Numerical Analyses of Underwater Friction Stir Welding Using Computational Fluid Dynamics for Dissimilar Aluminum Alloys

Nowadays, investigation is going on to improve the weld joint Quality of dissimilar material in convectional friction stir welding process (CFSW) by using different surrounding medium such as water, liquid nitrogen, and compressed air. Water is the favorable medium having potential to produce better weld joint quality to CFSW for dissimilar material. The objective of the article is to identify the effect of water as a surrounding medium, a process known as underwater friction stir welding (UFSW), for joining of 6061-T6 and 5083-H12 aluminum alloys. For the purpose, comparative study of temperature flow, material flow and mechanical properties of the weld joint UFSW and CFSW have been investigated using computational fluid dynamics (CFD) techniques. The simulations are performed while keeping the tool rotation speed and welding speed constant. Additionally, the mechanical properties of the weld joints produced UFSW and CFSW are compared. The numerical analysis reveals that using water as a medium in the CFSW process results in a 20% reduction in the peak temperature generated during welding, as compared to using air. This reduction in temperature also affects the material flow, thereby impacting the surface finish, weld joint quality, and mechanical properties. The use of water in the UFSW process leads to improved surface finish and the production of defect-free joints. This is attributed to the uniform slip rate achieved in the process. Furthermore, the water environment in UFSW prevents the formation of intermetallic layers and reduces their thickness by approximately 60 and 80% in the retreating side (RS) and advancing side (AS) regions, respectively, compared to CFSW. This reduction in intermetallic layer thickness contributes to a higher tensile strength of the weld joint in UFSW. The tensile strength of the weld joint is improved by more than 17% compared to CFSW, and the ductility is also enhanced.