Environment friendly frictionstirwelding (FSW) is a solid-state welding process invented by the The Welding Institute (TWI) in 1991 in the UK to join metals, more specifically aluminumalloys, which are used in trans- portation industries, having a low melting point and difficult to join with conventional techniques. FSW uses a rotating tool with a pin travelling along the weld path and plastically deforming the surrounding material to make the weld. The warmth created by the rubbing bet- ween the rotating tool and the plates encourages a local increase in the temperature and softens the materials underneath the tool shoulder and simultaneously the plunged rotating tool pin moves and mixes the softened materials by intense plastic deformation, joining both in a solid-state weld. Attractive benefits of the FSW of alu- minum alloys compared to fusion-welding processes are less distortion, lower residual stresses, fewer weld defects, no hot cracking and execution without a shield- ing gas. 1–3 The fine microstructure in friction-stir welds
Abstract— Modern structural application demands reduction in both the weight and as well as cost of the fabrication and production of materials. Aluminium alloys are the best choice for the reduction of weight, cost and replacing steels in many applications and FrictionStirWelding (FSW) process efficient and cost effective process. FSW is solid state welding process in which material is not melted during welding process so it overcomes many welding defects compared to conventional fusion welding process which is initially used for low melting materials. This process is initially developed for low melting materials like Aluminium, Magnesium, Zinc but now process is useful for high melting materials like steel and also for composites materials. The present study describes the effect of FSW process involving butt joining of similar Aluminium alloy combinations of AA6351 with AA6351 and dissimilar Aluminium ally combinations of AA6351 with AA5083 on the tensile, hardness and impact behaviour.
Abstract— Fusion welding of aluminum and its alloys tends to degrade the mechanical strength at the weld joint area due to high thermal diffusivity and high melting point. FrictionStirWelding (FSW) is the best alternative for joining of these materials against fusion joining. FSW is an emerging solid state joining process in which the material that is being welded does not melt and recast. The main objective of this research is to use FSW for joining of 5 mm thick AA5083-H321 and AA6061 T6 aluminumalloys using taper cylindrical threaded tool pin profile and scrolling on shoulder surface. The microstructure and mechanical characterization of dissimilarfrictionstir welded AA5083-H321 and AA6061-T6 aluminumalloys were studied. Four different welding speeds (40, 63, 80 and 100 mm/min) were used to weld the dissimilaralloys at constant tool rotational speed of 1120 rpm, tilt angle 2.5 0 . The effect of welding
developing materials for structural application due to their high specific weight, modulus, and resistance to corrosion and wear, and high temperature strength. A FrictionStirWelding Exploits its solid state process behavior of join aluminumalloys. As a solid state joining process, frictionstirwelding has proven to be a promising approach for joining aluminium alloys. However, challenges still remains in using FSW to join aluminumalloys. This review investigates the distinction and characteristic of aluminium and its alloys and also specific attention and critical assessment have given to: (a) the macrostructure and microstructure of al alloys joints, (b) the evaluation of mechanical properties of joints. This review concludes with recommendation for future research directions.
However, the dissimilar FSW involved with UFGed materials has never been reported according to the best of our knowledge. The FSW of dissimilaralloys has been significantly studied including dissimilaraluminumalloys, Al/Mg alloys, Al/Steel pairs, etc. The main salient feature of FSW of dissimilar metals and alloys is thought to be the variation in asymmetry or the degree of symmetry with reference to the weld centerline [ 16 ]. For example, Lee et al. evaluated the joint microstructure of the dissimilar welds between cast A356 and wrought 6051 aluminumalloys produced at various welding speeds [ 17 ]. Palanivel et al. [ 18 ] studied the effect of the tool rotational speed and pin profile on the microstructure and tensile strength of dissimilar FSW between the AA5083-H111 and AA6351-T6 aluminumalloys. They found that joint strength was affected due to the variations in the materials behavior. It is evident that an important aspect in the FSW of dissimilar materials is the selection of the appropriate alloys for the advancing and the retreating sides to obtain the optimum mixing and weld properties due to the asymmetric material flow in the joints. It was found that the maximum tensile strength was achieved for the dissimilar FSW AA2024/AA7075 aluminum alloy joints only when the 2024 Al alloy was located on the advancing side [ 19 ]. Kwon et al. successfully obtained Al/Mg dissimilar FSW joints when the AZ31 alloy and Al alloy were located on the RS and AS, respectively. However, the reason of the work-piece configuration was not explained in detail [ 20 ]. According to the investigation of dissimilar FSW between Al and Cu alloys, the suitable configuration and even the amount of offset of the tool from the joint centerline were considered to play an important role in obtaining high joints properties [ 21 – 23 ]. More recently, Sun et al. conducted the dissimilar spot FSW between the UFGed 1050Al and 6061-T6 aluminumalloys [ 24 ]. However, the UFGed materials have not been reported to be dissimilar FSW processed with other materials.
The authors are grateful to the Department of Metallurgical and Materials Engineering, IITM, Chennai, Tamil Nadu, India for extending the facilities of Metal Joining Laboratory to carry out the experiments. The authors also wish to express their sincere thanks to Mechanical Engineering Department, Osmania University to carry out the investigations
III. CONCLUSIONS AND FUTURE RESEARCH FSW process is an eco-friendly solid state joining technique compared to the conventional welding techniques. The joining of aluminium to copper using FSW has been reviewed to open a research window to researchers in order to expand the technique to other aluminium and copper alloys with the aim of achieving optimised parameters thereby leading to the commercialization of joints between these materials. Research on frictionstirwelding between aluminium and copper has not yet been thoroughly researched; much of the work has been focused on welds characterizations and study of the material flow. There is however, a strong need in developing the industrial applications of FSW between aluminium and copper in the manufacturing sector for the enhancement of the industries. Thus, the use of the FSW technique to join aluminium and copper alloys and material shapes is of importance in the development of their industrial applications.
In the current investigation, two aluminium alloys widely used in welding fabrication were studied, namely, the AI 5083 aluminium alloy (non-heat treatable), supplied in plates of 4 and 6 mm thickness, and the AI 7075 aluminium alloy (heat treatable, supplied in plates of 3 and 6 mm thickness. These base materials have markedly different mechanical behaviours, where their corresponding tensile stress– strain curves. From these curves it is possible to conclude that, for each base material, the mechanical properties are consistent although they were supplied in plates of different thicknesses, and so were from different batches. If the curves plotted in Fig. 5 are compared, it is possible to conclude that the AI 5083 alloy, with 148 MPa yield strength, is much softer than the AI 7075 alloy, with 290 MPa yield strength. However, despite being softer, the AA 5083 exhibits strong Portevin–Le Chaˆ telier effect and pronounced hardening with plastic deformation, attaining tensile strength values close to that of the AI 7075 alloy. This pronounced difference in plastic deformation behavior will naturally influence the FSW weldability of both types of alloys.
FrictionStirWelding (FSW) is a solid state welding process in which the relative motion between the tool and the work piece produces heat which makes the material of two edges being joined by plastic atomic diffusion. This method relies on the direct conversion of mechanical energy to thermal energy to form the weld without the application of heat from conventional source. The rotational speed of the tools, the axial pressure and welding speed and the (weld time) are the principal variables that are controlled in order to provide the necessary combination of heat and pressure to form the weld. These parameters are adjusted so that the interface is heated into the plastic temperature range (plastic state) where welding can take place. During the last stage of welding process, atomic diffusion occurs while the interfaces are in contact, allowing metallurgical bond to form between the two materials. The functional behaviour of the weldments is substantially determined by the nature of the weld strength characterized by the tensile strength, metallurgical behavior, surface roughness, weld hardness and micro hardness. In this project an attempt is made to determine and evaluate the influence of the process parameters of FSW on the weldments. The Vickers hardness, tensile strength and radiography are considered for investigation by varying tool speed, tool feed and maintaining constant depth of penetration of weld. Experiments were conducted on AA6351 Aluminium alloy in a CNC Vertical Machining Centre. The output factors are measured in UTM, Vickers hardness tester and Radiography equipment. Results show strong relation and robust comparison between the weldment strength and process parameters. Hence FSW process variable data base is to be developed for wide variety of metals and alloys for selection of optimum process parameters for efficient weld.
The weld mechanical integrity is directly related to the stir zone microstructure. A classical “onion ring” structure is com- monly found in the stir zone of similar material FSW joints  . In dissimilar material FSW however, a swirl-like pattern, banded or lamella structure, as well as vortex-type microstruc- tures, are formed in the stir zone, TMAZ and also in the heat-affected zone (HAZ)  . Fig. 5 (a) represents an example of a typical cross-section of AA5083 (AS) to copper dissim- ilar metal FSW joint welded at 1000 rpm and 100 mm/min. Towards the aluminium side ( Fig. 5 (b&e)), relatively small cop- per particles were observed as regularly distributed between the aluminium interface zone and the upper surface of the stir zone. Fig. 5 (c&f) illustrate that at the stir zone, larger copper particles (fragments) were stretched and irregularly distributed along the stir zone and towards the bottom of the interfacial region between the stir zone and the copper side. The irregular copper particles created a lamella structure of copper and aluminium at the bottom of the TMAZ towards the copper side ( Fig. 5 (d&g)).
Techniques for joining of lightweight dissimilar materials, particularly metals and polymers, are becoming increasingly important in the manufacturing of hybrid structures and components for engineering applications. The recent trend is towards lightweight construction in the aerospace and automotive industries, which has led to increased requirement in lightweight metallic and non-metallic materials with the aim of achieving specifically optimized versatility. Hence, suitable joining methods are necessary, in order to reliably join these dissimilar materials and to integrate them in engineering structures. Understanding of the various joining technologies that exist for multi-material, metal-to-metal, polymer-to-polymer, and metal-to-polymer hybrid structures is consequently becomes important. The objective of current study is to examine and summarize information and results from previous research and investigations on frictionstirwelding (FSW) for joiningdissimilar materials. The findings presented serve to further understanding of the FSW advantages over other convectional processes and optimization of processes for metal-to-metal, polymer-to-polymer and metal-to-polymer hybrid joints.
ABSTRACT :- The comprehensive body of knowledge that has built up with respect to the frictionstirwelding (FSW) of aluminumalloys since the technique was invented in 1991 is reviewed on this paper. The basic principles of FSW are described, including metal flow and thermal history, before discussing how process parameters affect the weld microstructure and the likelihood of defects. Finally, the range of mechanical properties that can be achieved is discussed. It is demonstrated that FSW of aluminum is becoming an increasingly mature technology with numerous commercial applications.
To date it is with aluminium alloys that FSW is most successfully applied. The reason for the predominant use of FSW on aluminium alloys is a combination of process simplicity in principle and the wide use of aluminium alloys in many major industries. It is especially the case where some aluminium alloys are difficult to fusion weld as, for example, is clearly evident in FSW application made by Boeing for making the Delta 2 rocket tanks. FSW allowed them to dramatically reduce their defect rate to nearly zero. Maximum temperature during FSW can reach just below the solidus of the workpiece alloy. For most aluminium alloys, it is significantly less than 660 ºC. Thus, H13 tool steel or high-speed tool steel, which is quite inexpensive, is a satisfactory tool material. Thus, FSW of aluminium alloys is relatively straightforward, although FS engineering, particularly for components and structures of high geometry complexity, can be quite challenging.
Some studies are conducted earlier by researches to investigate the effect of residual stress on work- piece. Zhu and Chao (2004) developed a three-dimensional nonlinear thermal and thermo-mechanical simulations using finite element analysis code–WELDSIM on 304L stainless steel. They reported that the maximum temperature during the FSW is on the weld line and within the tool shoulder and the residual stress on the welds decreased significantly after fixture release as compared to those before fixture release. Chen and Kovacevic (2003) proposed a three-dimensional model based on finite element analysis to understand the thermo-mechanical process in the butt-welding of AA 6061-T6. They observed that the residual stress was greater in the longitudinal direction than that of the lateral. Dattoma et al. (2009) evaluated the residual stress fields in similar and dissimilar joints and they showed that in thicker joints very high longitudinal stresses were present and adequate shoulder geometries resulted in reduction of residual stress values. Staron et al. (2004) conducted experimental study on residual stress states in FSW joints and they are successful in reducing the tensile residual stress in the weld zone by induction of large compressive stresses through mechanical tensioning.
Frictionstirwelding (FSW) is a solid-state joining process that uses a non- consumable tool to join two facing workpieces without melting the workpiece material. Heat is generated by friction between the rotating tool and the workpiece material, which leads to a softened region near the FSW tool. While the tool is traversed along the joint line, it mechanically intermixes the two pieces of metal, and forges the hot and softened metal by the mechanical pressure, which is applied by the tool, much like joining clay, or dough.
Numerous different fusion and solid-state welding processes are able to weld Cu and Cu alloys. Common fusion processes such as oxy-fuel welding, resistance welding and arc welding processes are typically chosen to weld Cu and its alloys, while diffusion welding, frictionwelding, explosion welding and roll welding are common solid-state welding techniques used for the same task. In welding of Cu, its high thermal conductivity is a major factor affecting the weldability of the material. The thermal conductivities for the various alloys differ. Pure and nearly-pure Cu such as Oxygen-free Cu (C10200) and electrolytic tough pitch Cu (C11000) have a thermal conductivity of 391 W/m ∙ K while heavily alloyed Cu such as Cu nickel (C71500) and nickel silver (C75200) have thermal conductivities as low as 29 W/m ∙ K. Other Cu alloys have thermal conductivities somewhere in between. When arc welding Cu with high thermal conductivities it is important to adjust the welding parameters so that it maximizes the heat input of the process into the joint. Some volatile, toxic alloying chemicals are often existent in Cu and Cu alloys. This generally results in much more release of toxic fumes than when welding ferrous metals so that it requires a more effective ventilation system to protect the welding operator than normally. This is generally avoided in solid-state welding processes that operate under the fusion temperature of the material. Solid-state techniques are also much more suitable for weldingdissimilar materials. Al-Cu joints are made by techniques such as diffusion welding, frictionwelding, cold welding, ultrasonic welding and recently FSW .
Abstract: FrictionStirWelding (FSW) is a solid state joining process which possesses a great potential to revolutionise the aerospace industries. Distinctive materials are selected as aerospace alloys to withstand higher temperature and loads. Sometimes these alloys are difficult to join by a conventional welding process but they are easily welded by FSW process. The FSW process in aerospace applications can be used for: aviation for fuel tanks, repair of faulty welds, cryogenic fuel tanks for space vehicles. Eclipse Aviation, for example, has reported dramatic production cost reductions with FSW when compared to other joining technologies. This paper will discuss about the mechanical and microstructure properties of various aerospace alloys which are joined by FSW process.
The small, equiaxed grains have resulted from the (a) high thermal conductivity of Al, the temperature cooled down too fast for new grains to grow; (b) pinning effect of the uniformly dispersed broken second phase particles. The fine second phase particles (mainly aluminum- copper compounds) in the FSP A206 could have resulted from the (a) mechanized breaking effect of the tool and (b) dissolution and precipitation of the second phase particles. From the Al- Cu phase diagram, the phase (CuAl 2 ) could fully dissolve when the temperature reached 520 0 C. The measured temperature during FSP in this experimental condition was approximately 400 0 C and the actual temperature in the center of the FSP zone was higher than this value. Moreover, the diffusion rate of these second phase particles increased because the (a) refined grains had more grain boundaries where high way diffusion took place and the (b) high dislocation density that was introduced by the intense plastic deformation and mixing of material allowed the occurrence of pipe diffusion , which facilitated the dissolution of the phase. The dissolved phase precipitated along the grain boundaries in the subsequent cooling stage. The grains were fine and the second phase particles dispersed uniformly.
Yazdipour and Heidarzadeh  studied the effect of tool traverse speed, offset and rotation direction during dissimilar butt frictionstirwelding of Al 5083-H321 and 316L stainless steel plates at constant rotational speed of 280 rpm. The tensile and hardness tests were conducted to evaluate the mechanical properties of the joints. The results showed that defect free joint with maximum tensile strength of 238 MPa was produced at a traverse speed of 160 mm/min, pin offset of 0.4 mm, and clockwise rotation condition. The reduction in tensile strength of the other joints was due to their surface and cross-sectional defects such as tunnel defect, voids, non-uniform distribution and large particles of the steel and micro cracks developed in the interface of the dissimilar parts. Uzun et al.  worked on joining of dissimilar Al 6013-T4 alloy and 304L stainless steel using frictionstirwelding. The microstructure, hardness and fatigue properties of fiction stir welded 6013 aluminium alloy to stainless steel have been investigated. The weld nugget, the heat affected zone (HAZ), thermo-mechanical affected zone (TMAZ) were observed under optical microscope. Fatigue properties of Al 6013-T4 and 304L stainless steel joints were found to be 30% lower than that of the Al 6013-T4 alloy base metal.