A Detailed Study on Friction Stir Welding and Friction ...

International Journal of Industrial Engineering & Technology. ISSN 0974-3146, Volume 4, Number 1 (2014), pp. 1-22 © GBS Publishers & Distributors (I) http://www.gbspublisher.com

A Detailed Study on Friction Stir Welding and Friction Stir Processing–A Review Paper Deepak Bakshi1, Chander Prakash2, Supreet Singh3, Rajeev Kumar4 and Deepak Ashri5 1, 2, 3, 4 & 5

Galaxy Global Group of Institutions Dinarpur Shahabad E-mail: *[email protected]

Abstract Friction stir processing (FSP) is an emerging metalworking technique that can provide localized modification and control of microstructures in near-surface layers of processed metallic components. It selectively modifies the microstructure in specific areas with a view to improving local mechanical properties. The microstructure and mechanical properties of the processed zone can be controlled by optimizing the tool design and FSP parameters. These properties include obtaining a dense solid without porosity, homogeneous distribution of reinforcement particles in matrix and strong bonding between reinforcements and matrix as a result of reaction between them due to the thermo mechanical condition during FSP. Friction stir processing has been used with aluminum-and magnesium based alloys for improving mechanical properties and inducing super plasticity through grain refinement. Aluminum alloys used in process of FSP are attracting considerable interest worldwide because of their low density, high ratio of strength to weight, high thermal conductivity and good corrosion resistance. Magnesium alloys have become alternative candidate for applications in automotive, aerospace, audio and electronic industries. The current trend in the automotive industry shows two main application ranges for Mg pressure die castings, the power train and the body structure. FSP is a versatile technique with a comprehensive function for the fabrication, processing and synthesis of materials. Nano composites in FSP also have superior properties than those produced with conventional methods such as mechanical alloying, casting, rapid solidification, combustion synthesis, etc. In the review paper study has been focused on basic geometry for FSW tool

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Supreet Singh et al and Tool Design, FSW defects, welding parameters, applications of FSP, Advantages of FSP and disadvantages of FSP. Keywords: Friction Stir Processing (FSP), Friction Stir Welding (FSW), Super plasticity, microstructure, composite and tool, Parameters, Filling Friction Stir Welding (FFSW)

1. Introduction The friction stir processing is an adaptation of the friction stir welding process. The friction stir processing technique presents several characteristics, between which can provide localized modification and control of microstructures in near-surface layers of processed metallic components in order to modify the correspondent mechanical behavior. Friction stir Processing (FSP) uses the same techniques and equipment as Friction Stir Welding (FSW). Friction stir welding (FSW), which is a solid-state welding process that involves severe plastic deformation, has been widely used in joining of light alloys and ferrous alloys. Based on the basic principles of FSW, a new processing technique friction stir processing (FSP) has been developed for microstructural modification [1]. In process of FSP in Fig. 1.1 as shown, a non-consumable tool comprising a shoulder and pin rubs against the work material and produces enormous frictional heat. The heat, combined with deformation by the stirring action of tool pin and pressure due to tool shoulder, produces a defect-free, recrystallized, fine-grained microstructure.FSP is an effective method for producing fine-grained structure and surface composite, modifying the microstructure of materials, and synthesizing the composite and intermetallic compound in situ [2]. Recently, FSP has been successfully used for producing UFG microstructures in Al, Mg, Cu alloys and steel [3-7].

Fig. 1.1: Process and the mechanism of Friction Stir Processing.

A Detailed Study on Friction Stir Welding and Friction Stir Processing

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The above Fig. 1.1 also show the mechanism of FSP which has been divided into four zones as defined the first is affected material or parent metal: This is material remote from the weld that has not been deformed and that, although it may have experienced a thermal cycle from the weld, is not affected by the heat in terms of micro - structure or mechanical properties. Second is the Heat-affected zone: In this region, which lies closer to the weld-center, the material has experienced a thermal cycle that has modified the microstructure and/or the mechanical properties. However, there is no plastic deformation occurring in this area. A third region is Thermo mechanically affected zone (TMAZ): In this region, the FSW tool has plastically deformed the material, and the heat from the process will also have exerted some influence on the material. In the case of aluminum, it is possible to obtain significant plastic strain without recrystallization in this region, and there is generally a distinct boundary between the recrystallized zone (weld nugget) and the deformed zones of the TMAZ. Lastly the Fourth region is defined as Weld nugget: The fully recrystallized area, sometimes called the stir zone, refers to the zone previously occupied by the tool pin. The term stir zone is commonly used in friction stir processing, where large volumes of material are processed.[8-10]

2. Literature Review The most used techniques for joining different aluminum components are MIG and Tungsten Inert Gas (TIG) welding processes. However, these welding techniques can lead to different drawbacks as porosity, lack of wetting, hot cracking, strength reduction, distortion and residual stresses. The strength reduction, stress concentration and weld defects lead to global static and fatigue strength reduction in aluminum alloys welds in comparison with the base materials [11–14]. Some techniques have been applied to increase the fatigue behavior of MIG or TIG welds such as shot peening, remelting, hammering and blasting. Recently, a new technique called Friction stir processing (FSP) arose as an alternative for improving the fatigue behavior of MIG welds. The FSP [15, 1] is an adaptation of FSW, developed by the Welding Institute (TWI) [16]. In both techniques a non-consumable rotating tool, with or without shoulder and profiled pin, penetrates in the components and advancing along a selected path, induces frictional heating and plastic deformation, thus producing recrystallized and refined microstructures. The final objective of FSP is the improvement of specific properties through the localized microstructure modification. The concept of friction-stir processing (FSP) was first proposed by Mishra et al. [17] and initially employed for Al alloys according to the fundamentals of friction-stir welding (FSW), which is invented by The Welding Institute (TWI) of UK [18]. After recent years of research, it has been reported that the coupled thermal– mechanical effect of FSP procedure can be utilized to provide localized microstructure modifications in the surface layer of various metals of Al, Mg and Cu based component, including grain-refining and even preparing nano-crystalline [18]

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In FSP a non-consumable rotating tool is used for inducing frictional heat and plastic deformation, in the surface of the materials to be modified, which promotes the formation of extremely refined material layers by dynamic recrystallization [19]. Local enhancement of substrate properties by FSP was already performed by several authors in aluminium and aluminium alloys [20–24], magnesium alloys [25–27], NiAl [28], titanium alloys [29], copper [30] and steels [31,32]. In all these studies important grain refinement, microstructural homogenization and improved mechanical properties were registered for the processed materials. Some of these works even report the formation of relatively uniform ultrafine grained microstructures (UFG) [22,26,32,33]. Friction stir processing has been applied extensively to Al and Mg alloys. However recently, with the great progresses in FSP tool materials, there has been increasing interest in FSP on the surface of high melting point materials such as titanium, iron and nickel based alloys [34-36]. Due to that Ti has low thermal conductivity and high softening temperature, it is difficult to generate sufficient heat-input to soften material and realize considerable plasticized deformation without causing local overheating. Consequently, understanding of the influences of FSP processing parameters on the microstructure evolutions and the resulted surface properties of Ti and its alloys is quite important. Several literatures on FSP of Ti–6Al–4V alloy, especially for refining the coarseness, fully lamellar microstructure of investment-cast and hot isostatic pressed Ti–6Al–4V Alloys [35,37,38]. Aluminum alloys are attracting considerable interest worldwide because of their low density, high ratio of strength to weight, high thermal conductivity and good corrosion resistance; however their poor wear resistance causes some limitations for their applications. Metal matrix composites (MMCs) are novel materials with superior mechanical and tribological properties. For use in tribological applications, metal– matrix composites must be able to support a load without undue distortion, deformation, or fracture during performance [39]. Presence of ceramic particles can provide these needs. Hybrid MMCs are engineering materials that include two or more different reinforcements in order to achieve the combined advantages of them [40]. Sharma et al. [41] reported an improvement in the fatigue stress threshold greater than 80% in the nugget of friction stir processing samples of a cast A356 alloy. This behavior was achieved taking advantage of the microstructural refinement, elimination of casting defects and the breakup and uniform distribution of Si particles in the aluminum matrix. Fu et al. [42] studied the effects submerging conditions on the mechanical properties of friction stir welded 7050 Aluminum alloy. FSW in air and submerged with cold and hot water were considered. Their results showed that hot water was the optimal choice, resulting in a ratio of 92% ultimate tensile strength and 150% elongation. Another study by Liu et al. [43] compared the mechanical properties of 2219 Aluminum alloy friction stir welded in air and underwater. They reported that the tensile strength of the under-water weld was higher; however, the plasticity deteriorated in comparison with the weld done in air.


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Zhang et al. [44] investigated the microstructure and the mechanical properties of FSW of 2219-T6 under submerging conditions. The study showed that the tensile strength was very sensitive to the rotational speed. They also observed that increasing the rotational speed above 1400 rpm caused void defect to form in the stir zone. Increases in grain size and in dislocation density in the stir zone were observed as rotational speed was increased. Hofmann and Vecchio [45] studied the effect of submerging FSP on grain size of Aluminum alloy Al-6061-T6 compared to in air FSP. Their results showed that more grain refinement was attained under submerging conditions due to faster cooling rate. They also used boundary migration model to predict the grain size using measured thermal histories of the stirred material.

3. The Basic Geometry for FSW Tool and Basic Concept of FSW The basic geometry for a FSW tool is shown in Fig. 3.1 shows the various nomenclature where: Rs is the shoulder radius, Rp is the pin base radius, Rpt is the pin point radius L pin is the pin height and a is a tap angle. According to Edwards and Ramulu [46] a conical tool is needed because of the low thermal conductivity of titanium. A cylindrical pin tool is not indicated for titanium because the heat generated in the shoulder is not able to flow to the root of the joint, allowing the mixing of material in the lower plate. Simple geometries are generally used on pin tool for titanium alloys. In all FSP experiments tool rotation rate, traverse speed and tilt of the spindle towards trailing direction has been defined differently in many studies by various authors, also the rpm of tool, feed rate and angle of tool need to be set up before experimentation.

Fig. 3.1: Basic geometry for a FSW tool [46]

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The basic concept of FSW is a rotating tool, made of non-consumable material, especially designed with a geometry consisting of a pin and recess (shoulder). This tool is inserted spinning on its axis at the adjoining edges of sheets or plates to be joined, and then it travels along the joining path line. Fig. 3.2 illustrates the process for the tool and the plate, typical steps of the process: (i) downward motion to penetrate the material; (ii) penetrating the material; (iii) time for the heat generation for deformation; (iv) linear movement on the part toward the processing direction; (v) end of processing and tool retraction [47].

Fig. 3.2: FSW process steps [47]. 3.1 Tool Design The main mechanics involved in FSW are, as already identified, the thermal and flow dynamics, and the metallurgy. These form the dominant topics within the research literature. There are two types of flow occurring under the tool. These are known as pin-driven flow and shoulder-driven flow [49]. Both shoulder and pin affect material plastic flow and deformation [1,48]. In addition, the design of the tool is also known to affect the shape, size and location of any unfilled welds (defects) [50]. Therefore, in achieving a sound weld in FSW, the role and effect of the tool design need to be understood. 3.1.1 Conventional friction stir welding tools Tool design has been an active area of research for single shoulder type CFSW tools [1,51]. The results can be categorised according to (1) pin features, (2) shoulder features and (3) tool dimensions. The known functional consequences of each are identified as follows. Pin features: vertical motion can be introduced with cylindrical threaded pin feature [52], while flutes and flat faced features influence horizontal motion which helps in mixing the weld material [53,54]. A maximum of four flutes/faces is preferred as with additional flutes/faces provide little differences [55]. In addition, a tapered pin reduces torque and bending moment because of reduced swept volume during mixing [57]. Shoulder features: the primary design feature is the overall shape: flat, concave, or convex form. The concave design is common and is believed to provide a reservoir of material that feeds into the flow generated by the pin. Meanwhile for convex shapes the shoulder can be engaged with the work piece at any location along the convex surface. This allows for a larger degree of flexibility in the


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contact area between the shoulder and workpiece [57,56–59]. Secondary features are also possible, the most common being a scrolled shoulder [72,55,56,58,60,61]. The intended purpose of this feature is to move material from the outer shoulder inwards. Edge fillet/chamfer features have also been used to reduce flash [61]. Each of the features can be combined in forming complex hybrid tools, some examples are contained within [49]. Tool dimensions: there are a number of heuristics that have emerged. For example, it is commonly stated that the pin diameter should be equal to the thickness of the materials to be welded, and pin length should be 0.2–0.3 mm shorter than the thickness of the material [50,52,53,62–65]. For the shoulder, the diameter should be three times the plate thickness [66]. 3.1.2. Bobbin friction stir welding tools The research described previously is for CFSW, the bobbin case has had much less research attention. While some of the underlying physics of CFSW is applicable to bobbin tools, this has not been demonstrated conclusively. Nor is it certain that the tool-features and process-settings are transferable, because of the fundamental differences in heat generation and flow characteristics. The notable works in this area are [71,57,67–69]. The implications, from these relatively small bodies of literatures, are that tool features have the following consequences: a) A cylindrical pin with threaded features can produce a clear macrostructure boundary and higher bending strength. Alternatively three flats can be used. b) A tapered tool pin with three flats enables a diameter reduction in the lower shoulder which then contributes low torque and bending moment. c) When weld plates have high flatness variations, convex and scroll shoulder features can be useful. A common design of BFSW is a cylindrical tapered threaded pin with three flats. Heuristics for tool dimensions are not directly transferrable from the CFSW case [9], because of the full pin penetration. Recommended process settings have been specified as follows: for thinaluminium(4–8 mm),spindlespeedsof450–600 rpm and travel speeds of 75–100 mm/min; for thicker material (about 25 mm) a spindle speed of 170– 300 rpm and travel speed of 100–500 mm/ min. However other variables e.g. dwell time, tool gap, support/ clamp setting and plate condition, were not defined [71,57,67,69]. To the extent that thermal mechanisms dominate the welding process (which is a simplification, albeit a necessary one), the amount of heat generated is related to the spindle and travel speeds, but not solely to those variables. Other variables are tool geometry, features-on-tools, and other process settings. These should ideally be dealt with in an integrated way, though this is difficult to achieve because of the complexity of the interactions. It is therefore understandable that much of the research has approached these factors in a piecemeal manner. There have been some attempts at unravelling the interactions of these multiple factors, though at present the results are limited in scope [72] and weld quality is not yet predictable [70].

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3.2 Various Tool Materials Tool steel is the most common tool material used in friction stirring. This is because a majority of the published FSW literature is on aluminum alloys, which are easily friction stirred with tool steels. The advantages to using tool steel as friction stir tooling material include easy availability and machinability, low cost, and established material characteristics. AISI H13 is a chromium-molybdenum hot-worked airhardening steel and is known for good elevated-temperature strength, thermal fatigue resistance, and wear resistance. In addition to friction stir welding aluminum alloys, H13 tools have been used to friction stir weld both oxygen-free copper (Cu-OF) and phosphorus-deoxidized copper with high residual phosphorus (Cu-DHP).However, the limited travel speed in Cu-DHP would limit the production use of H13 .Shoulder inserts consisted of mainly Inconel 718, Nimonic 105 and Pins made from Nimonic 90, Inconel 718. Nimonic 105 was able to produce 20 m (66 ft) long friction stir welds with no fracture or change in dimensions. Selection of Nimonic 105 was attributed to good creep rupture strength up to 950 °C (1740 °F) and consistent ductility up to 900 °C (1650 °F). Densimet was selected as the shoulder material based on higher thermal conductivity (130 W/m°C) than nickel-base (10 to 20 W/m°C) and cobalt-base alloys (70 W/m°C), where the author assumed that faster heating of the tool shoulder is preferred in FSW. The evaluated tool materials included H13 tool steel, IN738LC, IN939, IN738LCmod, sintered TiC:Ni:W (2:1:1), hipped TiC:Ni:Mo (3:2:1), pure tungsten, and PCBN [72]. 3.3 New techniques of filling friction stir welding A new technique of filling friction stir welding (FFSW) relying on a semi consumable joining tool has been developed to repair the keyhole left at the end of friction stir welding (FSW) seam. The conventional non consumable tool of FSW was transformed, and a semi consumable joining tool consisting of alloy steel shoulder and aluminum alloy joining bit was designed to create a solid state joint. Using the combined plastic deformation and flow of the consumable joining bit and the wall of the keyhole, the FFSW process is able to repair the keyhole with both metallurgical and mechanical bonding characteristics, and the FSW seam can be achieved without keyhole or other defects [73].

4. Welding Parameters FSW involves complex material movement and plastic deformation. Welding parameters, Tool geometry and joint design exert significant effect on the material flow pattern and temperature distribution, thereby influencing the micro structural evolution of material [1]. Therefore, welding speed, the tool rotational speed, the tilt angle of the tool, tool material and the tool design are the main independent variables that are used to control the FSW process. As the tool (rotates and) moves along the butting surfaces, heat is being generated at the shoulder/work-piece and, to a lesser extent, at the pin/work-piece contact surfaces, as a result of the frictional-energy


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dissipation [74].The welding speed depends on several factors, such as alloy type, rotational speed, penetration depth, and joint type [75]. Higher tool rotation rates generate higher temperature because of higher friction heating and result in more intense stirring and mixing of material. During traversing, softened material from the leading edge moves to the trailing edge due to the tool rotation and the traverse movement of the tool, and this transferred material, are consolidated in the trailing edge of the tool by the application of an axial force [76].

Table 4.1: The process parameters and there effects in friction stir welding [72]

4.1 Friction stir welding (FSW) defects FSW may be of any orientation, size, or shape. However, like arc welding, the process moves in a linear fashion, usually at a constant rate along the joint line, and therefore has a similar tendency to produce defects which propagate for some length and have their major dimension parallel to the travel direction. However, defect formation in FSW is otherwise very different from arc welding and requires new defect definitions. FSW defects include excessive flash, excessive concavity, tool particulate inclusions, foreign substances, voids, wormholes, lack of penetration (LOP) root defects and kissing bond defects which may occur in the root or in the weld interior. When discussing methods of detection it is helpful to divide FSW defects into inclusions, volumetric defects, and non-volumetric (laminar) defects. When discussing the mechanical and structural significance of defects it can be useful to additionally classify by non-surface breaking (interior) and surface breaking (face or root). Flash is produced by displacement of material from the face (tool-side surface) of friction stir welded components. Flash is not in all cases undesirable and is often used as a visual indicator that the proper tool depth has been achieved for a given application. If the insertion depth is too deep, excessive flash is created. Excessive flash may also result from improper tooling or parameter settings. Shoulder scrolling and reduced rotation rate are example flash mitigation techniques. Due to a conservation of volume, excessive flash may result in a significantly concave weld, causing thinning of the weld [77]. Excessive face concavity and excessive flash can be readily detected visually. The flash and associated concavity can then be processed by grinding or machining to meet surface finish requirements for the part. If the flash and associated concavities are too great then the part may not be reparable by simple surface processing as the resulting thickness may below the acceptable dimensional tolerance. The FSW tool is nominally non-consumable. However, as discussed in the previous section, wear does occur to the tool and this can result in dimensional changes to the

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tool which cause weld defects. Additionally, particles of tool material can be left in the welded material. In some applications, this is acceptable. In other cases, the embedded tool particles have a significant detrimental effect on the joint properties and are not acceptable. The size and distribution of inclusions within the joint should be considered along with the composition of the tool material and welded material. In addition to tool material inclusions, foreign substances (e.g. oil, grease, dirt) can contaminate the material surface and adversely affect the FSW joint produced. Many friction stir welded materials develop a surface oxide layer. This layer can sometimes be seen as a partially dispersed, visible trace of the original joint line in a FSW lateral macro section. The traces are referred to as remnant oxide layers (ROL), joint line remnants (JLR), entrapped oxides, residual oxides, lazy-S curves, or kissing bonds. There are cases in the literature where a visible trace of the original joint line (usually called JLR or ROL) can be present in the weld macro section and present in the root with no significant mechanical detriment to the joint [78]. Caravaca et al. [79, 80] of TWI stated that a visible trace of the original joint line (referred to as JLR in the work) through the weld thickness should not necessarily be considered a flaw as this is ordinary to FSW. Kahl et al. [81] also find that a visible remnant does not imply a mechanical detriment. In other cases, often referred to as kissing bonds, a mechanical detriment is seen because processing conditions or the thickness of the oxide layer are such that abutting faying surfaces have not been stirred sufficiently to disperse the oxides or allow for ideal and complete bonding [81–84]. In some cases, cleaning or machining the abutting faces just prior to welding can eliminate this problem [77,78]. Root flaws are surface-breaking discontinuities that are present on the material surface which is opposite the tool. Root defects are important because they can have significant mechanical effects and can be difficult to detect by non-destructive testing (NDT), often being narrow and lacking in volume. Lack of penetration (LOP), lack of consolidation (LOC), and kissing bond type root defects are caused by excessive penetration ligament (distance between bottom of probe and root-side surface of material), inadequate tool-joint alignment (missing the joint), or inadequate disruption (poor stirring) of the abutted parent material surfaces near the root respectively. Both LOP and kissing bonds imply that there is some portion of the abutted joint surfaces which remains unbonded or inadequately disrupted. The definitions of these terms are somewhat muddled, and the decision on nomenclature in a particular case in the literature is one of preference or of degree. Of the two terms, LOP is generally used when the root defect is more severe and is sometimes referred to as an unwelded or unbonded portion of the joint. The kissing bond is generally less severe and can involve significant distortion of the jointline. In still less severe cases, the terms for a partially dispersed oxide layer, listed earlier, are sometimes used. According to the literature, depending on location and extent, LOP defects can have significant effects on mechanical properties, including fatigue life, impact strength, root bend survival, and through-thickness load-bearing capacity. Depending on location and extent, kissing bonds may have deleterious effects on mechanical properties. The mechanical effect of a root defect is dependent primarily on its through-wall height and degree of


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bonding or width. Changes in root defect orientation also change mechanical properties. Laterally offset root defects due to welding off of the planned travel path (LOC) should be considered as a separate case from LOP (see Widener et al. [79] and Smith et al. [80]). Very generally and in aluminum alloys, root defects exceeding 0.25 mm (0.010 in.) in through-wall height have a significant mechanical effect (30% reduction in fatigue characteristics) according to the literature [81-83]. This mechanical effect is more pronounced in fatigue tests than in tension tests. A root bend test is a good predictor of fatigue test performance with respect to root flaws. Failure in root bending is accompanied by a measurable and generally significant reduction of fatigue life in fatigue tests according to the literature surveyed. Root bend tests are a good predictor of root flaw presence. Voids and wormholes (single voids extending longitudinally along the weld) can be found in FSW under non-ideal process conditions. Things like insufficient forging pressure, excessive travel speed, inappropriate tool design, or an overly worn tool may cause the formation of voids [84,85]. These defects may be surface breaking or contained entirely within the volume of the weld, with the former being significantly more detrimental to mechanical properties. Kahl et al. [86] and Chimbli et al. [87] have performed studies on the effects of non-surface breaking wormholes on mechanical properties such as tensile strength, ductility, and fatigue strength in aluminum alloys. In some cases, reductions in tensile strength could be limited to something similar to the ratio of void diameter to material thickness. The effects on fatigue were found to be more significant. include modifications to the tool-shoulder geometry as well as changes in the joining methodology from continuous welding to a discrete joining method, as in Friction Stir Spot Welding (FSSW). Additional variants not covered here include Twin-stirTM, dualrotation FSW, and Pro-stirTM (an additive FSW technology), all of which were developed and investigated by TWI [88]. Production Applications of FSP FSP having many advantages, including improved mechanical properties (tensile and fatigue), improved process robustness, lack of consumables, less health and environmental issues, and operating cost advantages, the majority of production applications have involved joining extruded shapes to make some useful product [97, 98]. FSP has gained significant interest in the sectors of Hollow heat exchangers, Marine Aluminum , Commercial shipbuilding, Delta II rockets Boeing , Commercial shipbuilding , Automotive components , Laser system housings , Motor housings Hydro Aluminum (formerly Marine Aluminum) , Automotive components Showa , Train bodies , Automotive components Tower Automotive , Aircraft structure Eclipse , Commercial shipbuilding , Space shuttle external tanks , Food trays.

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Benefits of Friction Stir Processing–Shown in Table 4.2 Table 4.2: Key benefits of Friction stir Welding. Metallurgical benefits Solid-phase process Low distortion

Environmental benefits Energy benefits No shielding required

gas Decreased fuel consumption in lightweight aircraft, automotive, and ship applications No loss of alloying Minimal surface Improved materials use (e.g., elements cleaning required joining different thickness) allows reduction in weight Fine recrystallized Eliminate grinding Only 2.5% of the energy microstructure wastes needed for a laser weld Weld all aluminum No harmful emissions alloys Post-FSW formability Consumable materials saving, such as rugs, wire, or any other gases Absence of solidification Decreased fuel cracking consumption in lightweight aircraft, automotive, and ship applications Good dimensional stability Excellent mechanical properties in the joint area


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CASE STUDIES OF FRICTION Stir Welding/Friction Stir Processing S. Author No & Year of publicati on 1 Aruri Devaraju et al(2013)

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Substrate & tool material

Welding parameters

Conclusion

Substrate - Travelling speed 1 Microhardness increases due to presence and Al 6061- -40mm/min pining effect of hard SiC and Al2O3 particles. T63 Sheet thickness- 2 Low wear rate was exhibited in the Al– SiC+Gr+Al 4mm SiC/Gr surface hybrid composite. O Shoulder 3. The presence of SiC particles serves as load 2 3 diameter-24mm bearing elements and Gr particles acted as Pin diameter- solid lubricant. Tool - H13 8mm 4 Tensile properties are decreased as compared steel Force-5 KN to the base Angle-2.5 material Degree Kurt AlSl 1050 For good 1. FSP was an appropriate method to modify Adam et steel 1050 dispersions of the microstructure and mechanical properties al (2010) aluminium SiCpof 1050 Al-alloy, FSP decreased the grain size alloy + Sic w-100rpm and and increased the hardness of processed Particles V=20mm\min material. 2. Increased rotation speed and low travelling Thicknessspeeds caused more heat input which affects speed the thickness of the surface layer, grain size 100um-15mm and distribution of the precipitates and 30um -30mm reinforcing particles. 3.A good dispersion of SiCp can be obtained for the composite layer produced by ω= 1000rpm and v = 20 mm/min. 4. The depth of the surface layer can be tailored by welding parameters or probe design which could be used with pin or without pin.. 6. The microhardness of the plain surface of Aluminium increased significantly with increasing travelling speeds. The highest microhardness value was obtained 80Hv for the plain specimen by ω= 500rpm and Feed rate = 30mm/min 7. The microhardness of the SiCp added composites surface increases significantly with increasing rotation speed. The highest microhardness value was obtained 150Hv for the plain specimen by ω= 1000rpm and _ = 15mm/min

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Supreet Singh et al 8. The high microhardness of Al/SiCp composite can be attributed to the presence of reinforcement particles, which also improved the bending strength. Izadi Alumix Travelling 1.The material flow in the stir zone during FSP H(2013) 431D alloy speedwas successful in uniformly distributing the H13 steel 88mm\min SiC particles.However, when samples with 16 Tool rotaional vol% SiC were processed there were residual speed-454rpm pores and lack of consolidation Shoulder diameter-12mm 2 . The increase in hardness with SiC Pin-0.7 pitch at concentration in the end friction stir processed samples appeared to be Pin -5.1 at base related to the mean inter-particle spacing. In this regard, a possible quantitative linear correlation has been proposed. Mahmou Substrate- Shoulder 1 . FSP eliminates the cavities, refines the d.T.S A390 diameter-16mm grain structure and refines the coarse acicular (2013) Hypereutec Pin diameter- Si particles in tic 4mm the eutectic structure as well as the primary Si Force-0.5 KN particles. Rotatinal speed- 2. FSP significantly reduced both the mean Tool-H13 single pass- size and the aspect ratio of the steel 1800rpm and Si particulates. feed rate 3. The FS-processed samples exhibited less 12mm/min scattered and higher hardness values than the as-cast alloy. Rotatatinal speed-multi pass-1200rpm and feed rate 20 mm/min Anvari Substrate Travelling 1- As a result of performing FSP on the surface S.R(2013 Al 6061+ speedof coated Al with Cr2O3, Al–Cr–O nano) Al-Cr-O 100mm/min composites were fabricated. Rotational rate- 2- A homogenous distribution of reinforcement Tool-H13 630rpm particles over the nugget zone was produced by steel Angle-3Degree FSP without any defects. 3- FSP reduced the wear resistance of Al6061T6 without reinforcement due to the loss of hardening precipitates during process. 4Adhesive and abrasive are the dominant wear mechanisms for as-received Al6061-T6 and FSPed samples, while results showed delamination wear for the nano-composite.

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Hutsch .L.L (2013)

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Albakri A.N (2012)

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Chai Fang

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Substrate- Daimeter-13mm 1-High speed FSP was successfully formed on AZ31 pin diameterMg AZ31 sheet material at processing speed Cr-Mo -V tapered between 1 and 10 m/min in single and steel diameter-4mm multiline configurations successfully 2-Tensile testing supported by DIC analysis tip diameter- confirmed the TMAZ to be most prone to 2.5mm enhanced deformation as the samples underwent the highest amount of local deformation in this region Rpm Force(K 2000 N) 2250 8 3250 14 3500 15 20 Mg Shoulder 1-Slightly higher temperature in the range of AZ31B Diameter-13mm 20-40 K were developed on the AS of the sheet H13 steel Pin diameter- as compared to the RS under all processing 6mm conditions. Pin length-3mm 2- It was shown that a combination of high translation and low rotational tool speeds were ideal to cause effective grain refinement . 3-The finest grains were located around the root of the pin/material interface.

AZ91+Al+ Rotational (1) Compared with Normal FSP and SFSP 4Mg+Zr speed-800rpm leads to enhanced superplasticity H13 Steel Speed -60 (2) GBS is the main superplastic deformation mm/min mechanism for the normal FSP and SFSP AZ91 alloys (3)Grain growth and cavities coalescence is the main failure mechanism for the normal FSP and SFSP alloys during superplastic deformation Albakri. Ti-6Al-4V Shoulder (1) Basically slightly higher temperature in the A.N(201 Tooldiameter-15mm ramge of20-40 K 3) WC13WT Pin length - Were developed on the AS of the sheet as %Co 2.2mm compared to the RS under all processing matrix Pin thickness conditions material >2.2mm (2)high translational and low rotational tool speeds were ideal to cause effective grain refinement (3) The finest grains were located around the root of the pin/material interface

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10 Farias.A( TI-6Al-4V Rotational(rpm) 2013) WC,W1100 25%Re 1000 densiment 1200 W+1%LaO

11 Arora H.S

12 Arora H.S

Feed rate(mm/ min) 40 50 50

(1) WC tools are used to inc wear resistance (2) The tool is deformed by the actoin of high temperature and vertical pressure at the end. 2 (3) Tool is also deformed due to strong adhesion from the work piece material. Mg AE42 Rotation(rpm)- (1) Wear rates of AE42 alloy are reduced by alloy 700 FSP process. Velocity(2) wear rates are reduced due to stainless 60mm/min microstructural refinement resulting in higher steel Plunge Depth- hardness, greater work hardening capability 0.35mm and improved ductility. Passes no-3 Substrate- Rotational (1) AE42 was successfully FS processed Mg AE42 speed-900rpm without appearance of any defect. Alloy Linear speed- (2) Multi[pass FSP has a profound effect on Tool-High 60mm/min the refinment of the partical sige. speed steel Plunge depth- (3) The smallest partical size was prioduced by 0.3mm double pass FSP. Shoulder (4) A significant increase in the microhardness diameter-12mm value was obtained. Pin diameter4mm Pin length-2.7

5. Discussions The above case studies show that various alloys of aluminum, magnesium, titanium etc were used in process of FSP/FSW to improve the mechanical and microstructural properties of alloys. The welding parameters were also compared for defined alloys with respective tools used in welding process. Review Paper gives the detailed study on tool geometry & tool design. FSP Defects were also discussed as inclusions, volumetric defects, and non-volumetric (laminar) defects. Studies reveal that FSP having many advantages, including improved mechanical properties (tensile and fatigue), improved process robustness, lack of consumables, less health and environmental issues, and operating cost advantages, the majority of production applications have involved joining extruded shapes to make some useful product.


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