高温合金活性剂激光微焊接接头的组织性能研究（英文）

采用配方均匀设计法,配制了SiO2-MnO2-CaO-TiO2-CaF2-NaF多组元活性剂,利用微型脉冲激光器对500μm厚GH4169高温合金进行了活性剂激光焊接试验。分析并讨论了焊接接头的显微组织和力学性能。试验结果表明,与传统激光焊相比,所配制的20种活性剂均增加了焊缝熔深,并且其中F12系混合活性剂增加熔深能力最为显著,使焊缝深宽比增加了159%,证明通过使用活性剂来增加微激光焊焊缝熔深,降低高温合金板激光焊接的成本是可行的。在活性剂作用下,焊缝显微组织仍由柱状晶和等轴晶组成,接头抗拉强度达到927 MPa,为母材强度的92.7%。     

焊接热输入对高温熔池形态的影响

焊接熔池形态对焊接过程和焊接质量有着重要影响,熔池的形状不仅决定了焊缝的形状,而且对焊缝的组织、力学性能和焊接质量均有重要影响。本文使用ANSYS有限元软件,采用"生死单元"技术,对X80管线钢复合型坡口多层焊的焊接过程进行二维模拟,研究各填充焊层受后一焊层热影响后,其高温停留时间和熔深随焊接热输入的影响规律。结果表明,焊层的峰值温度随着热输入的增加而增大,填充焊层焊接热输入从13.25 kJ/cm增加到14.57 kJ/cm,高温停留时间的百分比增量是热输入从12.04 kJ/cm增加到13.25 kJ/cm的一半;而各焊层熔深的增加值不变,均为0.45 mm。     

Research on air tightness of image intensifier tube during laser sealing北大核心CSCD

采用高功率YAG激光焊接机对高性能三代像管管壳后端(4J34可伐合金)与荧光屏屏环(4J49可伐合金)进行封接试验。研究了激光功率、脉冲宽度对焊接接头成型及表面热扩散的影响规律。研究表明:4J34合金与4J49合金表面成型质量在设备最大工作电流100 A,激光功率195 W及脉宽1.7 ms时最好,相对于激光功率,脉冲宽度对焊缝熔宽和熔深的影响更加显著,接头焊接中心区硬化最为严重,其硬度最大,热影响区次之。     

Inconel690镍基合金/SUS304不锈钢激光焊接接头组织与力学性能

Inconel690镍基合金具有良好的综合力学性能，其焊接结构已经被广泛应用于核电产业中，通过改变热输入与填丝可以改善其焊接接头的力学性能。对Inconel690镍基合金与SUS304不锈钢进行激光对接焊试验，分析接头显微组织和力学性能。研究发现，焊缝呈现激光焊接典型的高脚杯形状，焊缝区域弥散分布含钛相。当未填充焊丝时，低热输入(1.5 kJ/cm)接头与高热输入(2.6 kJ/cm)接头相比，焊缝晶粒尺寸减小约40%，接头抗拉强度提高约9.7%，焊缝平均硬度提高约7.7%。在填充焊丝后，焊缝中Ni元素含量提高，Fe元素含量下降，出现弥散分布的富铬相，结合X射线衍射(XRD)结果分析，推测其为Cr_0.19Fe_0.7Ni_0.11相。与高热输入接头相比，低热输入填丝焊的焊缝平均硬度与接头抗拉强度均有所提高，其中焊缝平均硬度提高约22.6%，抗拉强度提高约16.2%。     

5083铝合金光纤激光-TIG复合焊接工艺研究

采用IPG YLS-6000光纤激光器和Fronius MagicWave3000job数字化焊机,对4mm厚5083H116铝合金进行了复合焊接试验。研究了电源特性、电流大小和热源间距等工艺参数对光纤激光-钨极惰性气体保护焊(TIG)复合焊接焊缝成形的影响规律,并分析了焊接接头的缺陷、显微硬度及力学性能。结果表明,光纤激光-TIG复合焊接5083铝合金,能够明显改善焊缝成形,提高焊接过程稳定性,特别是与变极性TIG电弧复合效果更为显著;光纤激光与变极性TIG电弧复合焊接,采用激光在前的方式,电弧电流150A,且热源间距不大于4mm,可以得到具有明亮金属光泽和均匀鱼鳞纹的焊缝,焊缝无气孔和裂纹缺陷,其表面有少量的下凹;复合焊接接头抗拉强度为318MPa,达到母材强度的93%,延伸率为7.6%,高于单光纤激光焊接,断口分析为韧性断裂。     

等离子体电弧现象的高速摄影及分析研究

通常TIG（Tungsten Inert Gas）进行不锈钢焊接时，熔深一般为2-3mm，对于厚板材料的焊接就必须来用其它工艺方法，焊接效率低。其原因是TIL焊时电弘在空间上分散，电弧的热流密度和电弧电压强较低。目前国内外为提高TIG焊的熔深，正在研究在焊接工件表面涂数活性焊剂的ATIG（Actire Tungsten Inert Gas）这一全新焊接方法。对ATIG焊时增加熔深的机理，各研究报道多处于假设与猜想阶段，尚无实验证明。本实验中用表面涂敷SiO2、TiO2、氟化物单一纯净物及三者按一定比例混合的混合物，对不锈钢进行TIG焊，通过高速摄影技术及照片分析，对ATIG的等离子体电弧及焊缝熔深进行了实验研究。结果表明：表面涂敷活性焊剂后，TIG焊电弧形态发生显著变化。氟化物使电弧更加分散，而SiO2、TiO2及三者混合物促使电弧明显收缩，电弧内高温等离体流速增大，热量集中。与正常TIG焊相比熔深增加2-3倍，大大提高了焊接效率。     

激光工艺参数对钛合金表面NiCrBSi合金熔覆层组织及硬度的影响

在TC4合金表面进行了激光熔覆NiCrBSi合金涂层的试验 ,利用SEM和XRD等对熔覆层的微观组织进行了分析 ,测试了熔覆层的显微硬度。结果表明 ,激光工艺参数对熔覆层的组织和硬度有极大的影响 ,随稀释率的增加 ,激光熔覆层中形成了TiB2 和TiC等颗粒增强相 ,熔覆层的硬度明显提高。     

核级阀门唇焊焊缝熔深的超声检测方法*

核电阀体唇焊焊缝熔深不足可能导致其在服役期内无预期断裂,由此引起的流质泄露将引起严重的安全事故。因此,极有必要在阀体焊接完成后进行熔深测量以保证足够的焊缝强度。本研究针对阀体唇焊缝粗糙余高曲面声学耦合差、熔深测量难的问题,提出基于喷水式超声聚焦检测技术的唇焊焊缝熔深测量方法。首先,根据核电阀体唇焊焊缝结构特点提出唇焊熔深的超声聚焦测量方法;其次,通过构建检测过程的有限元模型分析焊缝余高曲率对声场聚焦能力的影响,给出余高曲率各异的焊缝检测时的水距修正方法,以便在预定熔深范围内形成高能聚焦声场;最后,分析和提取与唇焊结构相关的检测信号特征,结合金相分析方法修正声速。研究结果显示：通过水距修正可改善焊缝曲率半径变化对聚焦声场的不利影响,曲率半径28.5 mm时焦区声压幅度仅下降11%,基于特征脉冲时间间隔及声速修正可测定焊缝熔深;与金相试验对比,绝对误差小于0.06 mm,满足核电阀门唇焊焊缝熔深测量的需求。     

焊后热处理对核聚变用316LN焊接接头的影响

采用了TIG对核聚变用316LN奥氏体不锈钢进行焊接,并对焊接接头进行了焊后热处理,利用光学显微镜、扫描电镜分析手段研究了焊后热处理对焊接接头微观组织和力学性能的变化。试验结果表明,焊缝中为奥氏体组织,并未发现第二相析出物存在。焊后热处理对接头的拉伸性能影响不大,均断裂在母材位置,但显著提高了接头的延伸率。接头低温冲击试验也展现了良好的抗低温冲击性能。断口分析发现,接头呈韧性断裂。     

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采用了TIG对核聚变用316LN奥氏体不锈钢进行焊接,并对焊接接头进行了焊后热处理,利用光学显微镜、扫描电镜分析手段研究了焊后热处理对焊接接头微观组织和力学性能的变化.试验结果表明,焊缝中为奥氏体组织,并未发现第二相析出物存在.焊后热处理对接头的拉伸性能影响不大,均断裂在母材位置,但显著提高了接头的延伸率.接头低温冲击试验也展现了良好的抗低温冲击性能.断口分析发现,接头呈韧性断裂.     

Influences of laser in low power YAG laser-MAG hybrid welding process

The influences of laser defocusing amount △z, laser power P, space distance DLA between laser and arc on weld penetration, arc modality and stability are investigated in low power YAG laser and metal active gas （laser-MAG） hybrid welding process. The experimental results indicate that the effects of laser-induced attraction and contraction of MAG arc are emerged in hybrid welding process, which result in the augmentation of hybrid welding energy. When DLA ： -0.5 - 2 mm, △z = -2 - 2 mm and P ≥ 73 W, the synergic efficiency between laser and MAG arc is obvious, the cross section at the root of hybrid arc is contracted and the hybrid weld penetration is increased. The maximal ratio of hybrid/MAG weld penetration is 1.5 and the lowest YAG laser power that augments MAG arc is 73 W. The input of YAG laser makes the stabilities of arc ignition and combustion prominent in hybrid welding process.     

Characterization of Kovar-to-Kovar laser welded joints and its mechanical strength

For the packaging of a pump laser in butterfly package, the most crucial assembly step is the fiber-to-laser diode coupling and attachment. The use of laser welding as the joining method offers several advantages if compared with the adhesive joints: strong joining strength, short process time and less contamination. This paper reports on laser welding process characteristics; weld strength and its fracture mode. The penetration depth and melt area of laser spot welds were found to be complicated functions of laser pulse energy, intensity, and beam diameter. Effects of pulse width, input power and size of the focal spot on the rate of energy input to the workpieces and consequently, the weld strength were reported. The weld strength was found to be dependent on the overlapping area between the two joining materials. Surface roughness, R_a, has influence on the fraction of energy absorbed, A, and therefore, affecting the penetration depth. Thermal analysis was carried out on the laser-welded joints and its heat-affected zone (HAZ) induced by various power densities was examined. These data are important in order to optimize and utilize the laser welding process as an effective manufacturing tool for fabrication of reliable pump laser.     

Parametric optimisation and microstructural analysis on high power Yb-fibre laser welding of Ti–6Al–4V

In this work thin sheets of Ti–6Al–4V were full penetration welded using a 5 kW fibre laser in order to evaluate the effectiveness of high power fibre laser as a welding processing tool for welding Ti–6Al–4V with the requirements of the aircraft industry and to determine the effect of welding parameters including laser power, welding speed and beam focal position on the weld microstructure, bead profile and weld quality. It involved establishing an understanding of the influence of welding parameters on microstructural change, welding defects, and the characteristics of heat affected zone (HAZ) and weld metal (WM) of fibre laser welded joints. The optimum range of welding parameters which produced welds without cracking and porosity were identified. The influence of the welding parameters on the weld joint heterogeneity was characterised by conducting detailed microstructural analysis.     

3D transient multiphase model for keyhole,vapor plume,and weld pool dynamics in laser welding including the ambient pressure effect

The physical process of deep penetration laser welding involves complex, self-consistent multiphase keyhole, metallic vapor plume, and weld pool dynamics. Currently, efforts are still needed to understand these multiphase dynamics. In this paper, a novel 3D transient multiphase model capable of describing a self-consistent keyhole, metallic vapor plume in the keyhole, and weld pool dynamics in deep penetration fiber laser welding is proposed. Major physical factors of the welding process, such as recoil pressure, surface tension, Marangoni shear stress, Fresnel absorptions mechanisms, heat transfer, and fluid flow in weld pool, keyhole free surface evolutions and solid–liquid–vapor three phase transformations are coupling considered. The effect of ambient pressure in laser welding is rigorously treated using an improved recoil pressure model. The predicated weld bead dimensions, transient keyhole instability, weld pool dynamics, and vapor plume dynamics are compared with experimental and literature results, and good agreements are obtained. The predicted results are investigated by not considering the effects of the ambient pressure. It is found that by not considering the effects of ambient pressure, the average keyhole wall temperature is underestimated about 500 K; besides, the average speed of metallic vapor will be significantly overestimated. The ambient pressure is an essential physical factor for a comprehensive understanding the dynamics of deep penetration laser welding.     

Sheet metal welding using a pulsed Nd: YAG laser-robot

This paper presents a pulsed Nd: YAG laser-robot system for spot and seam welding of mild steel sheets. The study evaluates the laser beams behaviour for welding, and then investigates pulsed Nd: YAG laser spot and seam welding processes. High pulse power intensity is needed to initiate the key-hole welding process and a threshold pulse energy to reach full penetration. In seam welding, a weld consists of successive overlapping spots. Both high pulse energy and high average power are needed to keep the key-hole welding going. A 70% overlap is used to define overlapping spot welding as seam welding and to optimize process parameters because a high tensile strength joint compatible with the strength of the base material can be obtained when the overlap is ≥70%; at the same time a smooth seam with full penetration is obtained. In these cases, the joints in pulsed Nd: YAG laser welding are comparable in strength to those obtained with CO₂ laser welding. Robot positioning and motion accuracies can meet the demands of Nd: YAG laser sheet metal welding, but its cornering accuracy affects the welding processes. The purpose of the study is to evaluate the YAG laser-robot system for production in the automotive industry.     

Effects of relative positioning of energy sources on weld integrity for hybrid laser arc welding

This study is concerned with the effects of laser and arc arrangement on weld integrity for the hybrid laser arc welding processes. Experiments were conducted for a high-strength steel using a 4 kW Nd: YAG laser and a metal active gas (MAG) welding facility under two configurations of arc–laser hybrid welding (ALHW) and laser–arc hybrid welding (LAHW). Metallographic analysis and mechanical testing were performed to evaluate the weld integrity in terms of weld bead geometry, microstructure and mechanical properties. The morphology of the weld bead cross-section was studied and the typical macrostructure of the weld beads appeared to be cone-shaped and cocktail cup-shaped under ALHW and LAHW configurations, respectively. The weld integrity attributes of microstructure, phase constituents and microhardness were analyzed for different weld regions. The tensile and impact tests were performed and fracture surface morphology was analyzed by scanning electron microscope. The study showed that ALHW produced joints with a better weld shape and a more uniform microstructure of lath martensite, while LAHW weld had a heterogeneous structure of lath martensite and austenite.     

Analysis of droplet transfer mode and forming process of weld bead in CO2 laser–MAG hybrid welding process

In this paper, CO₂ laser–metal active gas (MAG) hybrid welding technique is used to weld high strength steel and the optimized process parameters are obtained. Using LD Pumped laser with an emission wavelength of 532 nm to overcome the strong interference from the welding arc, a computer-based system is developed to collect and visualize the waveforms of the electrical welding parameters and metal transfer processes in laser–MAG. The welding electric signals of hybrid welding processes are quantitatively described and analyzed using the ANALYSATOR HANNOVER. The effect of distance between laser and arc (D_LA) on weld bead geometry, forming process of weld shape, electric signals, arc characteristic and droplet transfer behavior is investigated. It is found that arc characteristic, droplet transfer mode and final weld bead geometry are strongly affected by the distance between laser and arc. The weld bead geometry is changed from “cocktail cup” to “cone-shaped” with the increasing D_LA. The droplet transfer mode is changed from globular transfer to projected transfer with the increasing D_LA. Projected transfer mode is an advantage for the stability of hybrid welding processes.     

Process Window for Nd:YAG Laser Welding of Super Duplex Stainless Steel

Super duplex stainless steel (SDSS), an advanced duplex stainless steel with higher alloying concentration, is employed widely in acidic atmospheres. In this study, we make an attempt to develop a process window for the pulsed mode Nd:YAG laser welding of SDSS, as reference maps, to identify the range of process parameters viz., laser power, welding speed, defocusing distance, and pulse frequency for obtaining a defect free full penetration welds. The eminence of the welds, based on the macrostructure, microstructure, and tensile strength, is reported. We obtain a complete penetration weld devoid of undercut, crating at the top and minimum heat affected zone (HAZ) with a overlapping factor of 80–90% and heat input at 100–200 J/mm. The experimental settings prevailing inside the preferred region of the process window exhibit a higher tensile strength as well.     

激光深熔焊焊缝表面形状的影响因素

从理论和实验两方面研究了各种物理和工艺参数对激光深熔焊焊疑表面形状的影响,并对改善表面质量的激光焊接工艺提出了建议。