TA2薄壁钛管双TIG焊温度场和残余应力分布对接头组织性能的影响

针对纯钛TA2薄壁管的钨极氩弧焊(TIG)高速焊接时出现的咬边、驼峰等成形缺陷,以及焊接效率低等问题,提出采用双TIG焊接工艺,可有效提高焊接速度,改善焊缝成形的解决措施。同时采用ABAQUS对两种焊接方法建立焊接热弹塑性有限元模型,对比分析焊接温度场和焊后残余应力分布,并进一步对焊接TA2薄壁钛管进行显微组织分析及力学性能测试。试验结果表明:模拟所得的两种接头的焊缝轮廓尺寸与实际接头相近,双TIG焊接时焊缝中心温度低于TIG焊接,且双TIG焊缝附近Von Mises应力大于200 MPa的宽度小于TIG焊缝,焊后稳态时焊缝中心的Von Mises应力相近。双TIG焊缝中心及热影响区显微组织比TIG焊细小,两种接头的各项力学性能和耐海水腐蚀性能均满足相关标准要求。φ19 mm×0.7 mm的TA2钛管在获得良好焊缝成形的条件下,采用双TIG焊接工艺的焊接速度可达5 m/min。与TIG焊接工艺相比,生产效率大为提高,基本实现焊缝零缺陷。

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.

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.

Acoustic Emission Studies on Weld Bead Defects in Nuclear Grade SS 316L Materials

This paper contributes about the behaviour of Acoustic Emission (AE) signatures of implanted weld defects of SS 316L materials. Lack of penetration and lack of side fusion defects were implanted in weld bead region of the materials. Tungsten Inert Gas Welding (TIG) is adopted to weld the Stainless Steel (SS316L) nuclear grade materials. The material is fabricated with dimensions of 140 × 16 × 10 mm and AE signatures are studied under preload conditions. Mechanical Jig is fabricated to maintain constant load in concentrated weld region. When external load is applied on the weld region, the deformed specimen experiences acoustic emission signals form the weld defect region which are potential source of releasing stress energy. Liner Location Technique (LLT) is adopted for AE singal studies and the generated signal is processed by 2-channel USB—AE node and AE-WIN software. The tests are conducted on two different samples having each defect. A conventional NDT method i.e. X-ray Radiography is conducted on the samples to know the defect ranging and correlated with AE signatures. This study will be helpful to standardize the AE signals for different implanted weld defects of SS 316L materials and it is found that, the parameter “counts vs. amplitude” has given the widest distinction with respect to the type of defects.

Cavitation Erosion Behavior of as-Welded Cu12Mn8Al3Fe2Ni Alloy

Cavitation erosion behavior of as-welded Cu12Mn8Al3Fe2Ni alloy in 3.5% NaCl aqueous solution was studied bymagnetostrictive vibratory device for cavitation erosion. The results show that the cavitation erosion resistance ofthe as-welded Cu12Mn8Al3Fe2Ni alloy is much more superior to that of the as-cast one. The cumulative mass lossand the mass loss rate of the as-welded Cu12Mn8Al3Fe2Ni alloy are almost 1/4 that of the as-cast one. SEM analysisof eroded specimens reveals that the as-cast Cu12Mn8Al3Fe2Ni alloy is attacked more severely than the as-weldedone. Microcracks causing cavitation damage initiate at the phase boundaries.

Effect of δ Phase on Microstructure and Hardness of Heat-Affected Zone in TIG-Welded GH4169 Superalloy

The GH4169 superalloy with different content ofδ-Ni3Nb phase was welded by tungsten inert gas welding.A detailed study of microstructure and hardness of heat-affected zone(HAZ)was performed in both as-welded and aged state.The results show that the precipitation ofδphase,especially the intergranularδphase,can lead to the enrichment of Nb and Mo elements,which promote the formation ofγ/Laves eutectic constituent at grain boundaries in HAZ.In as-welded state,the hardness decreases first and then increases(exhibiting a"V"shape)with distance away from fusion line in HAZ,which is governed by grain size.After aging treatment,however,theγ″phase plays a key role in hardness and leads to the"■"shape profiles of hardness in HAZ.

Influence of Filler on the Microstructure, Mechanical Properties and Residual Stresses in TIG Weldments of Dissimilar Titanium Alloys

The influence of titanium alloy(Ti–5 Al–2.5 Sn) and commercially pure titanium(cp Ti) as fillers on dissimilar pulsed tungsten inert gas weldments of Ti–5 Al–2.5 Sn/cp Ti was investigated in terms of microstructure, mechanical/nano-mechanical properties, and residual stresses. A partial martensitic transformation was observed in the weldments for all the welding conditions due to high heat input. The microstructure evolved in the FZ/cp Ti interfacial region was observed to be the most sensitive to the proportion of α stabilizer in the filler alloy. Furthermore, the addition of filler alloy improved the tensile properties and nano-mechanical response of the weld joint owing to the increased volume of metal in the weld joint. As compared to the Ti–5 Al–2.5 Sn wire, the use of cp Ti filler wire proved to be better in terms of energy absorbed during tensile and impact tests, tensile strength and ductility of the dissimilar welds. An asymmetrical residual stresses profile was observed close to the weld centerline, with high compressive stresses on the Ti–5 Al–2.5 Sn side for both the weldments obtained with and without filler wires. This was attributed to mainly the low thermal conductivity of Ti–5 Al–2.5 Sn. The presence of residual stresses also influenced the nano-hardness profile across the weldments.

Particle Swarm Optimization of Printing Parameters for Open-source TIG-based Metal 3D Printing

Proprietary metal 3D printing is still relegated to relatively expensive systems that have been constructed over years of expensive trial-and-error to obtain optimum 3D printing settings.Low-cost open-source metal 3D printers can potentially democratize metal additive manufacturing;however,significant resources are required to redevelop optimal printing parameters for each metal on new machines.In this study,the particle swam optimization(PSO)experimenter,a free and open-source software package,is utilized to obtain the optimal printing parameters for a tungsten inert gas-based metal open source 3D printer.The software is a graphical user interface implementation of the PSO method and is designed specifically for hardware-in-loop testing.It uses the input of experimental variables and their respective ranges,and then proposes iterations for experiments.A custom fitness function is defined to characterize the experimental results and provide feedback to the algorithm for low-cost metal additive manufacturing.Four separate trials are performed to determine the optimal parameters for 3D printing.First,an experiment is designed to deposit and optimize the parameters for a single line.Second,the parameters for a single-layer plane is optimized experimentally.Third,the optimal printing parameters for a cube is determined experimentally.Fourth,the line optimization experiment is revised and reconducted using different shield gas parameters.The results and limitations are presented and discussed in the context of expanding wire arc additive manufacturing to more systems and material classes for distributed digital manufacturing.

Unveiling the Residual Stresses,Local Micromechanical Properties and Crystallographic Texture in a Ti-6Al-4V Weld Joint

In this work,the micromechanical properties,crystallographic texture,welding residual stresses and their evolution after plastic strain were investigated in a Ti-6Al-4V alloy tungsten inert gas weld joint.It was found that the welding process affected the Young modulus and microhardness values in bothαandβphases in the different regions of the weld joint.The highest microhardness and Young modulus values of a phase were recorded in the heat-affected zone,whereas the highest values of these characteristics for theβphase were found in the fusion zone(FZ).The change in the micro mechanical properties was accompanied by a change in the crystallographic texture components of the dominant a phase from(0001)<10-10>and(11-20)<10-10>components in the base material to(10-10)<11-20>and(11-20)<3-302>components in the FZ.The introduction of tensile testing resulted in a continuous stress relaxation and improved the weld joint performances.