Microstructure and hardness of friction stir welded 7075 aluminium alloy joints

Friction stir welding (FSW) is a process which induces a reduction in flow stress owing to friction heat generated by pressing a protruded object into a solid material and rotating it at high speed. It induces part of the material to have plastic flow owing to friction force in order to join materials together.¹ The FSW method was developed for the welding of aluminium alloy plates which have an extremely large number of restrictions when using fusion welding processes. However, the range of its employable usages has been expanding rapidly by including, as its applicable materials and processes, alloys with Cu,² Ti,³ Mg⁴ and Fe⁵ as well as dissimilar material welding of these materials.     

Microstructures and properties of friction stir welded 304 austenitic stainless steel

Friction stir welding (FSW) is a solid phase joining process which makes use of friction and was developed in 1991 by TWI (The Welding Institute) of Britain.¹ This welding process received attention as a joining process to solve the problems associated with fusion welding of Al alloys and active research into the applications of this technique has been progressed by numerous research institutions, at home and abroad. As a result, this process was made fit for practical use in less than ten years of development and has been applied extensively in the manufacture of aerospace equipments,² rolling stock³ and automobile components.⁴     

Comparative study on fatigue properties of friction stir and MIG-pulse welded joints in 5083 Al-Mg alloy

The objective of this investigation was to compare the fatigue properties of friction stir welds with those of MIG-pulse welds. The 5083 Al-Mg alloy was welded by single pass friction stir welding（FSW） and double-sided MIG-pulse welding. The results show that friction stir（FS） welds have a better appearance than MIG-pulse welds for the lack of voids, cracks and distortions. Compared with the parent plate, FSW welds exhibit similar fine grains, while MIG-pulse welds display a different cast microstructure due to the high heat input and the addition of welding wire. The S-N curves of FSW and MIG-pulse joints show that the fatigue life of FS welds is 18 - 26 times longer than that of MIG-pulse welds under the stress ratio of 0.1 and the calculated fatigue characteristic values of each weld increase from 38.67 MPa for MIG-pulse welds to 53.59 MPa for FSW welds.     

Friction stir welding of copper and copper alloys

Copper, through having good thermal conductivity and a relatively high melting point, generally requires preheating treatment to maintain satisfactory penetration during arc welding, ranking as a hard-to-weld material. Like aluminium and magnesium, however, copper is basically a soft metal and can therefore be relatively easily joined by friction stir welding. Available FSW research has focused on fabrication of copper (oxygen-free copper) containment canisters for nuclear waste,^1-6 fabrication of copper backing plates for sputtering devices by FSW seal welding,^{7, 8} and some other applications,⁹ whereas FSW research on copper alloys has thus far been little documented.^{10, 11} Related research topics include studies of Al alloy to Cu alloy dissimilar joints^{12, 13} as well as - although not quite the same as friction stir welding - friction stir processing of Ni-Al bronze for casting structure modification^14-16 and friction stir processing of a Cu-Mn alloy for surface modification purposes.¹⁷     

Development of an all-position YAG laser butt welding process with addition of filler wire

Construction of electric power generating stations and chemical plants routinely involves the provision of large numbers of fixed welded pipelines. Conventional arc welding, while only achieving a slow welding speed, specifically requires welds to be laboriously built up in multiple layers inside large grooves during welding of thick plates in what is essentially a highly elaborate and time-consuming process.^{1, 2} On the other hand, laser welding, in the wake of high-power enhancement of welding facilities seen in recent years, while allowing high-speed welding of thick plates, requires welds to be fitted up with a high degree of accuracy and small gap tolerance in order to produce good-quality joints. Electron beam welding has further been developed as an alternative process for welding of fixed pipelines,³ although this process faces some important problems, such as availability of bulky equipment for evacuation of welds and restricted applications to large-diameter pipes to ensure sufficient access for evacuation of pipes on their inside.     

Flashing phenomena in square wave alternating current. Flash welding control by use of PWM inverter power supply

Flash welding, through conferring a number of important advantages, such as high productivity, good-quality welds, and suitability for welding of components with large cross-sections, is extensively used for shop welding of rails, plating of hot coils, welding of wheel rims, etc.^1-3 More compact welding facilities are also being sought through further exploitation of mechanical control technology for practical applications in job-site welding of rails, H-steel sections, etc.⁴     

喷射成形7475铝合金FSW工艺与性能

采用搅拌摩擦焊（FSW）方法对厚度为4 mm的喷射成形7475铝合金进行了焊接工艺及性能研究,通过优化搅拌头的形状和尺寸,调整焊接工艺参数得到了表面成形良好的焊接接头,经过力学性能测试和微观分析.结果表明,当焊接工艺参数选择合适时,可得到外形美观、无缺陷的焊缝;如果工艺参数选择不当,则会出现沟槽、飞边和隧道形缺陷;还发...     

基于温度场分析的航空铝合金薄壁件搅拌摩擦焊工艺参数优化设计

目前已经有对于不同厚度的铝合金的搅拌摩擦焊接(friction stir welding,FSW)进行研究,并研发出一系列的焊接设备和工艺保证焊接质量的可靠与有效.但对于超薄的铝合金焊接,搅拌摩擦焊还存在一定的限制,如由于工艺参数选取不当造成焊接温度的太低或过高,严重降低焊缝的力学性能.通过分析搅拌摩擦焊传热机理,研究薄壁件徽搅拌摩擦焊接工艺参数选取的计算模型,并对模型计算出的工艺参数进行DEFORM焊接温度场分析,最后通过设计基于立式加工中心的微搅拌摩擦焊试验来验证计算模型和焊接温度场分析的合理性.     

Effects of welding parameters and tool geometry on properties of 3003-H18 aluminum alloy to mild steel friction stir weld

Defect-free butt joints of 3003 Al alloy to mild steel plates with 3 mm thickness were performed using friction stir welding (FSW). A heat input model reported for similar FSW was simplified and used to investigate the effects of welding speed, rotation speed and tool shoulder diameter on the microstructure and properties of dissimilar welds. The comparison between microstructure, intermetallics and strength of welds shows the good conformity between the results and the calculated heat input factor (HIF) achieved from the model. The joint strength is controlled by Al/Fe interface at HIF of 0.2–0.4, by TMAZ at HIF of 0.4–0.8 and by intermetallics and/or defects at HIF>0.8.     

1060／3003铝合金搅拌摩擦焊焊接接头材料流动规律研究

搅拌摩擦焊中，材料的流动状态对焊件性能有很大影响。对5mm厚的1060／3003铝合金板材进行了搅拌摩擦焊连接。通过对1060／3003铝合金焊件焊核区腐蚀，研究了焊核区金属的流动形态。分析了不同工艺参数下垂直截面和水平截面的金属流动形态。结果表明：工参数对搅拌摩擦焊焊核区金属的流动形态有很大影响。通过使用较高的工具旋转速度和合适的焊接速度可以获得稳定、质量良好的搅拌摩擦焊接头。     

Friction welding of Cr-Zr copper alloy

Copper and copper alloys have a higher thermal conductivity than even aluminium, itself regarded as having good heat conduction. When materials with high thermal conductivity are joined, the heat rapidly diffuses in the base metal in a way that generally results in poor weldability due to the difficulty of concentrating heat in welds. To obtain sound welds with satisfactory penetration during fusion welding of copper alloys, it is necessary to ensure high-temperature preheating and high interpass temperatures. Copper alloys are also reported to face problems such as solidification cracking and blowhole formation.¹ To solve these problems, it is necessary to perform welding at low heat input for a short time, which are conflicting requirements because of the high heat conduction.     

Laser weldability of high-strength steel sheets in fabrication of tailor welded blanks

Tailor welded blanks (TWBs) - pressing blanks arranged to combine, by welding, multiple steel sheets of different thicknesses and properties, and which may or may not have been surface-treated - are now extensively used in the automotive industry for fabrication of car body panels. TWBs were initially used at mass production level in Germany in the early 1980s and have since seen rapidly increasing engineering applications worldwide.^{1, 2} TWBs were originally viewed as a way of boosting material yields through reuse of pressed-off edge material as well as of cutting manufacturing costs by reducing the number of component spot welds, number of welding operations, and number of pressing dies through integral forming of multiple pressings after pre-welding of blanks from conventional spot welding production.     

2219铝合金FSW/VPPA交叉焊缝气孔缺陷

2219铝合金在搅拌摩擦焊（FSW）后,进行变极性等离子弧焊（VPPA）十字交叉焊接,其交叉接头存在气孔缺陷.针对6 mm 2219铝合金进行FSW/VPPA交叉焊接试验,探究了交叉焊缝的气孔类型,分别对比不同FSW热输入量、不同的VPPA焊接速度对交叉焊缝气孔缺陷程度的影响.结果表明,FSW热输入量越大,交叉焊缝气孔缺陷程度呈下降趋势,这与FSW过程产生瞬时空腔有关;而VPPA焊速越大,交叉焊缝气孔缺陷程度呈上升趋势.因此,为了抑制FSW/VPPA交叉焊缝气孔的产生,可以对FSW过程进行惰性气体保护、适当地提高FSW热输入量以及降低VPPA焊接速度.     

Joint characteristics and dissimilar materials joining of pure-Al/5083 by friction stir welding

Friction stir welding (FSW)^1,2, developed in 1991 by The Welding Institute, UK is a joining process which overthrew welding concepts which existed at the time; its application has been progressed not only for soft alloys including aluminium, but also, in recent years, for steel.³ Sato and others carried out friction stir welding on 1080-O and 5083-O materials and investigated variations in the hardness.⁴ Ten years or so have passed since the development of friction stir welding, the process has been globally investigated and widely employed in various sectors such as vehicles, ships and the aerospace industry. Furthermore, investigations have also been carried out into the manufacture of dissimilar metal joints. For example, Enomoto studied 2024/AC4C cast alloy and reportedly obtained satisfactory joints.⁵ Li and others have investigated 2024/6061 and reported that both alloys are distributed at the weld zone in a stratified and complex manner.⁶     

Microstructure and properties of friction stir welded aluminium alloys

Aluminium alloy 7136 belongs to the Al–Zn–Mg–Cu group of aluminium alloys strengthened by precipitation. These alloys offer very good properties, i.e. high strength combined with good corrosion resistance, which makes them suitable for aerospace applications. The limited range of applications of these alloys is due to problems associated with their welding. The Al–Zn–Mg–Cu alloys are classified as non-weldable. The aim of this study was to determine the quality and properties of friction stir welded (FSW) joints of alloy 7136-T76. This article presents the results of a detailed study into the microstructure and mechanical properties of FSW welds. The paper demonstrates that the FSW method is suitable for joining Al–Zn–Mg–Cu alloys. The FSW joints are of good quality and high mechanical properties. Tests of joints created at various tool rotation speeds have shown that joints of suitable quality, in terms of microstructure and properties, can be obtained for a relatively wide range of process parameters. The tool rotation speeds applied during the welding process did not have a significant influence on the quality of the welds.     

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     

Joining of dissimilar AZ31B magnesium alloy and SS400 mild steel by hybrid gas tungsten arc friction stir welding

The joining of dissimilar materials, magnesium alloy (AZ31B) and mild steel (SS400), was performed using a hybrid gas tungsten arc-friction stir welding (HGTAFSW) method that applied a preceding gas tungsten arc welding (GTAW) preheating heat source to a mild steel plate surface during friction stir welding (FSW). The mechanical and microstructural characteristics of the HGTAFS welds were evaluated and compared to those of FS welds to confirm the effect of the additional GTAW preheating heat source. The tensile strength of the HGTAFS welds was approximately 91% of that of the magnesium alloy base metal but higher than that of the FS welds. This was attributed to the enhanced material plastic flow and partial annealing effect in the magnesium alloy and mild steel materials by GTAW reheating of the mild steel side, which induced a significant increase in the elongation of the welds. The concentration profiles indicated that no intermetallic FeAl and FeAl₃ compounds had formed according to the phase diagram, which led to a decrease in joint strength. Overall, the use of HGTAFSW by applying a GTAW preheating heat source to a mild steelplate surface resulted in a mechanically sounder and metallurgically defect-free welds compared to FSW.     

异种铝合金摩擦塞补焊工艺与组织性能

采用顶锻式摩擦塞补焊方法,以2219-T6铝合金为塞棒材料,分别对8 mm厚2024-T3和7075-T6两种铝合金FSW接头进行了摩擦塞补焊试验研究,深入探讨了不同焊接压力下塞补焊接头的微观组织、显微硬度、力学性能及断口形貌特征. 结果表明,塞棒和母材或FSW焊缝是由等轴晶进行过渡,获得了紧密结合的接头,热力影响区和热影响区晶粒发生长大. 整个塞补焊接头塞棒区软化最严重,硬度在85 ~ 95 HV之间. 2024铝合金塞补焊接头抗拉强度和断后伸长率分别达到了母材的70%和65%以上,7075铝合金塞补焊接头抗拉强度和断后伸长率分别达到了母材的62%和48%以上. 塞补焊接头断裂模式为韧性特征.     

6061铝合金搅拌摩擦焊接头组织及性能

对厚度6 mm的6061铝合金进行了搅拌摩擦焊对接焊,采用光学显微镜、扫描电子显微镜、拉伸试验机及电化学工作站等设备对焊接接头的金相组织、断口形貌、拉伸性能和腐蚀性能进行了测试和分析.结果 表明,当焊接速度为80 mm/min、旋转速度在600 ～1500 r/min之间时,焊接接头的外观良好,无明显缺陷.随着旋转速度...     

Three-dimensional friction stir welding using a high payload industrial robot

The present study investigates the friction stir welding (FSW) process of extremely curved surfaces using a high payload industrial robot. The welding process of aluminum alloys in a butt joint configuration has been investigated over convex surface radii ranging from 104.5 to 14.5 mm. The weld qualities of the produced joints have been assessed by macrographs and tensile tests. It was shown that the FSW process needs an optimization of the welding path as well as an optional adaptation of the process parameters in the curved region in order to produce sound and reproducible joints without inner or outer defects. The results contribute to further fields of application where non-linear welds have to be produced.