Friction Stir Welding Technology Research Articles

Friction Stir Spot Welding Technology and its Application in Aerospace Industry

The friction stir welding technology is a new type of welding technology of solid phase, with advantages of high quality, few defects, and small deformation in joint, which has obvious advantages in welding light alloys of aluminum, magnesium and other new materials, which will replace the traditional resistance spot welding and riveting technology to be one of the main manufacturing methods of aerospace industry, and has wide application prospects in this industry, which have great significance in upgrading the manufacturing level of aerospace industry, reduce the production cost and improve our manufacturing technology.

Use of technology of friction stir welding for aluminum alloys

This paper presents experimental data on the effect of mode of friction stir welding of aluminum alloy on the distribution of hardness over the cross section of the weld.

Using torque sensitivity analysis in accessing Friction Stir Welding/Processing conditions

The use of Friction Stir Processing (FSP) techniques for the joining and/or transforming of metallic materials is being object of intensive research since the earliest development of the Friction Stir Welding (FSW) technology in 1991. Despite of this, an accurate understanding of the main welding/processing mechanisms and its relation with the process parameters is still missing. Current paper intends to provide some further insight on this subject by discussing the relations between processing parameters, classified as independent variables, and the corresponding welding results, classified as dependent variables, using torque sensitivity analysis. The relation between base materials properties, plate thickness, welding conditions and torque evolution were also explored, which constitutes a novelty relative to the previous studies on this subject.

Process Parameters Effect on Mechanical Properties and Fatigue Behavior of Friction Stir Weld AA6060 Joints

Friction stir welding (FSW) is the most remarkable welding technology that has been invented and developed in the last decade. It is a solid-state welding process in which a rotating tool is driven into the material and translated along the interface of two or more plates. This technology has been successfully used to join materials that are considered difficult to be welded by fusion welding methods. FSW has potentially significant applications in many industrial fields such as aerospace, automotive, and naval industry. Anyway, FSW technology requires a meticulous understanding of the process and consequent mechanical properties of the welds in order to be used in the production of high performance components. The present work deals with an experimental campaign aimed at the evaluation of the mechanical properties of AA6060 T6 friction stir welded joints. The butt joints obtained using two different tool geometries (standard and threaded) were performed by varying the welding parameters, namely, tool rotating speed and feed rate. The standard tool was a very simple device fabricated using AISI 1040 steel, with a flat shoulder and a cylindrical pin. The threaded tool was a more complex device based on two main components: a tool holder, with a flat shoulder, and a threaded probe obtained using a commercial thread forming tap. The quality of the joints was evaluated in terms of both tensile strength (UTS) and fatigue behavior. The study of axial pulsing fatigue properties required the fabrication of a specific testing device able to avoid parasite bending moments. In order to estimate the more efficient and effective tool type, the welding forces (axial and longitudinal) were also measured.

Microstructure and mechanical properties of mild steel joints prepared by a flat friction stir spot welding technique

With the successful application of the flat spot friction stir welding technology to aluminum alloys, this technique was expanded to the spot lap welding of 1mm thick mild steel in this study. It reveals that sound joints can be successfully obtained with smooth surfaces and without any internal welding defects. Two welding strategies based on the welding parameter can be used to obtain the welds that fracture through plug failure mode at high shear tensile strength. One way is to weld the sheet at low heat input in the first step and the second step is used to generate large stir zone and flatten the sample surface. However, the microstructure in the stir zone is not homogeneous and a coarse columnar grain structure forms at the bottom of the stir zone. Another way is to make the stir zone penetrate into the lower sheet during the first step and the second step is only aimed to flatten the sample surface. In this case, the total heat input can be reduced and the microstructure of the stir zone can be remarkably refined. The sound joints fractured along the circumstance of the stir zone and reached about 6600N during the shear tensile tests.

Metallurgical Joining of Magnesium Alloys by the FSW Process

This paper deals with welding AZ 31Mg alloy by FSW (Friction Stir Welding) technology. Welds were fabricated with new equipment supplied from China for VUZ-PI Bratislava (Welding Research Institute — Industrial Institute). Welding parameters and conditions were proposed and tested. Joint quality was assessed by optical microscopy and microhardness measurements. The fabricated joints were sound, apart from minor inhomogeneities (cracks). It is considered that after certain adaptations of the welding parameters, and perhaps also of the welding tool, that this equipment will be capable of producing welded joints of excellent quality that can compete with any fusion welding technologies, including concentrated power sources.

Friction Stir Processing (FSP) of Cast Metals: Processing - Microstructure - Property Relationships

FSP is an allied technology of friction stir welding (FSW). These processes are reviewed and the additional considerations such as processing pattern and step over distance in FSP are introduced. The application of FSP to cast metals including AA5083, Al-7Si and NiAl bronze is summarized. As-cast microstructures may be converted to a wrought condition in the absence of external shape change and the extent of grain refinement and homogenization of microstructure is documented. The FSP-induced superplastic response of AA5083, enhanced ductility of Al-7Si and surface hardening of NiAl bronze are summarized as examples of properties developed by FSP.

摩擦攪拌接合技術の現状と展望

Over twenty years has passed since the friction stir welding was developed. During this period, various improvements and developments have been made, and this method has been put to practical use in a very wide range of industry. Because, in this method, the welding is performed in a solid state, and a refined microstructure is formed due to severe plastic deformation by the rotation tool, a variety of excellent joint properties is obtained, and in some cases, the joint strength exceeds that of the base material. However, at present, this method is put to practical use only for light metals such as Al alloys. Accordingly, the friction stir welding technology of high melting point materials such as steel has been strongly desired. Based on the current status, in this paper, prospects of the friction stir welding technology are discussed.

Weld Quality Improvement with Hybrid FSW Technology Assisted by Preheating for Copper T2/Aluminium 5A06 Dissimilar Materials

Copper and aluminium alloy could be welded by friction stir welding (FSW) but it is quite difficult to achieve a defect-free welding joint for welding dissimilar materials because of the enormous difference of their thermo-physical performances. In this paper, another friction stir tool was applied as a heating source to preheat the copper side to 150~200°C in the welding direction. Preheating temperature can make up the lost heat, improve the temperature of copper plate before the FSW process, achieve the refining grains, and then obtain a high quality welding joint. We concentrated on hybrid heat-source equipments design and procedure optimization in our studies. The microstructure, mechanical properties and phase constituents of FSW joints were studied through mechanical test and metallographic analysis. The results indicated that the hybrid FSW technology with preheating for copper T2/aluminium 5A06 dissimilar materials can not only improve the welding efficiency, but also obtain the high quality welding joint. This special welding technology could solve the welding problems of Al-Cu dissimilar materials and had a good potential for application in aerospace manufacturing.

Friction stir processing (FSP): refining microstructures and improving properties

FSP is reviewed as an allied technology of friction stir welding (FSW) and additional considerations such as processing pattern and step over distance are introduced. The application of FSP to continuously cast AA5083 material in the as-cast condition is described and the extent of grain refinement and homogenization of microstructure is documented. The FSP-induced superplastic response of this material is compared to the response of conventionally processed AA5083 and the improved ductility of the FSP material is related to grain refinement and microstructure homogenization.

The use of friction stir welding for manufacturing small-scale structures

Friction stir welding (FSW) is a relatively new joining process and is being used commercially in several industry sectors. In small and medium enterprises, however, this novel technology has not been applied despite its remarkable advantages because of the drawbacks of FSW. A database has been assembled and drawbacks have been analyzed then solved appropriately in the Industry-Government-Academia Collaboration Project. As an outgrowth, the optimum and individual know-how of practical FSW technology could be transferred to medium and small enterprises.

Simulation of friction stir welding using industrial robots

PurposeThe purpose of this paper is to establish a model‐based framework allowing the simulation, analysis and optimization of friction stir welding (FSW) processes of metallic structures using industrial robots, with a particular emphasis on the assembly of aircraft components made of aerospace aluminum alloys.Design/methodology/approachAfter a first part of the work dedicated to the kinetostatic and dynamical identification of the robotic mechanical system, a complete analytical model of the robotized process is developed, incorporating a dynamic model of the industrial robot, a multi‐axes macroscopic visco‐elastic model of the FSW process and a force/position control unit of the system. These different modules are subsequently implemented in a high‐fidelity multi‐rate dynamical simulation.FindingsThe developed simulation infrastructure allowed the research team to analyze and understand the dynamic interaction between the industrial robot, the control architecture and the manufacturing process involving heavy load cases in different process configurations. Several critical process‐induced perturbations such as tool oscillations and lateral/rotational deviations are observed, analyzed, and quantified during the simulated operations.Practical implicationsThe presented simulation platform will constitute one of the key technology enablers in the major research initiative carried out by NRC Aerospace in their endeavor to develop a robust robotic FSW platform, allowing both the development of optimal workcell layouts/process parameters and the validation of advanced real‐time control laws for robust handling of critical process‐induced perturbations. These deliverables will be incorporated in the resulting robotic FSW technology packaged for deployment in production environments.Originality/valueThe paper establishes the first model‐based framework allowing the high‐fidelity simulation, analysis and optimization of FSW processes using serial industrial robots.

Mechanical properties of friction stir welded aluminum alloys 5083 and 5383

The use of high-strength aluminum alloys is increasing in shipbuilding industry, particularly for the design and construction of war ships, littoral surface craft and combat ships, and fast passenger ships. While various welding methods are used today to fabricate aluminum ship structures, namely gas metallic arc welding (GMAW), laser welding and friction stir welding (FSW), FSW technology has been recognized to have many advantages for the construction of aluminum structures, as it is a low-cost welding process. In the present study, mechanical properties of friction stir welded aluminum alloys are examined experimentally. Tensile testing is undertaken on dog-bone type test specimen for aluminum alloys 5083 and 5383. The test specimen includes friction stir welded material between identical alloys and also dissimilar alloys, as well as unwelded (base) alloys. Mechanical properties of fusion welded aluminum alloys are also tested and compared with those of friction stir welded alloys. The insights developed from the present study are documented together with details of the test database. Part of the present study was obtained from the Ship Structure Committee project SR-1454 (Paik, 2009), jointly funded by its member agencies.

Friction Stir Lap Welding of Magnesium Alloy and Zinc-Coated Steel

AZ31 Mg alloy and zinc-coated steel were lap welded using friction stir welding technology. The microstructures and mechanical properties of the joints were examined. The lap shear tensile test results showed that the welding speed had a significant effect on the failure loads of the joints at the rotation speed of 1500 rpm. The maximum failure loads of 3.4 kN, 65% of that of the zinc-coated steel base material, could be obtained when the welding speed was 150 mm/min. Microstructure analysis showed that the intervention of zinc coat promoted the formation of Mg-Zn low-melting-point eutectic structure at the interface. The joining mechanism and the role of Zn coat on friction stir lap welding of Mg alloy and zinc-coated steel were put forward. (doi:10.2320/matertrans.M2009022) Magnesium alloys, the lightest of the structural metals, with a density two-thirds that of aluminum alloy are a promising structural material in vehicle fabrication. Zinc- coated steel with excellent corrosion resistance and good durability is a promising structural material in vehicle applications. In order to achieve combined properties of magnesium alloys and zinc-coated steel, development of reliable joints between magnesium alloy and zinc-coated steel is necessary. As a solid state welding technology, friction stir welding (FSW) process 1) can be used to join Mg alloys 2-6) and steel 7-14) and gets high quality joints than fusion welding technology. Such good merits are also expected for joining dissimilar metal materials. Watanabe et al. 15) studied the weldability of FSW AZ31 magnesium alloy/SS400 steel, and reported that the rotation speed, the position of the pin axis had a significant effect on the strength and the microstructure of the joint. The maximum tensile strength of a butt joint reached about 70% of that of the magnesium base metal and the fracture path was along the joint interface. Liu et al. 16) studied the lap joining of the dissimilar alloys of AZ31B Mg alloy and 304 steel by a laser-GTA hybrid welding technique. A transitional zone formed at the interface of the Mg-Fe during laser-GTA hybrid welding and Mg diffused into the matrix of Fe in the form of oxides and reacted in the transitional zone. During tensile testing, the joints fractured at the interface between the Mg alloy and the steel. The metallic oxides produced at the Mg-Fe interface deteriorated the mechanical properties of the joints. Up to date, current studies only report the weldability of FSW or a laser-GTA hybrid welding of magnesium alloy/ steel and the preliminary results of mechanical properties and microstructure evolution of the joints. 15,16) Investiga- tions on FSW of magnesium alloy and zinc-coated steel have not yet been reported. The object of the present study is to examine microstructure evolution and mechanical properties in FSW magnesium alloy and zinc-coated steel. In this study, AZ31 magnesium alloy and low carbon zinc- coated steel are selected for friction stir lap welding. The magnesium alloy sheet is put on the zinc-coated steel sheet. The inserting depth of the tool, being strictly controlled, is less than the thickness of the magnesium alloy. That is, the probe tip of the tool does not reach the surface of the zinc- coated steel sheet during welding. The emphasis is to study the interface microstructure evolution and clarify the joining mechanism.

The Fatigue Behaviour of Friction Stir Welded Aluminium Joints

The friction stir welding (FSW) technology enables the production of high-strength joints of light weight metal sheets. In this paper, the fatigue properties of AA5454-FSW-joints will be discussed. High-resolution plastic strain amplitude, temperature and electrical resistance measurements were performed to describe and evaluate the fatigue behaviour in detail. The plastic strain amplitude determined in mechanical stress-strain hysteresis measurements is qualified to describe the proceeding fatigue damage. Additionally, the change in temperature caused by plastic deformation work and measured with thermocouples fixed on the specimen surface allows a precise fatigue assessment. The electrical resistance measurements are directly related to the fatigue-induced defect structure and density in the welding zone. The fatigue behaviour of the welding zone, which corresponds to the specimen gauge length, is characterized by pronounced cyclic hardening leading to a plastic strain amplitude nearby zero. Additionally, results of microscopic investigations of the welding zone are presented for a microstructure-related interpretation of the fatigue properties.

Microstructural characterization and mechanical properties in friction stir welding of aluminum and titanium dissimilar alloys

Al–Si alloy and pure titanium were lap joined using friction stir welding technology. Microstructure and tensile properties of joints were examined. The maximum failure load of joints reached 62% of Al–Si alloy base metal with the joints fractured at the interface. X-ray diffraction results showed that new phase of TiAl 3 formed at the interface. The microstructure evolution and the joining mechanism of aluminum–titanium joints were systematically discussed.

Welding Technology of Lightweight Alloys

The trend of the welding technology of lightweight alloys such as aluminum alloy and magnesium alloy has been studied. The lightweight alloys in the automobile, high-speed light aircraft and modern aerospace industry can reduce vehicle weight, while stringently demanding the high quality and efficienct welding techniques, to produce the best weldments. Among the production technologies, welding plays an important role in the fabrication of lightweight vehicle structure. This has led to an increasing attention towards the use of modern welding technology such as laser beam welding process, ultrasonic welding process, friction stir welding technology and laser hybrid welding technology, etc. This paper covers the recent technical trends of welding technologies of lightweight alloys including the COMPENDEX DB analysis of welding metallurgy, welding process, and welding fabrications.

Role of zinc coat in friction stir lap welding Al and zinc coated steel

AC4C cast Al alloy and Zn coated steel were successfully lap welded using friction stir welding technology. Full strength joints could be obtained and the joints fractured at Zn coated steel base metal side, while Al alloy and unzinced steel could not be welded in the same welding conditions. The joining mechanism and the role of Zn coat on friction stir lap welding of Al alloy and Zn coated steel were put forward. The intervention of Zn coat promoted the formation of Al–Zn low melting point eutectic structure at the interface, which significantly improved the weldability of Al and steel.

On the fatigue behaviour and design curves of friction stir butt-welded Al alloys

The advantages of the friction stir welding (FSW) process over competing fusion welding process for the welding of aluminium alloys have been clearly identified. One of the main advantages compared to conventional fusion welding processes is the improvement of fatigue strength, implying that structural reliability of friction stir welded components can be substantially increased. A major issue, however, is that no general overview is available to help structural designers in determining design strength values for friction stir welded joints or their dependence on material type or process parameters. During the last 10 years several studies have dealt with the issue of structural performance of friction stir welded joints (particularly in aluminium alloys). This paper collects available fatigue data on FSW of Al alloys and statistically analyses these deriving a first set of reference fatigue curves. It is envisaged that a comparison of the reference curves obtained with the design curves given by design standards or recommendations (concerning conventional joining techniques) can assist, at the design stage, thereby giving a quantitative comparison of the influence FSW technology on structural dimensioning and design.

Recent Topics of FSW Technology in Japan

Friction Stir Welding (FSW) is the most remarkable welding technology that has been invented and developed in last decade. It made it possible to join a number of light metals that were previously believed difficult to weld in a reliable manner, i.e. without defects including distortion. This summarising report tries to clarify the recent trend of this new technology in Japan. It reveals that the Japanese industry has a strong development potential, particularly in the field of practical applications. Examples of practical products are the rolling stock industry, automobile industry, shipbuilding and aircraft.. Major research works are concentrated on the clarification of the mechanical properties for the particular products. General agreements of their results showed that static and fatigue strengths were distributed between base metal and MIG properties of aluminium. Fundamental research work is also carried out to investigate heat input estimation, microstructural characterisation during FSW and motion of metal using dissimilar aluminium plate combinations including process tolerance.