# Investigating the Welding Parameters in Friction Stir Welding of Yellow Brass 405-20
## 1 Introduction  
Friction stir welding (FSW) is an eco-friendly and solid-state joining technology. Due to this reason, industries are keenly adopting this joining process in various applications, e.g., automobile, aerospace, marine, etc. Several materials have already been welded by FSW including aluminum, copper, steel, alloys of these materials, plastics, and composites. Friction stir welding is a famous joining technique in industry and research laboratories due to its various advantages, e.g., it is fumeless, the external medium melts less due to its solid-state nature, no protective equipment is required, etc. [1, 2]. FSW was first used for aluminum and its alloys at the Welding Institute of the United Kingdom and patented by [PERSON] et al. in 1991 [3]. Now, it has become a state-of-the-art technique that is used to weld various other materials, e.g., steel, magnesium, copper, plastics, composites, and dissimilar materials [4]. To determine the effect of FSW factors (FSWFs), a few trial experiments with different combinations of FSW factors are usually conducted under the guidance of the most relevant literature. Sometimes, trial experiments seem essential in the absence of background knowledge when a research study is not found before in a particular field. In this context, numerical studies play an exceptional role in minimizing the cost and time required for trial experiments. For example, [PERSON] et al. [5] performed thermal simulations towardsevaluating the suitability of weld factors, which may lead to very few trial experiments to validate the evaluation of weld factors' appropriateness. [PERSON] et al. [5] developed a new numerical approach based on computational fluid dynamics (CFD) to comprehend the mixing flow of materials during FSW. They strived to establish a link between the mixing materials and bonding of materials before and after FSW, respectively. Although the authors have provided the research community with a novel idea of applying CFD on FSW of Al-Mg-Si alloy T-joints, a numerical study based on CFD was not validated using appropriate empirical methods. [PERSON] et al. [6] also described that joint microstructure and mechanical properties are the strong functions of both thermal processes and material flow, as they perceive the FSW process in terms of a complex interaction of thermal, mechanical, and geometrical effects. They found that the phenomenon of dynamic recrystallization is more available on the advancing side with tiny void defects. Another CFD study was conducted by [PERSON] et al. [7] on aluminum material with an introduction of mechanical anisotropies in the material in terms of grain shape, grain orientation, and grain texture. The prediction was found accurate on the joint morphology. Other CFD studies were carried out by [PERSON] et al. [8], [PERSON] et al. [9], and [PERSON] et al. [10] providing brief guidance about modeling the heat source development during FSW as a function of probe geometry, tool-workpiece interaction, affecting the FSW of dissimilar metal alloys when ultrasonic assisted FSW (UAFSW) is used, and affecting the overall welding of materials as a function of the stationary shoulder of tool, respectively. Therefore, numerical studies may be divided into two types, namely computational solid mechanics (CSM) and CFD. Computational solid mechanics of welded joints is a better technique than computational fluid mechanics (as CFD has an emphasis on material flow only), e.g., to check the effect of introducing mechanical anisotropies in materials to be joined. Moreover, the flow of materials like fluids is not possible in FSW, since the melting of solid materials has never happened in FSW, which is a solid-state welding technique. Hence, prediction trials involving computational solid mechanics must proceed with more focus on brass materials instead of other materials such as aluminum materials. In other words, a transient thermal model using finite element analysis (FEA) is needed in the domain of CSM.