Microstructure analysis and mechanical characteristics of tungsten inert gas and metal inert gas welded AA6082-T6 tubular joint: A comparative study

The present study is aimed to compare the microstructure characteristics and mechanical properties of AA6082 in T6 condition of tubular joints fabricated by tungsten inert gas welding （TIG） and metal inert gas welding （MIG） processes. The effect of welding processes was analysed based on optical microscopy image, tensile testing, and Vickers micro-hardness measurements. The results showed that the tensile strengths of the TIG-welded joints were better than those of the MIG-welded joints, due to the contribution of fine equiaxed grains formation with narrower spacing arms. In terms of joint efficiency, the TIG process produced more reliable strength, which was about 25% higher compared to the MIG-joint. A significant decay of hardness was recorded in the adjacent of the weld bead zone, shown in both joints, related to phase transformation, induced by high temperatures experienced by material. A very low hardness, which was about 1.08 GPa, was recorded in the MIG-weldcd specimens. The extent of the heat-affected-zone （HAZ） in the MIG-welded joints was slightly wider than those of the TIG-welded specimens, which corresponded with a higher heat input per unit length.

Synthetic LiFePO4/C without using inert gas

LiFePO4/C was synthesized by high temperature solid-state method with cheap Fe2O3, LiH2PO4 and glucose as raw materials in absence of inert gas. The sample had ordered olivine-type structure other impurities characterized by the test of X-ray diffraction （XRD）. The charge-discharge test showed the sample could demonstrate 120.5 mAh/g at 0.2C rate with good cyclic capability. The powder microeleetrode cyclic voltammetry test indicated that the redox process of the sample had good reversibility.

Microstructure and mechanical characteristics of AA6061-T6 joints produced by friction stir welding,friction stir vibration welding and tungsten inert gas welding:A comparative study

This study compared the microstructure and mechanical characteristics of AA6061-T6 joints produced using friction stir welding(FSW),friction stir vibration welding(FSVW),and tungsten inert gas welding(TIG).FSVW is a modified version of FSW wherein the joining specimens are vibrated normal to the welding line during FSW.The results indicated that the weld region grains for FSVW and FSW were equiaxed and were smaller than the grains for TIG.In addition,the weld region grains for FSVW were finer compared with those for FSW.Results also showed that the strength,hardness,and toughness values of the joints produced by FSVW were higher than those of the other joints produced by FSW and TIG.The vibration during FSW enhanced dynamic recrystallization,which led to the development of finer grains.The weld efficiency of FSVW was approximately 81%,whereas those of FSW and TIG were approximately 74%and 67%,respectively.

Liquation cracking in the heat-affected zone of IN939 superalloy tungsten inert gas weldments

The main aim of this study was to investigate liquation cracking in the heat-affected zone(HAZ)of the IN939 superalloy upon tungsten inert gas welding.A solid solution and age-hardenable filler metals were further studied.On the pre-weld heat-treated samples,upon solving the secondaryγ′particles in the matrix,primaryγ′particles in the base metal grew to"ogdoadically diced cubes"of about 2μm in side lengths.The pre-weld heat treatment reduced the hardness of the base metal to about HV 310.Microstructural studies using optical and fieldemission scanning electron microscopy revealed that the IN939 alloy was susceptible to liquation cracking in the HAZ.The constitutional melting of the secondary,eutectic,and Zr-rich phases promoted the liquation cracking in the HAZ.The microstructure of the weld fusion zones showed the presence of fine spheroidalγ′particles with sizes of about 0.2μm after the post-weld heat treatment,which increased the hardness of the weld pools to about HV 350 and 380 for the Hastelloy X and IN718 filler metals,respectively.Application of a suitable solid solution filler metal could partially reduce the liquation cracking in the HAZ of IN939 alloy.

Feature Extraction and Dimensionality Reduction of Arc Sound under Typical Penetration Status in Metal Inert Gas Welding

Arc sound is well known as the potential and available resource for monitoring and controlling of the weld penetration status,which is very important to the welding process quality control,so any attentions have been paid to the relationships between the arc sound and welding parameters.Some non-linear mapping models correlating the arc sound to welding parameters have been established with the help of neural networks.However,the research of utilizing arc sound to monitor and diagnose welding process is still in its infancy.A self-made real-time sensing system is applied to make a study of arc sound under typical penetration status,including partial penetration,unstable penetration,full penetration and excessive penetration,in metal inert-gas（MIG） flat tailored welding with spray transfer.Arc sound is pretreated by using wavelet de-noising and short-time windowing technologies,and its characteristics,characterizing weld penetration status,of time-domain,frequency-domain,cepstrum-domain and geometric-domain are extracted.Subsequently,high-dimensional eigenvector is constructed and feature-level parameters are successfully fused utilizing the concept of primary principal component analysis（PCA）.Ultimately,60-demensional eigenvector is replaced by the synthesis of 8-demensional vector,which achieves compression for feature space and provides technical supports for pattern classification of typical penetration status with the help of arc sound in MIG welding in the future.

Microstructure and mechanical properties of friction pull plug welding for2219-T87 aluminum alloy with tungsten inert gas weld

The friction pull plug welding(FPPW)of the 2219-T87 tungsten inert gas(TIG)welded joint was investigated,and the microstructures,precipitate evolution,mechanical properties,and fracture morphologies of this joint were analyzed and discussed.In this study,defectfree joints were obtained using a rotational speed of 7000 r/min,an axial feeding displacement of 12 mm,and an axial force of 20-22 kN.The results indicated that within these welding parameters,metallurgical bonding between the plug and plate is achieved by the formation of recrystallized grains.The microstructural features of the FPPW joint can be divided into different regions,including the heat-affected zone(HAZ),thermomechanically affected zone(TMAZ),recrystallization zone(RZ),heat-affected zone in the TIG weld(TIG-HAZ),and the thermomechanically affected zone in the TIG weld(TIG-TMAZ).In the TIG-TMAZ,the grains were highly deformed and elongated due to the shear and the extrusion that produces the plug during the FPPW process.The main reason for the softening in the TMAZ is determined to be the dissolution ofθ’and coarsening ofθprecipitate particles.In a tensile test,the FPPW joint welded with an axial force of 22 kN showed the highest ultimate tensile strength of 237 MPa.The locations of cracks and factures in the TIG-TMAZ were identified.The fracture morphology of the tensile sample showed good plasticity and toughness of the joints.

Oxidation during the production of FGH4095 superalloy powders by electrode induction-melt inert gas atomization

Super-clean and super-spherical FGH4095 superalloy powder is produced by the ceramic-free electrode inductionmelt inert gas atomization（EIGA） technique.A continuous and steady-state liquid metal flow is achieved at high-frequency（350 k Hz） alternating current and high electric power（100 k W）.The superalloy is immersed in a high-frequency induction coil,and the liquid metal falling into a supersonic nozzle is atomized by an Ar gas of high kinetic gas energy.Numerical calculations are performed to optimize the structure parameters for the nozzle tip.The undesired oxidation reaction of alloying elements starts at 1000℃ with the reaction originating from the active sites on the powder surfaces,leading to the formation of oxides,MexOy.The role of active sites and kinetic factors associated with the diffusion of oxygen present in the atomization gas streams are also examined.The observed results reveal that the oxidation process occurring at the surface of the produced powders gradually moves toward the core,and that there exists a clear interface between the product layer and the reactant.The present study lays a theoretical foundation for controlling the oxidation of nickel-based superalloy powders from the powder process step.

A new understanding of inert gas narcosis

Anesthetics are extremely important in modem surgery to greatly reduce the patient,s pain. The understanding of anesthesia at molecular level is the preliminary step for the application of anesthetics in clinic safely and effectively. Inert gases, with low chemical activity, have been found to cause anesthesia for centuries, but the mechanism is unclear yet. In this review, we first summarize the progress of theories about general anesthesia, especially for inert gas narcosis, and then propose a new hypothesis that the aggregated rather than the dispersed inert gas molecules are the key to trigger the narcosis to explain the steep dose-response relationship of anesthesia.

Delivery of inert gas through a vertical borehole using inert gas generator: A theoretical study

The delivery of the inert gas through a vertical borehole using inert gas generator or IGG is investigated.Potential limitations and/or transient effects are highlighted.During the analysis,the borehole diameter,borehole length,type of borehole and partial condensation prior to entering the borehole were varied.A choked flow will occur for a contraction exit or borehole of 0.3 m in diameter if no condensation prior to the contraction occurs.If partial condensation takes place,a borehole diameter of 0.3 m will be possible if almost 50%of the water vapour condensates.However,pressure losses along boreholes with a diameter of 0.3 or 0.4 m are significant and could pose a challenge if trying to mitigate the pressure losses.Adding a booster fan prior to the inlet of the 0.4 m lined borehole would still be a challenge.The corresponding case with a 0.5 m borehole presents much more favourable pressure losses.The 0.5 m diameter lined borehole should be regarded as the lower threshold.The rapid heating of the unlined borehole surface will increase the risk of thermal spallation and possibly imposing restrictions.Understanding the mechanisms during gas delivery will increase the likelihood of a successful inertisation.

Influence of arc pressure on the forming of molten pool in tungsten inert gas arc butt welding with micro gap for tantalum sheet

Arc pressure is the key influencing factor to forming of molten pool. Countering the characteristic of tungsten inert gas arc welding with micro gap for tantalum sheet, according to the fundament of arc physics, a distribution model of arc pressure and forming mechanism of molten pool with micro butt gap are proposed, and the influences of arc pressure on forming of molten pool are discussed. Experimental researches for the dynamic formation process of weld molten pool by using high-speed vidicon camera show that when butt gap is appropriate, that is from 0. 1 to 0. 15 mm, molten metals formed on two workpiece uplift and grow up first, then are fused and form uniform molten pool finally.

A novel single wire indirect arc metal inert gas welding process operated in streaming mode

Dilution of a pad weld must be limited to a certain critical level to improve its wear and/or corrosion properties.To do that,a novel single wire indirect arc metal inert gas welding process operated in streaming mode was realized.A metal inert gas welding torch,arranged perpendicular to a substrate in vertical position,is fixed with an auxiliary tungsten electrode horizontally.The arc is ignited between a wire through the torch and the auxiliary electrode.The substrate is not electrically connected.The welding current is set in the range of streaming mode.304 stainless steel was pad welded on Q235 substrates in vertical position by this process.Microstructures were analyzed with optical microscope.Dilution ratios were measured with stereo light microscope and calculated.The results show that,after eliminating interference of the massive torch setup,the dilution ratio of the pad weld with optimized parameters is 5.07%,much less than that with a metal inert gas welding process,which is 26.46%.The pad weld is bonded to the substrate without defects.Microstructures of the pad weld consist of columnar austenite and ferrite between the columns.The dilution ratio increases with increasing welding current or welding velocity,and decreases with increasing distance to the substrate.

Comparative Study on Microstructures of Zincalume Steel(G550)Welded Joint Between Metal Inert Gas and Laser Beam Welding

Zincalume steel(G550)is commonly used in various construction fields because of its high corrosion resistance and good mechanical properties.In recent years,a number of steel companies have massively produced zincalume steel(G550)with large volumes of waste.For the reduction of massive industrial wastes,the zincalume steel(G550)was welded in the lap joint configuration using different welding parameters in the metal inert gas(MIG)welding and laser beam welding(LBW)process in this study.The MIG welding and LBW are more welcomed welding methods due to their high efficiency and low cost.However,they are different as the LBW offers welding speed three to five times faster than MIG welding,while LBW’s heat transfer to workpieces is much less than MIG welding,which can avoid some distortions.The microstructure of zincalume steel(G550)was investigated using scanning electron microscopy(SEM)and the microstructure characterizations of welded specimens were analyzed.The experiment found the columnar dendrites extended under the heat flow direction during the MIG welding and LBW process.Thus,the columnar grains were formed in between the equiaxed zone and fusion zone(FZ)at high heat input and slow cooling rate.Moreover,the grain size of FZ was comparatively smaller than heat affected zone(HAZ)and base metal(BM).

Effects of ignition voltage and electrode structure on electric ignition and combustion characteristics of Ammonium Dinitramide(ADN)-based liquid propellants in electric ignition mode in inert gas environment

Hydrazine is toxic and carcinogenic, which greatly increases the difficulty of application and no longer meets the needs of green aerospace. As a green propellant, the Ammonium Dinitramide(ADN)-based liquid propellant has the advantages of higher specific impulse, being non-toxic,pollution-free, and easy storage. However, an ADN-based space engine in orbit has exposed the problems of high-temperature deactivation of catalysts and cold-start failure. An active ignition technology—electric ignition technology was explored in this paper to break through the technical bottleneck of catalyst deactivation and the inability to a cold start. An experimental system of a constant-volume combustor for the ADN-based liquid propellant based on the electric ignition method was established. The electric ignition and combustion characteristics of the ADN-based liquid propellant in a volume combustor with an electric ignition method were studied. The influencing mechanisms of the ignition voltage and the electrode structure on the electric ignition characteristics of the ADN-based liquid propellant were investigated. An elevation of the ignition voltage could facilitate the ignition process of the ADN-based liquid propellant, curtail electric energy input and heating effect, while exerting an adverse impact on the combustion process of the propellant.An increase in the ignition voltage enhanced the ignition process of the propellant while simultaneously suppressing its combustion process when utilizing mesh electrodes. Compared to the strip electrodes, the mesh electrodes increased the contact area between the electrodes and the propellant,increased the electric energy input power in the electric ignition process, and reduced the ignition delay time. The mesh electrodes could promote the combustion process of the propellant to a certain extent.

Theoretical study of ullage washing with mixed inert gas in a non-equilibrium state

The Mixed Inert Gas(MIG)produced by the novel Green On Board Inerting Gas Generation System(GOBIGGS)mainly consists of carbon dioxide,nitrogen and oxygen.Because of the large solubility of carbon dioxide in jet fuel compared with nitrogen,the no gas release or equilibrium model could not be employed any more.In this paper,first,a mathematical model of the ullage washing was set up to predict the variation of the oxygen concentration on ullage and in the fuel,and the gas evolution and dissolution rate were calculated by Fick's second law.Then,an experimental apparatus was constructed to verify the accuracy of the model.Finally,the numerical comparisons of ullage washing using Nitrogen Enriched Air(NEA)and MIG are presented under various flow rates and fuel loads,and the result reveals that the variation of the oxygen concentration on ullage is nearly identical whatever the inert gas is NEA or MIG.However,the variation of the oxygen concentration in the fuel is disparate,and the oxygen concentration decreases rapidly if the inert gas is MIG,especially when the fuel load is low or the flow rate of the inert gas is high.Besides,MIG could suppress the rising trend of the oxygen concentration on ullage when the aircraft ascends if the fuel tank is fully washed into an equilibrium state on ground.

Prevention of carbon migration in 9% Cr/CrMoV dissimilar welded joint by adding tungsten inert gas overlaying layer

High chromium （9-12% Cr） steels with excellent heat resistance and CrMoV steels with good toughness were potential candidates for combined rotor for steam turbine operated over 620℃. Two welding techniques were used to fabricate 9% Cr and CrMoV dissimilar welded joint. The results show that the carbon migration only appears in the specimen using narrow gap submerged arc welding （NG-SAW） technique, yet it can be effectively prevented by adding tungsten inert gas （TlG） overlaying process before the NG-SAW. The carbon migration occurred in NG-SAW resulting from the sharp transition of the strong carbide-forming element Cr between the weld （-2.7 wt%） and the base metal （- 9 wt%）. On the contrary, the application of TIG overlaying layers can promote the diffusion of Cr element, and therefore result in its much smaller concentration gradient. That is to say, a gentle transition zone of Cr element can be created among the SAW weld, TIG overlaying layers and the base metal, which effectively prevents the carbon migration and therefore produces a decreased carbon concentration adjacent to the fusion line.

Group Contribution based Flammability Limit Estimation of Hydrocarbon-Inert Gas Mixture

As group contribution method is easy to apply and has a wide application range,current study has developed this model to predict flammability limit of hydrocarbons mixed with inert gas using the Marrero/Gani group contribution method,which is significative to the safe application of hydrocarbons in the ORC system.The whole modeling process is divided into two parts:pure compound prediction and mixture prediction.The contribution factors of inert gases and dilute concentration were first introduced in the group contribution method.Moreover,the respective 95%-confidence interval of the mixture based on linear superposition method has been proposed in the developed group contribution model to improve the safety coefficient.For CO2 as inert gas,the average relative error and correlation coefficient are 5.34%and 0.88 for lower flammability limit while 6.99%and 0.95 for upper flammability limit.For N2 as inert gas,the average relative error and correlation coefficient are 7.47%and 0.84 for lower flammability limit while 6.68%and 0.97 for upper flammability limit.Most importantly,this group contribution method has extended the application range to make up the shortcomings of other flammability limit prediction methods aiming at hydrocarbon and inert gas mixtures and proposed the uncertainty analysis to provide reliable prediction range.

Analysis of Arc Physical Property of Pulsed Tungsten Inert Gas Welding Based on Fowler-Milne Method

Pulsed tungsten inert gas （TIG） welding is widely used in industry due to its superior properties, so the measurement of arc telnperature is important to analyse welding process. Arc image of spectral line in 794.8 nm is captured by high speed camera; both the Abel inversion and the Fowler-Milne method are used to calculate the temperature distribution of the pulsed TIG welding. Characteristic of transient variation in arc intensity and temperature is analyzed. When the change of current happens, intensity and temperature of arc jump as well, it costs several millisoconds. The flirther the axial position from the tungsten is, the greater the intensity jumps, and the smaller the temperature changes.

Influence of shielding gas and non-consumable electrode configuration on weld formation

The effect of the shielding gas composition and the cathode processing history on the weld formation quality during welding with a non-consumable electrode at high current was studied. The major reasons for pores, “waists” and undercuts formation during welding at high currents and speed are discrete melt movement to the solidification front due to the arc decline from the cathode axis and significant melt overhanging in the pool tail part caused by excessive peak pressure on the discharge axis. Cathode flow dispersion causes the lack of displacement of the molten metal which results in its laminar flow in the weld pool, uniform flow of the metal to the crystallization front and sound weld formation. The melt movement in the weld pool and eventually the welded joint quality is determined by the pressure distribution pattern on the welded metal surface and the anode spot lag from the electrode. It was demonstrated that non-consumable electrode configurations that provide arcing with a diffuse cathode spot and increased helium concentration in the inert atmosphere during welding with a conical electrode allow sound weld formation.

Investigate Weld Quality of Gas Metal Arc Welding Process Through Online Monitoring of Input Parameters

Gas metal arc welding(GMAW)is also referred as the metal inert gas(MIG)welding which is a process of welding done by the formation of an electric arc between the consumable wire electrode and the workpiece.Through the welding process,a continuous flow of inert gas is supplied,and it avoids the weld being subjected to react with atmospheric air.The process can be automatic or semi-automatic where the main input parameters like current and the voltage can be direct and constant,respectively.Not only the current and voltage the welding quality depends on some more input parameters such as arc gap,velocity,and temperature.In this paper,we explain about a setup which is capable of real-time monitoring of input parameters mentioned above and selecting the best MIG welding parameters for the mild steel.The setup is composed of several sensors and microcontrollers for the collection and the measurement of the input parameters.The samples were categorized according to the federate and the voltage adjustment of the selected welding machine.Then the final objective was to identify the samples of the weld with different parameter changes which are monitored through the system.For the analysis,the samples were subjected to tensile and hardness tests,and microstructure tests to find the dependence of the input parameters which effect for the weld quality.Finally,the experimental results verified the effectiveness of the system for the selection of the quality weld.

The effect of activating fluxes on the cathode spots in the activating TIG welding

The cathode spots are a common phenomenon in the TIG(tungsten inert gas)welding process.However,it is rarely observed in the activating TIG welding process.This research is mainly focused on the effect of activating flux on cathode spots in the activating TIG welding.The characteristics and behaviors of cathode spots were investigated in activating TIG welding by the high-speed camera and the spectrograph.Three kinds of oxide(TiO_(2),SiO_(2),MnO_(2))and two halide(MnCl_(2),CaF_(2))activating fluxes are used in the activating TIG welding process.The results show that differ from the TIG welding,the oxide activating flux increases the number of cathode spots and decreases the velocity.The effect is the opposite for the halide activating flux.Moreover,the number of spots no longer varies with the current except TiO2 activating flux.As the temperature of the weld pool surface increases the spot moves away from the center.But this rule is not valid when silica and manganese compounds activating fluxes are used.The variation of cathode spots is caused by the oxide film reformed and the distribution of weld slag.The formation mechanism of cathode spots might be the impact of ions on the cathode surface and the strong electric field formed near the cathode surface.