One of the most common and effective method for joining metal structures is conventional welding. In conventional welding process such as TIG/MIG, the weight of workpiece increases due to deposition of filler material. Aluminium alloys are extensively used as a main engineering material in various industries such as automotive industries, the mould and die components manufacture and the industry in which weight is the most important factor. These materials help machining and possess superior machinability index. Additionally, due to high thermal and electrical conduction, conventional fusion or resistance welding of aluminium alloys encounters many problems and some aluminium alloys are even regarded as non- weldable due to a risk of hot cracking. For critical applications, aluminium alloys are fusion welded with extreme precautions to avoid possible weld defects such as formation of deleterious oxides, porosity, hot cracking and hydrogen entrapment related delayed cracking. Frictionstirwelding (FSW) is a solid-state joining technique that has expanded rapidly since its development
Vill, Kinley and Fomichev [1, 2and 3] studied the frictionwelding set-up and the strength of the joints. Murti et al.  Directed a study about parameter optimization in frictionwelding of dissimilar materials. Yılbas et al.  investigated the mechanical and metallurgical properties of friction welded steel aluminum and aluminum-copper bars. Yılbas et al.  investigated the properties of friction-welded aluminum bars. Rhodes et al.  examined microstructure of 7075 aluminum using frictionstirwelding. Fukumoto et al. [8, 9] investigated amorphization process between aluminum alloy and stainless steel by frictionwelding. Then, Sahin and Akata  studied joining of plastically deformed steel (carburizing steel) with frictionwelding. Sahin and Akata  carried out an experimental study on joining medium- carbon steel and austenitic stainless steel with frictionwelding. Sahin [12, 13] studied joining austenitic-stainless steel with frictionwelding. Surface cleanliness in terms of contaminants, especially grease, reduces the quality of joints. Furthermore, the cleanliness of the parts must be considered as important. Therefore, the ends of the parts were cleaned with acetone prior to the welding process to minimize the effect of organic contamination in the welding zone. Frictionwelding of aluminum and austenitic stainless steel has been studied experimentally ([5, 8, 9]), however, the aim of the present study is to suggest optimum welding parameters to investigate the effect of factors related with joint performance of the friction-welded aluminum and austenitic stainless steel pair.
The joining of dissimilar AA2024 and AA6061 aluminium plates of 5mm thickness was carried out by frictionstirwelding (FSW) technique. Optimum process parameters were obtained for joints using statistical approach. Five different tool designs have been employed to analyse the influence of rotation speed and traverse speed over the microstructural and tensile properties. In FSW technique, the process of welding of the base material, well below it’s melting temperature, has opened up new trends in producing efficient dissimilar joints. Effect of welding speed on microstructures, hardness distribution and tensile properties of the welded joints were investigated. By varying the process parameters, defect free and high efficiency welded joints were produced. The ratio between tool shoulder diameter and pin diameter is the most dominant factor. From microstructural analysis it is evident that the material placed on the advancing side dominates the nugget region. The hardness in the HAZ of 6061 was found to be minimum, where the welded joints failed during the tensile studies.
FrictionStirWelding (FSW) is invented by The Welding Institute (TWI), England, U. K. for joining of light metals in 1991. It allows considerable weight savings in lightweight construction compared to conventional joining technologies along with high strength. The process of frictionstirwelding has numerous advantages over the conventional welding technologies. FSW process is carried out in the solid phase below the melting point of the metals and is able to weld numerous materials including aluminium, bronze, copper, titanium, steel, magnesium, and plastic. It also yields significantly less distortion than the fusion welding processes, allowing for high cost reductions in many applications. Thus, the problems related to the solidification of a fused material are avoided. Materials classified as difficult to fusion weld like the high strength aluminium alloys used in the aerospace industry could be joined with a minor loss in strength .
In this case we will discuss about the dissimilar metal welding where the base metal of the alloy differ from each other entirely and have wide difference in their melting point. The welding of Al/Mg alloys to Cu/Ti/ferrous alloys are some examples which fall in this category. But in this section dissimilarwelding of Cu – Al alloy will be discussed.For the experimental measurements there were used tin alloy Al - EN-AW-1050A with a thickness of 2 mm and Cu99 sheet with a thickness of 2 mm, joined by FSW weld overlay . The pin was positioned 90% on Al, and the rotation of the pin was clockwise. The parameters used to obtain the joint were rotation speed 1400 [rev / min] and speed of 50 [mm / min]. Joint microstructure and chemical composition in zones (sites) marked in Figure 4 are presented in Figures 5. It can be observed the presence of the two base metals of materials used in the joining process, copper and aluminium, as well as the mixing area. Analysis of figures and spectra presented in these tables highlight the following issues: a) the joining area has an irregular shape (the outline of the joint area is approximately shown in Figure 5 and many "gap" type defects have an acceptable quality of the joining process; b) pieces of Copper are ripped and brought to the site of Al and in the zone where should have been the nugget.
Once these SN ratio values are calculated for each factor and level, they are tabulated as shown below and the range R (R= high SN – low SN) of the SN for each parameter is calculated and the final values entered into the table. The larger the R value for a parameter, the larger the effect the variable has on the process. This is because the same change in signal causes a larger effect on the output variable being measured.
The investigation is on effect of welding parameters 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 dissimilar joint can be characterized both by the recrystallization of SSM 356 grains and AA 6061-T651 grain layers .
The hardness traverses of joints at a travel speed of 100 mm/min measured are presented in Fig. 7. In the stir zone of the Al alloy, the hardness was partly increased by Ti alloy chips. The hardness near the joint interface of the Ti alloy side was higher than that of the Ti alloy base metals. This region with a higher hardness near the interface of the Ti alloy side was much wider than that of the mixed region observed by SEM and EDS. Hence, it is considered the cause of the increased hardness in the Ti alloy side observed near the joint interface is not the formation of an intermetallic compound. It is due to the plastic deformation of the Ti alloy Ti
The main objective of the presented study is to analyse the effect of the welding parameters on the weld strength with the new developed stationary FSW tool. Initially, peel tests were performed in order to evaluate the weld bead materials configuration for the different probe geometries. Consequently, two pin geometries with the best results, were selected, and were characterized by a conical shape with two flat surfaces and a triangular shape circumscribed inside a 6mm diameter probe. These probe geometries were selected as a result of their increased angle of attack and, consequently, their ability to generate more heat. However, in order to weld polymeric materials, probes should have grooves or threads to allow the softened material to flow, rather with significant turbulence. Without grooves the material tends to stick on the advancing side of the weld and do not stir sufficiently to promote a satisfactory joining.
As reported by researchers, tensile strength of frictionstir welded joint of similar or dissimilar metal joint increase with tool rotational speed (RS) up to certain optimum value then decreases [7-9]. This effect is attributed to grain coarsening, blur and overheating at higher RS due to higher frictional heat. This leads to lower joint strength. Tensile strength analysis of frictionstir welded joint of metal to polymer reported by various researches is described in following section.
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 welding tool 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 welding parameters 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.
Joining of aluminium alloys by fusion welding pro- duces defects like hot cracking, porosity, slag inclusion, etc. with the mechanical and metallurgical properties. Usually, the frictionstir welded joints are free from these defects since the absence of melting duringwelding; metals are joined in the solid state due to the heat gene- rated by the friction and flow of metal by the stirring action. However, FSW joints are likely to have other defects like pinhole, tunnel defect, piping defect, kissing bond, cracks, etc. due to the improper flow of metal and insufficient consolidation of the metal in the weld zone.
Tool geometry affects the heat generation rate, traverse force, torque and the thermo-mechanical environment experienced by the tool. The flow of plasticized material in the work piece is affected by the tool geometry as well as the linear and rotational motion of the tool. Important factors are shoulder diameter, shoulder surface angle, pin geometry including its shape and size, and the nature of tool surfaces. We have selected tool with square probe pin to analysis their effect on joint Properties.
industries for various applications like bridge decks, ship panels, aerospace, and transportation components due to their light weight and low distortion . AA5086 is representative of non-heat-treatable 5xxx series of aluminium alloys having high formability and moderate strength. It has applications in marine, automotive, and aerospace industries in fabrication of light struc- tural components, where strength to weight ratio is a major concern and has to be as much as possible . Colligan investigated the relevance of FSW to oshore and marine industries and suggested it as a cost-diminishing and defect-free joining method as compared to conventional joining methods . Taban and Kaluc showed the superiority of FSW to the conventional joining methods in fabrication of AA5086 aluminium alloy joints . Inuence of rotational and welding speeds on microstructural and mechanical properties of AA5086 joints was studied by Aval and Loureiro and a sensible correlation between the studied parameters was found . Jamalian et al. suggested the appropriate combination of welding parameters to get sound and defect-free AA 5086 aluminium alloy joints produced using FSW . Amini and Gharavi experimentally set up the proportional relation be- tween corrosion current density in heat aected zone and welding speed of tool in FSW of AA5086 alu- minium alloy . The microstructural and mechanical properties of AA5086 joints are dierent from those of the base material as explained by the numerous studies reported in the literature; on the other hand, corrosion behavior of the joints has received rare attention.
nique for broadening the industrial application of magnesium alloys. As it is a solid-state process, FSW can avoid or limit solidiﬁcation problems conventional fusion welding tech- niques have and thereby it can provide defect-free welds having good properties even in materials that are generally thought to be not appropriate for fusion welding. On the other hand, a material being subjected to FSW usually undergoes extreme levels of plastic deformation and thermal exposure, and these can lead to a signiﬁcant microstructure reﬁnement in the central part of the weld zone. This characteristic of the process allows us to consider FSW as a potential tool for superplastic property enhancement in magnesium alloys.
The temperature fields obtained from the thermal model are used as input for the mechanical simulation for calculation of residual stresses. Figure (8) and Figure (9) shows the predicted longitudinal and transverse stress distributions after 15sec respectively. It can be seen that the longitudinal stresses at around the weld center line are compressive, and their nature gradually changes to tensile beyond the heat-affected zone and as the welding proceeds, the longitudinal stresses increase gradually because of the effect of mechanical constraint of the fixtures as well as higher thermal stress produced at longer welding durations. The maximum tensile longitudinal stress obtained is approximately 57 MPa, while 82 MPa is observed also for the maximum transverse stress.
Figure 4 show the surface roughness proﬁles along the centerlines to the tool traverse direction of the SZ in the TWBs produced at the tool rotation speeds of (a) 800, (b) 1000, (c) 1200, (d) 1400 and (e) 1600 rpm under the constant tool traverse speed of 300 mm/min. Note that the scale of vertical axis is diﬀerent in each proﬁle. For (a) 800 rpm, the SZ had the very rough surface with the roughness distribution range of 4.64 mm, which was associated with the large macroscopic defects foamed in the SZ. The relatively smooth surfaces were obtained at (b) 1000, (c) 1200 and (d) 1400 rpm, where the sound surfaces without large defects were successfully obtained. In these cases, the roughness distribution ranges were (b) 0.18, (c) 0.12 and (d) 0.08 mm, showing that the surface roughness was decreased with the increase in the tool rotation speed. However, for (e) 1600 rpm, the surface roughness was again increased, and distributed at a range of 5.87 mm, which was attributed to the large macroscopic defect. These results show that there are optimum tool rotation speeds in order to obtain the sound SZ with the smooth surface for the dissimilar FSW between the A5052P-O aluminum and AZ31B-O magnesium alloys.
Abstract—FrictionStirWelding (FSW) is a solid state welding process used for welding similar and dissimilar materials. The process is widely used because it produces sound welds and does not have common problems such as solidification and liquefaction cracking associated with the fusion welding techniques. The FSW of Aluminium and its alloys has been commercialised; and recent interest is focused on joiningdissimilar materials. However, in order to commercialise the process, research studies are required to characterise and establish process windows. In particular, FSW has inspired researchers to attempt joiningdissimilar materials such as aluminium to copper which differ in properties and sound welds with none or limited intermetallic compounds has been produced. In this paper, we review the current research state of FSW between aluminium and copper with a focus on the resulting weld microstructure, mechanical testing and the tools employed to produce the welds and also an insight into future research in this field of study.