Effect of Conventional and Pulsed TIG Welding on Microstructural and Mechanical Characteristics of AA 6082-T6 Repair Welds

Repair welding of AA 6082-T6 joints was carried out using ER 4043 filler through the TIG welding process with or without pulsed current.Microstructure and mechanical characteristics of the joints before and after repairing were investigated by examining macrostructure,microstructure,and distributions of porosity in the weld metal(WM),and by hardness,tensile,and bending tests.We observed that the welding current,phase transformations in heat-affected zone(HAZ)and porosity introduced in the WM during welding influence on its mechanical properties in sequence.The experimental results showed that the bead width and penetration as well as size of pores in the joints were mainly influenced by the welding currents.The sound joints were obtained at a welding current of 140 A with or without pulsed current when welding speed and gas flow rate were set at 20 cm·min-1 and 15 L·min-1,respectively.Among them,the decrease in mechanical properties of repair weld(RW)was directly related to the phase transformations in the over-ageing zone due to the double welding thermal cycles and elevated distribution of porosity in the WM.In addition,it was observed that the comparatively smaller grain size and lower porosity in WM of the RW produced by pulsed TIG welding gave a positive effect on its mechanical properties.

Research on key control technologies of all-position automatic welding machine

The pipeline all-position automatic welding machine system is a special welding system for automatically welding circumferential joint of pipeline on site, which has been widely used to the long-distance pipeline construction projects due to the advantages of automatic control for welding parameters at all-position, moving speed of bugs and operating. In this paper, the key control technologies of PAWM all-position automatic welding machine （ developed by Pipeline Research Institute of CNPC） such us the automatic control system, control software, personal digital assistant （PDA） software and complex programmable logic device （ CPLD ） program as well us the control method of welding parameter have been described detailedly. With the higher welding quality, higher welding effwiency and lower labor intensity, PA WM all-position automatic welding machine has been successfully applied in many famous pipeline construction projects.

Numerical simulation of applied electromagnetic field and electromagnetic force in all-position welding

All-position welding is an important technology in energy sources, chemical, shipbuilding and other industries. When welding current is larger than 200 A, the molten metal tends to flow down due to the force of gravity. In order to ＂push＂ the molten metal into the weld, a new kind of U-frame excitation model, which could produce electromagnetic force to balance the gravity of the molten pool, was designed. The related parameters of the excitation model were simulated by Maxwell 3D, and the relationships between the parameters and the magnetic induction intensity were analyzed. Finally, the electromagnetic force in the molten pool was calculated, and the appropriate parameters of the U-frame excitation model were determined. The results of the simulation verify the feasibility of the all-position welding excitation model.

Influence of high frequency vibration on microstructure and mechanical properties of TIG welding joints of AZ31 magnesium alloy

A device for superimposing vibration on workpiece in both horizontal and vertical directions during tungsten-arc inert gas （TIG） welding was developed, with maximum power output of 2 kW at frequency of 15 kHz. AZ31 sheets with thickness of I and 3 mm were used in the vibratory welding. Microstructures along with the mechanical properties of the weld joints under different vibrating conditions （vibration direction, vibration amplitude and groove angle） were examined. It is observed that the grain size in welding zone decreases remarkably with the application of vibration, while the amount of second phase β-Mg_17Al_12 within the zone decreases slightly; meanwhile, microhardness of the weld joints, macroscopic tensile strength and elongation of the weldment increase. Vibration, especially the one along vertical direction, has more impact on the performance of the thick weldments. Influence of vibration on mierostructure and mechanical properties of weldments is affected by wave energy transferring in the melt and depends on the processing and geometric parameters including amplitude and direction of vibration, thickness, and groove angles.

FeCrAl合金管TIG焊焊接接头的组织及性能

采用TIG(Tungsten inert gas welding,TIG)焊对FeCrAl合金管同质材料进行焊接,通过扫描电子显微镜、透射电子显微镜及能谱仪等手段研究了焊后接头的显微组织特征、焊后接头不同区域氧化物颗粒的分布情况及焊接接头的力学性能。FeCrAl合金TIG焊通过填充等成分的FeCrAl合金丝材进行焊接,焊后焊接接头主要由焊缝区、热影响区及母材组成。其中焊缝区为粗大的铁素体组织,热影响区为细小的等轴晶组织。焊缝区的Y_(2)O_(3)氧化物颗粒发生了明显粗化并与基体反应生成复合氧化物Y_(3)Al_(5)O_(12)。TIG焊焊接FeCrAl合金管热处理后,焊接接头最大抗拉强度值为530 MPa,约为母材强度的80.8%,可以实现大口径、大壁厚的FeCrAl合金管材的对接接头的力学性能要求。

核电厂定位销局部干法水下TIG焊接工艺

以核电厂定位销水下焊接为研究对象,研制双层气体保护的局部干法水下TIG旋转焊枪,运动轨迹通过直流电机带动钨极绕固定直径转动实现.对核级材料Z2CN19-10控氮奥氏体不锈钢进行焊接,研究局部干法水下TIG焊接焊缝成形,优化工艺参数,结合热循环曲线及电弧形态,分析焊接接头显微组织及力学性能.结果表明,当焊枪的内层和外层保护气均通氩气时,焊缝成形良好,电弧形态稳定;增大焊接电流或减小焊接速度均使焊缝熔深增大,熔宽增大;对比水下焊接接头和陆上焊接接头发现,水的快速冷却作用会促使熔合线附近的铁素体的形态由树枝状转变为板条状,奥氏体含量减少,焊缝中心晶粒细化;水下焊接接头的显微硬度和力学性能略高于陆上焊接接头.

焊前热处理对J55钢自动TIG焊接头组织性能的影响

目的针对J55钢焊接性较差、接头热影响区(HAZ)易出现脆硬马氏体组织等问题,在焊前对J55钢母材进行热处理,研究其焊接接头。方法在焊前对J55钢母材进行了760℃与880℃的热处理,采用TIG焊方法进行了焊接,研究了热处理前后TIG焊对接头显微组织和力学性能的影响。结果经焊前760℃热处理后,母材中的珠光体(P)含量显著减少并且发生细化,焊后接头HAZ组织转变为晶界铁素体(GBF)、针状铁素体(AF)和P;经焊前880℃热处理后,母材的显微组织主要为多边形铁素体(PF)和AF,在焊后接头的HAZ中形成了PF、贝氏体(B)和M-A组元。2种热处理接头焊缝区(WZ)的盖面层组织为GBF和AF,靠近和远离盖面层的打底层组织主要为PF和P;未热处理接头HAZ组织为PF、B和马氏体(M)。与2种热处理接头相比,未热处理接头的显微硬度居中,抗拉强度最高,延伸率最低,拉伸断裂位于熔合线与HAZ之间,断口呈脆性断裂特征。与760℃热处理相比,经880℃热处理的焊接接头HAZ显微硬度最高值达523HV,为760℃热处理的2.2倍,接头抗拉强度提高了2.2%,但延伸率降低了7.6%。2种热处理接头拉伸后均断裂在母材,断口均呈韧性断裂特征。结论先在焊前对J55钢母材进行热处理再采用TIG焊进行焊接,可获得力学性能优异的焊接接头,在焊前760℃热处理的条件下,得到的接头力学性能最优。

Microstructure and mechanical properties of Mg-Li alloy after TIG welding

Tungsten inert gas weld was carried out on super-light magnesium-lithium alloy plates with a thickness of 2 mm, using argon gas as a protecting atmosphere. The microstructure and mechanical properties of the welded joints were investigated. The results indicate that the microstructure in the fusion zone is fine, and the microstructure in the heat-affected zone is coarser than the parent metal. The tensile strength of the welded joint is about 84% that of the parent metal. The fracture occurs in a mixed type of toughness and brittleness in the heat-affected zone. During the welding process, aluminum and cerium are enriched at grain boundaries in the fusion zone.

L360QS+UNS N08825双金属复合管热丝TIG自动焊接工艺

双金属复合管作为一种油气输送管道材料,具有较强的耐蚀性能,特别适用于输送强腐蚀性介质。我国川渝地区的油气资源含有较高的硫化氢(H2S)和其他硫化物,管道内部形成了复杂的腐蚀环境,易导致管道内壁腐蚀、应力腐蚀开裂等多种失效形式。川渝地区油气管道常采用镍基合金、不锈钢等高性能的耐腐蚀材料,其中铁山坡项目中选用了L360QS+UNS N08825双金属复合管作为输送管道材质。针对825镍基复合管传统手工焊接方式效率不高,质量受人为因素影响大的问题,通过焊材匹配、自动焊接设备选型、焊接工艺参数优化等手段,开展焊接试验,研发了L360QS+UNS N08825双金属复合管热丝TIG自动焊接工艺,并在铁山坡项目中进行了实施应用,取得了显著的效果,一次焊接合格率可达99.2%,同时针对焊接缺陷返修和易出现的质量问题进行了分析,提出了相应的工艺措施。该工艺对于同类材质管道焊接具有重要的指导意义和参考价值。

TA18钛合金TIG焊接头组织及耐腐蚀性能研究

采用2B实芯焊丝对12 mm厚的TA18钛合金板进行了TIG焊试验,研究了TA18钛合金TIG焊接头的显微组织,不同腐蚀介质中的电化学和应力腐蚀行为。结果表明:TA18钛合金接头焊缝区域分布大量粗大的柱状晶和少量等轴晶,在盖面、打底及中间填充层存在部分网篮组织;热影响区主要由针状的α’(α’)相、残余α相和β相组成。在3.5%NaCl溶液中进行电化学腐蚀试验,TA18钛合金接头各区域的耐腐蚀性能从高到低为:母材>焊缝>热影响区。比较TA18钛合金接头在大气环境和模拟海水环境中的慢应变速率拉伸应力-应变曲线,表明该接头的力学性能受海水影响不明显,且对海水的应力腐蚀敏感性较低。

2A12/6061异种铝合金TIG搭接接头的疲劳性能

对3 mm厚的2A12/6061异种铝合金板材进行搭接钨极惰性气体保护焊(TIG),利用光学显微镜、显微硬度仪、扫描电镜和疲劳实验机等对接头的疲劳性能进行分析。在实验结果的基础上,对搭接试样建立有限元模型,采用热点应力法预测接头的疲劳寿命,并与实验结果进行比较。结果表明:焊缝区组织为均匀的等轴晶,2A12侧焊缝与母材熔合较差,且与母材强度差异较大,导致2A12侧焊趾处更容易产生冶金缺陷和较大的应力梯度,进而加速疲劳裂纹的萌生;在不同载荷水平下,试件断裂位置均位于强度差异较大的2A12侧焊趾处,呈脆-塑性复合断裂特征,焊趾处冶金缺陷及焊缝局部强度差异为影响接头疲劳性能的主要因素。寿命预测结果表明:采用考虑板厚效应的热点应力法预测寿命准确,误差在两倍误差带内,采用IIW推荐的FAT40 S-N曲线是安全可靠的。

Microstructure and porosity analysis in ultrasonic assisted TIG welding of 2014 aluminum alloy

The ultrasonic assisted tungsten inert gas （U-TIG） welding is a newly developed arc welding method, which is aimed at improving the weld quality and efficiency. TIG welding and U-TIG welding of 2014 aluminum alloy with 5 mm thickness were experimentally carried out in this paper. The microstructure and porosity of welded joints were analyzed. Compared with conventional TIG welding, the columnar crystals are changed into equiaxed crystals at the centre of weld zone and the grain of fusion zone in U-TIG welding is refined and equiaxed. The porosities of joint decrease after the ultrasonic was applied on the arc. The mechanism of crystal grain refinement is discussed in this paper and the reasons of porosity decrease in U-TIG welded joint may be due to the effect of acoustic streaming and cavitation, which need further research.

The element transfer behavior of gas pool coupled activating TIG welding

This paper deals with a novel dual shield TIG welding method named gas pool coupled activating TIG( GPCA-TIG)welding. The welding method divides the shielding gas into two layers. Inert gas such as Ar is adopted as the inner layer gas to protect the tungsten electrode and the molten pool metal. Pure O_2,N_2 or mixture of them are used as the outer layer gas to increase the weld penetration and improve the low temperature toughness of weld metal. Through analyzing the interaction between outer gas and arc and the distributions and existing forms of oxygen and nitrogen elements,the transfer behaviors of nitrogen and oxygen from arc to pool were investigated. The results show that,the interaction between the outer gas and arc plasma makes the arc slightly constrict. The incoming oxygen enriches on the molten pool surface and exists in the form of iron oxide,chromium oxide,manganese oxide and silicon oxygen compounds. The incoming nitrogen evenly distributes in the molten pool and exists in the form of nitrogen atom.

Numerical simulation of temperature fields for T-joint during TIG welding of titanium alloy

Three-dimensional finite element model was established to simulate temperature fields of T-joint titanium sheets during TIG welding with finite element method （FEM） software. Temperature dependent material properties and the effect of latent heat were considered. A technique of element birth and death was used to simulate the process of welded metal filling. Dynamic variation process of temperature fields during T1G welding was achieved. The simulated results agreed well with the measured results.

Characteristics of AZ31 Mg alloy joint using automatic TIG welding

The automatic tungsten-inert gas welding（ATIGW） of AZ31 Mg alloys was performed using a six-axis robot. The evolution of the microstructure and texture of the AZ31 auto-welded joints was studied by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction. The ATIGW process resulted in coarse recrystallized grains in the heat affected zone（HAZ） and epitaxial growth of columnar grains in the fusion zone（FZ）. Substantial changes of texture between the base material（BM） and the FZ were detected. The {0002} basal plane in the BM was largely parallel to the sheet rolling plane, whereas the c-axis of the crystal lattice in the FZ inclined approximately 25° with respect to the welding direction. The maximum pole density increased from 9.45 in the BM to 12.9 in the FZ. The microhardness distribution, tensile properties, and fracture features of the AZ31 auto-welded joints were also investigated.

Vision-based detection of weld pool width in TIG welding of copper-clad aluminum cable

In order to realize automatic control of the width of weld pool, a visual sensor system for the width of weld pool detection is developed. By initiative arc light, the image of copper plate weld pool is taken back of the torch through the process of weakening and filtering arc light. In order to decrease the time of processing video signals, analog circuit is applied in the processing where video signals is magnified, trimmed and processed into binary on the datum of dynamic average value, therefore the waveform of video signals of weld pool is obtained. The method that is used for detecting the width of weld pool is established. Results show that the vision sensing method for real-time detecting weld pool width to copper-clad aluminum wire TIG welding is feasible. The response cycle of this system is no more than 50 ms, and the testing precision is less than 0. 1 mm.

Realizing precision pulse TIG welding with arc length control and visual image sensing based weld detection

Methods of arc length control and visual image based weld detection for precision pulse TIG welding were investigated. With a particular all hardware circuit, arc voltage during peak current stage is sampled and integrated to indicate arc length, deviation of arc length and adjusting parameters are calculated and output to drive a step motor directly. According to the features of welding image grabbed with CCD camera, a special algorithm was developed to detect the central line of weld fast and accurately. Then an application system were established, whose static arc length error is ±0.1 mm with 20 A average current and 1 mm given arc length, static detection precision of weld is 0.01 mm , processing time of each image is less than 120 ms . Precision pulse TIG welding of some given thin stainless steel components with complicated curved surface was successfully realized.

火箭贮箱侧壁法兰结构TIG焊接变形仿真与顺序优化

文中针对火箭贮箱侧壁法兰结构TIG焊接的变形情况开展有限元分析,建立2A14铝合金贮箱侧壁法兰结构TIG焊接有限元模型,采用双椭球模型模拟马鞍形焊缝的焊接热输入情况,并根据焊接过程温度检测结果及焊缝宏观形貌校核热源模型,重点探究焊接起始位置、焊接顺序对关键部位(焊缝、密封槽)焊接变形的影响。模拟结果表明,焊后变形主要集中在焊缝区域,密封槽变形较小;焊缝与密封槽的焊接变形分布趋势相近,均在B(B')点出现变形峰值。此外,与改变焊接起点相比,改变焊接顺序对焊接变形的影响更为显著。贮箱侧壁法兰结构焊接顺序优化结果显示,在盖面反向焊(方案四)下,焊接变形分布较为均匀,焊缝和密封槽焊接变形最小。在这种情况下,焊缝最大变形量为1.022 mm,密封槽最大变形量为0.505 mm。

Numerical analysis for weld pool of pulsed TIG welding

A two-dimensional axisymmetric mathematical model of weld pool of pulsed TIG welding was established. Numerical simulation for weld pool of pulsed TIG welding was done using FLUENT software by selecting the appropriate boundary conditions and strongly coupled control equations. The distributions of temperature field and flow field of weld pool under the periodic change of welding current were obtained. According to the maximum temperature of upper and lower surface of workpiece and depth and width of weld pool, the distributions of temperature field and flow field under different pulsed frequencies and current duty cycles were obtained and periodic variation was analyzed under pulsed current. The analysis results show that with the increase of pulsed frequency, weld pool width increases slightly while depth decreases slightly, and with the increase of current duty cycle, the width and depth of weld pool both increase significantly, and the depth increases greatly.

Effect of preheat on TIG welding of AZ61 magnesium alloy

The effects of preheat treatments on the microstructures and mechanical properties of tungsten inert gas （TIG）-welded AZ61 magnesium alloy joints were studied by microstructural observations, microhardness tests and tensile tests. The results showed that the vol- ume fraction of the lamellar β-Mg17（Al,Zn）12 intermetallic compound of in fusion zone （FZ） increased from 15% to 66% with an increase in preheat temperature. Moreover, the microhardness of the FZ and the ultimate tensile strength of the welded joints reached their maximum values when the preheat temperature was 300℃ because more lamellar β-Mg17（Al,Zn）12 intermetallic compounds were distributed at the α-Mg grain boundaries and no cracks and pores formed in the FZ of the welded joint.