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.

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.

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.

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.

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.

Effect of Pulsed Current TIG Welding Parameters on Pitting Corrosion Behaviour of AA6061 Aluminium Alloy

Medium strength aluminium alloy （Al-Mg-Si alloy） has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding process for aluminium alloy is frequently TIG （tungsten inert gas） welding due to its comparatively easier applicability and better economy.In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. A mathematical model has been developed to predict pitting corrosion potential of pulsed current TIG welded AA6061 aluminium alloy.Factorial experimental design has been used to optimize the experimental conditions. Analysis of variance technique has been used to find out the significant pulsed current parameters. Regression analysis has been used to develop the model. Using the developed model pitting corrosion potential values have been estimated for different combinations of pulsed current parameters and the results are analyzed in detail.

Metal vapor behavior in double electrodes TIG welding

In present paper, the metal vapour behavior in double electrodes TIG welding was investigated by a numerical model, including the arc plasma and weld pool. The thermodynamic parameters and transport coefficients of the arc plasma were dependent on both the local temperature and the mass ratio of the metal vapour. A second viscosity approximation was used to formulate the diffusion coefficient of the metal vapour in the arc plasma. The temperature and flow fields together with the metal vapour concentration were simulated, and the influences of metal vapour on the arc plasma and the weld pool were analyzed. It was found that the metal vapour transport in the arc plasma was significantly influenced by the flow of the arc plasma, and the distribution of the metal vapour was more extended in the direction perpendicular to the line through the double electrodes tips. Both the arc plasma and the heat flux at the weld pool were constricted by the presence of the metal vapour, while the metal vapour had a minor effect on the total heat input to the work piece and the weld pool profile as a whole.

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.

Diagnosis of TIG welding based on ultraviolet radiation

Through collecting the radiation of tungsten inert gas （TIG） welding arc, the radiation distribution in ultraviolet zone is analyzed in order to study the variation rule of ultraviolet radiation versus welding condition. The explanation for the variation is also provided based on spectral radiation theory of arc light. Furthermore, through analysis of disturbance factors, the integral intensity signal of radiation in ultraviolet zone is applied for diagnosis of welding process. The spectral signal of ultraviolet radiation can reflect the disturbance factors and welding conditions, which can be used for online diagnosis of welding process.

Fracture behavior of double-pass TIG welded 2219-T8 aluminum alloy joints under transverse tensile test

2219-T8 aluminum alloys were butt welded by the double-pass tungsten inert gas （TIG） arc welding process. The transverse tensile test of the joint showed that the fracture mainly occurred in the partially melted zone （PMZ）. Effects of the PMZ on the fracture behavior were systematically studied. Continuous intergranular eutectics were observed in the PMZ close to the fusion line. Away from the fusion line, the intergranular eutectics in the PMZ became discontinuous. The fracture morphology and the microhardness distribution of the joint showed that the PMZ was gradient material with different mechanical properties, which strongly affected the fracture process. It was observed that the crack initiated in the PMZ near the front weld toe, and propagated in the PMZ away from the fusion line. Then, the crack tip was blunt when it propagated into the PMZ with higher plasticity. Finally, the rest part of the joint was shear fractured.

Effects of aging treatment and heat input on the microstructures and mechanical properties of TIG-welded 6061-T6 alloy joints

Aging treatment and various heat input conditions and mechanical properties of TIG welded 606I-T6 alloy joints were adopted to investigate the microstructural evolution by microstructural observations, microhardness tests, and tensile tests. With an increase in heat input, the width of the heat-affected zone （HAZ） increases and grains in the fusion zone （FZ） coarsen. Moreover, the hardness of the HAZ decreases, whereas that of the FZ decreases initially and then increases with an increase in heat input. Low heat input results in the low ultimate tensile strength of the welded joints due to the presence of partial penetrations and pores in the welded joints. After a simple artificial aging treatment at 175℃ for 8 h, the microstructure of the welded joints changes slightly. The mechanical properties of the welded joints enhance significantly after the aging process as few precipitates distribute in the welded seam.

Investigation on the process parameters of TIG-welded aluminum alloy through mechanical and microstructural characterization

Multi-pass TIG welding was conducted on plates(15×300×180 mm^(3))of aluminum alloy Al-5083 that usually serves as the component material in structural applications such as cryogenics and chemical processing industries.Porosity formation and solidification cracking are the most common defects when TIG welding Al-5083 alloy,which is sensitive to the welding heat input.In the experiment,the heat input was varied from 0.89 kJ/mm to 5 kJ/mm designed by the combination of welding torch travel speed and welding current.Tensile,micro-Vicker hardness and Charpy impact tests were executed to witness the impetus response of heat input on the mechanical properties of the joints.Radiographic inspection was performed to assess the joint’s quality and welding defects.The results show that all the specimens displayed inferior mechanical properties as compared to the base alloy.It was established that porosity was progressively abridged by the increase of heat input.The results also clinched that the use of medium heat input(1-2 kJ/mm)offered the best mechanical properties by eradicating welding defects,in which only about 18.26% of strength was lost.The yield strength of all the welded specimens remained unaffected indica ted no influence of heat input.Partially melted zone(PMZ)width also affected by heat input,which became widened with the increase of heat input.The grain size of PMZ was found to be coarser than the respective grain size in the fusion zone.Charpy impact testing revealed that the absorbed energy by low heat input specimen(welded at high speed)was greater than that of high heat input(welded at low speed)because of low porosity and the formation of equiaxed grains which induce better impact toughness.Cryogenic(-196℃)impact testing was also performed and the results corroborate that impact properties under the cryogenic environment revealed no appreciable change after welding at designated heat input.Finally,Macro and micro fractured surfaces of tensile and impact specimens were analyzed using Stereo and Scanning Electron Microscopy(SEM),which have supported the experimental findings.

Microstructure and properties of pure iron/copper composite cladding layers on carbon steel

In the present study, pure iron/copper composite metal cladding was deposited onto carbon steel by tungsten inert gas welding. The study focused on interfacial morphological, microstructural, and mechanical analyses of the composite cladding layers. Iron liquid–solid-phase zones were formed at copper/steel and iron interfaces because of the melting of the steel substrate and iron. Iron concentrated in the copper cladding layer was observed to exhibit belt, globule, and dendrite morphologies. The appearance of iron-rich globules indicated the occurrence of liquid phase separation（LPS） prior to solidification, and iron-rich dendrites crystallized without the occurrence of LPS. The maximum microhardness of the iron/steel interface was lower than that of the copper/steel interface because of the diffusion of elemental carbon. All samples fractured in the cladding layers. Because of a relatively lower strength of the copper layer, a short plateau region appeared when shear movement was from copper to iron.

Cavitation Erosion Behavior of as-Welded Cu12Mn8Al3Fe2Ni Alloy

Cavitation erosion behavior of as-welded Cu12Mn8Al3Fe2Ni alloy in 3.5% NaCl aqueous solution was studied bymagnetostrictive vibratory device for cavitation erosion. The results show that the cavitation erosion resistance ofthe as-welded Cu12Mn8Al3Fe2Ni alloy is much more superior to that of the as-cast one. The cumulative mass lossand the mass loss rate of the as-welded Cu12Mn8Al3Fe2Ni alloy are almost 1/4 that of the as-cast one. SEM analysisof eroded specimens reveals that the as-cast Cu12Mn8Al3Fe2Ni alloy is attacked more severely than the as-weldedone. Microcracks causing cavitation damage initiate at the phase boundaries.

Microstructure and mechanical properties of TIG/A-TIG welded AZ61/ZK60 magnesium alloy joints

The dissimilar joints of AZ61 and ZK60 magnesium alloys were obtained by tungsten inert gas arc(TIG)welding and activating tungsten inert gas arc(A-TIG)welding processes.Microstructure characterization shows that,the fineα-Mg equiaxed dendrite crystals contained Mg17Al12 and MgZn2 particles in the fusion zone.The average size of theα-Mg grains in the fusion zone was refined to 19μm at welding current of 80 A,which resulted in the largest tensile strength of 207 MPa.The tensile strength and the width of the beam of the A-TIG welded AZ61/ZK60 joints showed strong dependence on the amount of TiO2.However,the inhomogeneity of the heat-affected zone near different base metals presented no significant effect on the mechanical properties of the welded joint.

Microstructural evolution and its effect on mechanical properties in different regions of 2219-C10S aluminum alloy TIG-welded joint

Microstructural evolution and its effect on mechanical properties in different regions of 2219-C10S aluminum alloy tungsten inert gas(TIG)welded joint were analyzed in detail.In weld zone(WZ),α+θeutectic structure formed at grain boundaries with no precipitates inside the grains.In partially melted zone(PMZ),symbiotic eutectic or divorced eutectic formed at grain boundaries and needle-likeθ′phases appeared in the secondary heated zone.In over aged zone(OAZ),the coarsening and dissolution ofθ′phases occurred and mostθ′phases transformed intoθphases.In general heat affected zone(HAZ),θ′phases coarsened.Factors such as the strengthening phases,the grain size,the Cu content in matrix and the dislocation density can affect the mechanical properties in different regions of the joint.Moreover,a model describing the relationship between mechanical properties of the material and the volume fraction of precipitates,the average diameter of precipitates and the concentration of soluble elements was proposed.

Effects of graphene nanoplates on microstructures and mechanical properties of NSA-TIG welded AZ31 magnesium alloy joints

The effects of graphene nanoplates(GNPs)on the microstructures and mechanical properties of nanoparticlesstrengthening activating tungsten inert gas arc welding(NSA-TIG)welded AZ31magnesium alloy joints were investigated.It wasfound that compared with those of activating TIG(A-TIG),and obvious refinement ofα-Mg grains was achieved and the finestα-Mggrains of fusion zone of NSA-TIG joints were obtained in the welded joints with TiO2+GNPs flux coating.In addition,thepenetrations of joints coated by TiO2+GNPs flux were similar to those coated by the TiO2+SiCp flux.However,the welded jointswith TiO2+GNPs flux coating showed better mechanical properties(i.e.,ultimate tensile strength and microhardness)than those withTiO2+SiCp flux coating.Moreover,the generation of necking only occurred in the welded joints with TiO2+GNPs flux.

Real-time K-TIG welding penetration prediction on embedded system using a segmentation-LSTM model

Keyhole tungsten inert gas(K-TIG)welding is capable of realizing single-sided welding and double-sided forming and has been widely used in medium and thick plate welding.In order to improve the accuracy of automatic weld identification and weld penetration prediction of robot in the process of large workpiece welding,a two-stage model is proposed in this paper,which can monitor the K-TIG welding penetration state in real time on the embedded system,called segmentation-LSTM model.The proposed system extracts 9 weld pool geometric features with segmentation network,and then extracts the weld gap using a traditional algorithm.Then these 10-dimensional features are input into the LSTM model to predict the penetration state,including under penetration,partial penetration,good penetration and over penetration.The recognition accuracy of the proposed system can reach 95.2%.In this system,to solve the difficulty of labeling data and lack of segmentation accuracy,an improved LabelMe capable of live-wire annotation tool and a novel loss function were proposed,respectively.The latter was also called focal dice loss,which enabled the network to achieve a performance of 0.933 mloU on the testing set.Finally,an improved slimming strategy compresses the network,making the segmentation network achieve real-time on the embedded system(RK3399pro).

Corrosion resistance and antibacterial activity of different zones in TA2 weldment by TIG welding

The corrosion resistance behavior of TA2 pure titanium processed by tungsten inert gas(TIG)welding was investigated in artificial saliva solution at 37℃.By metallographic examination,electrochemical measurement technology,and electrochemical impedance spectroscopy(EIS),the corrosion resistance of the base metal(BM),heat-affected zone(HAZ),and weld metal(WM)were investigated.Metallographic examination experiments show that welding process would cause the growth of grain size.In addition,phase change happens in the HAZ and WM.The change of grain size and phase would influence the generation of the original passive film.The electrochemical tests show that the BM,HAZ,and WM are all equipped with good corrosion resistance.The welded joint shows a better corrosion resistance than the original TA2.It is shown that the BM with the lowest corrosion potential and the biggest corrosion current has a worse corrosion resistance than WM as well as HAZ.Silver(Ag)nanoparticles can be distributed on the WM zone of Ti uniformly.The WM zone of Ti with Ag coating considerably enhances the antibacterial activity of Ti implants.

Corrosion Behaviors of Pure Titanium and Its Weldment in Simulated Desulfurized Flue Gas Condensates in Thermal Power Plant Chimney

The corrosion behaviors of pure titanium and its weldment welded by tungsten inert gas （TIG） welding in simulated desulfurized flue gas condensates in thermal power plant chimney were investigated using potentiodynamic polarization, electrochemical impedance spectroscopy （EIS） and immersion tests. The effects of heat input and shielding gases on the corrosion behavior of the welded titanium were also studied. Grain coarsening and Widmanst^itten structure were found in both the fusion zone and the heat-affected zone. The welded titanium exhibited active-passive behavior in the simulated condensates. Both the polarization curves and EIS measurements confirmed that TIG welding process with different parameters had few effects on the corrosion behavior. It was proved that the microstructure changes were not the key material factors affecting the corrosion behavior of pure titanium under the test conditions, while the oxide film had remarkable effect on improving the corrosion resistance.