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Metal joining techniques are categorized into two main groups i.e. fusion and solid-state welding. Categorizing these techniques depends on the operating principle of each welding. Friction stir welding (FSW) is one of the techniques that fall under the solid-state welding category. The invention of this technique is associated with The Welding Institute (TWI) from the United Kingdom in the early 1990s, (Unnikrishnan & Dhas, 2017). The earlier application of FSW is mostly linked with joining soft metals such as aluminum alloys, copper, etc. These materials were known to be not weldable through fusion techniques as they possess a low melting temperature (Adamowski et al., 2007). FSW operating principle does not produce smoke or fume hence it is described as green technology (Bozorgzadeh & Idris, 2015; Mishra & Ma, 2005).
Friction stir welding joins materials through the use of a non-consumable rotating tool which generally has a specific pin and shoulder. This rotating tool is plunged between the materials to be joined and settles for a short time (dwell time). After elapsing the dwell time, the tool moves parallel to the plates being joined i.e. from the beginning to the end of the plates. The rotating tool softens and mixes the plasticized material. The joint is formed by the restricted material movement caused by the tool shoulder (Ahmed et al.,2020; Silva-Magalhaes et al., 2019). Friction stir welding is considered to have reached a stationary state when the quality of the weld is the same throughout the weld (Kumar et al., 2020; Ratnam et al., 2019; Tongne et al., 2016; Yang et al., 2019). Various works have been done in evaluating the impact of different welding parameters on the quality of joints. This includes the rotational speed, welding speed, tool tilt angle, pin profiles, and many more. The evaluation of these parameters includes the similar and dissimilar materials (Raturi et al., 2019; Thilagham & Muthukumaran, 2020; Chanakyan et al., 2020; Swaminathan et al., 2020; Kumar & Ramana, 2020).
Boccarusso et al. (2019) have evaluated the impact of the welding force on the microstructural arrangement of a 3 mm thick AA6082/AZ31 Mg dissimilar joint. The H13 steel tool with 13 mm diameter concave shoulder and 3.7 mm long threaded tapered pin was used in welding the two dissimilar materials. The FSW was performed using different rotational speeds and the traverse speed. The investigation of force influence was studied in conjunction with speed variations. The presence of the hard intermetallic compounds on the weld bead was observed. These intermetallic compounds were found to be influencing the microhardness at the stir zone. The vertical force was found to have more influence on the occurrence of liquation phenomenon. Maneiah et al. (2020) used the Taguchi method in performing FSW parametric optimization using the AA6061 plate. The rotational speed, tool tilt angle, and the traverse speed were the parameters considered for this study. The H13 tool steel with 20 mm shoulder diameter and 3 mm long hexagonal pin was used in producing the welds. It was discovered that the tensile strength is influenced mostly by the factor feed than the tilt angle and the rotational speed. The optimum parameters suitable for high tensile strength of the joint were also discovered