Frictionstirwelding is solid state welding and involves heating the metal with a suitable amount of pressure so that homogeneous and complete microstructural welding is possible without melting of the parts to be joined. The process uses a rotating tool with a profiled pin that penetrates the parts to be joined; the tool then starts to travel along the join line. By keeping the tool rotating and moving it along the join line to be welded, the softened material due to the frictional heat is stirred and mixed together by the rotating pin forming a weld in solid state without melting. Frictional heat generated by rotation of the tool due to the high compressive pressure and shearing action of the shoulder along the joint line causes a softened zone of material without melting. Localized severe deformation around the tool results in refinement of the microstructure and the material flow produces coalescence and formation of a weld. FSW provides superior welding over conventional fusion welding and is preferred for joining of Al-Li alloys. The present work is to investigate was to study the effect of frictionstirwelding parameters on mechanical and microstructural properties of AA2195-T0 and T8. Since FSW is both a deformation and a thermal process, temperature distribution during FSW is measured. The microstructure and mechanical properties of welded joint were investigated for different frictionstirwelding conditions. This paper describes the results of an experimental study to investigate the mechanical and microstructure evolution of AA2195 frictionstir welded joint. The optimum welding condition is also provided for different heat treated AA2195 alloys.
300, 600, 1200 emery paper. After that, they are polished with 3μm, 1μm diamond and 0.03μm colloidal silica. Both optical microscope and scanning electron microscope (SEM) are applied for the characterization of the joint cross section. The energy dispersive X-ray spectroscopy (EDS) is utilized to analyze the elemental distributions at the interface between the steel and aluminum. Since the keyhole refilled FSSW consists of two steps, the operation parameters of each step are summarized in Tables 4-1 and 4-2 respectively. To find out a proper rotation speed for the refilled step, several trials have been made at the beginning stage of the experiment. When the rotation speed is chosen as 1000 rpm, the refilling quality is low due to lots of voids and a rough surface. The reason behind this is that the low rotation speed generates less heat, which in return constrains the material flow and lead to a poor joint quality. Thus, a higher rotational speed helps to enhance the material flow and to improve the joint quality. Therefore, a higher rotational speed is chosen in the refilled step. The traveling radius in Table 4-2 refers to the radius of the circular path during the keyhole refilling step. It is equal to the offset distance that the tool moves away from the center of the original keyhole after the regular FSSW step. In this study, the plunge depth is defined as the distance between the end surface of the tool pin and the original top surface of the aluminum sheet. During welding, the aluminumalloy sheet is placed on top of the TRIP 780 steel sheet and the experimental configuration is shown in Figure 4-5. As indicated in Figure 4-5, the welding tool is operated in the welding region for both the welding and refilling process.
The steady state welding stage is modeled in the Eulerian formulation, where materials flow into the computational domain with the prescribed welding speed while the tool stays at the same location with only the rotational motion. Solid state metals are treated as non-Newtonian fluids with high viscosities. Accordingly the flow field belongs to laminar regime and the viscosity is a function of temperature and strain rate. Aluminum and steel are treated as different phases. Based on the topology of phase distribution, multiple phase flow can be categorized into two general groups: separated flow and dispersed flow. In the former one, different phases are continuous and separated by a clearly-defined interface. The latter group corresponds to flow of discrete phases, such as bubbles, droplets and particles, in a continuous primary phase. According to experimental observations of weld cross section macrostructure in Chapter 3, both aluminum and steel are basically continuous. Only a small amount of steel or intermetallic compound particles are dispersed in the aluminum matrix. However, the quantity and sizes of these particles are small, which are neglected in the current model for simplification. The dissimilar FSW process is therefore modeled as a separated multiple phase flow problem.
S. Hong et al  studied the fatigue crack propagation (FCP) behavior of frictionstirwelding of similar 5083-H32 aluminum alloys at a tool rotating speed of 1600 rpm and welding speed of 0.25 m/min. They examined the microstructure of three zones. Dynamically recrystallized zone (DXZ), thermo-mechanically affected zone (TMAZ) and base metal (BM). Number of measurements of grain size in these zones showed that the DXZ has much finer grain structure compared to BM because of dynamic recrystallization during FSW process. They found that the (FCP) strongly influenced by grain refinement in the dynamically recrystallized zone (DXZ). They observed that the FCP rates in the DXZ tended to be lower than those in base metal. The presence of frictionstir zone delay the FCP. S. Kasmanand and F. Kahraman, have noticed that while using triangular pin in frictionstirwelding method of similar 5083-H111 aluminum alloys, by visual inspection that the nugget zone is formed in to circular or elliptical shape consisting of onion rings. They stated that the thermo- mechanically affected zone (TMAZ) consists of plastically deformed and elongated grains. They found that the maximum hardness values were measured in nugget zone and the hardness values of nugget zone and thermo- mechanically affected zone (TMAZ) are similar due to temperature reduction gradient from nugget zone to TMAZ while the hardness values of base metal and heat affected zone are almost similar. M.S. Han et al  studied the optimum frictionstirwelding conditions of similar 5083-O aluminum alloys by evaluating the mechanical characteristic. They found that the optimum FSW conditions are 124 mm/min as a welding speed with 800 r/min as a rotational speed. With these conditions the button shape at the end point was good and the stir zone had a soft appearance. D. Rao et al [18
----------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - In this work, the current understanding and development of friction-stirwelding of titanium and aluminum alloys are briefly reviewed. The critical issues of dissimilar alloys are addressed. A particular emphasis is given on the strength at welded part as compared to fusion weldingprocess and other factors which affects the strength of dissimilar alloys of Ti & Al. This paper also explains about the effect of probe offset distance on the interfacial microstructure and mechanical properties of the welded joint and gives the information about the proper range of probe offset distance so that sound dissimilar joints are produced, which have comparatively high tensile strength and fracture. In this review it was observed that the hardness, tensile strength, appearance, interface macrograph of Ti and Al alloy of the welded part using frictionstirwelding.
Abstract - Frictionstirwelding (FSW) is a solid state joining process for joining high conductivity materials like aluminum and its alloys. In the present study T-joint at various parameters were produced by the frictionstirwelding. Some parameter provides defect free joints while the other parameters show defects. The tool pin is used in all the parameter is helical shaped. T-joints of AA 1065 aluminumalloy is made without defects. Experimentation will be carried out by changing principle parameters of FSW process. Macro and micro images of traverse section of the weld were captured and analyzed to identify the defects and the bead geometry values were found out using macro images. Most of the defects occur at advancing side at top side of the weld joint. The liquid penetrant inspection (LPI) test was performed for all the joints and no surface cracks were formed on weld line. Scanning electron microscopy (SEM) with Energy dispersive X-ray spectroscopy (EDS) spectra was taken at various weld zones, which shows the topography of welded zone and oxides formation. Tensile properties and micro hardness of the joints were experimentally evaluated for joints formed at different process parameters.
Frictionstirwelding (FSW) process is an emerging solid state joining method in which the material that is being welded does not melt and recast. The welding parameters such as tool rotational speed, welding speed and axial force plays a major role in deciding the joint characteristics. In this investigation central composite design technique and mathematical model was developed by response surface methodology with three parameters, three levels and 20 runs, was used to develop the relationship between the FSW parameters (rotational speed, traverse speed, axial force,) and the responses (tensile strength, Yield strength (YS) and %Elongation (%E) were established.
The aluminium alloy AA2219 (AleCueMg alloy) is widely used in the fabrication of lightweight structures with high strength-to-weight ratio and good corrosion resistance. Welding is main fabrication method of AA2219 alloy for manufacturing various engineering compo- nents. Frictionstirwelding (FSW) is a recently developed solid state weldingprocess to overcome the problems encountered in fusion welding. This process uses a non-consumable tool to generate frictional heat on the abutting surfaces. The welding parameters, such as tool pin profile, rotational speed, welding speed and axial force, play major role in determining the microstructure and corrosion resistance of welded joint. The main objective of this work is to develop a mathematical model to predict the corrosion resistance of frictionstir welded AA2219 aluminium alloy by incorporating FSW process parameters. In this work a central composite design with four factors and five levels has been used to minimize the experimental conditions. Dynamic polarization testing was carried out to determine critical pitting potential in millivolt, which is a criteria for measuring corrosion resistance and the data was used in model. Further the response surface method (RSM) was used to develop the model. The developed mathematical model was optimized using the simulated annealing algorithm optimizing technique to maximize the corrosion resistance of the frictionstir welded AA2219 aluminium alloy joints.
During FSW process, the material experiences severe plastic deformation and thermal exposure, this normally leads to formation of fine, recrystallized grain structure. The grain size of the nugget zone is measured from optical image that are depicted in Fig. 7 for different welding conditions of Table 1. The average grain size for base materials is ~ 100 μm. After processing, the grain size in nugget zone at four different conditions varies between 20 μm to 23 μm. The increase in degree of deformation during FSW results in the reduction of grain size according to the general mechanism of recrystallization. The combination of lower temperature and shorter excursion time at the bottom of nugget effectively retards the grain growth and results in smaller recrystallized grains . It is observed that lower rotational speed resulted in lower peak temperature and consequently the reduction in grain size due to higher plastic deformation and strain rate at low temperature [287-288]. At the circumference of the pin, the material flow is shown to be governed by the simple shear deformation induced by the rotating pin, which led to the formation of a fine equiaxed grains.
Taguchi concept of practices of an L9 orthogonal array was worked with to improve the FSW parameters of 2024 aluminum metals. The FSW guidelines decided on for this study were Rotational speed (W), travel velocity (V) as well as Device pin geometry as received table.1. The tensile strength, Impact strength as well as hardness as output characteristics. The signal to noise proportion (S/N) for each and every quantity of procedure criteria was analyzed . Signal to noise evaluation was actually made use of to minimize changes in preferred characteristics. Consequently results of ultimate Tensile strength(UTS), impact strength, and Hardness worth's were actually even more appropriate and comparable. The objective of this particular research was to attain much better mechanical homes(tensile strength, Hardness & Impact strength) of joints for selected alloys. The S/N proportion which shows the quality characteristics was computed utilizing the formula 1 :
shapes. Besides, rotational speed and travel speed are the second and third main process characteristics. the process parameter could adjusted properly after tool, machine and material documents consideration .In complex applications the CNC machine need to programed by CAM methods accurately , while in simple applications an ordinary CNC milling machine programing could applied in a linear path. Same CNC program could apply for work piece backside in reverse direction . Schematic diagram of FSW shown in figure 1.
The plates are positioned in the fixture, which is prepared for fabricating FSW joints by using mechanical clamps so that the plate will not be separated during welding illustrated in Figure4. The tool is fixed in the tool holder of the milling machine and the milling head is tilted with a rake angle of 0 0 to 3 0 to the vertical axis. The tool speed can be selected in the range between 710 to 1800 rpm based on the plate material and it thickness to be welded. Tool is lowered while in rotation and plunged in to the plates when the shoulder touches the plate, heat is generated. After a few second, table movement is given and it can be varied from 16 to 800 mm/min. This paper design of two newly developed tools which were used in the present work is illustrated in Figure3. It should be noted that, in each design shape and size is same and having shoulder under
The proposed study will mainly focus on studying the effect of the tool profile of FSW process on the weld characteristics by studying the mechanical property of the weld joint such as tensile strength, hardness and ductility in term of elongation. Moreover, the effect of tool geometry on tool durability will be investigated. At present, few studies had been carried out to determine the strengths of welded materials using different tool geometry. In this study, three parameters are selected which are rotating speed, welding tool geometry and feed rate.
The metal flow and heat generation in the softened material around the tool are fundamental to the frictionstirprocess. Material deformation generates and redistributes heat, producing the temperature field in the weld. But since the material flow stress is temperature and strain rate sensitive, the distribution of heat is itself governed by the deformation and temperature fields. In fact their control lies at the core of almost all aspects of FSW, for example, the optimization of process speeds and machine loading, the avoidance of macroscopic defects, the evolution of the microstructure, and the resulting weld properties. Early work on the mode of material flow around the tool used inserts of a different alloy, which had a different contrast to the normal material when viewed through a microscope, in an effort to determine where material was moved as the tool passed [2,3]. More recently, an alternative theory has been advanced that advocates considerable material movement in certain locations . This theory holds that some material does rotate around the pin, for at least one rotation, and it is this material movement that produces the "onion-ring" structure in the stir zone. The researchers used a combination of thin copper strip inserts and a "frozen pin" technique, where the tool is rapidly stopped in place. They suggested that material motion occurs by two processes: 1. Material on the advancing front side of a weld enters into a zone that rotates and advances with the pin. This material was very highly deformed and sloughs off behind the pin to form arc-shaped features when viewed from above (i.e. down the tool axis). It was noted that the copper entered the rotational zone around the pin, where it was broken up into fragments. These fragments were only found in the arc shaped features of material behind the tool. 2
invented at The Welding Institute (TWI) in 1991. 20) Sanderson et al. 15) have reported that this welding technique can be applied to a large number of aluminum alloys. In addition, recent studies have demonstrated that the frictionstir welded zone was composed of ﬁne recrystallized grains resulting from severe plastic deformation experienced during welding. 16,17,21) Then, we focused our attention on this unique characteristic of FSW and have studied this process not as a welding technique but as a new grain reﬁnement process. 22) Figure 1 shows the schematic illustration of the basic principle of the frictionstirprocess (FSP) in the present research. In this process, a headpin rotating at high speed is inserted into a workpiece and then traversed horizontally to the top surface of the workpiece. Frictional heat is generated by the contact between the rotating tool and the workpiece. This heat induces the decrease in the deformation resistance of the workpiece with the increase in its temperature. The softened workpiece is severely plastically deformed by the
signiﬁcantly diminish a material’s resistance to localized cor- rosion. The corrosion behavior of intermetallic precipitates depends mainly upon their redox potential with respect to the matrix. Intermetallic precipitates more noble than the matrix serve as cathodes; therefore, the surrounding matrix experiences anodic dissolution, and localized corrosion would subsequently progress . As a part of the fabrication pro- cess, welding is one of the most important manufacturing technologies used in the aluminumalloy industry. In fact, the main problem associated with this kind of joint process can arise from the focus on heat-treatable alloys. Accordingly, heat generated by the weldingprocess, can change the microstruc- ture of aluminumalloy and chemistry as well as dimension and distribution of the intermetallic particles in the matrix of aluminumalloy. Thus, the welded joints of aluminumalloy have different localized corrosion behavior in an aggressive medium.
Frictionstirwelding (FSW) is a solid-state joining process where a rotating tool, made up of a shoulder and a pin, moves along the butting surfaces of two rigidly clamped plates put on a support plate. The shoulder stays in contact with the top surface of the workpiece. A portion of the heat originates from the rubbing between the shoulder and workpiece, while others are the consequence of material stirring. This heat will certainly soften the materials that are to be welded. This will lead to intense plastic distortion and the plasticized metal will stream toward of the welding.
metallurgical properties, and reduced need for human skill are amongst the most important advantages of FSW in comparison with conventional fusion welding methods . FSW uses a rotating cylindrical tool with a pin to heat the material by friction. The tool pin stirs the plasticized material and therefore joins two pieces together when it is moved along the welding line. Advantages of this
However, despite the aeronautic industry’s growing interest for FSW joints of Al-Cu-Li alloys, it is worth noting that very few works concern their corrosion behavior. The present work aims to contribute to a better understanding of the corrosion behavior of welded Al-Cu-Li alloy joints. The weld studied was a FSW joint in 2050 Al-Cu-Li alloy. The material was welded in the T351 metallurgical state and submitted, after the weldingprocess, to T8 heat treatment. The purpose of the present manuscript is to study the influence of post-welding heat treat- ment on the corrosion behavior of the FSW structure. The microstruc- ture of the welded joint was first studied by optical microscopy (OM) combined with hardness measurements to identify the different metal- lurgical zones generated by the weldingprocess. The corrosion behav- ior of the global welded joint and that of each individual zone of the weld were studied in 1 M NaCl solution by using stationary electro- chemical tests (open circuit potential measurements, plotting of current-potential curves). The corrosion damage observed in 1 M NaCl solution was compared to that obtained after Mastmaasis Wet Bottom tests which is a frequently used industrial test. Combination between electrochemical results and transmission electron microscopy (TEM) observations performed for both metallurgical states, i.e., with or with- out the post-welding heat treatment, was helpful in correlating the cor- rosion behavior observed for each individual zone and for the global welded joint to their microstructure. However, comparison of the results obtained for the whole welded joint to those of each individual zone allowed some galvanic coupling phenomena to be revealed and galvanic coupling tests were performed to obtain further understanding of the corrosion behavior of the welded joint.