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.

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.

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.

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.

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.

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.

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%.

TIG焊电弧-熔池传热与流动数值模拟

针对钨极惰性气体保护(Tungsten inert gas,TIG)焊,采用一组满足整个求解域的偏微分方程组和合理的边界条件,建立包括钨极、电弧和母材的三维瞬态统一模型。以SUS304不锈钢为母材,求解获得电弧-电极(熔池)的温度场、流场、压力、电流密度、电磁力等结果,并与已有的试验结果和其他相关的研究结果做对比。在此基础上,通过分析阳极热输入,求得焊接热效率为86.3%。重点比较浮力、电磁力、等离子流拉力和Marangoni剪切力单独作用下的熔池流动特性,并将计算结果和格拉晓夫数Gr、磁雷诺数Rm和表面张力雷诺数Ma相结合,分析了这几种驱动力的相对作用大小,将计算结果和Peclet数Pe相结合强调了熔池热对流与热传导的相对作用。结果表明,与等离子拉力和Marangoni剪切力相比,浮力和电磁力对熔池对流的作用较小;等离子拉力和Marangoni剪切力处于同一数量级,而Marangoni剪切力大于等离子流拉力,两者共同作用使熔池表面金属由内向外流动。与热传导相比,熔池金属这种向外流动导致的热对流主导传热过程,是造成TIG焊宽而且浅的焊缝形貌的本质原因。

5554铝合金TIG焊缝组织与性能

针对厚度为10 mm的5554铝合金进行TIG焊接试验研究,分析焊缝的组织结构及力学性能。结果表明,在选用S311焊丝的焊接试样中,焊接试样的抗拉强度和屈服强度均在母材的50%左右,断后伸长率为母材的65.4%。通过拉伸断口扫描电镜观察,5554铝合金及其焊接试样的拉伸断口均为韧窝断裂断口,断裂为韧性断裂。对焊接试样各区域的显微硬度测试,显示焊缝区域硬度高于其他部位,其中熔合线和热影响区之间的显微硬度最低。并且焊接试样的整体区域硬度均比未焊接的母材低,通过试验验证,得出焊接后的退火消除应力热处理是导致这一结果的主要原因。

WC-Co系硬质合金TIG焊接头界面扩散分析

采用Ni-Fe-C填充材料对WC-30Co硬质合金与45钢的钨极氩弧(TIG)焊进行了研究,观察分析了焊接接头的组织形貌,提出了块体界面扩散的板片模型和管道模型,并采用板片模型对WC-30Co硬质合金与钢TIG焊焊接的WC-30Co/焊缝界面的各元素的扩散行为进行了分析.界面显微观察结果表明,采用Ni-Fe-C合金作为填充金属获得了良好的焊接接头,焊缝与WC-30Co硬质合金之间发生界面扩散,在界面原子间机械力的作用下,发生了牢固的冶金结合.利用多项式进行曲线拟合,并用Matlab进行计算,可以解决焊接过程时间参数过小而无法应用板片模型的困难,是一种可行的数据处理方法.采用板片模型可以有效地描述界面元素的扩散行为,η相周围基体中元素较强的扩散能力是其形成的重要原因.

AZ71镁合金TIG焊焊接接头微观组织与力学性能

采用钨极氩弧焊接方法对2.2mm厚镁合金AZ71薄板进行焊接加工。焊后对接头进行拉伸试验和硬度测试,结果表明:采用90A的电流焊接时,接头抗拉性能最好(281.23MPa),达到母材的89.58%。断裂发生在焊缝区,焊接接头断口呈准解理断口,接近解理断口;母材断裂为延性断裂,断口呈韧窝断口;焊缝区显微硬度最高,其次是母材,热影响区硬度最低。

焊接接头TIG熔修的疲劳强度及低温性能研究

以海洋石油钻井平台桩腿所用的普通低合金钢角焊缝为例 ,研究TIG (tungsteninert gasarc)熔修对焊接接头性能的影响。TIG熔修可提高接头疲劳强度及低温性能 ,其效果取决于熔修工艺及规范。文中对多种规范的TIG熔修试样和未熔修试样 ,进行疲劳试验及落锤试验 ,推出疲劳寿命公式 ,并得到S—N曲线 ,确定了本试验条件下的最佳工艺规范参数 ,应用该工艺参数可提高疲劳强度 189% ,降低脆性开裂温度 70℃。该熔修工艺已试用于海洋平台实际结构的桩腿裂纹补焊修复中 ,使补焊焊缝的疲劳寿命大幅度提高 。

双DSP并行控制的超音频脉冲TIG焊机及其适用性

基于两套桥式逆变直流回路并联调制模式的新型主回路,采用双数字信号处理器并行全数字控制方式研制了新型大功率超音频直流脉冲TIG焊机。该焊机脉冲电流的上升沿和下降沿变化速率不小于50A/μs,脉冲频率可达30kHz以上。适用性试验表明,该焊机产生的超音频脉冲电弧具有电弧超声作用和电弧高频效应,对提高焊缝接头质量与性能有明显作用。

304不锈钢旋转双焦点激光-TIG复合焊接

为了提高激光-电弧复合焊接质量,提出了一种新的焊接方法——旋转双焦点激光-TIG(Tungsten InertGas)复合焊接.运用自行研制的旋转双焦点激光-TIG复合焊接头对304不锈钢进行了不同焊接参数下的工艺试验,并分析了焊接参数对焊缝成形的影响.结果表明在旋转双焦点激光-TIG复合焊接过程中,焊接电流和激光功率的大小和相互配合是2个热源能否有效耦合的关键因素,而旋转频率的大小对焊缝的熔深、熔宽影响不大,通过旋转双焦点激光和电弧的耦合作用可以有效地提高焊接热源的利用率.

铝合金TIG焊自适应控制方法

通过分析铝合金焊接过程的特点,将随机系统理论引入焊接过程,建立了焊接参数与熔池几何参数之间的随机系统模型.针对铝合金TIG焊特点,设计了基于电流最小方差调节的焊缝熔宽自适应控制器,通过实时调控焊接电流,使其适应焊接过程散热条件的随机变化.焊接试验结果表明,电流自适应控制方法可以实现对铝合金TIG焊缝成型的良好控制.

汽车用铝合金TIG焊接工艺

针对厚度为3mm的6061和6101铝合金板材进行TIG焊接试验研究,分别采用四种不同的填充材料进行焊接,并分析焊接接头力学性能和显微组织。研究结果表明:所有接试验力学性能均低于母材,采用ER5356焊丝的焊接接头抗拉强度达到母材的63.2%,断后延伸率为母材的62.5%。测试焊接试样各区域的显微硬度,显示焊缝区域硬度高于其他部位。采用ER5356焊丝和ER4043焊丝的焊接接头,在焊缝区域可见晶界清晰的等轴晶粒,其热影响区的晶粒较粗大。通过对比分析显微组织和力学性能,四种填充材料中,ER5356适合作为汽车用6101和6061铝合金板材的焊接填充材料。

基于熔池图像的304不锈钢焊管氩弧焊钨针损耗检测

钨极氩弧焊(TIG焊)是目前大部分不锈钢焊管制管企业采用的焊接工艺。该种工艺通常使用钨针作为电极材料,正常的钨针顶部一般为尖锥形,而随着焊接的进行,钨针针尖会逐渐产生烧损,烧损后的钨针会对焊缝的成型造成极大的影响,极易产生焊洞、咬边、漏焊等缺陷。该文通过分析氩弧焊焊接图像中的熔池轮廓模型及图像信息,发现熔池宽度与焊接电流、钨针损耗之间的联系,提出一种基于熔池轮廓的钨针损耗检测方法,通过实验证明,该文所提出的通过熔池宽度的变化检测钨针损耗的方法具有较好的准确性和可行性。

厚壁管TIG根焊摇摆手法焊接技术

介绍了手工钨极氩弧焊在厚壁管道全位置根焊层的焊接工艺、摇摆手法焊接操作要领及注意事项。实践证明,采用摇摆手法进行手工钨极氩弧焊,可以解决压力管道手工钨极氩弧焊根焊层焊接过程中易出现熔池保护不好、管内外焊缝成型不佳、气孔、夹钨等缺陷问题。

2219铝合金变极性TIG焊熔透状态识别方法

铝合金焊接熔透状态有效识别是其焊缝成形及接头质量表征的一个关键因素.设计了2219铝合金变极性TIG多元信息传感系统,实时获取焊接动态过程熔池宽度、送丝速度、焊接电流、间隙和错边等多元信息,并以此信息作为模型输入变量,构建了2219铝合金变极性TIG熔透状态预测模型,通过支持向量机建模对2219变极性TIG焊接熔透状态:未熔透、熔透和过熔透进行分类,支持向量机的核函数和惩罚因子通过网格搜索法寻优获得,模型分类准确率达93.294 1%.