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.

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.

Cladding on metallic products is relatively applicable in industries, e.g. aerospace, automotive and oil.One layer cladding on metallic specimens could improve mechanical, thermal and corrosion resistance properties considerably. Nowadays carbon steels have the highest share of metallic materials among different industries. One layer cladding on this type of steel with the aim of enhancing the corrosion resistance could decrease the price of them when they are put into use in different conditions. In this study, for the first time, cladding of the carbon steel by 6061-T6 Al alloy via FRICTION STIR was carried out successfully. In order to control cladding, the effect of different rotational speeds and traverse speeds on mechanical properties and structure of cladded layer was inspected. Results of shear test showed that by increasing the traverse speed the shear strength of the cladded layer increases due to the addition of material into the joint area uniformly. By decreasing the rotational speed and increasing the traverse speed, the generated heat from FRICTION decreases and prevents over-STIRring in joint area and as a result the shear strength of the joint will increase.

Application of thermoplastic materials has increased dramatically in recent decades due to its recyclability, low density, resistance to chemical changes. The FRICTION STIR WELDING process is one of the new METHODs of solid state WELDING, which has recently undergone a significant improvement. In this research, using a new tool Made of plain carbon steel st37 in FRICTION STIR WELDING and low cost turning machine, composite sheets of thermoplastic polymer base have 12% continuous carbon fiber in the form of buttocks with two rotational speeds of 250 and 355 rpm and two advance speeds of 5/6 and 9 mm/min Optical microscope images (OM) showed the complete connection of materials. Increasing the inlet temperature resulted in the formation and growth of cavities and converting them into tunnel cavities. In general, the parameters affecting the connection quality in this study included the main shoulder diameter and rotational speed, so that, based on the results of scanning electron microscopy (SEM), the increase in rotational speed resulted in the grinding of continuous carbon fibers and thus increased tensile strength. The results of the tensile test showed that the failure of the samples is due to microstructural changes in the HAZ, in the joint zone of the WELDING zone and the base materials. According to the results, it can be said that using this new tool in the FRICTION STIR WELDING METHOD, because of the reduction of rotational speed compared to previous studies and the lack of use of a multi-axial milling machine, can save energy.

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.

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.

The present study investigated the feasibility of producing strong and defect-free joints between 1050 aluminum and pure copper sheets by micro FRICTION STIR WELDING using ordinary and new tools. By analyzing the results of the tensile test and signal to noise analysis, the average maximum ultimate tensile strength of the joints is reported to be 88 MPa, when using the parameters of rotational speed, traverse speed, and offset of the tool with levels of 2400 rpm, 40 mm/min and 0. 25 mm. The variance analysis also showed that the parameters of rotational speed and traverse speed had the most significant effect on the joints' tensile strength. The maximum and minimum values obtained from the microhardness test were recorded for the weld nugget zone and the heat-affected aluminum zone, respectively, equal to 192 HV and 21 HV. The X-ray diffraction test results on optimal samples showed intermetallic compounds such as CuAl2 and Cu9Al4 in the WELDING area. The tensile strength of the joints created is strongly dependent on the formation of these intermetallic compounds.