氮氩气体保护的TIG焊接电弧等离子体流场的数值分析

以直流TIG焊接电弧为对象,依据磁流体动力学理论构建电弧的数学模型,运用ANSYS有限元分析软件对二维稳态下轴对称的、氮氩混合气体保护的TIG焊接电弧进行了数值分析,得到了ψ(N2)50% Ar混合气体保护下焊接电弧的温度场、速度场的形态分布特征.分析表明,氮氩电弧的最高温度出现在近阳极区域,电流密度、等离子体速度和电弧压力的最大值均出现在近阴极区.同时分析了不同电流、弧长对阳极表面电流密度的分布的影响,随着电流的增大,阳极表面电流密度增大,而随着弧长的增大,电流密度减小.     

氮氩气体保护TIG焊接电弧数值分析

以TIG焊接电弧为对象,依据磁流体动力学理论构建电弧的数学模型,运用ANSYS有限元分析软件对二维稳态下轴对称的、氩氮混合气体保护的TIG焊接电弧进行了数值分析,得到了50%N2 Ar混合气体保护下焊接电弧的温度场、速度场的形态分布特征.并通过与纯氩气保护的TIG焊接电弧温度、压力以及等离子体速度等分布的比较,得出了加入氮气作为保护气体时,TIG焊接电弧能量及形态的分布变化.对比结果表明,加入氮气作为保护气体提高了TIG焊接电弧的电弧温度、等离子体速度和电弧压力,能得到更高能量密度的焊接电弧.     

氮氧元素联合过渡对气体熔池耦合活性TIG焊电弧的影响

针对外层引入氮氧混合气体的气体熔池耦合活性TIG焊电弧,采用Boltzmann作图法分析在不同耦合度下电弧等离子体的温度分布和电弧电压的变化规律,并与传统TIG焊及外层只引入氧气的气体熔池耦合活性TIG焊进行比较. 结果表明,氮氧联合过渡时气体熔池耦合活性TIG焊电弧的中心区域温度和电弧电压均高于传统TIG焊与外层只引入氧气时的气体熔池耦合活性TIG焊的数值;当耦合度由0变为+2时,电弧中心区域温度与电弧电压均略有升高.     

低镍含氮奥氏体不锈钢激光-电弧焊电弧特性及组织性能

采用100%Ar_2,98%Ar + 2%N_2,92%Ar + 8%N_2,85%Ar + 15%N₂四种混合比例的保护气体对08Cr19MnNi3Cu2N低镍含氮奥氏体不锈钢进行激光-脉冲MAG电弧复合焊接,研究保护气体中氮气比例对焊缝中气孔数量、焊缝熔深和熔宽、电弧形态、微观组织及铁素体含量等影响机制. 结果表明,随着保护气体中氮气比例的增加,焊缝气孔数量增多,气孔的体积也随之增大;焊缝熔深显著增加,而焊缝熔宽变窄,焊缝平均硬度有所下降,电弧收缩明显,电弧弧柱宽度随着氮气比例的增加而减小,焊接飞溅数量随之增加且体积增大,电弧稳定性变差;焊缝中铁素体含量由6.91%,6.80%减少至5.38%和4.62%,铁素体枝晶也逐渐变细,二次枝晶臂变短. 焊缝组织中只仅存在少量δ和γ两相;从4个晶面观察奥氏体晶粒的尺寸也随着氮气比例的增加而逐渐减小.     

不锈钢电弧辅助活性TIG焊

针对不锈钢,提出了一种新型活性YIG焊方法--电弧辅助活性TIG焊,即AA-TIG焊(arc assisted activating TIG welding).该焊接方法通过在正常TIG焊前以活性混合气体作为保护气体,采用小电流钨极电弧预熔待焊焊道表面,可使熔深显著增加,焊接效率大大提高,而且具有可全自动化焊接和工艺可重复性好等优点.分别采用O2+Ar,CO2+Ar,空气作为小电流钨极电弧的保护气体进行了单弧AA-TIG焊.与传统TIG焊比较,发现O2+Ar,CO2+Ar和空气都可显著增加熔深,减小熔宽,焊缝表面成形良好.采用CO2+Ar作为活性混合保护气体进行双弧AA-TIG焊,焊缝成形良好,熔深显著增加.熔深随着焊枪间距减小而增大.     

氩-氦和氩-氮TIG常温焊接厚壁紫铜的试验分析

为实现厚壁紫铜的常温焊接，分别对氩-氦和氩-氦混合气体TIG电弧进行了静特性和热功率测定，并在此基础上进行了焊接对比试验。测试和焊接试验结果表明，只有φ（He）〉80％的氩-氦TIG电弧，才具有很高的电孤能量。和较理想的电孤形态，可以实现厚壁紫铜的常温焊接；而氩-氮TIG电弧虽然也具有较高的能量，但由于焊缝表面成形不良和存在较多焊缝气孔，故其不适合厚壁紫铜的常温焊接。     

铝合金三元气体保护焊工艺

氩氦氮三元混合气体保护焊工艺在铝合金焊接中表现出一定的性能优势。文中从电弧电信号、温度场特征等方面进行系统测试,总结三元保护气焊与纯氩保护气焊的技术特点差异,测试分析三元混合气体保护焊的冲击韧性、接头硬度、微观组织,与纯氩保护焊进行对比。试验结果及实际焊工操作表明,三元气体保护焊电弧更为集中稳定,焊接接头韧性更高,气孔率更低,接头软化改善明显,焊接熔深增大,电弧更易控制,可以获得优良的焊接接头。     

Ar与H2混合气体保护下GTAW电弧特性数值模拟

针对Ar与H₂混合气体保护下GTAW焊接电弧的传热与流动特性,建立基于磁流体动力学的二维轴对称数学模型,结合麦克斯韦方程组与流体动力学理论对电弧的温度、电势、电弧压力以及电流密度等进行求解,又分别将传统氩弧与氩氢混合气体保护下电弧的阳极热进行分析与对比.结果表明,加入10%氢气后的电弧轮廓较传统氩弧略微收缩,电磁力增至约传统氩弧的2倍,温度、等离子体流速、电势、电流密度等都明显增大,导致更多热量传递给阳极,在一定程度上提高了焊接热效率.可为高效GTAW焊接工艺的进一步开发提供理论参考.     

换热器管板先胀后焊的焊接工艺

介绍了采用氦－氩混合气体保护焊焊接黄铜制换热器管子与管板先胀后焊的焊接工艺，并将焊接结果与氩弧焊作了对比，还分析了氩弧焊，氩－氮混合气体保护焊，氦－氩混合气体保护焊成败的原因。     

钨极氩-氮电弧的高热特性

采用多信号微机控制光谱快速测试装置对氩—氮电弧进行了研究,揭示了氩—氮电弧的高热效果和它的机理,指出它与氩—氢,氩—氮电弧的不同之处.施焊结果表明,用氩—氮电弧焊接紫铜和超低碳奥氏体不锈钢有独特优点.     

高铬镍奥氏体焊丝Ar/He/CO2保护脉冲GMAW电弧形态与熔滴过渡

为解决高强度Cr-Ni奥氏体焊丝脉冲GMAW电弧挺度不足,熔滴过渡不稳定的问题,文中采用高速摄像手段对Ar/He/CO₂不同组合气体保护下的脉冲GMAW电弧形态与熔滴过渡进行了对比研究,以期优化混合气体成分.结果表明,氩气弧熔滴过渡容易,但电弧漂移、挺度差;氦气和CO₂气体的加入可提高电弧挺度、增大电弧能量、熔滴过渡变为1脉多滴,先一个大滴,接着几个小滴;氦气的比例越大,第一个熔滴的尺寸越大;CO₂气体可克服阴极斑点漂移,但比例不能超过5%;40% Ar+58% He+2% CO₂三元组合的电弧挺度大,熔滴过渡均匀平稳,是奥氏体焊丝脉冲GMAW厚板焊接较理想的混合气体组分.     

Effects of shielding gas composition on arc characteristics and droplet transfer in tandem narrow gap GMA welding

The effects of shielding gas composition in tandem narrow gap gas metal arc welding were studied. The shielding gas included argon, carbon dioxide and helium. The arc characteristics and droplet transfer process were analysed. The results show that in the same welding parameters, the trail wire welding current is higher than the lead wire welding current. With the increase of carbon dioxide content, the welding currents of two wires decrease, and the trail wire droplet transfer mode transforms from spray transfer to projected transfer. With the increase of helium content, the welding currents increase and the lead wire droplet transfer mode transforms from projected transfer to spray transfer. The weld width is the largest when the shielding gas mixture is 80%Ar10%CO₂10%He.     

Analysis of dynamic plasma behaviours in gas metal arc welding by imaging spectroscopy

For gas metal arc welding, the effect of CO₂ mixture in a shielding gas on a metal transfer process was investigated through the observation of the plasma characteristics and dynamic behaviour at the droplet’s growth-separation-transfer by the temperature measurement methods which were suitable, respectively, to the argon plasma region and the metal plasma region. At the present experimental conditions, the metal transfer process was a spray transfer type with 100%Ar shielding gas. On the other hand, with 85%Ar + 15%CO₂ shielding gas, the metal transfer process was a globular transfer type in which the arc length was shorter, the width was narrower and the time interval of the droplet separation was longer. For both shielding gases, the metal plasma region near the arc central axis exhibited 6500–7500 K, which was lower than the argon plasma region. With 85%Ar + 15%CO₂ shielding gas, when the metal droplet grew below the electrode wire, the region below the droplet has a high plasma temperature and a high concentration of iron vapour which surrounded the droplet. The region also exhibited a remarkably high electron number density. At the spray transfer process, the argon plasma region had an electron number density twice as high as the metal plasma region. Meanwhile, at the globular transfer process, the metal plasma region had a higher electron number density than the argon plasma region, which corresponded to a higher electrical conductivity near the arc axis. This means that the electric current goes through the arc axis easier than the spray transfer process. This condition increases the temperature below the droplet. The thermal expansion increases the force preventing the droplet from falling down. In consequence, the metal transfer takes the globular transfer type.     

Effect of shielding gas composition on low temperature toughness of Al5083–O gas metal arc welds

Abstract

There is an ever increasing range of shielding gases, which vary from the pure gases to complex mixtures based on argon, helium, oxygen, and carbon dioxide. The commercially available gas mixtures should be considered in terms of their suitability for ensuring arc and metal transfer stability, performance, and weld quality. The objective of the present paper is to study the toughness of Al5083–O aluminium alloy, to evaluate the variation of welding zone toughness as a function of the shielding gas composition and the testing temperature. To achieve these objectives, gas metal arc welding was performed with four different shielding gas compositions (100%Ar?0%He, 67%Ar+33%He, 50%Ar?50%He, and 33%Ar+67%He), and tests were carried out at four different temperatures, namely,+25°C (+77°F), ?30°C (?22°F), ?85°C (?121°F), and ?196°C (?321°F). The welding zone was divided into four subzones for analysis, namely, weld metal, fusion line, heat affected zone, and base metal according to the notch position. Tensile and yield strengths did not show a great effect of testing temperature at +25°C to ?85°C, but increased greatly at ?196°C. Also, strain tended to increase as test temperature decreased. Shielding gas composition does not have a great influence on mechanical properties. The size and number of defects were least in the 33%Ar?67%He mixture. This shows that the higher the helium gas content, the lower the number of defects detected via radiographic inspection. In the impact test, the maximum load was lowest in the weld metal and highest in the base metal at room temperature, and the maximum load and displacement were higher and lower respectively at ?196°C than those at other test temperatures, showing that the lower the test temperature, the higher the maximum load, without any special features related to the phase composition being observed in the load–deflection response. The absorbed energy of the weld metal notched specimens did not depend significantly on test temperature and shielding gas mixture. Conversely, the other specimens showed that as temperature was decreased, absorption energy increased slightly up to a maximum at ?85°C, but then decreased markedly at ?196°C.     

高气压环境脉冲MAG焊气体混合比对焊接稳定性的影响

分析了压力环境下气体混合比对脉冲MAG焊飞溅率及焊缝熔池形状的影响. 结果表明,压力环境下相同比例的保护气体在流速不变的情况下,起活性作用的气体组分相对较多,电弧弧柱紊乱加剧,飞溅剧烈,焊接过程极不稳定. 为获得高气压环境下稳定的焊接过程,减小飞溅率,通过提高混合气体配比中氩气体积分数来降低活性气体造成的能量损失,从而减少飞溅. 防止缺陷的产生. 综合考虑飞溅率、熔滴过渡稳定性及焊缝熔池形状等因素,在0.3 MPa环境压力下使用90%Ar+10%CO₂混合气进行焊接可获得最佳的焊接效果. 气体配比的有效调节对于提高高气压环境下脉冲MAG焊焊接过程稳定性和焊接质量具有显著作用.     

保护气体对440MPa HSLA钢GMAW焊缝组织及韧性的影响

采用不同保护气体对440 MPa级低合金高强钢(HSLA钢)进行气保焊焊接,通过光学显微镜(OM)、透射电镜(TEM)、扫描电镜(SEM)和电子背散射衍射技术(EBSD)对焊缝微观组织及夹杂物形貌进行了观察,研究了保护气体组成对焊缝组织及韧性的影响,并分析了不同成分保护气体对焊缝夹杂物大小、数量及其成分的影响.结果表明,保护气体为100％ CO2,焊缝金属韧性较差;保护气体(体积分数)为80％ Ar+20％ CO2和90％ Ar+ 10％ CO2,焊缝金属韧性较好.100％ CO2气体保护焊焊缝组织主要为铁素体和贝氏体,混合气体保护焊(20％ CO2和10％ CO2)焊缝组织主要为针状铁素体和少量侧板条铁素体.随着保护气体中CO2含量的减少,焊缝金属中夹杂物数量、尺寸均降低,且成分发生变化.对于440 MPa级HSLA钢,合理的保护气体组成可以得到良好的焊接质量.     

高强度铝合金厚板焊接气孔形态分析及混合保护气体效应

进行了高强度铝合金的混合气体保护气焊接试验,对采用MIG焊接高强度铝合金厚板时产生的气孔形貌及其机理进行分析,研究了影响气孔产生倾向的因素。试验结果表明,采用50％He 50％Ar保护气体施焊,能明显减少气孔产生,减小HAZ宽度,使软化区宽度相应减小,焊接接头力学性能有所提高。     

Oxide contributions on arc plasma in tungsten inert gas welding of magnesium alloy

Abstract

To study the effects of oxide activating flux on the arc plasma, the investigation is carried out in tungsten inert gas (TIG) welding on magnesium alloy. In this study, five oxides, ZnO, MnO₂, Cr₂O₃, CeO₂ and CdO, are selected to study the roles of activating flux on the plasma characteristics (shape, electron temperature and electron density) and the arc voltage. The mechanism is also discussed by comparisons between single TIG welding processes with and without fluxes. Results reveal that the electron temperature of arc plasma decreases sharply under the influence of oxide; however, the electron density and the arc voltage get enhanced. The reasons for the increase in arc voltage are the greater electricity resistances that result from the improved welding current density and the constriction of conduction channel.