Finite Element Method and Experimental Study of Self-reacting Friction Stir Welding of Aluminium Alloy AA6061-T6

Self-Reacting Friction Stir Welding is a variant of Friction Stir Welding (FSW) in which through a modification in the tool design, welding can be carried out in the absence of a backing plate. In this variant, the tool has two shoulders connected by the pin. Due to this small modification in tool design, the process is significantly influenced. In the present work, the effect of tool traverse speed using a fixed gap bobbin tool on the weld quality has been studied using a Finite Element Method (FEM) model and experimental study. The present work has been carried out on 4-mm-thick aluminium alloy AA6061-T6 plates, which have been welded in butt configuration. Uniaxial tensile tests of the welded samples have been carried out to correlate the traverse speed with yield strength and ultimate tensile strength. Three-point bend tests have been carried out to expose any flaws present in the joints and compare mechanical properties on the two sides of the joints. In addition to this, the joint macrostructure has been studied and has been compared with the stir zone developed in the FEM model. The microstructure in the various zones of the welded joints for different traverse speeds has been studied and compared with the grain structure of the base material to reveal its effect. A relationship has been established between the process parameters and the resulting average grain size in the joint.