Research and Progress in Laser Welding of Wrought Aluminum Alloys. I. Laser Welding Processes

With the wide application of Al alloys in automotive, aerospace and other industries, laser welding has become a critical joining technique for aluminum alloys. In this review, the research and progress in laser welding of wrought Al alloys have been critically discussed from different perspectives. The primary objective of this review is to understand the influence of welding processes on joint quality and to build up the science base of laser welding for the reliable production of Al alloy joints. Two main types of industrial lasers, carbon dioxide (CO₂) and neodymium-doped yttrium aluminum garnet (Nd:YAG), are currently applied but special attention is paid to Nd:YAG laser welding of 5000 and 6000 series alloys in the keyhole (deep penetration) mode. In this part of the review, the main laser welding processing parameters including the laser-, process-, and material-related variables and their effects on weld quality are examined. In part II of this article in this journal, the metallurgical microstructures and main defects encountered in laser welding of Al alloys such as porosity, cracking, oxide inclusions, and loss of alloying elements are discussed from the point of view of mechanism of their formation, main influencing factors, and remedy measures. In part II, the main mechanical properties such as hardness, tensile, and fatigue strength and formability are also discussed.     

Nd:YAG激光与半导体激光复合焊接对铝合金焊缝组织和性能的影响

目的 提高铝合金的焊缝抗拉强度,解决铝合金焊接过程中的裂纹缺陷。方法 采用脉冲Nd:YAG激光与半导体激光复合焊接铝合金,先用Nd:YAG激光形成焊接熔池,然后用半导体激光对熔池进行加热保温,获得无裂纹的焊缝,并对焊缝进行抗拉强度测试。结果 与单独的Nd:YAG激光焊接相比,Nd:YAG激光与半导体激光复合焊接的铝合金焊缝抗拉强度提高了50%,达到193MPa,为母材抗拉强度的90%。结论 2束激光的结合延长了熔池的冷却凝固时间,从而有效避免了热裂纹,减少了焊接缺陷,提高了焊接质量。     

Effect of laser welding parameters on fusion zone morphological,mechanical and microstructural characteristics of AISI 304 stainless steel

Nowadays, the Nd:YAG laser has been a promising key tool for joining thin components. In this research, mechanical and microstructural properties of laser welded thin austenitic stainless steel sheets were investigated with experimental investigations, as a function of laser welding parameters. Butt welded joints were made using a Nd:YAG laser in the pulsed wave mode. The appropriate laser welding parameters were found in order to obtain quality and strong weld seam. The pulsed laser seam welding process is controlled by a variety of parameters. We focus on the effects of the several processing parameters on mechanical and microstructural characteristics of joint and weld quality. The aim of this research was to evaluate the influence of these processing parameters on joint strength and microstructure. And also we examined the weldability of stainless steels in butt joint configuration by a pulsed Nd:YAG laser beam.     

Continuous Wave ND:YAG Laser Welding of Sand-Cast ZE41A-T5 Magnesium Alloys

A continuous wave 4 kW Nd:YAG laser system was used to weld 2-mm butt joints of sand-cast ZE41A-T5 magnesium alloys at a power of 2.5 kW, welding speed of 6.0 m/min, and defocusing distance from - 2 to + 3 mm for the material in the machined surface conditions. It was found that the adjustment of defocusing distance greatly influences the establishment of conduction or keyhole mode welding. Conduction welding is obtained at a power density of 4.0 × 10⁵ W/cm². Keyhole welding is reached at a threshold irradiance of 1.5 × 10⁶ W/cm². The fusion zone consists of refined equiaxed grains formed through cellular growth in the Zr-containing magnesium alloys. The partially melted zone is rather narrow, only a few grains wide. No grain growth or coarsening but softening is observed in the heat affected zone (HAZ). The weld defects observed include three main types: imperfect shape, cavities, and weld cracks. The mechanisms of their formations are discussed. In addition, the original cast quality was found to have a significant influence on the formation of defects such as underfill, surface depression, porosity, and burn-through during laser welding.     

Microstructural and mechanical characterization of laser beam welded AA6056 Al-alloy

Laser beam welding is considered to be a suitable joining process for high speed, low distortion, and high quality fabrication of aircraft structures manufactured from aluminum alloys, which are mainly preferred due to their favourable properties, such as high strength to weight ratio, ease of forming and high thermal and electrical conductivity. However, the laser beam welding of 6000 series aluminum alloys may exhibit a tendency to solidification cracking, and porosity may be a major problem unless appropriate welding parameters and filler metal are employed.In this study, the microstructural aspects and mechanical properties of laser beam welded new generation aluminum alloy, namely 6056, developed especially for aircraft structures, are investigated. A continuous wave CO₂ laser using AlSi12 filler wire was employed. A detailed microstructural examination of the weld region was carried out by Scanning Electron Microscopy (SEM). Standard tensile and microflat tensile specimens extracted from the welded plates were tested at room temperature for the determination of general and local mechanical properties of the welded joints. Extensive microhardness measurements were also conducted. Crack growth mechanisms of the joints produced were also determined by conducting fatigue tests under various stress ratios (i.e., 0.1 ≤ R ≤ 0.7).     

Laserstrahlschweißen von Titanwerkstoffen unter Berücksichtigung des Einflusses des Sauerstoffes

Influence of the oxygen content in the shielding gas on microstructure and mechanical properties of laser welds of titanium and titanium alloys In the present work, a new tool concept for laser welding of titanium in high volume production has been presented and evaluated. Through the innovative application of a six‐layer metal web it is possible to calm the argon gas flow and avoid pernicious turbulences during welding. The integration of the mentioned metal web at the base of an open welding chamber allows the automated welding of highly reactive materials, such as titanium, under atmospheric pressure and inert shielding conditions. The higher density of argon relative to air offers the unique possibility to leave the chamber open on the top, so that a higher degree of flexibility than gas shielding devices for TIG welding, especially for industrial robots, is attained and can be successfully used for industrial mass production. Furthermore this device is important for welding three‐dimensional contours or to shield the regions of overlap (in overlapped joints) where shielding gas trailers are unsuccessful. By means of the presented gas shielding procedure and a modern laser welding process such as Nd:YAG laser welding, systematic investigations on the effect of oxygen on the microstructure as well as on the mechanical properties of reference bead‐on‐plate weldments could be performed for the first time. As a result of these welding trials it can be concluded that in order to avoid discolorations and hardness increase, lower restrictions to the purity of the shielding gas, in comparison to TIG welding condition, can be allowed. The maximum tolerable value of oxygen in the welding atmosphere was found to be approximately 1000 ppm for laser welding. On the contrary the maximum value for TIG welding is about 30 ppm. Further investigations on the microstructural and mechanical properties of the joints confirm that the optical quality assurance criteria for TIG welding due to the standards of aircraft construction transferable to Nd:YAG welding are.     

GH4145激光点焊工艺及接头性能研究

目的研究不同工艺参数下高温合金的微激光点焊接头性能。方法利用Nd:YAG激光器对厚度为0.23 mm和0.13 mm的GH4145进行搭接点焊,利用微型拉伸机、金相显微镜、硬度计对接头的物理性能进行测试,并观察组织结构。结果脉宽长度为6.0 ms,输出功率百分比为20%(输出功率16 W)时,最大拉伸剪切力为178.59 N,靠近焊点中心位置两边测试点硬度分别达到HV517和HV506。结论接头表面熔化尺寸、焊接接头的拉伸剪切力和硬度随着激光功率的增大而增大,增大到一定值时停止变化,不同参数下达到不同的最大值,组织无明显规律变化。近表面处出现等轴晶,表面以下至熔合线的显微组织为树状晶。通过激光搭接点焊将两片GH4145连接,接头处拉伸剪切力、硬度均低于母材,功率增大有助于提高接头的抗拉强度。     

6009铝合金光纤激光-MIG电弧复合焊和光纤激光焊工艺对比研究

采用光纤激光-MIG 复合焊和光纤激光焊分别对6009铝合金进行焊接,研究两种焊接方式下焊接接头的成型性、显微组织、拉伸性能、显微硬度、断口形貌的不同。研究表明：激光电弧复合焊的焊接速度是激光焊接的3倍;相比于激光焊,激光电弧复合焊焊缝中心显微组织更加细小;接头的抗拉强度达到母材的63%以上,而激光焊接的抗拉强度仅仅只有母材的38%;显微硬度试验表明：复合焊存在软化区,而激光焊接几乎没有软化区;断口分析表明：复合焊和激光焊的拉伸断口都是典型的韧窝状态,但是复合焊接的韧窝更加均匀。     

Fügen von Magnesium und Magnesiumlegierungen

Welding of Magnesium and Magnesium alloys Magnesium is mainly connected by screws. In this paper the results of experiments with different welding processes will be presented. The following methods have been applied: TIG, MIG, Nd: YAG‐Laser and CO₂‐Laser welding, electron beam welding and High Power Diode Laser welding.     

钛/铝异种合金脉冲激光焊接接头裂纹产生机理

目的 对0.8 mm厚的Ti6Al4V钛合金和2 mm厚的AA6060铝合金薄板进行脉冲激光焊接,分析异种轻合金激光焊接裂纹产生的机理及界面结合机理。方法 采用扫描电镜、EDS能谱以及显微硬度计等微观表征分析方法,对焊接接头的形貌特征、成分以及显微硬度进行分析,探索焊接接头处裂纹产生的原因。结果 钛/铝脉冲激光焊接性较差,接头存在严重的裂纹缺陷,裂纹多集中在焊缝与铝母材交界处以及焊缝中心区域位置,主要以热裂纹为主;接头焊缝可能存在大量的Ti-Al金属间化合物以及少量未熔的钛,其界面层主要成分推测为层状TiAl和外层锯齿状的TiAl3;接头整个焊缝区域的平均显微硬度为HV0.1420,其硬度水平远远高于焊缝两侧铝合金母材,也高出钛合金母材很多。结论 钛铝金属间化合物使钛铝焊接接头焊缝区脆性增大,另外接头焊缝区存在较大的组织应力、热应力、拉压应力、拘束应力等复杂应力,致使焊缝内存在较严重的裂纹缺陷。     

Optimization of weld bead geometry of laser welded ANSI 304 austenitic stainless steel using grey-based Taguchi method

This paper investigates the quality characteristics of the welding geometry of the laser welding process for the ANSI 304 austenitic stainless steel, with the use of a pulsed Nd:YAG laser welding system. Laser welding of 2 mm thick ANSI 304 stainless steel is performed at three different levels of three factors, i. e., peak power, welding speed and pulse duration. In this study, a multi-response optimization problem is developed to achieve weld bead geometry with full penetration as well as a narrow bead width and minimum crater. Grey relational analysis based on Taguchi orthogonal array is used to present an effective approach for the optimization of laser welding process parameters. Regression equations between the welding parameters and the bead dimensions for laser welded austenitic stainless steels are developed, which are used in predicting the penetration, width and crater. Finally, the equations are tested for values different from the levels of the parameters in the orthogonal array. It will be beneficial to engineers for continuous improvement in laser welded product quality.     

The influence of laser welding parameters on the microstructure and mechanical property of the as-jointed NiTi alloy wires

The Nd:YAG laser welding was used to join the binary NiTi alloy wires with different compositions(Ti-50.0 at.%Ni and Ti-50.9 at.%Ni) which had the same diameter of 1 mm. The wires were welded with different parameters, including impulse width and welding current. The aim was to assess the influence of the laser-welding process on the microstructure and mechanical properties of the welded joint of binary NiTi wires. The optical microscopy (OM) and the metallographic microscopy (MM) were used to analyze the microstructure of the welded joints. The tensile test and the differential scanning calorimetry (DSC) were carried out to examine the ultimate tensile strength and the reverse martensitic transformation temperatures of the welded joints. It was found that the welding current and the impulse width had great influence on the quality of the welded joints, an optimal parameter combination would remove the pores and micro-cracks appeared in the fusion zone, and result in good mechanical properties such as higher fracture strength and elongation. The laser welding had a few effect on the reverse martensitic transformation temperatures of the welded joints.     

激光选区熔化成形高强铝合金晶粒细化抑制裂纹研究现状EI北大核心CSCD

高强铝合金(2×××,7×××等)因具有比强度高、加工性好等优点而被航空航天、汽车等领域广泛应用。随着大推重比飞行器设计及汽车轻量化技术的发展,轻质结构材料的需求日益增加,同时零部件也面临着“薄壁化、中空化、复合化”的发展趋势,高强铝合金的传统加工方法越来越难以满足要求。近年来,激光选区熔化成形(selective laser melting,SLM)作为一种常见的金属增材制造技术(additive manufacturing,AM)在复杂零部件成形领域受到关注,有望成为进一步拓宽高强铝合金应用领域的新兴技术。然而,SLM成形高强铝合金因易产生周期性热裂纹和粗大柱状晶不良组织等问题而发展缓慢,晶粒细化是克服增材制造高强铝合金这一固有热裂问题的关键所在。本文综述了近年来SLM成形高强铝合金显微组织和力学性能调控等方面的研究进展,归纳了不同体系合金的力学性能,重点阐述了抑制SLM成形高强铝合金中热裂纹形成的主要策略,包括SLM工艺参数优化以及通过微合金化或添加纳米颗粒细化晶粒等方法。指出当前研究存在的主要问题是合金成分的改变对材料综合性能以及热处理制度的影响规律尚不清晰等,并展望了未来的发展趋势,如SLM成形新型高强铝合金成分设计与综合性能评价、利用后处理工艺等手段进一步提升合金综合性能以及专用晶粒细化剂的设计与细化机制探究等。     

Q-switch Nd:YAG laser welding of AISI 304 stainless steel foils

Conventional fusion welding of stainless steel foils (<100 μm thickness) used in computer disk, precision machinery and medical device applications suffer from excessive distortion, formation of discontinuities (pore, void and hot crack), uncontrolled melting (melt-drop through) and poor aesthetics. In this work, a 15 ns pulsed, 400 mJ Nd:YAG laser beam was utilized to overcome these barriers in seam welding of 60 μm thin foil of AISI 304 stainless steel. Transmission electron microscopy was used to characterize the microstructures while hardness and tensile-shear tests were used to evaluate the strengths. Surface roughness was measured using a DekTak profilometer while porosity content was estimated using the light microscope. Results were compared against the data obtained from resistance seam welding. Laser welding, compared to resistance seam welding, required nearly three times less heat input and produced welds having 50% narrower seam, 15% less porosity, 25% stronger and improved surface aesthetics. In addition, there was no evidence of δ-ferrite in laser welds, supporting the absence of hot cracking unlike resistance welding.     

不锈钢和钛合金异种金属焊接研究进展

不锈钢和钛合金异种焊接在化工、航空和核工业等领域均有广泛的应用,但不锈钢和钛合金因理化性能的差异,焊接界面常形成大量脆性金属间化合物,无法得到优质的焊接结果。以扩散焊、激光焊和电子束焊为主总结了不同焊接方法的工艺参数和接头组织成分对不锈钢和钛合金焊接质量的影响,展望了不锈钢与钛合金异种金属焊接的发展趋势。     

Fatigue Strength Assessment of Laser Beam Welded Joints Made of AA7075 and Magnetic Pulse Welded Joints Made of AA7075 and 3D-Printed AlSi10Mg

The use of 7000 aluminum alloys has an important role in future lightweight structures in the field of mobility due to the low density and high strength. However, these alloys can only be fusion welded to a limited extent because welding defects can rarely be prevented. For this reason, investigations are carried out to identify the most suitable welding parameters for two processes: laser beam and magnetic pulse welding. Herein, laser beam welding is successfully used to manufacture a roll-formed and longitudinally welded pipe made of AA7075 and joined by magnetic pulse welding with a 3D-printed lug-tube made of AlSi10Mg. The fatigue strength of these pipe joints and of laser beam welded butt joint specimens is determined using load-controlled fatigue tests. For the characterization of the specimens, cross sections are prepared and examined metallographically, which reflect the local weld seam geometry in the joining area. A fatigue assessment is made using linear-elastic approaches. The reference radius concept is applied to map the influence of geometric notches on the fatigue strength, assuming linear-elastic stress–strain behavior. It is shown that the recommended notch stress fatigue class FAT 178 (von Mises stress) can be applied for a safe and reliable fatigue assessment.     

Nd:YAG激光焊接对铝锂合金组织和织构的影响

采用Nd:YAG激光进行了5A90铝锂合金薄板的对焊实验,借助光学显微镜、扫描电镜及EDS能谱、背散射衍射技术测试了焊缝的显微组织、合金元素分布及焊缝中的微观织构,并与母材进行了比较。结果表明:Nd:YAG激光焊接使5A90铝锂合金的微观组织和微观织构发生了很大的变化。焊缝区呈现出大量的等轴枝晶组织,这是由于焊缝中存在较多的异质形核点和较高的成分过冷度。焊缝中织构呈随机分布的状态,激光焊接完全改变了母材面心立方金属的冷轧织构组织。     

Nd∶YAG激光透明陶瓷的研究进展

作为新一代固体激光增益介质,Nd∶YAG透明陶瓷以容易制造、成本低、易于实现大尺寸生产等优势,正逐步取代单晶和玻璃材料,应用前景十分广阔。从Nd∶YAG透明陶瓷光学质量的提升、激光输出特性以及实现Nd∶YAG透明陶瓷高功率激光输出3个方面,分别回顾并总结了我国、日本、美国、欧洲和俄罗斯关于Nd∶YAG激光透明陶瓷的研究进展,并概述了我国及日本关于复合结构及共掺杂Nd∶YAG透明陶瓷的发展情况。最后总结并展望了当前Nd∶YAG激光透明陶瓷的发展趋势和存在的主要问题。     

Materials Behavior in Laser Welding of Hardmetals to Steel

Tool manufacturing industry faces the problem of permanently joining hardmetals to steel holders with high shear strength. The mostly used welding process still is brazing. However, brazed joints have poor lifetimes, mostly when high temperatures are achieved and often break in operation. In a previous study about the ability of CO₂ and Nd:YAG lasers to weld hardmetals to steels, it was found that Nd:YAG lasers, working in continuous wave mode, could be used especially for welding hardmetals with Co content around 12%. This article discusses the materials behavior under laser radiation and analyzes the microstructural features observed.     

Gap-free fibre laser welding of Zn-coated steel on Al alloy for light-weight automotive applications

As a result of new policies related to global warming announced by the European Union, avoiding unnecessary energy waste and reducing environmental pollution levels are becoming a major issue in the automotive industry. Accordingly, the lap welding of Zn-coated steels process, which is commonly used for producing car doors, has been gradually developed to lap welding of Zn-coated steel to light materials, such as Al alloy, Mg alloy and composite materials, in order to effectively reduce the vehicle weight. In certain part of car manufacture, organic glues are used to temporally join the Zn-coated steels and Al alloys before permanent welding takes place. The stability of such temporary joining by glues needs improving. Laser “stitching” or low strength welding could be considered as an alternative. However, challenges exist in joining Zn-coated steel on Al alloy by laser welding, due to significant differences of material properties between the two welding materials. Porosity, spatter and intermetallic brittle phases are readily produced in the weld. In this study, the effects of welding speed, laser power, number of the welding passes and type of shielding gas in gap-free welding of Zn-coated steel on Al alloy were investigated using a 1 kW single mode continuous wave fibre laser. Results show that a weld with higher shear strengths in the laser stitching application and less intermetallic phases could be obtained when nitrogen gas was used as the shielding gas. The corrosion resistance and the surface finish of the weld could be improved in double pass welding, especially when argon gas was used as the shielding gas.