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 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.

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.

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。

TIG电弧复合熔滴沉积增材制造45钢/铅合金双金属结构工艺研究

传统钢/铅粘接结构在使用或长期贮存过程中存在粘接层局部脱粘、老化或强度退化等问题,严重影响复合结构的完整性和长期稳定性。本工作提出采用钨极惰性气体(Tungsten inert gas,TIG)电弧复合熔滴沉积成形新方法实现45钢/铅合金双金属结构的直接冶金复合增材制造,利用金相显微镜、扫描电镜、能谱仪、硬度实验以及拉伸实验等方法对钢/铅双金属结构成形试样的界面组织特征与力学性能进行分析。结果表明,铅合金沉积层特征尺寸随TIG电弧热输入的改变呈现出明显的非线性依赖特征;45钢/铅合金双金属结构界面未被发现明显孔隙、裂纹等冶金缺陷;界面化合物(Intermetallic compounds,IMCs)层的厚度约为30~70μm;钢/铅双金属成形试样的界面剪切强度平均值为28.4 MPa,远高于文献报道的强度(4.2 MPa),试件剪切拉伸断裂均发生在铅合金沉积层侧而非结合界面。

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.

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.

层间超声冲击对TIG电弧增材制造2219铝合金组织和力学性能的影响

针对铝合金电弧增材构件存在的气孔等内部缺陷,开展不同层间超声冲击工艺参数下电弧增材制造2219铝合金的晶粒形貌、力学性能和气孔缺陷试验研究,分析了层间超声冲击对试件性能的强化效果。结果表明,降低冲击扫描速度和提高冲击次数,晶粒尺寸减小,顶部圆弧区的树枝晶被破碎向等轴晶转化;相比无冲击的增材制造材料,以2mm/s速度扫描冲击三次试样的抗拉强度提升了10.2%,屈服强度提升了32.4%;TIG电弧增材制造构件的气孔数量、平均直径和圆度随超声冲击增加而降低,部分直径小的气孔直接闭合。本研究对电弧增材制造应用于大型铝合金薄壁构件成形及组织性能控制有参考价值。

Sliding Wear Behavior of a Grey Cast Iron Surface Remelted by TIG

The sliding wear behavior of a grey cast iron surface remelted by tungsten inert gas （TIG） was studied and compared with the unremelted one in the current work. To evaluate the wear behavior a Pin-on-Disk wear test machine was used. Pins which were prepared from the samples with the remelted layers of different thicknesses of 1.2, 1.8, 2.5 and 3 turn were worn on an AISID3 steel counterface having a hardness of 63HRC under the applied loads of 54, 76 and gg N at a constant sliding velocity of 0.45 m/s. Scanning electron microscopy （SEM） equipped with energy dispersive X-ray analysis （EDS） and X-ray diffraction （XRD） techniques were used to characterize worn surface and subsurface and also wear debris obtained from the wear tests under different test conditions. Results showed that surface remelted grey cast iron have better wear properties for all applied normal loads in comparison with unremelted ones. Microscopic studies on the worn surfaces and subsurfaces of samples revealed that dominant wear mechanism for surface remelted samples was mild oxidative, while it was severe for unremelted samples. Increasing remelted layer thickness and then forming grosser microstructure lead to a decline of wear properties, whereas lower thickness of remelted layer with finer microstructure due to having higher cooling rate through remelting process can withstand better against wear.

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.

核电站钢衬里壁板安装脉冲TIG自动焊试验

采用脉冲TIG自动焊对6 mm厚核电站钢衬里壁板用钢P265GH进行横焊、立焊试验,并分析焊接接头的组织和力学性能。结果表明:钢衬里壁板对接焊采用I形坡口和适当的焊接工艺,能够得到成形良好且无缺陷的焊接接头;横焊和立焊焊接接头的焊缝组织均主要为侧板条铁素体(FSP)+针状铁素体(AF)+晶界铁素体(GBF)+粒状贝氏体(GB),粗晶热影响区(CGHAZ)组织均主要为侧板条铁素体(FSP)+上贝氏体(UB)+晶界铁素体(GBF)。横焊和立焊焊接接头的力学性能试验结果表明,其横向抗拉强度均≥470 MPa,断裂位置均位于母材;焊缝的0℃冲击功吸收均≥130 J,热影响区的0℃冲击吸收功均≥140 J;焊接接头硬度均≤HV10350,未出现硬化倾向;焊接接头弯曲试样均未出现裂纹,焊接接头的力学性能符合RCC-M标准要求。

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.

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.

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.

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.

稀土钨电极材料及稀土氧化物的作用

介绍了焊接钨电极材料的发展历史和研究现状。从焊接工作特性分析了对电极材料的要求，比较了纯钨、钍钨电极材料的特点。着重对近年来代钍钨稀士钨电极材料研究及稀土氧化物的作用等有关理论研究问题进行了讨论。有关研究表明：添加２％稀土氧化物的钨电极材料具有可加工性能。电极的使用性能强烈地依赖于稀土金属氧化物，燃弧过程中它们的行为是影响电极使用、电极温度、逸出功和电弧稳定性的最重要因素。稀土氧化物的补给与表面蒸发之间的平衡是实现稳定和长寿命工作的关键。一般情况下稀土氧化物与钨反应生成钨酸盐或氧化钨酸盐，这些盐的熔点低于稀土氧化物和钨的熔点，在燃弧过程中熔化、迁移和蒸发。不同成分和配比的稀土氧化物，对它们与钨反应生成的钨酸盐和氧化钨酸盐的迁移与蒸发的平衡调节作用各异，同时也影响燃弧后钨的再结晶晶粒组织，这些因素综合影响了电极的燃弧特性、抗烧损性和电弧的稳定性。在复合稀土钨电极中，比例为１∶１∶３的ＣｅＯ２－Ｌａ２Ｏ３－Ｙ２Ｏ３－Ｗ电极的工作温度最低，热发射最高。

La-W、Ce-w、Y-W电极材料热发射性能研究

研究了稀土元素Ｌａ．Ｃｅ．Ｙ对钨极材料热电子发射能力和稳定性的影响．利用粉末冶金和压力加工方法，制备了系列稀土钨电极材料，并对它们分别进行了引弧、静特性等焊接性能研究，借助于扫描电镜和Ｘ－ｒａｙ能谱仪对镧钨、钇钨、铈钨等燃弧后的４种电极（含用于参照的钍钨电极）进行显微观察，分析了稀土元素在钨电极热发射过程中的行为和作用机制．研究表明：在中小电流时ｗ（Ｌａ２Ｏ３）＝２．２％的Ｌａ２Ｏ３－Ｗ电极具有较好的电子发射能力和稳定性，钇钨和铈钨次之，在大电流工作时，钇钨电极热电子发射能力和稳定性最好．

钨极惰性气体保护焊熔池三维自由表面特征参数的激光视觉测量

针对现有的钨极惰性气体保护焊熔池三维自由表面测量方法难以应用于强弧光、高温辐射、液态金属表面镜面反射等问题,提出一种激光视觉测量法.利用小功率点或线阵模式结构激光照射覆盖整个熔池表面,采用高速摄像机实时采集经熔池液态金属表面反射畸变的激光图像.设计图像处理算法提取成像激光点位置坐标,建立与投射激光点位置坐标的空间转换数学模型,离线获得熔池三维自由表面的几何特征参数值,对比实测凝固熔池表面对应参数值发现,所提取的几何特征参数值与实测值吻合较好,熔宽、长度和凸度误差分别为0.8%、0.6%和4.7%,证明激光视觉法能够实现熔池自由表面三维信息的动态测量,为采用几何特征参数调整熔池自由表面形貌变化控制焊缝成形及缺陷提供一种新方法.

电弧超声激励共熔池双钨极氩弧焊接方法

提出了一种附加电弧超声激励共熔池的双钨极氩弧焊接新方法.使用附加超声电弧和主电弧完成焊接过程,附加超声电弧向焊接熔池注入超声波激励,主电弧作为主要的焊接热源,以实现改善焊缝金属性能及其焊接效率的功能.同时,以304钢为例,采用所提出的焊接方法进行试验.结果表明,所提出的焊接方法可以提高焊接过程的稳定性和焊接效率,有效细化焊缝金属组织并提高焊缝金属的拉伸性能.