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.

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.

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.

One of the interesting state-of-the-art approaches to Welding is the process of Friction Stir Welding (FSW). In comparison with the fusion processes, FSW is an advantageous method as it is suitable for the non-fusion weldable alloys and polymeric materials joining. Regarding the materials pure solid state joining, it also provides joints with less distortion and enhanced mechanical properties. In the present work, a three-dimensional (3D) model based on finite element analysis was applied to study the thermal history and thermomechanical procedure in Friction Stir Welding of high density polyethylene plate. The technique includes the tool mechanical reaction and the weld material thermomechanical procedure. The considered heat source in the model, includes the Friction among three items: the material, the probe and the shoulder. Finally, the model was validated by measuring actual temperatures near the weld nugget using thermocouples, and good agreement was obtained for studied materials and conditions.

Three mm thick plates of commercial pure copper were welded via Friction Stir Welding method using a floating bobbin tool. The effect of different process variables such as the tool transverse speed and the tool rotation speed were examined in order to create a weld with the desired properties. A defect-free weld was obtained at a rotation speed of 1400 rpm and a transverse speed of 18 mm/min with a shoulder pinching gap of 2. 7 mm. After the Welding process, the soundness of the welds was confirmed by non-destructive methods of visual inspection and X-ray radiography. The results of the transverse tensile test showed that the as-weld joint efficiency was 86. 4%, which was higher than the joint efficiency made by the fusion Welding method. The strength of the welds was such that the fracture of the workpiece was in the heat affected zone after the tensile test. On the other hand, the grain size of the weld was significantly less than the base metal. The lowest hardness around 40VHN was attributed to the middle of the thickness of the weld, while the highest hardness was in the vicinity of the lower shoulder of the tool, which was about 80 VHN.