Optimizing the Pulsed Current Gas Tungsten Arc Welding Parameters

The selection of process parameter in the gas tungsten arc （GTA） welding of titanium alloy was presented for obtaining optimum grain size and hardness. Titanium alloy （Ti-6Al-4V） is one of the most important non-ferrous metals which offers great potential application in aerospace, biomedical and chemical industries, because of its low density （4.5 g/cm^3）, excellent corrosion resistance, high strength, attractive fracture behaviour and high melting point （1678℃）. The preferred welding process for titanium alloy is frequent GTA welding due to its comparatively easier applicability and better economy. In the case of single pass （GTA） welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. Many considerations come into the picture and one needs to carefully balance various pulse current parameters to reach an optimum combination. Four factors, five level, central composite, rotatable design matrix were used to optimize the required number of experimental conditions. Mathematical models were developed to predict the fusion zone grain size using analysis of variance （ANOVA） and regression analysis. The developed models were optimized using the traditional Hooke and Jeeve＇s algorithm. Experimental results were provided to illustrate the proposed approach.

Assessment of gas tungsten arc welding thermal cycles on Inconel 718 alloy

Heat moving source models along with transient heat analysis by finite element method were used to determine weld thermal cycles and isothermal sections obtained from the application of a gas tungsten arc welding beads on Inconel 718 plates. Analytical (Rosenthal’s thick plate model) and finite element results show an acceptable approximation with the experimental weld thermal cycles. The isothermal sections determined by numerical simulation show a better approximation with the experimental welding profile for double-ellipse model heat distribution than Gauss model. To analyze the microstructural transformation produced by different cooling rates in the fusion and heat affected zones, Vickers microhardness measurements (profile and mapping representation) were conducted. A hardness decrement for the heat affected zone (~200 HV0.2) and fusion zone (~240 HV0.2) in comparison with base material (~350 HV0.2) was observed. This behavior has been attributed to the heterogeneous solubilization process of the γ″ phase (nickel matrix), which, according to the continuous-cooling-transformation curve, produced the Laves phase,δ and MC transition phases, generating a loss in hardness close to the fusion zone.

Optimization of pulsed current gas tungsten arc welding process parameters to attain maximum tensile strength in AZ31B magnesium alloy

An empirical relationship to predict tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy was developed. Incorporating process parameters such as peak current, base current, pulse frequency and pulse on time were studied. The experiments were conducted based on a four-factor, five-level, central composite design matrix. The developed empirical relationship can be effectively used to predict the tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy joints at 95% confidence level. The results indicate that pulse frequency has the greatest influence on tensile strength, followed by peak current, pulse on time and base current.

Gas tungsten arc welding of CP-copper to 304 stainless steel using different filler materials

The dissimilar joining of CP-copper to 304 stainless steel was performed by gas tungsten arc welding process using different filler materials. The results indicated the formation of defect free joint by using copper filler material. But, the presence of some defects like solidification crack and lack of fusion caused decreasing tensile strength of other joints. In the optimum conditions, the tensile strength of the joint was 96% of the weaker material. Also, this joint was bent till to 180° without any macroscopic defects like separation, tearing or fracture. It was concluded that copper is a new and good candidate for gas tungsten arc welding of copper to 304 stainless steel.

In situ synthesis and hardness of TiC/Ti_5Si_3 composites on Ti-5Al-2.5Sn substrates by gas tungsten arc welding

TiC/TisSi3 composites were fabricated on Ti-5A1-2.5Sn substrates by gas tungsten arc welding （GTAW）. Identification of the phases was performed using X-ray diffraction （XRD）. The microstructures were analyzed using scanning electron microscopy （SEM） combined with energy-dispersive X-ray spectrometry （EDS） and optical microscopy （OM）. The Vickers hardness was measured with a micro-hardness tester. The TiC/TisSi3 composites were obtained in a double-layer track, and the Vickers hardness of the track increased by two to three times compared with the Ti-5A1-2.5Sn substrate.

A NEURAL NETWORK FOR WELD PENETRATION CONTROL IN GAS TUNGSTEN ARC WELDING

Realizing of weld penetration control in gas tungsten arc welding requires establishment of a model describing the relationship between the front-side geometrical parameters of weld pool and the back-side weld width with sufficient accuracy. A neural network model is developed to attain this aim. Welding experiments are conducted to obtain the training data set （including 973 groups of geometrical parameters of the weld pool and back-side weld width） and the verifying data set （108 groups）. Two data sets are used for training and verifying the neural network, respectively. The testing results show that the model has sufficient accuracy and can meet the requirements of weld penetration control.

A Study of Microstructure and Mechanical Properties for the Autogenous Single-Pass Butt Weldment of a Ferritic/Martensitic Steel Using Gas Tungsten Arc Welding

A 12%Cr ferritic/martensitic steel,HT-9,has been used as a primary core material for nuclear reactors.The microstructure and mechanical properties of gas tungsten arc butt welded joints of HT-9 in as-welded,and as-tempered conditions have been explored.In as-welded condition,the fusion zone(FZ)contained a fresh martensite matrix with delta(δ)-ferrite.Theδ-ferrite was rich in Cr and depleted in C compared with the matrix.The heat-aff ected zone(HAZ)could be divided into three areas as the distance from the fusion line increased:δ-ferrite/martensite duplex zone,fully recrystallized zone,and partly recrystallized zone.Prior austenitic grains did not coarsen in theδ-ferrite/martensite duplex zone due to the newly nucleatedδ-ferrite grains and incompletely ferritizing(δ-ferrite)during the welding thermal cycle.The weldment microhardness distributed heterogeneously with values above 600 HV_(1.0)in the HAZ and FZ and 250 HV_(1.0)in the base metal(BM).Solute C in the matrix,induced by the dissolution of carbide during the welding process,dominated the microhardness variation.Low toughness was observed in the FZ with a quasi-cleavage fracture tested from-80 to 20℃.The tensile fracture occurred in the relatively soft BM tested from 20 to 600℃.In as-tempered condition(760℃for 1 h),M_(23)C_6-type carbides precipitated within the martensitic laths,the lath boundaries,and theδ-ferrite/martensite interfaces.Moreover,V,Cr,Mo-rich nitrides with very small size also precipitated in theδ-ferrite/martensite interface.The tempering treatment improved the homogenous distribution of weldment hardness significantly.Tensile fracture still occurred in the BM of the weldment specimens tested from 20 to 600℃.The impact toughness improved significantly,but the ductile–brittle transaction temperature was-12℃which was higher than that of the normalized and tempered(N&T)BM.δ-ferrite was considered to be one of the major factors aggravating the impact toughness in the FZ.

Effect of pulsed current on temperature distribution,weld bead profiles and characteristics of gas tungsten arc welded aluminum alloy joints

Temperature distribution and weld bead profiles of constant current and pulsed current gas tungsten arc welded aluminium alloy joints were compared. The effects of pulsed current welding on tensile properties, hardness profiles, microstructural features and residual stress distribution of aluminium alloy joints were reported. The use of pulsed current technique is found to improve the tensile properties of the weld compared with continuous current welding due to grain refinement occurring in the fusion zone.

Effect of post weld heat treatment on microstructure and mechanical properties of gas tungsten arc welded AA6061-T6 alloy

Double-V butt TIG welding process was performed on two plates of AA6061-T6 using ER5356 filler. The microstructure,mechanical and nanomechanical properties of the joint were evaluated in as-welded and after post weld heat treatment (PWHT) usingXRD, FESEM, EBSD, nanoindentation and tensile tests. The results show that PWHT led to microstructural recovery of the heataffected zone (HAZ) in addition to the appearance of β-phase (Al3Mg2) at the grain boundaries of weld zone. The hardness (Hnano) inall zones increased after PWHT while the elastic modulus (Enano) was improved from 69.93 GPa to 81 GPa in weld area. All resultsindicate that PWHT has created a homogenous microstructure in the weld zone in addition to outstanding improvement inmechanical properties for the weld zone which surpass the base metal.

Study on stress and deformation of keyhole gas tungsten arc-welded joints

Keyhole gas tungsten arc welding(K-TIG)of Q345 low alloy steel plates was simulated by using SYSWELD software.The temperature field of the K-TIG welding process was simulated with three different combined heat sources and was compared with the weld profile that was obtained experimentally.The temperature field that was obtained by a combination of a double ellipsoid heat source on the upper half and a three-dimensional Gauss heat source on the lower half was similar to the real situation.The effects of plate thickness,gap and welding speed on the deformation and stress of the K-TIG welded joints were investigated by K-TIG welding numerical simulation.A reduction in the thickness of the weld plates reduced the z-direction deformation and transverse residual stress;an appropriate gap reduced the residual stress and an increase in the welding speed reduced deformation after welding,but did not help to control the residual stress after welding.

Influence of Sn addition on mechanical properties of gas tungsten arc welded AM60 Mg alloy sheets

The effects of Sn addition on the microstructure and mechanical properties of gas tungsten arc butt-welded Mg?6Al?0.3Mn (AM60) (mass fraction, %) alloy sheets were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and microhardness and tensile tests. The results indicate that both the average microhardness and joint efficiency of AM60 are improved by the addition of 1% Sn (mass fraction). The ultimate tensile strength of Mg?6Al?1Sn?0.3Mn (ATM610) reaches up to 96.8% of that of base material. Moreover, fracture occurs in the fusion zone ofATM610 instead of in the heat-affected zone of AM60 welded joint. The improvement in the properties is mainly attributed to the formation of Mg2Sn, which effectively obstructs the grain coarsening in the heat-affected zone, resulting in a relatively finemicrostructure. The addition of 1% Sn improves the mechanical properties of AM60 welded joint

Microstructure characterization and mechanical properties of gas tungsten arc welded cast A356 alloy

The microstructure and mechanical properties of the gas tungsten arc welded cast A356 alloy were investigated with fillers ER1100,ER4043,ER4047 and ER5356 under the pulse frequencies of 1,3 and 5 Hz.Results showed that the filler metal and pulse frequency affected the grain structure of fusion zone considerably.The highest fraction of eutectic（44%） was formed with filler ER4047.Tensile fracture of all specimens indicated that fracture did not occur in the fusion zone.The greatest impact toughness（about 4 J） was achieved for the welds with filler ER4047 while the largest hardness（HV 90） was obtained with filler ER5356.

Effects of distance between arc and heat sink on stress and distortion in DC-LSND welding technology

The characteristics of temperatures, stresses and strains fields have been studied numerically for a titanium alloy sheet welded with an improved gas tungsten arc welding method, in which a trailing spot heat sink is introduced to control the welding stress and distortion. The impinging jet model is employed to describe the internee heat transfer between the cooling media and the top suufuce of the workpiece. The influcnee of the distance between arc and heat sink is investigated. Results show that there is an ideal range of distance. Using the ideal distance, a low stress and no distortion welding structure can be derived.

Effect of combinative addition of Ti and Sr on modification of AA4043 welding wire and mechanical properties of AA6082 welded by TIG welding

To improve the mechanical properties of AA6082 weld welded by tungsten inert gas welding using AA4043 welding wire, the effect of addition of Ti and/or Sr on continuous cast and rolled AA4043 welding wire was investigated. Experimental results indicated that Ti and Sr are excellent modifiers, which improve the microstructure of the AA4043 welding wire and enhance the mechanical properties of the AA6082 weld. It was found that the combinative addition of Ti and Sr can effectively modify both the α（Al） dendrites and eutectic Si phases compared with individual addition of Ti or Sr. In addition, Ti and/or Sr also changed the microstructure of the AA6082 weld. The tensile strength of the AA6082 weld reached the maximum value when 0.08% Ti and 0.025% Sr were added simultaneously. These results indicate that the combinative addition of Ti and Sr can be an effective composite modifier.

Effect of welding processes on AA2219 aluminium alloy joint properties

AA2219 aluminium alloy square butt joints without filler metal addition were fabricated using gas tungsten arc welding （GTAW）, electron beam welding （EBW） and friction stir welding （FSW） processes. The effects of three welding processes on the tensile, fatigue and corrosion behaviour were studied. Microstructure analysis was carried out using optical and electron microscopes. The results show that the FSW joints exhibit superior tensile and fatigue properties compared to EBW and GTAW joints. It is also found that the friction stir welds show lower corrosion resistance than EB and GTA welds. This is mainly due to the presence of finer grains and uniform distribution of strengthening precipitates in the weld metal of FSW joints.

Influence of welding processes on microstructure, tensile and impact properties of Ti-6Al-4V alloy joints

Titanium alloys have been successfully applied for aerospace, ship and chemical industries because they possess many good characteristics such as high specific strength, superior corrosion resistance and excellent high temperature resistance. Though these alloys show reasonable weldability characteristics, the joint properties are greatly influenced by the welding processes. Weld thermal cycle of the processes will control the weld metal solidification and subsequent phase transformation and resultant microstructure. The welded joints of Ti-6Al-4V alloy were fabricated by gas tungsten arc welding （GTAW）, laser beam welding （LBW） and electron beam welding （EBW） processes. The joints fabricated by EBW process exhibit higher strength compared with the GTAW and LBW joints; but the joints by GTAW process exhibit higher impact toughness compared with the LBW and EBW joints. The resultant tensile and impact properties of the welded joints were correlated with the weld metal microstructures.

Effects of pulse parameters on arc characteristics and weld penetration in hybrid pulse VP-GTAW of aluminum alloy

A novel ultrafast-convert hybrid pulse variable polarity gas tungsten arc welding process （HPVP-GTAW） is developed. High frequency pulse square-wave current which has a frequency of more than 20 kHz is exactly integrated in the positive polarity current duration. The effects of pulse current parameters on arc characteristics and weld penetration have been studied during the HPVP-GTAW process using Al-5. 8 Mg alloy plates. The arc characteristics studied by arc voltage and its profile, weld penetration noted by the ratio of weld depth to width have been found to be influenced significantly by the pulse current. The experimental results show that the HPVP-GTA W process can improve the arc profile predominantly and obtain the higher weld penetration with lower heat input. The observation may help in understanding the weld characteristics with respect to variation in the pulse current parameters which may be beneficial in using the novel HPVP-GTAW process to produce the better weld quality of aluminum alloy plates.

The study of arc behavior with different content of copper vapor in GTAW

In order to understand the effects of different content of copper vapor entering the arc plasma on the arc behavior,the tungstencopper materials with copper contents of 0%,10%,20%and 30%were made into special tungsten electrodes,which replaced the melting electrode to generate copper vapor.The effects of different content of copper vapor on the arc morphology,arc voltage,arc pressure,current density and arc axial temperature were studied.When copper vapor was transported into the arc plasma,the arc consisted of two parts:a high brightness arc core and the surrounding green luminous area.Through the observation and measurement of the stabilized arc,the results showed that as the content of copper vapor increased,the radius of the greenish region gradually increased,the brightness and size of the core area gradually decreased,the axial temperature of the arc gradually decreased and arc voltage gradually increased with a maximum difference of 1.5 V.This is because the increase of copper vapor concentration changes the net emission coefficient,resulting in a decrease in arc temperature and electrical conductivity.The distribution of arc pressure and current density showed unimodal distribution on the anode surface,and as the content of copper vapor increased,the distribution curves were gradually flattening.A factor contributing to this is that with the increase of copper vapor concentration,the current tends to flow through the edge of the electrode,which expands the conductive path and makes the arc disperse.And the coupling mathematical model of tungsten electrode and arc were established to further explain the experimental results.

Influence of welding parameters on nitrogen content in welding metal of 32Mn-7Cr-1Mo-0.3N austenitic steel

The transfer behavior of nitrogen into the welding metal during gas tungsten arc welding process of 32Mn-7Cr-1Mo-0.3N steel was investigated. The effects of gas tungsten arc welding process variables, such as the volume fraction of nitrogen in shielding gas, arc holding time and arc current on the nitrogen content in the welding metal were also evaluated. The results show that the volume fraction of nitrogen in gas mixture plays a major role in controlling the nitrogen content in the welding metal. It seems that there exhibits a maximum nitrogen content (depending) on the arc current and arc holding time. The optimum volume fraction of nitrogen in shielding gas is 4% or so. The role of gas tungsten arc welding processing parameters in controlling the transfer of nitrogen is further (confirmed) by the experimental results of gas tungsten arc welding process with feeding metal.

A Generalized Rough Set Modeling Method for Welding Process

Modeling is essential, significant and difficult for the quality and shaping control of arc welding process. A generalized rough set based modeling method was brought forward and a dynamic predictive model for pulsed gas tungsten arc welding (GTAW) was obtained by this modeling method. The results show that this modeling method can well acquire knowledge in welding and satisfy the real life application. In addition, the results of comparison between classic rough set model and back-propagation neural network model respectively are also satisfying.