Showing papers on "Shielded metal arc welding published in 2008"

Study of the Performance of Stainless Steel A-TIG Welds

Abstract: The purpose of the present work was to investigate the effect of oxide fluxes on weld morphology, arc voltage, mechanical properties, angular distortion and hot cracking susceptibility obtained with TIG welding, which applied to the welding of 5 mm thick austenitic stainless steel plates. A novel variant of the autogenous TIG welding process, oxide powders (Al2O3, Cr2O3, TiO2, SiO2 and CaO) was applied on a type 304 stainless steel through a thin layer of the flux to produce a bead on plate welds. The experimental results indicated that the increase in the penetration is significant with the use of Cr2O3, TiO2, and SiO2. A-TIG welding can increase the weld depth to bead-width ratio, and tends to reduce the angular distortion of the weldment. It was also found that A-TIG welding can increase the retained delta-ferrite content of stainless steel 304 welds and, in consequence, the hot-cracking susceptibility of as-welded is reduced. Physically constricting the plasma column and reducing the anode spot are the possible mechanism for the effect of certain flux on A-TIG penetration.

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

Abstract: 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.

Influence of shielding gas composition on arc properties in TIG welding

Abstract: The influence of shielding gas composition on arc properties including temperature, voltage, heat flux and shear stress at the anode and also the weld depth as indicated by the maximum temperature of a water cooled anode is investigated. It is found that the additions of helium, hydrogen and nitrogen to argon all increase the arc and anode temperature. For helium, this is due to the lower electrical conductivity; in the other cases, it is due to the higher specific heat.

Effect of Welding Processes and Consumables on Tensile and Impact Properties of High Strength Quenched and Tempered Steel Joints

Abstract: Quenched and tempered steels are prone to hydrogen induced cracking in the heat affected zone after welding. The use of austenitic stainless steel consumables to weld the above steel was the only available remedy because of higher solubility for hydrogen in austenitic phase. In this investigation, an attempt was made to determine a suitable consumable to replace expensive austenitic consumables. Two different consumables, namely, austenitic stainless steel and low hydrogen ferritic steel, were used to fabricate the joints by shielded metal arc welding (SMAW) and flux cored arc welding (FCAW) processes. The joints fabricated by using low hydrogen ferritic steel consumables showed superior transverse tensile properties, whereas joints fabricated by using austenitic stainless steel consumables exhibited better impact toughness, irrespective of the welding process used. The SMAW joints exhibited superior mechanical and impact properties, irrespective of the consumables used, than their FCAW counterparts.

Microstructure of the Fe-based hardfacing layers reinforced by TiC-VC-Mo2C particles

Abstract: In this study, the hardfacing alloys with different measures of ferrotitanium (Fe–Ti), ferrovanadium (Fe–V), ferromolybdenum (Fe–Mo) and graphite were deposited on AISI 1020 steel substrates by shielded manual arc welding (SMAW). Fe-based hardfacing layers reinforced by carbide particles were produced. The thermodynamic analysis for carbide and effect of the carbide forming elements on the properties of hardfacing layers were also discussed. The experimental results showed that TiC-VC-Mo 2 C carbides could be synthesized by metallurgic reaction during SMAW process. Carbides with particle sizes in the range 1–3 μm are uniformly dispersed in the matrix. The hardfacing layer with good cracking resistance and high hardness could be obtained when the amounts of graphite, Fe–Ti, Fe–V and Fe–Mo were controlled within a range of 8–10%, 12–15%, 10–12% and 2–4%, respectively.

Predicting the dilution of plasma transferred arc hardfacing of stellite on carbon steel using response surface methodology

Abstract: Control of dilution is important in hardfacing, where low dilution is typically desirable. At present, most fabrication industries use shielded metal are welding, gas metal arc welding, gas tungsten arc welding and submerged are welding processes for hardfacing purposes. In these processes, the percentage of the dilution level is higher, ranging between 10% and 30%. In Plasma Transferred Arc (PTA) hardfacing, a solidified metallurgical bond between the deposit and the substrate is obtained with minimum dilution (less than 10%). This paper highlights the application of response surface methodology to predict and optimize the percentage of the dilution of a cobalt-based hardfaced surface produced by the PTA process. Experiments were conducted based on a fully replicable five-factor, five-level central composite rotatable design and a mathematical model was developed using response surface methodology. Furthermore, the response surface methodology was used to optimize the process parameters that yield the lowest percentage of dilution.

Metal vapour behaviour in thermal plasma of gas tungsten arcs during welding

Abstract: A gas tungsten arc in helium and argon was modelled taking into account the contamination of the plasma by metal vapour from the weld pool. The whole region of gas tungsten arc atmosphere including the tungsten cathode, arc plasma and weld pool was treated using a unified numerical model. A viscosity approximation was used to express the diffusion coefficient in terms of viscosity of shielding gas and metal vapour. The transient two-dimensional distributions of the temperature, velocity of plasma flow and iron vapour concentration were predicted, together with the weld penetration as a function of time for a 150 A arc current at the atmospheric pressure, both for helium and argon welding gases.It was shown that the thermal plasma in gas tungsten arcs is influenced by iron vapour from the weld pool surface and that the concentration of iron vapour in plasma is dependent on the temperature of the weld pool.

Weld microstructure and shape of laser–arc hybrid welding

Abstract: A series of CO2 laser–metal inert gas arc hybrid welding experiment was carried out to investigate the effects of laser/arc energy ratio and groove parameters on the shape and microstructure of hybrid weld The results showed that increasing arc current and groove cross-section area can reduce dimension difference of laser zone and arc zone by enhancing the uniform of energy distribution in molten pool The arc current can speed the melted metal flow to the pool root and drive more heat to the pool below by the arc pressure, and groove area can reduce the resistance of melted metal flowing to the pool root The microstructure of hybrid weld is simultaneously determined by the total line energy of hybrid welding and energy ratio of laser/arc (ER LA), and only under the proper or relatively smaller total line energy ER LA has obvious effects on microstructure Increasing the ER LA can increase the tendency of hybrid weld to obtain structure with higher hardness Furthermore, the mechanical performan

Relationship between the weldability and the process parameters for laser-TIG hybrid welding of galvanized steel sheets

Abstract: In the lap welding of zinc-coated steel, porosity formation is one of most significant weld defects. It is caused by zinc vapor generated between the steel sheets. Various solutions have been proposed in the past but development of more effective method remains a valuable subject to be investigated. In this study, laser-TIG hybrid welding was applied to the lap welding of zinc-coated steel without a gap. The weld defects could be eliminated by laser-TIG hybrid welding, as the leading TIG arc partially melted the upper sheet, and the coated zinc on the lapped surfaces were vaporized or oxidized before the trailing laser irradiated on the specimen. Optimization of the process parameters for laser-arc hybrid welding process is intrinsically sophisticated because the process has three types of parameters-arc, laser and hybrid welding parameters. In this paper, the relationship between weldability and the process parameters of the laser beam-arc distance, welding current and welding speed were investigated using a full factorial experimental design. Weld quality was evaluated using the weight of the spatter, as porosity formation is a major weld defect in the lap welding of zinc-coated steel sheets. It was found that the weld quality was increased as the laser beam-arc distance and welding current increased, and that this decreased as welding speed increased.

Effect of welding consumables on tensile and impact properties of shielded metal arc welded high strength, quenched and tempered steel joints

Abstract: Quenched and tempered (Q&T) steels are widely used in the construction of military vehicles due to its high strength to weight ratio and high hardness. These steels are prone to hydrogen induced cracking in the heat affected zone (HAZ) after welding and HAZ softening. The use of austenitic stainless steel (ASS) consumables to weld the above steel was the only remedy because of higher solubility for hydrogen in austenitic phase. Recent studies proved that high nickel steel (HNS) and low hydrogen ferritic (LHF) steel consumables can be used to weld Q&T steels, which can give very low hydrogen levels in the weld deposits. In this investigation an attempt has been made to study the effect of welding consumables on tensile and impact properties of high strength, Q&T steel joints. Three different consumables, namely ASS, LHF steel and HNS have been used to fabricate the joints by shielded metal arc welding (SMAW) process. The joints fabricated using LHF steel electrodes showed superior transverse tensil...

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

Abstract: 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.

The effect of shielding gas composition in CO2 laser—gas metal arc hybrid welding

Abstract: In carbon dioxide (CO2) laser—gas metal arc hybrid welding, a shielding gas is supplied to isolate the molten metal from the ambient air, suppress the laser-induced plasma, remove the plume out of the keyhole, and stabilize the metal transfer. In this study, a shielding gas consisting of helium, argon, and CO2 was used, and its effects on the composition of the welding phenomena, such as behaviours of laser-induced plasma generation, molten pool flow, and droplet transfer in gas metal arc welding, were investigated. High-speed video observation was used to investigate the welding phenomena inside the arc regime. Consequently, helium was found to have a dominant role in suppressing laser-induced plasma; minimum helium content at a laser power of 8 kW was suggested for laser autogenous and hybrid welding. Argon and CO2 govern the droplet transfer and arc stability. A 12 per cent addition of CO2 stabilizes the metal transfer and eliminates undercut caused by insufficient wetting of molten metal.

Influence of Pulse Parameters on Characteristics of Bead-on-Plate Weld Deposits of Aluminum and Its Alloy in the Pulsed Gas Metal Arc Welding Process

Abstract: A summarized influence of pulse parameters have been studied; these parameters are defined by a hypothetically derived factor ϕ = [(I b /I p )ft b ] on the characteristics of bead-on-plate weld deposits of aluminum and Al-Mg alloy, with respect to their geometry and microstructure. The weld geometry has been studied in reference to the depth, width, and area of fusion of the base plate, and the bead height, bead width, toe angle, form factor, area of weld deposit, fraction of base metal fusion per unit mass of weld deposition, and dilution. It is found that these aspects of geometry and the microstructure of the weld metal and heat-affected zone (HAZ) vary significantly with a change in the factor ϕ. The value of the factor ϕ at approximately 0.1 has been seen as critical to the change in the different aspects of the pulsed–gas metal arc (P-GMA) weld. It is also found that, at a given ϕ, the variation in mean current and heat input significantly affects the geometry and microstructure of the weld deposit.

Understanding the Parameters Controlling Plasma Transferred Arc Hardfacing Using Response Surface Methodology

Abstract: Control of dilution is important in hardfacing, where typically low dilution is desirable. At present, majority of the fabrication industries use shielded metal arc welding (SMAW), gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), and submerged arc welding (SAW) processes for hardfacing purposes. In these processes, the percentage of dilution level is higher, ranging between 10–30%. In plasma transferred arc (PTA) hardfacing, a solidified metallurgical bond between deposit and substrate is obtained with minimum dilution (less than 10%). This article highlights the application of response surface methodology (RSM) to predict and optimize the percentage of dilution of nickel based hardfaced surface produced by PTA process. The experiments were conducted based on five-factor, five levels central composite rotatable design with full replications technique and mathematical model was developed using RSM. Further, the RSM is used to optimize the process parameters that yield the lowest percentage of...

AC TIG welding with single-component oxide activating flux for AZ31B magnesium alloys

Abstract: Magnesium-based alloys are finding extensive applications foreground in aerospace and automotive applications. Weldability of magnesium alloys has recently been investigated with a variety of processes. In this article, the activating flux TIG (ATIG) welding of magnesium alloys with three single-component fluxes (TiO2, Cr2O3 and SiO2) under alternating current (AC) mode was studied. The effects of welding speed, weld current and electrode gap on the weld shape and the weld arc voltage in AC TIG welding with oxide fluxes were investigated on an AZ31B magnesium alloy substrate. The mechanisms of oxide fluxes on the arc shape and the arc voltage on the weld shape are discussed. The result showed that the TiO2 and Cr2O3 increase the weld penetration of AC TIG welding of magnesium with good bead cosmetics. The SiO2 increased the weld penetration with very poor formation of the weld surface. However, the arc voltage decreased with the used of TiO2 flux, and increased with the used of Cr2O3 flux. The mechanism of TiO2 and Cr2O3 fluxes increasing penetration should not accord with the “arc constriction”. It would comply with some potential effects of the flux interacting with the liquid metal of fusion zone.

Low-Power Laser/Arc Hybrid Welding Behavior in AZ-Based Mg Alloys

Abstract: The low-power laser/arc hybrid welding behaviors of the AZ-based Mg alloys in similar and dissimilar joints are examined in this study in terms of welding parameters, fusion-zone characteristics, mechanical properties, welding temperature fields, and laser-induced arc plasma/plume. Experiments were conducted using a low-power (300 W) pulsed Nd:YAG laser with a gas tungsten welding arc. The results show that the AZ-based Mg alloys can be easily welded by laser/arc hybrid welding process. The introduction of low-power laser beam can stabilize the welding arc even at a high-speed welding, and spattering behavior of laser welding disappeared due to the introduction of welding arc. With the increases of arc power, a higher weld depth can be obtained, and the weld depths for laser and arc acting in combination (laser/arc) are 2 times higher than those of for laser and arc acting separately (laser + arc) in optimal conditions. The postweld tensile strength of Mg alloys could recover ∼80 to 100 pct of the original strength in similar or dissimilar joints. The fatigue strength in laser/arc hybrid welded specimens is equal to that of the unweld base metal.

Laser welding of zinc coated steel: an alternative to resistance spot welding

Abstract: Laser lap welding of zinc coated steel using copper is found to be a promising alternative to resistance spot welding. Copper, which acts as an alloying element for zinc, is sandwiched between the lapped sheets in powder form. Such introduction of copper not only ensures a zero gap, but also assists in reducing violent vaporisation of zinc, the main cause of porosity and spattering during laser welding of zinc coated steel. Emission spectroscopy data recorded during the welding experiments validate the effect of copper on zinc vaporisation. Mechanical tests show acceptable results for laser welds made with copper. Moreover, minimal residual copper in the weld zone, and its extended solid solubility in iron due to non-equilibrium processing rules out the possibility of hot cracking. Concerns regarding electrochemical corrosion due to addition of copper in the weld are addressed and the results are found to be favourable. It is further shown that the fatigue life of a laser weld is ∼25% higher than ...

Flux-cored wires for arc welding and surfacing of cast iron

Abstract: (2008). Flux-cored wires for arc welding and surfacing of cast iron. Welding International: Vol. 22, No. 11, pp. 796-800.

Effects of oxide activating flux on laser welding of magnesium alloy

Abstract: The behaviours of laser welding wrought magnesium AZ31B alloy with oxide activating fluxes (TiO2, SiO2 and Cr2O3) were studied in the present paper. The results showed that the three fluxes all can increase the weld penetration of the laser welding. A larger grain size was exhibited in the weld metal prepared with flux than that in the fusion zone prepared without flux by optical microscopy. Oxide particles were found in the weld metal by electron probe microanalysis (EPMA), when flux was used. The results of tensile tests showed that weld metal without flux has nearly 90% of base metal strength when compared to the ones with flux. The mixed mode fracture was showed in the weld with flux. The main mechanism for the increases in penetration was that the flux coat absorbed more laser energy during the early period of laser action.

Double sided arc welding of AA5182 aluminium alloy sheet

Abstract: The feasibility and merits of using the double sided arc welding (DSAW) process for making square welds in 1˙2 mm thick AA5182-O aluminium sheets in the butt-joint configuration for applications such as tailor welded blanks (TWB) has been studied. Full penetration, conduction mode DSAW welds were made using a balanced square wave AC, constant current power supply at welding speeds of 30 to 40 mm s–1 when using 2˙1 kW welding power and between 40 and 60 mm s–1 when using 3˙4 kW welding power. There was good cathodic cleaning of the oxide on both sides of the sheet and the weld bead quality and properties were excellent. All welds exhibited a columnar to equiaxed grain transition with up to 40% equiaxed grain area. The DSAW process was found to be capable of producing welds of equal or better quality and at comparable welding speeds to those produced using more traditional welding processes for TWB applications.