Joining of dissimilar materials with friction stir welding

The welding and joining of dissimilar metals which have very different properties, such as aluminium and carbon steel, is considered to be a subject for research and development in the welding/joining sector continuing into the 21st century. There are also huge requirements and expectations for this sector.¹ Due to the aforementioned, the research and development of welding and joining of dissimilar materials have been carried out over many years; for instance, eutectic bonding of copper pipe and aluminium pipe was developed 30 years ago and this process is still applied for the heat pipes of refrigerators. Recently it has even progressed for applications in joining of wide plate materials of aluminium alloy and stainless steel by means of the vacuum rolling process² and also for weldments of aluminium alloy and carbon steel joined by means of friction welding and employed as automobile components.³ However, there are problems from aspects of cost and restrictions concerning the configurations for which joining is feasible using conventional welding and joining processes and these techniques have not yet reached the stage where they can be applied in a number of industrial sectors. Accordingly, an extensive programme of research and development has been deployed in recent years using fusion welding processes, such as electron beam and laser welding and brazing, diffusion bonding and also friction stir welding (FSW).⁴     

Methods of eliminating pollutant emissions from the work environment in welding and related processes

Abstract

The welding and joining of dissimilar metals which have very different properties, such as aluminium and carbon steel, is considered to be a subject for research and development in the welding/joining sector continuing into the 21st century. There are also huge requirements and expectations for this sector.¹ Due to the aforementioned, the research and development of welding and joining of dissimilar materials have been carried out over many years; for instance, eutectic bonding of copper pipe and aluminium pipe was developed 30 years ago and this process is still applied for the heat pipes of refrigerators. Recently it has even progressed for applications in joining of wide plate materials of aluminium alloy and stainless steel by means of the vacuum rolling process² and also for weldments of aluminium alloy and carbon steel joined by means of friction welding and employed as automobile components.³ However, there are problems from aspects of cost and restrictions concerning the configurations for which joining is feasible using conventional welding and joining processes and these techniques have not yet reached the stage where they can be applied in a number of industrial sectors. Accordingly, an extensive programme of research and development has been deployed in recent years using fusion welding processes, such as electron beam and laser welding and brazing, diffusion bonding and also friction stir welding (FSW).⁴     

异种材料真空电子束焊接研究现状分析

真空电子束焊接具有高能量密度、束斑直径和位置精确可控,焊接残余应力小,焊缝无污染等优点,因此,电子束焊接在异种材料连接领域的应用成为近年来研究的热点,并取得了大量的研究成果,部分已经在工业生产中得到了应用.由于电子束焊接属于熔化焊接,因此在异种金属连接中也存在冶金过程带来的困难.文中对异种材料的真空电子束焊接的研究现状进行了分析,对不同类型的异种材料接头真空电子束焊接中存在的问题和解决方法进行了总结,并提出了今后异种材料真空电子束焊接的研究重点.     

先进材料与异种材料电子束焊接研究进展

电子束焊接是近年来飞速进步、蓬勃发展的一种先进连接技术，随着技术工艺的日益成熟，其在工业领域的竞争力也日渐增强，已为工业部门所广泛接受.文中综述了电子束焊接在高温钛合金、高温合金、难熔金属、金属间化合物等先进材料与各类互相固溶的、难以互溶的异种材料连接方面的研究现状，对国内外在焊接缺陷控制、焊接工艺优化、焊接机理研究等方面取得的典型研究成果进行了简要介绍，并从中概括总结了先进材料与异种材料电子束焊接的具体问题，归纳阐述了先进材料与异种材料电子束焊接中所采用的能量控制与冶金调控等特色技术方法.     

Electrochemical corrosion behaviour of stir zone of friction stir welded dissimilar joints of AA6061 aluminium–AZ31B magnesium alloys

Joining of dissimilar metals will offer many advantages in transportation sectors such as fuel consumption, weight reduction and emission reduction. However, joining of aluminium (Al) alloys with magnesium (Mg) alloys by fusion welding process is very complicated. Friction stir welding (FSW) is a feasible method to join these two dissimilar alloys. Mixing these two metals together in stir zone (SZ) leads to poor corrosion resistance. In this investigation, an attempt has been made to understand the corrosion resistance of SZ of FSWed dissimilar joints of AA6061 Al alloy and AZ31B Mg alloy. Potentiodynamic polarization test was conducted by varying chloride ion concentration, pH value of the NaCl solution and exposure time. The corroded surfaces were analyzed using optical microscopy, scanning electron microscopy and XRD techniques. Of these three factors investigated, exposure time is found to be the most significant factor to influence the corrosion behaviour of SZ of friction stir welded dissimilar joints of Al/Mg alloys.     

激光滚压焊技术在异种金属连接中的应用

近来铝合金/钢、铝合金/钛合金等异种金属的连接在汽车等行业越来越受到重视。但是采用熔化焊来连接异种金属非常困难,同时扩散焊的效果也不很理想,主要是因为焊接过程中在界面处会产生较多的脆性金属间化合物。因此,急需一种高可靠性、高效率的新工艺对此类异种材料进行高质量的连接。激光滚压焊正是针对这一需求而开发的新型连接工艺。详细介绍了该工艺方法的提出背景、工作原理、界面上金属间化合物的特点以及所得到焊接接头的主要性能。     

Advances in friction welding process: a review

Abstract

Friction welding is now well established as one of the most economical and highly productive methods in joining similar and dissimilar metals. It is widely used in automotive and aerospace industrial applications. Friction welding is often the only viable alternative in this field to overcome the difficulties encountered in joining the materials with widely varying physical characteristics. This process employs a machine that is designed to convert mechanical energy into heat at the joint to weld using relative movement between workpieces, without the use of electrical energy or heat from other sources. This review deals with the fundamental understanding of the process. The focus is on the mechanism of friction welding, types of relative motions of the process, influence of parameters, heat generation in the process, understanding the deformation, microstructure and the properties of similar and dissimilar welded materials.     

Joining of molybdenum and its application

In this work fusion and solid state welding techniques for joining PM refractory metals are adressed. The weldability is discussed and evaluated by electron beam and friction welding experiments. EB-welding experiments were performed on rolled sheets made of different Mo-based materials. While a significant decrease in the mechanical properties was found for the weldments of unalloyed molybedenum and the alloy TZM, good weldability is given for Mo41Re. A welding procedure was established and used for the manufacturing of thin walled tubes. Rotary friction welding experiments were carried out on rod material of the Mo-alloys TZM and MHC. Suitable process parameter were determined and successfully transferred for the joining of tubular TZM parts.     

电镀阻隔层对钛/钢电子束焊接接头性能的影响

采用电子束熔化焊、电子束阻隔焊和电子束阻隔熔-钎焊方法来实现钛合金与不锈钢异种金属之间的连接。研究发现钛合金与不锈钢连接界面处产生的脆性金属间化合物是影响接头性能的关键因素。采用电子束直接熔化焊和阻隔熔化焊钛合金和不锈钢时,接头界面会产生贯穿性裂纹导致焊缝直接断裂。电子束阻隔熔-钎焊中利用熔化的不锈钢润湿未熔化的钛合金母材,并采用Ag、Cu作为中间层添加元素,在结合界面处形成了很好的阻隔屏障,减少了Ti/Fe界面的金属间化合物的产生,减缓了应力,实现了钛合金与不锈钢的冶金结合,接头抗拉强度约为100 MPa。电子束阻隔熔-钎焊得到的钛合金/不锈钢异种金属焊接接头焊缝正反面成形良好,X射线探伤未发现裂纹和气孔缺陷。     

Resistance spot welding aluminium to magnesium using nanoparticle reinforced eutectic forming interlayers

Successful joining of dissimilar metals such as Al and Mg can provide significant advantages to the automotive industry in the fabrication of vehicle bodies and other important components. This study explores dissimilar joining of Al–Mg using a resistance spot welding process to produce microstructurally sound lap joints and evaluates the impact of interlayer composition on microstructural evolution and the formation of intermetallic compounds within the weld nugget. The results indicated that mechanically sound joints can be produced, with fine equiaxed and columnar dendrites within the weld nugget. The presence of intermetallic compounds was also confirmed by the variation in the microhardness values recorded across the weld zone.     

Seal spot welding of steel and aluminium alloy by resistance spot welding: dissimilar metal joining of steel and aluminium alloy by Zn insertion

This research concerns a dissimilar metal joining of steel and aluminium (Al) alloys by means of zinc (Zn) insertion. The authors propose a joining concept for achieving strong bonded joints between Zn-coated steel and Al alloys. A eutectic reaction between Zn in the Zn coating and uniform Al–Fe intermetallic compound (IMC) layer at the joint interface, leading to a strong bonded joint. The ultimate aim of this research was to apply this joining concept in the resistance spot welding process for manufacturing vehicle bodies. As a practical issue characteristic to joints of dissimilar metals, anticorrosion measures against electrochemical corrosion must be undertaken. If there is moisture near a joint interface of dissimilar metals, electrochemical erosion will progress. Therefore, a sealing function that could prevent moisture intrusion is required. By applying the above-mentioned welding process to a set of metals with thermosetting resin spread in between, we realized seal spot welding, which not only prevented moisture intrusion but also retained high tensile strength. In this research, first, a cyclic corrosion test was performed on the seal spot-welded joint of galvanized (GI) steel, a steel grade widely distributed in Japan, and Al alloy was bonded by seal spot welding, and the following topics are discussed. Complete removal of sealant from the joint interface is the key to realizing the high tensile stress joint, because remaining sealant will lead to reduction in tensile strength. Therefore, heat generation at the interface was monitored by measuring electrical current and potential difference between the two electrodes, and a precise temperature control was performed. Moreover, the bonding process was clarified by stepwise analysis of the joint interface using optical microscopy, and a guideline for producing strong joints was proposed. And finally, a TEM observation also confirmed that the interface structure of the seal spot-welded joint was the same as joints without the resin; a thin and uniform Al–Fe IMC layer was formed and a strong metallurgical bonding was achieved.     

铝/钢搅拌摩擦焊金属间化合物调控研究进展

铝/钢异种金属的可靠连接是汽车行业实现轻质节能设计的重要途径. 铝和钢的热物理性能和化学性能差异大,采用固相焊方法连接较为适宜. 搅拌摩擦焊(friction stir welding, FSW)具有热输入低、高温停留时间短和焊接变形小等特点,在连接铝/钢异种金属上具有较大的优势和潜力. 铝/钢异种金属FSW高质量的核心技术之一为界面金属间化合物的调控. 基于铝/钢FSW固相连接机制,文中从焊接参数(焊接速度、焊具转速、偏移量、倾斜角和下压量)、焊具结构(搅拌针形貌、螺纹及锥角)和中间层(铝和锌等)设计等方面对界面金属间化合物调控的研究现状进行了综述,并围绕接头承载能力的提升总结了铝/钢FSW新技术(匙孔填充、自铆接及外源辅助FSW),并进一步展望了铝/钢FSW的发展趋势.     

Investigation of the Material Welding Using the High-Speed Liquid Impact

Feasibility to use the high-speed liquid impact for joining similar and dissimilar metals was investigated experimentally. An experimental setup that entails a launcher for projectiles formation and samples folders was constructed. The experiments involved joining of sandwiches containing two or three layers of metals were impacted by a high-speed projectile. The metals combinations included copper, brass, steel, and nickel alloys. The generated samples were examined visually, the strength of the joint was explored, and the integrity of the weld was estimated using ultrasound. In most of the experiments metallurgical bonding of joined metals was confirmed. The results of the ultrasound test demonstrated high quality of the generated joints. The performed experiments showed feasibility of the liquid impact-based welding. This process is the improvement of the explosion welding. Unlike the explosion welding impact-based process does not require special placing of work pieces while the stresses in the impact zone can be precisely directed and controlled. This article was presented at Materials Science & Technology 2007, Automotive and Ground Vehicles symposium held September 16-20, 2007, in Detroit, MI.     

Dissimilar friction welding of aluminium alloys to other materials

Friction welding makes it easier to set welding conditions and also confers greater reproducibility than other welding processes. Through being a solid-phase process, friction welding moreover makes it relatively easy to join dissimilar materials. Other advantages of friction welding include good operability, the lack of any need for special skills, and a convenient capability for incorporation in assembly lines without showers of sparks and similar hazards being generated. Friction welding is therefore extensively used in a wide variety of industries, such as automotive engineering, printing, etc. Joining of dissimilar materials as a characteristic friction welding application has been well researched,¹ reported,² and thoroughly explained with reference made to practical examples.³ In the current situation of materials development advancing apace in pursuit of various objectives, available data relating to joining of dissimilar materials remains scant. To meet resource- and energy-saving objectives, machinery and plant, transport machinery, etc. are now required to embody lighter weight in a well-established trend that can only serve to expand the use of light metals. Compared with ferrous metals, however, friction welding of light metals has been little documented.     

电子束钎焊的能量密度控制方法

基于电子束扫描轨迹和方式控制，提出了电子束钎焊能量密度控制方法及能量密度计算方法，以扫描电子束作为移动热源，电子束扫描轨迹和扫描方式根据钎焊接头的形状及要求设计，通过控制扫描点在工件加热区域的分配．可对接头各区域进行能量密度的高精度控制，在工件表面获得所需要的能量密度分布；也可以对异种金属电子束焊接进行能量输入比可调的不对称能量输入控制，可有效地控制接头两侧异种金属的熔化量，使接头两侧异种金属以适当的比例熔合。     

Al/Ni异种金属超声波点动焊接工艺及界面组织分析

对1060铝合金和N4镍合金异种金属进行了超声波点动焊接,优化了焊接工艺,分析了接头界面组织,焊接接头组织微观形貌和力学性能.结果表明,超声波焊接能够实现1060铝合金和N4镍合金异种金属的有效连接,能够得到韧性和强度都很高的焊接接头;确定了铝镍异种金属超声波焊接的焊接工艺参数为焊接压力25.2~36.0 MPa,焊接时间75~85 ms;当焊接压力为32.4 MPa,焊接时间为85 ms时,抗剪强度超过铝侧母材.焊接接头界面的XRD和EDS分析结果表明,接头界面存在由Al,Ni两种元素互扩散而形成的2 μm厚的反应扩散层.     

Study of weld strength variability for capacitor discharge welding process automation

Abstract

The capacitor discharge welding (CDW) process is an autogenous, rapid solidification joining process ideal for joining small parts incorporating dissimilar metals. Potential applications include welding of solderless electrical contacts, cutting tool inserts, and automotive valves. Because of high cooling rates, in excess of 10⁶ K s^-1, the production rate for CDW processes is potentially very high. However, potential industrial users are hesitant to use the CDW process, owing largely to the unavailability of automated process control. The objective of the present study was to investigate the source of weld strength variability in CDW as a foundation for process automation and control. Results show that welding time significantly affects weld strength variability for both high thermal conductivity and high gas content materials, independent of the t_w/2RC ratio.     

Ultrasonic Welding of Hybrid Joints

A central research field of the Institute of Materials Science and Engineering at the University of Kaiserslautern (WKK), Germany, is the realization of innovative hybrid joints by ultrasonic metal welding. This article gives an overview of suitable ultrasonic welding systems as well as of essential machine and material parameters, which influence the quality of the welds. Besides the ultrasonic welding of dissimilar metals such as Al to Cu or Al to steels, the welds between newly developed materials like aluminum foam sandwiches or flat flexible cables also can be realized. Moreover, the joining of glass and ceramic to sheet metals is a point of interest at the WKK. By using the ultrasonic metal welding process, it is possible to realize metal/glass welds with tensile shear strengths of 50 MPa. For metal/ceramic joints, the shear strengths values up to 150 MPa were measured. Finally, selected results about the occurring bonding mechanisms will be discussed.     

Refill Friction Stir Spot Welding of Similar and Dissimilar Alloys:A Review

Refi ll friction stir spot welding, also known as friction spot welding(FSpW), is a solid-state welding process suitable for spot joining of lightweight materials. Through the eff orts of improving joint quality for similar and dissimilar materials, for example, aluminum and magnesium, this joining technology is well developed. The joining mechanism and process characteristics of FSpW have been widely studied. However, the application of FSpW in industry has not been entirely successful. In this review article, the research of similar and dissimilar material joints, such as, Al/Cu, Al/Ti, Al/Mg and Al/Steel, is summarized. The microstructural features and mechanical properties of the joints, welding tool and the application development are discussed in detail.