Some previous studies  concluded that a traditional FSW tool is not appropriate for weldingpolymers due to the low melting point, thermal conductivity and hardness of polymeric materials . Thereby, since the tool plays a crucial role in the FSW process, the development of adequate FSW tools for polymers is considered a topic that must be addressed with high determination. So far, the most effective tool that has been established for polymer welding is considered to be the hot shoe, developed by Strand . This tool consists of a static shoulder made with aluminium, coated with polytetrafluoroethylene or “Teflon” on the contact surface area. In this tool a heater and a thermocouple are installed inside the stationary shoulder in order to monitor, control and compensate any overheating or heat shortage that might occur. One of the main advantages that makes this tool notable is the fact that it is able to trap the almost molten material inside the weld bead, promoting the formation of a good surface quality. With the absence of a rotating shoulder, the frictional heat is exclusively generated by the probe. Some other studies used the hot shoe with different probe geometries and analysed the results for different base materials .
encompassed a concave shoulder with diameter of 20 mm and a non-threaded cylindrical pin with length and diameter of 3.5 and 6 mm, respectively. Tilt angle of the rotating tool with respect to the z-axis of the milling machine was about 1.5 degrees for all the samples. The lap joining process was performed via FSW at the tool rotational speeds of 700, 900, 1120 and 1400 rpm and traverse speeds of 6.5, 12 and 25 mm/min. In order to characterize mechanical properties of the joint under various welding conditions, a set of lap shear tests was carried out according to ISO 12996 standard . The failure load was recorded for each sample. Shape of the test specimen was rectangular and width of each specimen was 15 mm.
Taguchi technique is statistical method developed by Genichi Taguchi to enhance the performance and quality of the products. Based on Taguchi, the main point just before analysis is establishment of the experiment. Only by this method, it's possible to enhance the quality of the process. This method could achieve the last output value and reduced the variability across the output value by minimum cost. He believed that the easiest way to enhance quality was to create and construct it into the product. The main purpose of this method is to create good quality product at inexpensive to the manufacturer. Taguchi developed a way for experiment design to examine how various parameters affect the mean and difference of a process performance characteristic. The fresh layout organized simply by Taguchi involves putting on orthogonal arrays to increase the guidelines impacting on the method plus the amount where they ought to be varies. Instead of experiencing to evaluate all possible mix just like the factorial layout, the actual Taguchi approach checks people of combinations. The following will allow for the quantity of the necessary facts to uncover which variables almost all have an effect on products top quality using lowest volume of experimenting, thus saving your time plus resources. The Taguchi arrays is often produced or even explored smaller arrays is often slow by hand; big arrays can be based for deterministic algorithms. Generally, arrays can be purchased online. The arrays are selected simply by the number of guidelines (variables) plus the number of ranges (levels).
of sheets and moving it along the weld line to heat and stir the sheets' materials by producing friction between the shoulder and the sheet sur-face and also the material flow by the pin movement. As the tool moves through the weld line, the heated materials of two sheets flow and mix together without melting and make the welded joint. Because in FSW the joining process is accomplished by material flow below the melting temperature, many joint defects caused by joint material melting such as porosity, grain boundary cracks and alloys segregation can be eliminated or adequately reduced. These process specialties have made FSW very practical for joining dissimilar alloys. Lately some researchers have been performed on frictionstirwelding of dissimilar aluminum lap joints [5-7]. AA5083 is a strain hardening structural alloy that is widely used in aerospace, marine and military industries mostly because of its light weight, admissible weld ability and elite corrosion resistance . Some recent researches have studied frictionstirwelding of this aluminum alloy in similar or dissimilar joints [9-12].
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.
Dinaharan et al.  investigated the effect of material locations and tool ro- tational speed on the microstructure and tensile strength of the dissimilar fric- tion stir welded, cast and wrought aluminum alloy AA6061. They concluded that the material placed in the advancing side (AS) occupied the major portion of the weld zone when tool rotational speed was increased, where the AS of the weld is hotter than the retreating side as proved by Cole et al. . In addition, Sunda- ram and Murugan  studied the effect of the pin profile used in FSW on the mechanical properties of 2024-T6/5083-H321 dissimilar aluminum alloys where the alloy of higher strength (2024) was located at the retreating side (RS). They proved that when the combinations of parameters create either very low or very high frictional heat, a plastic flow of material, lower tensile strength and elonga- tion is observed. Furthermore, Khodir and Shibayanagi  experimentally ex- amined the FSW of dissimilar materials, namely AA2024 and AA7075 and rec- ommended that the low-strength material should be placed on the AS to pro- duce better welds. On the other hand, Jata et al.  and Xue et al.  con- firmed that locating hard materials at the AS will improve the joint strength. Accordingly, the material flow and the joint performance, irrespective of materi- al placement, are dependent on the welding conditions and on their effects on generated heat and stir zone (SZ) temperatures  . Additionally, heat dis- sipation depends on material thickness, the welding speed and the ambient temperature  . The use of high heat input such as low welding speed and high rotation rate can result in improper tool/material contact conditions (slip- ping conditions) which can produce joints with defects . Otherwise, El-Sayed et al.  were proved, experimentally and theoretically, that tool pin profile has a minor effect on the maximum temperature of the welded joints at the same welding speed.
Elangovan and Balasubramanian studied welding of 6061 aluminum alloy using several frictionstirweldingtool pins like straight cylindrical, cylindrical taper, threaded cylindrical, square, and triangular with different shoulder pin diameters viz., 15, 18, and 21-mm. In their investigation, square pins provided superior tensile properties with least number of defects . The effect of tool pin profiles on mechanical and metallurgical properties of dissimilar 6351-5083 H111 aluminum alloy welds have been reported by Panaivel et al. Tool pin profiles such as straight cylindrical, threaded cylindrical, square, tapered square, and tapered octagon were used for the purpose and the square straight tool provided the best result .Vijay and Murugan investigated the effects of FSW tool pin profiles such as square, hexagon, and octagon, and concentric circular grooved shoulders on stir cast Al-10 wt-% TiB2 metal matrix composite welds and reported that the tapered pin produced narrower stir zones with coarser grains compared to that of the straight pin tools .
The investigation is on effect of weldingparameters on the microstructure and mechanical properties of frictionstir welded butt joints of dissimilar aluminium alloy sheets between Semi- Solid Metal (SSM) 356 and AA 6061-T651 by a Computerized Numerical Control (CNC) machine. The base materials of SSM 356 and AA 6061-T651 were located on the advancing side (AS) and on the retreating side (RS), respectively. FrictionStirWelding (FSW) parameters such as tool pin profile, tool rotation speed, welding speed, and tool axial force influenced the mechanical properties of the FS welded joints significantly. For this experiment, the FS welded materials were joined under two different tool rotation speeds (1,750 and 2,000 rpm) and six welding speeds (20, 50, 80, 120, 160, and 200 mm/min), which are the two prime joining parameters in FSW. A cylindrical pin was adopted as the welding tip as its geometry had been proven to yield better weld strengths. From the investigation, the higher tool rotation speed affected the weaker material’s (SSM) maximum tensile strength less than that under the lower rotation speed. As for welding speed associated with various tool rotation speeds, an increase in the welding speed affected lesser the base material’s tensile strength up to an optimum value; after which its effect increased. Tensile elongation was generally greater at greater tool rotation speed. An averaged maximum tensile strength of 197.1 MPa was derived for a welded specimen produced at the tool rotation speed of 2,000 rpm associated with the welding speed of 80 mm/min. In the weld nugget, higher hardness was observed in the stir zone and the thermo-mechanically affected zone than that in the heat affected zone. Away from the weld nugget, hardness levels increased back to the levels of the base materials. The microstructures of the welding zone in the FS welded dissimilarjoint can be characterized both by the recrystallization of SSM 356 grains and AA 6061-T651 grain layers .
of joints of AA6061 and AA7075 are investigated. The tensile strength of the dissimilar joints increases with decreasing heat input. When welding was conducted at highest welding speed and AA6061 Al plates were fixed on advancing side, the high strength of the joint was observed. The joints were failed at positions in HAZ on AA6061 side where the minimum hardness is located and observed that very good tensile strength and ductility. The tool process parameter plays a significant effect on the micro structural evolution . The tools used for FSW of aluminium alloys are straight, cylindrical, taper, triangular made of HSS . The process parameters can influence the frictionstirweldingjoint quality such as welding speed, rotational speed, tilt angle, vertical downward force applied between the tool shoulder and the surface of the work piece . The CNC operated Milling machine suited for frictionstirwelding process at low cost for joining heat treatable aluminium alloys for aerospace and automobile industries. A detailed review is given on how to convert a conventional milling machine into a CNC milling machine to perform the Frictionstirwelding. To join a couple of 3-mm thick AA2219 and designed suitable tool and analysed the performance of welded joint. They concluded that the tool profile plays an important role of frictionstir welding.The load bearing capacity of tool pin of L80 steel and AA7075 alloy and used a three dimensional heat transfer and visco-plastic model to observe the influence of pin length and diameter on traverse force during FSW. With increase in pin length the total traverse force increases significantly .
Frictionstirwelding (FSW) is a novel solid state welding process for joining metallic alloys and has emerged as an alternative technology used in high strength alloys that are difficult to join with conventional techniques and which avoids bulk melting of the basic material, hot cracking and porosity. The function of FSW process are used in several industries such as aerospace, rail, automotive and marine industries for joining aluminium, magnesium and copper alloy. In aerospace industries most of the component is manufactured with aluminium material by welding process. Aluminium welding cannot be done by conventional process because temper characteristics of material will be changed. To overcome this drawback, frictionstirwelding process is selected. To investigate the effect of weldingparameters and different tool pin profiles over FrictionStirWelding of dissimilar AA 6061 and AA 7175 and also compare single pass frictionstirwelding and multi pass frictionstirwelding. The parameters considered were tool rotation speed, welding speed, tool pin profiles, tilt angle and number of passes. Different tool pin profiles are Threaded Triangular, Threaded Cylindrical, Threaded Hexagonal and Threaded Taper pin profiles plays a vital responsibility in deciding the weld quality. This work includes tensile tests, hardness test and impact test. .
of dissimilar aluminum alloys . In frictionstirwelding, a non consumable tool with a profiled pin is rotated and slowly plunged into the joint line between the two pieces of plate material, which are butted together. Frictional heat is generated between the wear resistant weldingtool and the material of the work-pieces. This heat causes the latter to soften without reaching the melting point and allows traversing of the tool along the weld line. The plasticized material is transferred from the leading edge of the tool to the trailing edge of the tool pin and is forged by the intimate contact of the tool shoulder and the pin profile. It leaves a solid phase bond between the two pieces . The advancing side (AS) is the side where the velocity vectors of tool rotation and traverse direction are similar and the side where the velocity vectors are opposite is referred as retreating side . FSW parameters are tool geometry, axial force, rotational speed and traverse speed . Characteristics of frictionstir welded joints are influenced by material flow and temperature distribution across the weld which are dictated by tool design and weldingparameters such as welding speed and tool rotational speed. Tool design is one of the most important factors to consider when designing a FSW joining process. The tool must perform many functions, including generating heat, promoting mixing, breaking up the joint line, dispersing oxide layers, creating forging pressure, containing material within the joint, thereby preventing surface weld flash, and preventing the formation (or minimizing the impact) of defects such as wormholes, sheet- thinning, or hooking defects . The rotation of tool results in stirring and mixing of material around the rotating pin and the translation of tool moves the stirred material from the front to the back of the pin and finishes welding process.
FSW is a relatively simple process that produces a weld between two or more work pieces by thermal and material flow. The success of FSW has enabled the possibility to weld similar and dissimilar materials . The use of FSW is rapidly replacing the conventional mechanical fastening as far as joining is concerned. Aluminium and its alloys are important for manufacturing components and structures because of their good mechanical properties, which include low density and high strength. During the process of FSW, a non-consumable rotating cylindrical tool with a pin is inserted into the abutting edges of the work piece to be joined and travels along the joint line to form a weld. The result of various geometrical features on the tool, material movement around the pin can be complex, with gradients in strain, temperature and strain rate. The resulting nugget zone microstructure resulted after FSW; reflect these different thermomechanical histories that are inhomogeneous. Regardless of the central microstructural inhomogeneity of the weld interface, one of the crucial benefits of this technique is the formation of fully recrystallized, equiaxed, fine grain microstructure formed in the nugget by the severe plastic deformation at raised temperature. The fine grain microstructure produces excellent mechanical properties, fatigue properties, enhanced formability and excellent super-plasticity .
and more attention in the manufacture of lightweight structures for the automobile and the aircraft industry . Several authors have conducted frictionstirwelding of wide range materials and have reported changing the tool geometry or varying the input process parameters. The effect of both of these has been studied on the mechanical properties and necessary relations have been established . In this work the input parameters: tool rotational speed, feed and dwell time has been varied in two levels as per the full factorial method. The produced weld joints have been examined for various mechanical properties such as tensile strength, hardness and corrosion resistance. Also the influence of welding parameter on the force acting during the process has been investigated.
The frictionstirwelding of aluminum and its alloy with different initial microstructures were carried out under different welding conditions. The microstructural evolution and mechanical properties of weld joints were studied in the above research papers. Some grades of aluminium are difficult to weld by existing arc welding techniques, and a few, such as the very high-strength 2XXX and 7XXX series of alloys, unweldable. In FSW, its potential benefits in cost reduction, joint efficiency improvement, and high production accuracy make it even more attractive for the non-weldable series AA2xxx, AA6xxx and AA7xxx. Cavity or groove-like defect caused by an insufficient heat input in the frictionstirwelding. Cavity produced by the abnormal stirring.
TIG is suitable for joining thin sections because of its limited heat inputs. The feeding rate of the filler metal is somewhat independent of the welding current, hence allowing a variation in the relative amount of the fusion of the base metal and the fusion of the filler metal. Hence, the management of dilution and energy input to the weld can be achieved not including changing the size of the weld. Since the GTAW process is a very clean welding process, it can be used to weld reactive metals, such as titanium and zirconium, aluminum, and magnesium. (Anna, 2006)
TIG welding also known as gas Tungsten Arc Welding (GTAW) uses a non consumable electrode and a split filler metal with an inert shielding gas. TIG process welding set utilizes suitable power sources, a cylinder of argon gas, a welding torch that was linked to electric cable for current supply, and tubing for shielding gas supply. The characteristic of the torch formed is, having a cap at the back end to protect the quite long tungsten electrode against unintended breakage. (Ahmed, 2010). Figure 3.2 shows the Model Miller TIG welding machine is used in this experiment.
They concluded that Zn and Zr of alloying elements of Mg–Zn–Zr alloy improved the tensile strength of titanium and magnesium joints by forming the thin reaction layer at the joint interface during frictionstirwelding. Chemical compositions of titanium and Mg–Zn–Zr alloy is shown in the following table No1. Commercially used Mg–5.5 mass% Zn–0.57 mass% Zr alloy (ZK60) and 99.5 mass% magnesium (Mg) were joined to commercially used 99.5 mass% titanium (Ti) by FSW. In ZK60 alloy, Zn is soluble in magnesium, and Zr partly forms the compound with Zn.
Abstract— In the proposed work, two different aluminium alloys such as Al 6061 and Al 6063 of same family was selected to study the mechanical properties of the joint prepared by FrictionStirWelding. The experiments were conducted by changing the spindle speed in three different levels by maintaining the other parameters unvarying. Welded workpieces were tested for its tensile strength and micro structure in order to understand the behavior of the welding process. The results revealed that the tensile strength is increased initially when the spindle speed increases and decreased beyond the certain level. Microstructural analysis showed that, in stir zone grain refinement was happened due to which mechanical properties were improved.
and Mg-Zn eutectic point, which results in the formation of a liquid-phase. Moreover, from the welding heat cycle histories we can know that the dwell time at high temper- ature above zinc melting point and Mg-Zn eutectic point is about 3.6s and 5.8s in position 0 mm. The dwell time at high temperature above Mg-Zn eutectic point is about 5.4s in position 8 mm. It means liquid phase can form due to high peak temperature. Furthermore, the high-temperature dwell time is long enough for liquid phase to be pushed aside and ﬁlled into the clearance between two sheets. According to the above results, we put forward the following joining mechanism of frictionstirlapwelding of Mg alloy and zinc-coated steel. During frictionstirwelding, the metal in the lap interface undergoes the synthetic eﬀect of the thermal cycle and the mechanical cycle because of the actions of friction, stir and extrusion of the tool. Thus, high temperature and high pressure are generated at the interface. High temperature ﬁrstly leads to the melting of pure zinc on the surface of zinc coat and high pressure simultaneously results in the rupture of surface oxide ﬁlms at both sheets surface, which promotes the formation of low- melting Mg-Zn eutectic reaction products. High pressure then forces the liquid reaction products with broken oxide ﬁlms and surface contaminants far away from the weld center, which spread along the interface till pile into the natural clearance between two sheets. In this way, the fresh interfaces are exposed and they are tightly extruded together after liquid phase is pushed out. Elements mutual diﬀusion of Mg/Fe and Al/Fe occurs, which leads to the formation of a new IMC of Fe4Al13 at the lap interface of the weld. Finally, during the cooling after welding, liquid phase in the natural clearance between two sheets transforms into solid structure.
process and terminology. Several works on modeling of heat transfer and material flow during FSW have also been performed. Askari et al.,  have used a 3D finite difference hydrodynamics code to establish the coupling between tool geometry, heat generation, and plastic flow during FSW process. Zhao  has simulated the material flow around the tool using LS-DYNA code. In this study, arbitrary Lagrangian- Eulerian formulations have been used with a “moving mesh” in order to handle severe plastic deformation around the rotating tool. Colegrove and Shercliff  have proposed a 2D model for determining material flow around the weldingtool using commercial code based on fluid dynamic formulations, Fluent. Another study has been conducted by Hyoe et al., . They investigated hardness profile across a weld and thermal histories as a function of position in the weld cross- section. The thermal history in their works was simulated by applying a uniform heat flux over the contact surfaces and a prescribed power input. Schmidt and Hattel  have used a commercial FE code, ABAQUS, to predict severe plastic deformation during FSW process. Nandan et al.,  have presented a 3D visco-plastic finite element model for solving a coupled thermomechanical problem during FSW operations. Ulysse  has also used a visco- plastic approach to model 3D heat transfer and plastic flow during FSW where it has been assumed that heat is mainly generated from the rotational motion of the shoulder. Song and Kovacevic  have established a