Friction stir Welding (FSW) can be defined as a green technology, because the consumption of energy during this process is less than other Welding methods. In addition, during the process there is no gas, filler material or other consumables. It should be noted that, complex curved shapes are now commonly used in different industries in a bid to have lightweight structures. According to the above-mentioned descriptions, several investigations into the potential benefits of adopting Friction Stir Welding (FSW) in the production and joining different materials are being undertaken. The work presented in this paper is focused on thermal behavior of the curved FSW and its benefits for the green technology. Due to the robust nature of FSW process aluminum 6061-T6 alloy has been selected as the Welding material. The results of the study showed that, the total peak temperature value of 300° C happened at time, t = 3 s at the plunge stage (outside of the Welding seam). Meanwhile, at the dwell stage (between t = 3 s to t = 5 s), there is a stable situation in the amount of the generated heat from the plastic deformation as well as the contact shear stress at the tool-workpiece contact interfaces, thus the interfacial temperature is found to be stable. By the end of the dwelling step, the total generated heat is stable to the maximum value of 300° C. At the step time of t = 12. 8 s, the temperature is distributed asymmetrically across the workpiece until the time step of 19. 6 s which at this point the asymmetric contour expanded in the stir zone.

Researchers have worked on many facets of joining of similar/dissimilar aluminum alloys using different joining techniques and came up with their own recommendations. Friction Stir Welding (FSW) is widely preferred for joining aluminum alloys being an economical alternative to produce high-quality welds. However, obtaining high strength welded joints without the detrimental and visible effects still needs attention considering the effect of hybrid FSW techniques, tool material and geometry, process parameters (tool rotation, Welding speed, and plunge depth), and post Welding treatments. This study presents the state of the art with the authors’ own inferences on the evaluation of FSW performances in terms of joint tensile strength, fatigue strength, corrosion resistance, residual stresses, microstructure, and microhardness. This study also presents attempts made by the researchers on modeling and parametric optimization of FSW to finding scope for application of advanced optimization techniques and development of predictive models for mechanical properties of welded joints. This study emphasizes more studies required on the comparative evaluation of FSW performance with the application of ultrasonic frequency combinedly or individually on advancing and retreating sides of plates.

FSW material flow and phase transformation were studied at the interface of dissimilar Welding of Al 6013 to Mg. Defect free butt weld was obtained when aluminum and magnesium test plates were placed in the advancing side and retreating side respectively, and the tool was placed 1 mm off the weld centerline into the aluminum side. In order to understand how the materials flow during FSW, steel shots were implanted as indexes into the test plate’s intimate face and Welding was performed with determined optimum parameters. X-ray images were used to evaluate secondary positions of the steel shots at weld zone. It was revealed that steel shots implanted in the advancing side test plate were penetrated from advancing side into the retreating side with a relatively large rotational displacement of a. But shots implanted in retreating side test plate remained only in retreating side, without penetrating into the advancing side, and displaced by a low angle of b. It could be concluded that to reach defect free welds by FSW between two dissimilar metals, the tool should be inserted in harder metal and harder metal should be placed in the advancing side too. EDS analysis was performed in order to study formation and distribution of intermetallic phases in the welds interface. Two intermetallic compounds formed sequentially at Al6013/Mg interface were Al3Mg2 and Al12Mg17 in weld condition. Welded specimens were heat treated and their effects on mechanical properties of welds and formation of new intermetallic layers were investigated.

Although in recent years, Welding of polymers has been developed but Welding of polycarbonates is still faced with serious challenges such as improving the quality of welded section. In the present study, mechanical properties of polycarbonate Friction stir welded samples with different nano alumina content were investigated. For this purpose, firstly polycarbonate (as matrix) was melt compounded with nano alumina in variant weight percentages including 0, 1, 2 and 3% using a twin-screw extruder. Then, nanocomposite samples were produced using an injection molding machine and were Friction stir welded with a special tool on a milling machine. The effects of weight percentage of nano alumina, travel and rotational speeds (all in four levels) were investigated on the tensile strength and hardness of the welded nanocomposite samples according to a L16 orthogonal array of Taguchi method. According to the obtained results, the weight percentage of nano alumina is the most effective parameter on the tensile strength and hardness of welded nanocomposite specimens. By increasing the percentage of nano alumina to 1%, tensile strength increased. However, by increasing the nano alumina more than 1%, this strength reduced due to agglomeration of nanoalumina in high weight percentages. Results also demonstrated that processing parameters do not affect the mechanical properties of welded nanocomposite samples significantly.

The present study describes the effect of Friction Welding process on mechanical and metallurgical properties of AISI 304 steel. The joints were made by direct drive Friction Welding (DDFW) machine, while the characteristics of Friction welded joints were evaluated by macro-microstructure, microhardness, tensile test with 4 mm and 6 mm effective diameter, and scanning electron microscope (SEM). The results showed severe flash formation at stationary side related to rotating side, highly plastically deformed zone (HPDZ) was revealed at the interface with large dimension of 110 µm. Maximum microhardness values were recorded at welded center and increased from peripheral to central zones. Reducing ratio of ultimate tensile strength (UTS) and ductility for welded joint related to AISI 304 were 86 and 67%, respectively. Tensile fractures occurred adjacent to the interface at thermo-mechanically affected zone (TMAZ). Fracture morphologies by SEM were discovered cleavage features and mostly ductile mode with micro-porosities of different forms and dimensions

In the present paper, a three-dimensional thermo-mechanical model for Friction stir Welding is presented. Friction stir Welding (FSW) is a relatively new Welding process that may have significant advantages compared to the fusion processes. Although originally intended for aluminium alloys, reach of FSW has now extended to a variety of materials including steels and polymers. This study aims to numerically explore the thermal histories and temperature distributions in a work piece during a Friction stir Welding process involving the butt joining of aluminum 6061-T6. In this regard ABAQUS commercial software was utilized. The process is solid state and as such, temperatures experienced near the weld are lower than those experienced during fusion Welding and there are no large density changes due to a solid-liquid transformation.

Friction-stir Welding process is a novel method of solid state Welding, which produces heat due to Friction between the pin, the shoulder and the workpiece. This heat causes a paste area. Shoulder pressure and pin spin cause edges integration and lead to Welding. In this study, firstly, the feasibility of Welding of steel sheet (EN10130) with a thickness of 1.5mm has been tested by 58 experiments. After making perfect welds, the ranges of 500-1000 RPM and 30-160 mm/min were selected as the suitable upper and lower levels, respectively, for rotational speed and linear speed. To achieve a maximum tensile strength, 29 tests were designed by using the Box-Benken method considering specified levels of the parameters. Then, the response surface methodology was used for optimization of the parameters. Results showed that the optimal outputs and experimental data were in good agreement, which indicate the adequacy of the design of experiments and optimization predict results. Micro-hardness tests, metallography and normal tensile test were carried out on three series of plates produced with the most appropriate tensile strength and elongation. Results showed that heat-affected zone weaked the sheet of advancing side compared to other Welding zones.

In order to evaluate the possibility of the similar and dissimilar Welding of 5019 and 7039 aluminum alloys, plates of 3 mm thick from this alloy were welded via Self-Reacting Friction Stir Welding (SRFSW) method. Floating bobbin tool was designed and manufactured from heat –treatable hot working steel to perform the Welding process. The effect of various process variables such as the shoulders pinching gap, the tool transverse speed and the tool rotational speed were investigated to establish a defect-free joint. Following the visual inspection and X-ray radiography, it was found that a defect-free joint is obtained at the transverse speed of 22 mm/min and rotational speed of 1120 rpm. The results of tensile test, also, revealed that the joint efficiency of 5019-5019, 7039-7039 and 7039-5019 joints are 72, 76 and 91. 5%, respectively. Accordingly, these amounts were more than the joint efficiency of the fusion Welding, and comparable with/more than the joint efficiency of Conventional Friction Stir Welding (CFSW). Microscopic evaluation of the fracture surface of welded pieces indicated that the dominant fracture mechanism for similar joints is the soft fracture, while the one for non-similar fracture is the brittle fracture. Assessment of the cross-sectional hardness of the welded pieces near the upper and lower shoulders showed that the degree of hardness near the lower shoulder of the tool is always higher, which can be attributed to the lower temperature of the work piece in this area.