assumes the primary heat transfer to weld pool is the initial arc heating considered as continuous heat source (arc heat source) of double ellipsoidal nature followed by deposition of superheated filler metal considered as point heat source of interrupted nature superimposed on the first one. The dissimilar nature of the two heat sources is treated by different analytical techniques to estimate their temperature distribution in weld pool and HAZ at its vicinity. The geometry of the weld pool has been estimated by evaluation of the weld isotherms causing melting of the base metal under the influence of two heat sources acting on the weld pool. The impact of impinging droplets on weld pool has been considered to determine the depth at which the droplets transfer their heat in it. The predicted temperature and geometry of the weld pool as well as the temperature of HAZ are found well in agreement to the experimental values with a deviation of the order of ±10% in case of the weld deposition of Al–Mg alloy and commercial aluminium especially at high mean current of the order of 180 A and beyond the transition current of the filler wire. However, prediction of weld pool temperature and weld geometry is relatively different at comparatively lower mean current of 150 A below the transient current of the filler wires is not up to the mark.

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.