不同焊接位置对5A90铝锂合金激光焊接质量的影响（英文）

针对铝锂合金激光焊接产生的成形不良和气孔缺陷,探究不同焊接位置对焊缝成形及气孔的影响,并对比分析不同焊接位置熔池受力状态、熔融金属流动和小孔动态行为,解释缺陷形成及其抑制机理。研究发现:不同焊接位置熔池受力状态和熔融金属流动决定焊缝成形。平焊时焊缝成形差、下榻严重;横焊时背面焊缝不连续,有飞溅;立向上焊时背面焊缝内凹严重;立向下焊可得到最优焊缝成形和最优的气孔缺陷。焊缝气孔受小孔动态行为影响,不同焊接位置气孔随热输入的变化规律一致,气孔先增后减,在仅熔池透状态下有气孔最大值。立上焊时小孔不稳定,焊缝气孔多且分布杂乱;立向下焊时小孔稳定性高,气孔最少,主要分布在焊缝中心线上。     

等离子弧焊接穿孔、传热与流动的耦合过程

本文建立了考虑穿孔效应的等离子弧焊接传热与流动的三维数学模型。在该模型中,开发出一种新颖的随小孔连动的热源模型,即能量密度仿照实际的焊接热物理过程随小孔增长而动态变化,有效地表征了热量沿厚度方向传输过程。同时应用体积流函数(VOF)方法追踪小孔界面,将小孔深度作为热源参数调控热源分布,实现了穿孔过程与熔池内传热及流动的动态耦合。针对实验工况,数值求解了穿孔焊接过程中动态热量传输和相应的焊接温度场,并考察了小孔界面及其周围熔融金属流动的演变过程;焊接熔池形状尺寸和焊件穿孔时间的计算值与实验数据吻合较好,验证了本文模型的正确性。     

用磁搅拌技术减轻和消除铍的焊接缺陷

在焊接时利用电磁搅拌技术可以起到细化晶粒，减轻或消除各种焊接缺陷的作用，有利于焊接接头质量的提高。电磁搅拌是在交变磁场的作用下产生的电磁力迫使焊缝熔池的液态金属改变原有运动模式和结晶状态，从而达到控制焊缝凝固组织、减少焊接缺陷的目的。电磁场与焊缝金属的相互作用有2个显著特点：使枝晶破碎、游离，加速枝状晶向等轴晶转变，扩大等轴晶的形成，使晶粒细化；促使焊缝气泡的分离与浮出，对减轻和消除焊接气孔有利。铍的熔焊由于结晶组织粗大和焊缝的高应力状态将导致焊缝开裂。采用高能束（激光）焊接，并且在进行铍的熔焊时加Al-si合金填充材料，再辅以合适的焊接工艺措施可以改善铍的焊接性能和防止铍的开裂。采用磁搅拌技术减轻和消除铍的焊接缺陷，需要在技术上考虑3方面的问题：（1）铍和Al-si合金填充材料都是非磁性材料，非磁性材料对电磁搅拌产生何种效果和影响。（2）与TIG（氩弧焊）焊接相比，激光焊接为无焊接电弧柔性载流导体，电磁场能否对激光焊接实现搅拌。（3）磁场应加在焊缝区域的什么位置才能使搅拌获得良好的效果。对于非磁性材料又无焊接电弧柔性载流导体的激光焊接，交变磁场式电磁搅拌装置显然对熔池起不到搅拌作用，焊缝的原有液态金属的运动规律不能被打乱，起不到细化晶粒和消除焊接缺陷的目的。     

等离子弧焊接熔池演变过程的模拟和验证

本文建立了描述等离子弧焊接熔池相变传热与流动的三维数理模型,考虑表面张力、电磁力和浮升力的作用,并针对等离子弧焊接特点,改进组合式体积热源模型,上部采用双椭球热源,下部采用圆锥体热源。重点分析了焊接熔池形状和温度场的演变过程,熔合线的模拟形状与实验焊缝吻合,较好地呈现了焊缝的凸起和熔池宽度,验证了数学模型和热源模型的正确性。本文还进一步开展了焊接功率和焊接速度的影响分析。研究结果表明,流动对焊缝形状的影响不容忽略,而表面张力在三个流动驱动力中占主导地位;焊接功率越大,焊接速度越小,越有利于焊件焊透,数值模拟得到优化的焊接功率和速度有益于实际焊接生产质量及效率。     

Al-Si合金熔体的氢含量及其对铍焊接气孔的影响

铍为脆性材料，在焊接时容易使焊缝开裂。为了防止焊缝开裂，途径之一是加延展性比较好的金属或合金(如Al-Si合金或银等)作填充材料进行钎接焊。但是，铍在非真空条件下焊接，在焊缝中出现的主要缺陷是焊接气孔和缩孔。人们早已知道，纯铝在焊接或铸造时的加热过程中会吸收环境中的氢，冷却时熔体要释放氢从而形成以氢为特征的氢气孔，进而影响铝加工的质量。这表明铝及铝合金焊接形成的气孔主要是与焊接时熔体的氢含量有关。那么，在加Al-Si合金焊接铍时，产生的气孔是否也与氢含量的关系，Al-Si合金熔体随温度升高氢含量有何变化趋势，Al-Si合金中的Si对铝熔体的吸氢起何作用。     

铍焊接填充材料的应用

铍的焊接常出现裂纹和气孔。焊接时加填充材料，然后再考虑接头结构设计、焊接工艺参数调整、焊前预热和焊后缓慢冷却等措施，它们之间协调匹配，可有效地阻止铍焊接产生裂纹。在焊接不开裂的情况下设法减轻和消除气孔缺陷。填充材料的加入，主要是改善焊缝的性能，减少焊接应力进而改善材料的焊接性。     

基于激光焊接的网络滤波器无铅化封装

 采用激光直接焊接的方法,研究网络滤波器的无铅化封装技术,通过3种不同的方式进行了实验研究和理论分析,获得了将网络滤波器中直径为0.10 mm的极细铜芯漆包线在不去除绝缘漆的情况下直接焊接到铝引脚上的方法和途径。结果表明：焊接时用激光照射铜芯漆包线,去除绝缘漆后再熔化高熔点的、流动性好的铜芯,熔化后的液态金属铜向下流动,包覆难于焊接的、流动性差、易氧化、易形成气孔等焊接缺陷的铝材引脚,然后再与铝发生溶解、扩散,最后形成良好焊点。这种不需去除绝缘漆的方法使焊接过程大大简化,且满足无铅化的要求;通过辅助电路,能在一定程度上提高焊接的可靠性,便于进行自动化。     

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。     

氧引入对气体熔池耦合活性TIG焊电弧的影响

气体熔池耦合活性TIG焊接方法是一种新型的活性焊接方法,该方法采用内外两层气体进行TIG焊,内层惰性气体保护熔池金属和钨电极,外层气体引入活性元素O,使焊缝熔深增加,并通过调节内外喷嘴的相对位置,简单方便地调节外层活性气体与熔池表面的耦合度,实现对焊缝成形和焊缝性能的控制。外层气体的引入对焊接电弧有着重要的影响,因此针对气体熔池耦合活性TIG电弧,采用Boltzmann作图法分析了外层气体为O2时不同耦合度下电弧等离子体的温度分布,在此基础上研究了电弧电压和电弧形貌的变化规律。结果表明,与普通TIG电弧对比,气体熔池耦合活性TIG焊时,外层气体引入氧可使电弧略有收缩,电弧中心温度升高,同时电弧电压上升;与内外层气体都为Ar的情况相比,外层采用O2对电弧的收缩作用更明显。当耦合度从0增加到2时,电弧中心温度和电弧电压都略有上升。在气体熔池耦合活性TIG焊中电弧收缩不明显,进行不锈钢焊接时熔深显著增加的主要机理不是电弧收缩。     

等离子弧焊接熔池演变过程的格子Boltzmann模拟与验证

本文应用基于分子动理论的格子Boltzmann方法,建立了描述定点等离子弧焊接熔池动态演变过程的二维数理模型,对相变过程的传热与流动现象开展模拟;根据焊接过程能量分布特点改进等离子弧的组合式热源模型,采用total-enthalpy模型求解温度、速度分布及追踪相界面。研究结果表明,模拟的熔合线形状与实验焊缝吻合,格子Boltzmann模拟得到的计算精度及计算效率均优于基于连续流体假设的有限容积法,验证了格子Boltzmann方法用于等离子弧焊接模拟的可行性和优越性;熔池中出现两个方向相反的环流,流动对焊缝形状的作用不容忽略;熔池的流动方式影响了温度场、速度场及二者协同度,直接影响固相线上的热量传递,促进了焊缝中部凸起的形成。     

Real-time monitoring of laser welding of galvanized high strength steel in lap joint configuration

Two different cases regarding the zinc coating at the lap joint faying surface are selected for studying the influence of zinc vapor on the keyhole dynamics of the weld pool and the final welding quality. One case has the zinc coating fully removed at the faying surface; while the other case retains the zinc coating on the faying surface. It is found that removal of the zinc coating at the faying surface produces a significantly better weld quality as exemplified by a lack of spatters whereas intense spatters are present when the zinc coating is present at the faying surface. Spectroscopy is used to detect the optical spectra emitted from a laser generated plasma plume during the laser welding of galvanized high strength DP980 steel in a lap-joint configuration. A correlation between the electron temperature and defects within the weld bead is identified by using the Boltzmann plot method. The laser weld pool keyhole dynamic behavior affected by a high-pressure zinc vapor generated at the faying surface of galvanized steel lap-joint is monitored in real-time by a high speed charge-coupled device (CCD) camera assisted with a green laser as an illumination source.     

Effect of keyhole characteristics on porosity formation during pulsed laser-GTA hybrid welding of AZ31B magnesium alloy

This paper experimentally investigates the relationship between laser keyhole characteristics on the porosity formation during pulsed laser-GTA welding of magnesium alloy. Based on direct observations during welding process, the influences of laser keyhole state on the porosity formation were studied. Results show that the porosities in the joint are always at the bottom of fusion zone of the joint, which is closely related to the keyhole behavior. A large depth to wide ratio always leads to the increase of porosity generation chance. Keeping the keyhole outlet open for a longer time benefits the porosity restriction. Overlap of adjacent laser keyhole can effectively decrease the porosity generation, due to the cutting effect between adjacent laser keyholes. There are threshold overlap rate values for laser keyholes in different state.     

Vision-based weld pool boundary extraction and width measurement during keyhole fiber laser welding

In keyhole fiber laser welding processes, the weld pool behavior is essential to determining welding quality. To better observe and control the welding process, the accurate extraction of the weld pool boundary as well as the width is required. This work presents a weld pool edge detection technique based on an off axial green illumination laser and a coaxial image capturing system that consists of a CMOS camera and optic filters. According to the difference of image quality, a complete developed edge detection algorithm is proposed based on the local maximum gradient of greyness searching approach and linear interpolation. The extracted weld pool geometry and the width are validated by the actual welding width measurement and predictions by a numerical multi-phase model.     

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.     

大功率光纤激光焊焊缝跟踪偏差红外检测方法

精确控制激光束使其始终对准并跟踪焊缝是保证激光焊接质量的前提.针对大功率(激光功率10 kW)光纤激光焊接304型不锈钢紧密对接焊缝(间隙为0-0.1 mm),研究一种基于红外热像的焊缝跟踪偏差检测新方法. 采用红外传感高速摄像机摄取焊接区域熔池红外动态热像,分析激光束对准和偏离焊缝中心时的熔池温度分布和红外辐射特性,以熔池匙孔形变参数和热堆积效应参数作为激光束与焊缝中心偏差检测特征值,通过图像识别技术研究和分析特征值与焊缝偏差之间的关系. 激光焊接试验结果表明,熔池匙孔形变参数和热堆积效应参数与焊缝偏差 关键词： 大功率光纤激光焊 焊缝跟踪偏差 红外热像 检测     

Combination of laser keyhole and conduction welding: Dissimilar laser welding of niobium and Ti-6Al-4V

Pulsed Nd:YAG laser welding of pure niobium plate to titanium alloy Ti-6Al-4V sheet in butt joint is studied regarding the laser/metal interaction modes. To obtain the optimized process parameters in dissimilar welding of Ti-6Al-4V/Nb, the melting ratio of laser beam energy for each weld counterpart is evaluated experimentally. Different laser welding modes of keyhole and conduction are predicted regarding the absorbed energy from the similar laser pulses on each weld counterpart. Laser keyhole and conduction welding were observed simultaneously through direct visualization of laser interaction with dissimilar metals using High Speed Imaging (HSI) system.     

Spectroscopic characterization of low-nickel copper welding with pulsed Nd:YAG laser

Effects of various operating parameters of 400 W pulsed Nd:YAG laser on welding of nickel-alloyed copper have been investigated. The induced plume spectra in case of using different assist gases and preheat temperatures have been analyzed and the effects of these key factors on melt features such as penetration depth, porosity and spattering have been attributed to the spectroscopic behavior of the plume. Moreover, the CuI electron temperature and its standard deviation as the spectroscopic responses of the plasma plume to various laser process parameters have been quantitatively evaluated at different average and peak powers and pulse energies. Also, the mentioned responses were utilized to justify the weld bead profile features, involving weld depth, width and their stabilities, at similar process parameters. The operating conditions of welding were optimized, regarding the results of spectroscopic observations and attributing them to the qualitative aspects of the melt pool.     

Numerical simulation of nanosecond pulsed laser welding of eutectoid steel components

This paper considers the micro-closed seam laser welding of two nearly eutectoid carbon steel grades. These materials are difficult to weld due to their poor ductility. In particular, in closed seam welding, the laser beam starts and finishes in the same point thus increasing the risk of cracks. A numerical simulation of micro-welding of nearly eutectoid steels by nanosecond pulsed laser is carried out to evaluate the weld pool dimension and the heat-affected zone extension. Optimized welding parameters and strategy are determined by means of simulation and they are successfully applied in the welding of a 1.0%C shaft and a 0.7%C gear.     

A keyhole volumetric model for weld pool analysis in Nd:YAG pulsed laser welding

This study presents a new model for analyzing the temperature distribution and weld pool shape in Nd:YAG pulsed laser welding. In the proposed approach, a surface flux heat transfer model is applied in the low laser energy intensity region of the weld, while a keyhole heat transfer model based on a volumetric heat source is applied in the high laser energy intensity region of the weld. The correlation between the intensity of the laser input energy and the geometric parameters of the volumetric heat source is derived experimentally. A series of MARC finite element simulations based on the proposed single pulse model are performed to investigate the shape and size of the weld pool given different laser energy intensities. A good agreement is observed between the simulation results and the experimental results obtained under equivalent single pulse welding conditions. Thus, the basic validity of the proposed model is confirmed.     

Characteristics of deep penetration laser welding of dissimilar metal Ni-based cast superalloy K418 and alloy steel 42CrMo

Experimental trials of autogenous deep penetration welding between dissimilar cast Ni-based superalloy K418 and alloy steel 42CrMo flat plates with 5.0 mm thickness were conducted using a 3 kW continuous wave (CW) Nd:YAG laser. The influences of laser output power, welding velocity and defocusing distance on the morphology, welding depth and width as well as quality of the welded seam were investigated. Results show that full keyhole welding is not formed on both K418 and 42CrMo side, simultaneously, due to the relatively low output power. Partial fusion is observed on the welded seam near 42CrMo side because of the large disparity of thermal–physical and high-temperature mechanical properties of these two materials. The microhardness of the laser-welded joint was also examined and analyzed. It is suggested that applying negative defocusing in the range of Raylei length can increase the welding depth and improve the coupling efficiency of the laser materials interaction.