When welding two abutted plates in FrictionStir Welding (FSW), the presence of gap between the faying surfaces of the plates is a common problem and reality for manufacturing reasons. This gap between plates may be due to improper alignment, mismatch or clamping. Gap between two plates to be joined in FSW is limited to a percentage of the plate thickness above which the weld quality will be compromised  . In this work, a study on possible methods to increase weld gaptolerance requirements in Friction-Stir Welds of 8 mm thick 6082–T6 aluminum alloys was investigated and evaluated. FSW does not require the use of filler materials therefore; any gap between the abutting surfaces of the weld result to thinning and reduction in the cross-sectional area of the weld  . An ability to bridge these gaps without compromising weld integrity will be advantageous. When the FSW tool encounters a gap, material can possibly escape (not as flash) but from the processing zone and this causes poor welds due to lack of bonding and insufficient material mixing  . Both these effects can possibly weaken the weld therefore a method is required to increase gaptolerance while maintaining joint integrity. This method involves the use of novel tool designs and process parameter control to achieve adequate welds.
a maximum load of 19.71 kN (0.657N/m), while Tool2 exhibited the poorest performance with a maximum load of 7.63 kN (0.254N/m), and Tool3 provided intermediate performance with a maximum load of 12.35 kN (0.412N/m). As a brief comparison, studies that have examined the overlap shear strength of resistance spot weldedjoints for aluminum samples of similar size demonstrate maximum loads of between 2kN and 5kN ; and studies of adhesive bonded samples demonstrate maximum strengths between 4kN and 10kN  .The low strength of joints made with Tool2 is likely due to excessive thinning of the upper sheet; as well as a more severe hooking defect, which results in a smaller effective plate thickness (based on the distance between the tip of the hook flaw and the surface of the sheet). Increasing the travel speed to 180 mm/min resulted in an increase in strength for welds made with Tool1 and Tool3. Applying a speed of 250 mm/min, the strength of welds made with Tool3 increases further; however, overlap shear loads in welds made with Tool1 decrease significantly at this highest travel speed. This decrease in joint strength can be explained by the observation of voids in the welds noted in Figure 29b. The trend of higher strength at faster travel speeds is also commonly observed in other FSW studies using other heat treatable alloys such as AA7075-T6   , and is attributed to the fact that faster travel speeds produce lower heat input to the weld, which results in less softening of the heat-treatable material, producing a stronger joint overall. The highest joint strength of 20.45kN was achieved with Tool1 at a speed of 180 mm/min.
The butt joints of semi solid metal 6061 were produced in as cast conditions by frictionstir welding process (FSW). This experiment studied in pre/post heat treatment (T6) using the welding speed 160 mm / min with tilt angle tool at 3 degree and straight cylindrical tool pin. The factors of welding were rotating speed rates at 710, 1000, 1400 rpm and heat treatment conditions. They were divided into (1) As welded (AW) joints, (2) T6 Weld (TW) joints, (3) Weld T6 (WT) joints, (4) T6 Weld T6 (TWT) joints, (5) Solution treated Weld Artificially aged (SWA) joints and (6) Weld Artificially aged (WA) joints. Rotating speed and heat treatment (T6) condition were an important factor to micro, macro structure of metal and mechanical properties of the weld. Increasing rotating speed and different heat treatment condition impacted onto tensile strength due to the defects on joints. Therefore the optimum welding parameter on joint was a rotating speed 1400 rpm, the welding speed 160 mm/min, heat treatment condition of Solution treated Weld Artificially aged (SWA) which obtained the highest tensile strength 179.80 MPa, as well as, the maximum average hardness of 92.7 HV at tool rotation speed 1400 rpm, welding speed 160 mm/min, heat treatment condition of Weld T6 (WT).
The various parameters affecting the weld quality during the FSW process involving the butt joining of AA7075 T6 were investigated by Bahemmat et al. . Kumar et al.  studied the influence of the tool ge- ometry on the FSW of an aluminum alloy with specific reference to microstructural development, defect for- mation, and mechanical response. Some researchers concentrated on hardness property of the welded joint. Moreira et al.  studied hardness of various re- gions of dissimilar frictionstirwelded of AA6061-T6 and AA6082-T6. The results showed that the max- imum hardness occurs in the Nugget Zone (NZ) and the minimum occurs on the border between Thermo- Mechanically Affected Zone (TMAZ) and Heat Af- fected Zone (HAZ). Some scientists focused on the tensile strength of weldedjoints. For example in a study which was done by Palanivel et al. , var- ious tool shapes and rotational speeds were used to achieve the highest tensile strength for dissimilar fric- tion stirwelded of AA5083 and AA6351 aluminum al- loys. On the other hand, a study done by Mishra and Ma , illustrated that the tensile strength of frictionstirweldedjoints of AA2024 aluminum alloy increases by enhancing the rotational and transverse speed. Fur- thermore, Cavaliere et al.  investigated the me-
The higher hardness measured in the TMAZ especially for 7075 al alloy side could be attributed to both higher dislocation density and precipitates introduced during cool- ing. The minimum hardness values in the HAZs for two alloys indicate that overaging process occurred in these regions. The slight increase of hardness in HAZ with increasing rotation speed could be attributed to the relatively increasing of heating or cooling rates during welding by increasing rotation speeds. Increasing heating rate reduce the time for precipitates to grow and hence leads to hardness increase in HAZ. Also, increasing cooling rate after welding increases the amount of supersaturated solute which will be available for further precipitation reaction at room temper- ature. Although, there are some previous works 22–24) dealing
Sedmak et al. (2016) have developed a mathematical relationship between the speeds and temperature for FSW. The equation shows that rotational speed is directly proportional to the FSW temperature and inversely proportional to the melting temperature. Therefore, as the rotational speed increases the FSW temperature increases and the melting temperature decreases; whereas increasing the welding speed causes a decrease in FSW temperature and an increase in the melting temperature. This relationship was also reported by Sakthivel et al. (2009) when investigating the effect of welding speed on microstructural and mechanical properties of frictionstirwelded commercial aluminium alloys by using different welding speeds (50, 75, 100, 175 mm/min) with a constant rotational speed. It was found that the lower welding speed creates enough heat for the material to be stirred together in the weld zone producing finer grains.
FrictionStir Processing (FSP) was based on the principles of FrictionStir Welding (FSW), a solid-state joining process originally developed for aluminium alloys. It is an emerging metalworking technique which can provide localized modification and control of microstructures in near-surface layers of processed metallic components. In this research, FSP appears as an alternative to traditional methods for fatigue strength improvement of weld joints, such as re-melting, hammering and blasting,. This technique was applied on Metal Inert Gas (MIG) butt welds with and without reinforcement, performed on AA 6082-T6 alloy plates. The potential benefits of post-processing MIG welds by FSP were studied using microstructure analysis, hardness measurement, tensile strength, residual stress measurement, and fatigue testing. Fatigue tests were carried out under constant amplitude loading with the stress ratio R set to 0. Frictionstir processing of MIG welds does not change the hardness and mechanical strength of the weld substantially, but the fatigue strength was increased, due to the geometry modification in the weld toe, reduction of weld defects and grain refinement of the microstructure.
ABSTRACT: Joining the two facing workpieces without melting them by using non-consumable tool is referred as FrictionStir Welding which is a solid state joining process. This economic and technically advantages process was invented in 1991 by The Welding Institute, United Kingdom. Joining of Non-Ferrous and Ferrous materials like Aluminium to Steel finds its application in various industrial applications. Due to the large differences in melting temperature, physical and chemical properties makes it difficult to control weld and defects during welding. Formations of intermetallic compounds at the interface due to very low solubility of Fe in Al are detrimental to joint efficiency. The aim of the present work is microstructural investigation of optimized FrictionStir Welding butt joint between AA 6082-T6 and Soft Steel/Mild Steel. Radiography test is done to check weld joint is sound or not. Then microstructure evolution in frictionstir weld joints was studied by optical microscopy. Fine recrystallized grains were observed in the weld nugget zone, while thermo-mechanically affected zone showed distorted and unrecrystalized grains. Further, Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) investigations were implemented on the optimized specimen in order to study the development stages that occur during welding at the welding interface.
Schematic draw of the weld joint and tool is as shown in Fig.2. A non-consumable H-13 tool steel with concave shoulder and scrolling on the shoulder surface is chosen as tool material to fabricate the joints, due to its high strength at elevated temperature, thermal fatigue resistance, and low wear. The diameter of the shoulder and pin used were 18mm, 6mm respectively and length of the pin is 4.7 mm with taper cylindrical threaded tool pin profile is used to weld. After the welding process, the joints were visually inspected for exterior defects and it was found that the joints were free from any external defects. The butted plates were clamped on a steel backing plate. The welding tool is tilted by 2.5 degrees of angle with reference to the welded plates and tool was rotated in the clockwise direction. A constant axial force is applied to all the joints. A specimen was cut from the welded plate perpendicular to the FSW line to carry out the microstructural characterization. The test sample was prepared according to the standard metallographic procedure and etched with modified Keller reagent. The computerized picture of the macrostructure of the etched specimen was captured utilizing a digital optical scanner.
Initially a base metal of 4mm thickness of AL5083-AL6061 aluminum alloys was welded as but joint. These are welded under vertical milling machine having 1 HP motor and 3000 rpm. We have chosen H13 tool steel as it has Non-deforming characteristics and having high hot hardness. Specifications of tool shoulder and pin used are diameter of tool 20mm, diameter of the pin 3mm, and length of pin 3.7mm. A constant axial force of 5KN has been applied with four rotational and welding speeds. During FSW the welding and after welding the specimens were exposed to normal cooling (atmosphere or room temperature). After the completion of FSW specimens were cut for different tests (tensile test, compression test, micro hardness, and micro structure) as per ASTM standards. After weld specimens made they were go for test machines. Tensile specimens on universal testing machine, micro hardness on Vickers hardness machine, compression test on impact machine and microstructure on optical microscope was carried.
other two parameters on bond strength. Payeganeh et al.  investigated the effect of pin geometry and FSW process parameters on mechanical properties of pp composite welds. Their results indicated that pin geometry had a significant effect on weld surface appearance and weld tensile strength. Pirizadeh et al.  used a new tool named ‘‘self-reacting tool’’ to weld acrylonitrile butadiene styrene (ABS) sheets. They studied the effect of shape of the pin, rotational speed and transverse speed on mechanical properties. Their results show that pin shape has the greatest effect on tensile strength of welded parts. Azarsa et al.  investigated the effect of critical process parameters such as rotational speed, shoe temperature and traverse speed on the flexural strength of frictionstirweldedjoints of the high density polyethylene (HDPE). They concluded that welding at a lower level of tool travel speed and a high level of rotational speed increased weld flexural strength by reducing size of defects. Mendes et al.  studied the influence of axial force, tool rotational and traverse speed on quality of ABS plates. Their results show that high rotational speed and high axial force are required to produce welds free of defects. The past works show that there are no reported publications concerning modeling and optimization of process parameters in FSW of nanocomposites. In this work, an experiment is therefore designed using Box– Behenken design and a new hot tool to study the effect of rotational speed, welding speed, shoulder temperature and clay content on the weld strength of PP / ethylene-propylene diene monomer (EPDM) / Clay nanocomposite. The MINITAB software is used to create the design matrix and analyze the experimental data .
In this paper, a experimental study of frictionstirwelded Superplastic forming of the AA6061-T6 sheets are formed through die forming. The experimental and finite element analyses have been conducted for optimum forming time and optimum temperature for the given pressure. The fine meshed area bulge profile increases during the forming with consequent decrease thickness at the pole. The formability for the FSW 1000 rpm showed a very high pole height than the other two welding speeds.
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 FrictionStir Welding (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 development of sound joints between dissimilar materials is a very important consideration for many emerging applications, including ship building, aerospace, transportation, power generation, as well as the chemical, nuclear, and electronics industries. However, the joining of dissimilar materials by conventional fusion welding is difficult because of the poor weld ability arising from the different chemical, mechanical, and thermal properties of welded materials and the formation of hard and brittle inter metallic compounds. The Present work main focused on the Tensile Strength of Al-Cu weldements and their micro Structural behavior at different weld speeds and different spindle speeds.
This research results apply feasible welding parameters to the joining of aluminum alloy launch box parts. Through material preparation, machining and joining, the dimension and performance of the ﬁnished product is also tested. In the actual manufacturing of a launch box, the box is divided into four units based on cross-sectional shape, as shown in Fig. 3. Each unit adopts a single cross-sectional extruded 6061-T6 alloy. Through machining, the extruded unit is made to conform to pre-assembly dimensions. Afterwards this research conducts assembly welding after obtaining feasible welding parameters. Finally, this research carries out welding quality testing and precision measurements of important dimensions to verify the feasibility of FSW.
Both the top and bottom sheets, 152.40 mm long and 2.54 mm thick, were positioned as shown in Figure 1. Sheets were degreased prior to welding using acetone as a cleaner. After the FSW process, an optical specimen was taken out from each run; microscope observations of the cross sections were carried out to identify the exact position of the welding zones. At the same time, the cross sections of the welds were observed and analysed by image processing software to identify the position of the hook defects and measure the grain size. According to ASTM E 112, the grain size number is determined by using the general intercept method. For this purposes, standard metallographic polishing procedures were used with modiﬁed Keller’s reagent. Thanks to the aforementioned analyses, it was possible to remove three minitensile specimens from both the nugget and heat- aﬀected zones for each run by using a minimilling machine. Minitensile testing was carried out by following design of experiments. Figure 2 shows the minitensile specimen drawing with its geometrical dimensions. It is worth to note that smaller is the specimen higher are the mechanical properties recorded; experimental results of minitensile samples refer to local properties of the material which exceed the global ones . Each sample was pulled out from the lap joints; then, it was reﬁned and polished on both sides by using abrasive papers of 30 µm and 12 µm removing ex- ceeding material and leading the thickness from 1 mm to 0.50 mm. Abrasive papers of 9 µm and 3 µm were used to eliminate the surface scratches; ﬁnally, a diamond suspen- sion of 1 µm was used to create a like-mirror surface. The waiting time between the welding and the minitensile testing was typically 150 h. The minitensile testing was performed through a minitensile testing machine by imposing a strain rate equal to 10 −3 s −1 . The ultimate strength, the yield strength, and the elongation of the weld were measured. The last property was evaluated by using the Epsilon ONE optical high-precision extensometer, which is a noncontact device able to measure accurately the strain of this type of mini- tensile specimen at the narrow section.
Frictionstir welding (FSW) is a solid-state welding process in which the relative motion between the welding tool and the work pieces produces heat. This makes the material soft, and therefore it can be joined by plastic deformation and diffusion. This method relies on the direct conversion of mechanical energy to thermal energy forming the weld joint without any external source of heat. In the FSW process, a non-consumable rotating tool is forced down into the joint line under conditions where the frictional heating is sufficient to raise the temperature of the work pieces. It can plastically deform and locally plasticize.
The extraordinary mechanical strength of UFG metals stimulated the development of their production methods. Today, UFG metals can be efficiently produced by different variants of the severe plastic deformation (SPD) method. However, the major restriction in wide industrial application of UFG metals is the lack of a reliable welding process, which unlike riveting would give material continuity in the joint. There is also a requirement to weld UFG materials without losing their properties governed by the nanoscale structure. In this context, traditional welding processes based on melting, such as brazing or arc welding, are not applicable because they occur at high temperature causing a total change of structure leading to structure discontinuity and considerable decrease in mechanical strength along the joining line. In this work, FrictionStir Welding (FSW)  was chosen as an innovative bonding technology to weld aluminium. FSW takes place in the solid state without reaching the melting temperature of the base material . Stable connection is obtained by mixing the friction-heated, plasticized and deformed metal along the contact line of welded elements. It can be performed by moving a rotating tool (a pin with a shoulder) along a joining line. The key factor for obtaining a consistent joint is large plastic deformation at elevated temperature. It results in bringing-up atoms to a distance which allows creation of a metallic bond. Accompanied by increased density of lattice defects, the final microstructure in different joint areas is mainly dependent on dynamic recrystallization and/or recovery  what is common for materials such as aluminium, which is characterized by high stacking fault energy.
Dissimilar 2024-T3 aluminum alloy and AZ31 magnesium alloy of 3 mm thick plates were frictionstir butt welded using a tool made of a tool steel (SKD61). The welding tool is composed of 12 mm diameter shoulder and 4 mm diameter threaded probe. Figure 1 shows the schematic illustration of the tool. The tool axis was tilted by 3 degrees backward with respect to the vertical axis. After ﬁxing (clamping) the specimens on a rigid back plate of the FWS machine, the FSW tool was slowly pushed into the abutting surfaces of specimens to a 3 mm plunge depth. The probe depth and its vertical accurate position were controlled manually by using vertical computerized motor instead of the vertical force because of the limitation of the facility of FSW welding machine. The probe depth was constant for all joints. The chemical composition of base metals is listed in Table 1. Rotation speed was kept constant at 2500 min 1 and welding speeds were set at 200, 300, 400 and 550 mm/min. 2024-T3 aluminum alloy plate was located on the advancing side. Changing the ﬁxed location of two alloys led to failure in the dissimilar FSW joints. The chemical composition of base
The flow arm zone is on the upper surface of the weld and consists of material that is dragged by the shoulder from the retreating side of the weld, around the rear of the tool, and deposited on the advancing side. The Thermo- mechanically affected zone (TMAZ) occurs on either side of the stir zone. In this region the strain and temperature are lower and the effect of welding on the microstructure is correspondingly smaller. Unlike the stir zone the microstructure is recognizably that of the parent material, albeit significantly deformed and rotated. Although the term TMAZ technically refers to the entire deformed region it is often used to describe any region not already covered by the terms stir zone and flow arm.