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 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.

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.

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.

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.

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.

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.

Comparison of feasibility,microstructure and performance of hybrid laser arc,activated flux tungsten inert gas and friction stir welding for thick plate of innovative ultra-pure ferritic stainless steel

An innovative grade of ferritic stainless steel,ultra-pure 18Cr–2Mo thick plate,was designed and produced for special industrial application.In order to maintain its mechanical properties after joining,three advanced joining methods,hybrid laser arc welding,activated flux tungsten inert gas welding and friction stir welding,were selected and conducted to connect the thick plates.The feasibility of three joining methods,the microstructure and mechanical properties were compared,and the results have demonstrated that the sound joint was successfully produced using the selected parameters through friction stir welding.The obtained hardness and impact toughness of the weld zone were satisfying.In terms of activated flux tungsten inert gas welding,the crack will be created due to microstructural brittleness.And as for hybrid laser arc welding,the weld zone is narrow,and the addition of wire during welding for the top weld metal area leads to higher formation ratio of low-angle grain boundaries,which is beneficial to performance of the joint.However,there is still a weak area in the fusion line of the welded joint.The result has illustrated that the welding of innovative ultra-pure ferritic stainless steel thick plate by friction stir welding is feasible.

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.

镁合金摆动多道增材层成形特征参数与尺寸控制规律研究

针对AZ31B镁合金多道增材成形中尺寸精确控制的问题,定义了表面平整度、波峰平均高度差和波峰平均高度来表征摆动钨极氩弧多道增材层的成形特征,采用响应曲面法建立了摆动参数与多道增材层成形特征参数之间的回归模型,分析了摆动参数对成形特征参数的影响规律,并对通过模型优化得到的摆动参数进行了实际验证。建模与实验结果发现:表面平整度在摆动参数交互作用的影响下呈现先增大后减小的变化趋势;当偏移量大于11 mm时,摆动幅度小于3 mm、停留时间小于0.3 s和行进速度大于30 cm/min都能使波峰平均高度差趋于最小;波峰平均高度受停留时间和偏移量的影响最显著。回归模型优化获得的最佳摆动参数为:摆动幅度2.56 mm、摆动频率2.5 Hz、停留时间0.3 s、行进速度30 cm/min和偏移量11.46 mm。采用该参数获得的多道增材层各成形特征参数分别为:表面平整度0.98,波峰平均高度差为0.03 mm仅占波峰平均高度的1.07%,波峰平均高度为(2.80±0.02)mm与目标值间的误差仅为0.71%,多道增材层的成形得到优化。

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.

A Fuzzy Logic Approach to Predict Tensile Strength in TIG Mild Steel Welds

Welding defects influence the desired properties of welded joints giving fabrication experts a common problem of not being able to produce weld structures with optimal strength and quality. In this study, the fuzzy logic system was employed to predict welding tensile strength. 30 sets of welding experiments were conducted and tensile strength data was collected which were converted from crisp variables into fuzzy sets. The result showed that the fuzzy logic tool is a highly effective tool for predicting tensile strength present in TIG mild steel weld having a coefficient of determination value of 99%.

铝合金高频感应热丝TIG焊接方法

提出了高频感应热丝TIG焊接新方法，焊丝加热温度和深度可控，加热速度快，能适应高速送丝要求。高频感应加热消除了常规热丝TIG焊旁路电流磁场引起的电弧偏吹现象。另外，由于该方法不需利用焊丝本身的电阻产热，所以适用于铝合金等低电阻率金属焊丝。根据感应线圈的电感和工作频率要求，设计制造了适用于φ1．6mm铝合金焊丝的高频感应加热线圈和套筒。利用热电偶测量了不同送丝速度下的焊丝温度。结果表明，当送丝速度高达6～10m／min时，焊丝的温度完全能够满足热丝焊的要求。6～10m／min的送丝速度较常规TIG焊接提高了3倍以上，大大提高了焊接效率。

核用Inconel 690焊丝TIG焊微裂纹产生机理研究

针对国际上核用Inconel 690焊丝TIG焊微裂纹问题,利用扫描电镜、俄歇电子分析等方法对微裂纹断口微观组织形貌、特征点的成分进行研究。结果表明,Inconel 690焊丝TIG焊微裂纹主要是结晶裂纹,原因是由S,P在晶界偏析引起的低熔点共晶物。通过对结晶裂纹的产生机理和影响因素的系统研究,指出Inconel 690焊丝TIG焊微裂纹主要是由S,P引起的结晶裂纹,而不是只有DDC裂纹,通过定量分析S,P与裂纹关系,提出了防止微裂纹产生的条件,并制造出无微裂纹的HS690,HS690M焊丝。

铝合金双丝MIG焊熔池图像采集与处理

针对铝合金双丝熔化极氩弧焊，分析研究了电弧弧光辐射和熔池视觉传感的特征，结果表明，双丝电弧辐射更强，采用近红外窄带滤波传感熔池视觉传感双丝熔池相对易于提高信噪比，在10～35mm厚LY12和7A52铝合金V形坡口对接焊缝工艺试验的基础上，采用980nm窄带滤波和合适的减光系统获得了较为清晰的铝合金双丝熔池视觉图像，分析了双丝熔池视觉图像特征，采用自动阈值分割等方法设计了计算机图像专用处理软件，获得了准确的双丝熔池边界及几何参数，为基于熔池视觉的铝合金MIG焊质量控制打下良好基础。

电弧力对TIG焊接熔池液面形态影响的数值模拟

在建立TIG焊接熔池液面三维形状模型基础上,对电弧力作用于熔池液面进行了表征,采用Surface Evolver有限元分析软件进行数值模拟,研究了电弧力对TIG焊接熔池液面三维形态的影响。得到了有电弧作用时,熔池的三维形态和熔池各液面参数随电弧力大小变化的规律。结果表明,在熔池形状一定时(正面、背面熔化区域半径和板厚一定),电弧力的作用深度增加会引起熔池上、下液面和固液面的表面积均增加,其中电弧力的大小对TIG焊接熔池的上液面影响程度大于下液面。这些分析结果为探讨TIG焊接熔池的各类问题提供了基础。

无熔深堆焊铜熔池图像视觉检测方法研究

在分析了视觉法检测熔池的取像机理和钨极氩弧焊(TIG焊)电弧光谱的基础上,提出了近红外波段取像铜熔池的思路,并设计出基于不同取像机理的多种复合窄带滤光系统。采用普通电荷耦合(CCD)传感器从正面拍摄了铜熔池,并对不同观察窗口下的取像结果进行比较分析,找到了相对较佳、可获得较清晰的铜熔池图像的取像窗口。最后分析了TIG焊铜熔池图像的特征,并与TIG焊钢熔池图像比较后发现:在近红外波段,铜熔池比钢熔池难于获得清晰的图像。

电弧作用下熔透型TIG熔池液面行为的数值模拟

在正面熔化半径RZ和板厚h一定的条件下,基于对有电弧作用的熔透型TIG焊接熔池三维液面行为的分析,获得了不同背面熔化半径RB的熔池三维形状模型,利用有限元分析软件surface evolver进行数值模拟,研究了电弧对熔透型TIG焊接熔池液面的影响。结果表明,电弧的作用与否对熔池下液面的大小和形状无显著的影响;在背面熔化尺寸较小时(RB≤2.5 mm附近),电弧对上液面特征量有较大作用;电弧的作用从整体上是使熔池上液面压低。在从脉冲基值过渡到脉冲峰值期间,电弧电压(或弧光光强)增加的部分是由电流增加和熔池上液面被压低两部分引起的。

保护气氛中添加活性气体对焊接熔池形态影响的研究现状

在惰性保护气氛中添加活性气体可以有效地控制熔池形态,并且易于调节熔池中氧元素的含量(质量分数(wO),以下同).就氦(He)和氩(Ar)保护气氛下分别添加O2和CO2对焊接熔池形态的影响进行了综述,并总结出最优的活性气体添加量.讨论不同焊接工艺下焊接熔池形态变化程度,对优化生产工艺有一定的指导意义.