Evaluation on microstructure and mechanical properties of high-strength low-alloy steel joints with oscillating arc narrow gap GMA welding

Abstract with the purpose of improving weld joint quality and productivity, the oscillating arc narrow gap gas metal arc (GMA) welding was employed in welding quenched and tempered high-strength low-alloy thick steel. The microstructure and mechanical properties of weld joints were evaluated, namely micro-hardness, tensile strength, and low-temperature impact toughness. The test results indicated that mechanical properties of weld joints with oscillating arc narrow gap GMA welding were excellent and found to meet stipulated requirements. Oscillating arc narrow gap GMA welding is a promising process for welding quenched and tempered HSLA thick steels due to the low energy input and narrow square-butt groove.     

深窄间隙焊接技术在大厚度构件材料焊接中的应用研究

窄间隙焊接技术作为一种高效焊接方法以其大大降低熔敷量和节约制造时间的优点,使其在大厚度构件制造中具有广阔的应用前景,但是焊接过程的稳定性及侧壁熔合等缺陷的存在,成为影响构件高品质制造的关键问题。利用深窄间隙埋弧焊接方法成功制造了外径尺寸为2 500 mm,厚度达150 mm的转子模拟件,采用多层双道焊接方法,实现了良好的侧壁熔合效果,且未发现夹杂等缺陷,表面该焊接接头具有较高的成形质量。基于该焊接接头开展冲击韧度、拉伸等力学性能试验,表明该接头的力学性能完全满足使用需求。从而验证了深窄间隙焊接技术在大厚度核电转子焊接中应用的可靠性。     

Modeling of transport phenomena and solidification cracking in laser spot bead-on-plate welding of AA6063-T6 alloy. Part I—the mathematical model

In this work, the oscillating arc narrow gap all-position gas metal arc (GMA) welding process was developed to improve efficiency and quality in the welding of thick-walled pipes. The statistical models of narrow gap all-position GMA weld bead geometry were developed using response surface methodology (RSM) based on central composite design (CCD). The developed models were checked for their adequacy and significance by ANOVA, and the effects of wire feed rate, travel speed, dwell time, oscillating amplitude and welding position on weld bead dimension were studied. Finally, the optimal welding parameters at welding positions of 0° to 180° were obtained by numerical optimization using RSM.     

浅谈MAG焊和埋弧焊在箱式井架的应用

从箱式井架的结构形状和焊缝接头形式出发,针对MAG焊和埋弧焊的特点进行了论述,生产结果证明,通过两种优质、高效方法的运用,使焊接质量得到了保障,生产效率得到很大提高.     

压力容器用Q345R钢窄间隙MAG焊研究

以压力容器用Q345R钢为对象,进行了旋转电弧窄间隙熔化极气体保护焊试验。观察了焊接接头的宏观形貌,试件的拉伸、弯曲和冲击试验表明：焊接接头力学性能指标均满足标准要求。使用旋转电孤窄间隙方法,显著的改善了坡口两侧壁的熔透,其熔敷效率高,热输入低,是压力容器制造的一种高质,优效的技术。     

带状电极窄间隙MAG焊

为解决窄间隙焊接中普遍存在的侧壁和焊缝根部熔合不良的问题,基于减小间隙宽度让电弧直接加热间隙侧壁的思路,提出采用矩形截面的带状电极代替常规的圆形焊丝作为熔化极伸入到间隙中进行焊接,利用特殊形状的带状电极在间隙中自动形成的摆动电弧来改善对间隙侧壁和根部的加热,实现窄间隙焊接。研制专用的焊枪,研究间隙宽度、电弧电压和送带速度对间隙中带极端部电弧行为的影响。试验发现,电弧在间隙中的摆动受间隙宽度、电弧电压和送带速度的影响程度依次降低。间隙宽度对电弧的摆动具有决定性作用,间隙太宽电弧不能摆动;电弧电压过高导致电弧沿侧壁攀升得不到抑制,而送带速度主要与电弧电压搭配,保证焊接过程的稳定性,二者对间隙中电弧的摆动行为影响较小。结果表明,合理匹配间隙宽度、电弧电压和送带速度可以实现稳定的摆动电弧,获得侧壁和焊缝根部熔合良好的窄间隙焊缝。     

Nd:YAG激光+脉冲MAG电弧复合热源焊接参数对焊缝熔深的影响

试验研究Nd:YAG激光 脉冲MAG电弧复合热源焊接过程中焊接参数对焊缝熔深的影响.研究结果表明,复合热源焊缝熔深随电弧功率和激光功率的增大而增大,随焊接速度的增大而减小,并且在相同参数下,复合热源焊缝熔深稍大于激光焊缝熔深而显著大于脉冲MAG焊缝熔深.对于不同焊接电流,光丝间距在0～3 mm内复合热源焊缝取得最大熔深,且取得最大熔深的光丝间距与焊接电流大小有关;复合热源焊缝熔深在离焦量为2 mm时取得最大值.试验结果分析表明,在激光 电弧复合热源焊接过程中激光功率不仅决定复合热源焊缝熔深,而且可以极大地提高焊接速度:MAG电弧也可提高Nd:YAG激光焊的热效率.     

输送机链轮焊接工艺研究

煤矿用刮板输送机的链轮由链轮体和滚筒两部分焊接而成，其材质为低合金中碳调质钢35CrMo，焊接性差．且链轮结构的拘束度大，通过焊接性分析，并根据现场施工条件，采用了焊条电弧焊和CO2气体保护焊相结合的焊接方法，解决了链轮焊接难点。     

管道全位置焊接打底焊工艺研究

从单焊道全位置区段、送丝行为、焊接弧长(电压)、电流行为分析、 工艺试验和接头检验等几方面介绍管道全位置打底焊工艺特点,其研究成果对全位置焊接机的制造和调试具有普遍指导意义。     

刮板输送机中部槽高效双丝焊接工艺技术研究

刮板输送机中部槽采用50°X形对接焊缝和传统的单丝MAG焊焊接工艺,随着板厚的增加,导致中部槽焊接生产效率降低.为了在保证中部槽焊接质量的前提下,提高中部槽的焊接效率,采用不同坡口形式的焊接熔透性试验对中部槽焊接坡口形式进行了优化,并采用熔敷金属试验和焊接接头力学性能试验对双丝MAG焊焊接工艺进行了研究分析.研究结果表明在保证焊接质量的前提下,采用优化的36°X形焊接坡口形式和双丝MAG焊焊接工艺,使中部槽焊接生产效率得到大幅提高.     

异种钢窄间隙焊母材熔合比对碳迁移现象影响研究

异种钢窄间隙焊焊接接头两侧材料成分存在差异,在9%Cr侧熔合区内发生碳迁移现象。实际异种钢高温构件贫碳层内出现完全铁素体化组织,硬度极低,给焊接接头各项力学性能带来不良影响。设计不同焊道分布形式的异种钢堆焊试板,探究碳迁移程度及贫碳区内铁素体组织产生的影响因素。通过对不同热处理过程试样的金相观察发现,碳迁移主要在回火过程中产生。利用金相观察、显微硬度测试及电子探针成分测试等研究手段,比较焊道不同熔合比状态下的碳迁移现象。三层焊道堆焊试样的焊道交汇处碳迁移现象严重,在贫碳区内出现了完全铁素体化组织,硬度显著降低。电子探针测试结果表明,该位置母材熔合比较低,熔合线两侧铬元素质量分数差异明显导致碳元素活度梯度增加,因此碳迁移现象严重,对异种钢焊接接头的各项力学性能带来不良影响。     

低功率激光诱导电弧复合焊接钛合金薄板工艺研究

采用低功率脉冲YAG激光诱导非熔化极惰性气体保护(Tungsten inert gas,TIG)焊电弧复合热源实现了1 mm厚TC4钛合金薄板的优质焊接,研究激光诱导电弧复合焊接过程中热源能量匹配、热源间角度、对接间隙对焊缝成形的影响规律。结果表明,钛合金薄板低功率脉冲YAG激光诱导TIG电弧复合热源焊接过程中,激光能量与电弧能量之间的相互匹配将显著影响焊缝的表面成形。相对于电弧功率的变化,焊缝成形对激光功率变化的敏感度更高。随着热源间角度减小,激光诱导电弧复合热源传热能力增强;由于复合焊接速度快、热输入小、焊接试板横向变形小,当对接间隙为0~0.5 mm范围内时均能获得良好的焊缝成形。为了使焊缝成形均匀连续,焊接过程中需要对焊缝背面采用氩气进行保护,当保护气体流量为5~8L/min时获得最佳焊接接头。     

Modeling of multiple characteristics of an arc weld joint

Process parameters modeling have always been one of the key aspects in development of an adaptive control of arc welding process. The welding process parameters are inherently nonlinear, time-delayed, and interdependent, and their on-time adjustment highly influences a sound weld bead formation and process monitoring. During the welding process, parameters control is the primary goal to leads a quality welding. Moreover, the final weld joint behavior, i.e., residual stress, welding strength, and micro-crack formation are generally observed after cooling of the weld product. Thus, it has always been a difficult task to control mechanical properties of a final weld joint. To obtain the best mechanical properties, the final weld joint characteristics needed to be controlled and predicted during the process itself by precise adjustment of the process parameters. The paper presents a neuro-fuzzy modeling approach to provide adaptive control for the automatic process parameter adjustment. Three input parameters wire feed speed, welding gap, and torch speed are modeled with welding current output, providing control over weld bead formation during the welding. The same input process parameters are also modeled to predict final weld joint characteristics, i.e., dilution ratio, hardness of weld bead, hardness of fused zone, and bead width. In order to ascertain the effectiveness of the neuro-fuzzy modeling approach, multiple regression models were also developed to compare the performances.     

声发射在焊接质量实时控制中的利用前景研究

焊接过程的声发射信号是焊接工件内部的一种信号。对ＴＩＧ焊，ＭＡＧ焊和ＣＯ２焊时声发射的特征进行了研究，发现工件的熔透情况，熔滴过渡的形式和稳定性与声发射特征有紧密联系；声发射的传播与焊接热源对中情况不同有明显区别。所以可用焊接过程的声发射波某些参数作为被控制量进行焊接质量的实时控制。为焊接质量控制提供了新的途径。成功地进行了利用声发射信号的焊缝跟踪控制。     

Optimization of pulsed current in resistance spot welding of Zn-coated hot-stamped boron steels

Metallic coatings have been widely used for hot-stamped boron steel in automotive applications. Surface coating in hot-stamped boron steels has improved corrosion resistance. However, a thick coating layer degrades resistance spot weldability. In the case of a Zn-coated hot-stamped boron steel, the high contact resistance and material stiffness with low vaporization temperature of the alloyed layers result in a narrow current passage at the faying surface. Expulsion occurs at low current due to rapid heat development, resulting in a narrow weld current range. The pulsed current can control the heat input by applying a fast cool time during welding to improve the mechanical properties of the joint and acceptable current range. In this study, Zn-coated hot-stamped steels were resistance spot welded using various pulse current procedures, and welding condition was optimized via three pulsed current steps. Step 1: Contact area was controlled without nugget formation. Step 2: Nugget growth was minimized and contact area was maximized. Step 3: The maximum acceptable current range and nugget diameter were achieved. These welding conditions improved the acceptable current range and mechanical properties of spot welds due to increased spot weld size.

     

不锈钢AA-TIG焊接法

针对不锈钢,提出一种新型活性TIG焊方法——电弧辅助活性TIG焊,即AA-TIG焊。采用CO2+Ar作为小电流钨极电弧的保护气体进行单弧AA-TIG焊,分别研究小电流钨极电弧和正常TIG焊工艺参数对焊缝熔深的影响,并针对试验范围内的最佳焊接规范研究不锈钢AA-TIG焊的焊缝成形、焊缝显微组织、化学成分和焊缝性能。采用AA-TIG焊可以单道焊透10mm厚的不锈钢板材,单面焊双面成形。与传统TIG焊相比,焊缝组织和化学成分几乎没有变化,焊缝的耐Cu/CuSO4腐蚀性能和低温冲击韧度都满足相关标准要求。     

Prediction of metal deposition from arc sound and weld temperature signatures in pulsed MIG welding

The weld deposition efficiency is an important economic factor like productivity and weld quality in gas metal arc welding (GMAW). There is a strong relationship between arc sound signals and arc stability (or deposition efficiency) in GMAW. In this work, the variation of weld deposition efficiency with various pulse parameters in pulsed metal inert gas welding was investigated. The arc sound signal along with current and voltage signals were acquired and analyzed in time domain as well as in frequency domain. The sound signal kurtosis and arc power were found to be highly correlated with welding process stability. The weld deposition efficiency was also related to weld surface peak temperature. Finally, an attempt was made to correlate the sound time domain as well as frequency domain features of sound signal with the deposition efficiency. The variation of pulse shape with the duty factor also influenced the deposition efficiency as evidenced by in fast Fourier transform analysis.     

TP304不锈钢钢管环焊缝的A-TIG焊接研究

A-TIG焊接技术是基于TIG焊的焊接新工艺,具有大幅增加焊缝熔深、提高焊接生产率,降低成本等优点。本研究采用A-TIG焊接技术对TP304不锈钢50mm×6mm的管子进行全位置焊接,对得到的焊接接头进行射线探伤、显微组织分析以及力学性能测试,结果表明,接头的显微组织优于普通TIG焊接接头、接头质量和力学性能均达到标准要求。     

Effects of shielding gas control: welded joint properties in GMAW process optimization

One function of shielding gases used in welding processes, such as hydrogen (H₂), oxygen (O₂), carbon dioxide (CO₂), nitrogen (N₂), helium (He), argon (Ar) and their mixtures, is protection of the weld pool against harmful contamination that could generate defects. In addition to this primary function, shielding gases significantly affect the shape of the weld, weld geometry, seam appearance, metallurgical and mechanical properties, welding speed, metal transfer, arc stability or beam and fume emissions. The shielding gas is thus a key factor in determining weld joint properties and welding process efficiency. As welding processes have become enhanced and welding research has advanced, different combinations of shielding gas mixtures have become available under a wide variety of trademarks, each claiming to offer the best efficiency. The shielding gas flow rate in GMAW welding is usually set according to empirical experiment. The flow generally remains unchanged throughout the entire welding process and is set at maximum values of the welding parameters so that there is sufficient gas cover. This setting means, however, that unnecessarily large quantities of shielding gas may be consumed in other phases of the welding process. In view of constantly increasing prices and shortfalls in helium supply, there is a need to optimize the use of shielding gas. Consequently, an ability to closely monitor the shielding gas blend and reduce waste can provide valuable cost savings. This paper examines the effects of shielding gas mixtures and their components, presents a cross-comparison of shielding effects in fusion welding and suggests guidelines for adaptive controllability of shielding gas in advanced adaptive fusion welding. The study reviews scientific case studies and experiments from the point of view of the effect of the shielding gas on the process efficiency and process outcome. The study considers shielding gases for welding of both ferrous metals (i.e. carbon steels, stainless steels, high-strength steels) and non-ferrous metals (i.e. aluminium and its alloys, nickel and its alloys and copper and its alloys). Appropriate choice of shielding gas and use of an optimum flow rate results in better quality in terms of increased productivity, reduced gas consumption and improved weld geometry properties, microstructure and mechanical properties. Although some blends can be used effectively in many different processes, other blends appear process-dependent; they produce far poorer results when utilized in non-appropriate processes. Particle image velocimetry (PIV) and Schlieren techniques can be used for visual sensing of gas flow during fusing welding. Moreover, an adaptive alternative gas supply can improve welding performance and weld quality and reduce harmful fume emission.     

Study on arc characteristics and their influences on weld bead geometry in narrow gap GMAW of 5083 Al-alloy

As an efficient process, narrow gap gas metal arc welding (NG-GMAW) was employed to join thick plates of 5083 Al-alloy. In this paper, arc characteristics in NG-GMAW of 5083 Al-alloy and their influence on the weld bead geometry were studied with synchronous acquisition system for various groove types, welding modes, welding current levels, and swing frequencies. The arc profiles were measured and appear to be entirely different compared with that in bead-on-plate GMAW process, meanwhile the arc size changes with varied welding mode, welding current, and arc swing frequency. Arc characteristics highly affect the weld bead geometrical parameters such as bead width, welding penetration, sidewall penetration, and weld surface concavity. Linear regressions were made between the arc characteristics and the weld bead geometrical parameters both in swing and non-swing arc process. It showed that a negative linear correlation exists between welding penetration and arc length, sidewall penetration, and arc warpage, while a positive linear correlation exists between weld surface concavity and arc warpage in non-swing arc process. In contrast, a non-linear correlation exists among them and the variation tendency remains the same in swing arc process.