Multi objective optimization of FSW process parameters to enhance the tensile strength and hardness of AA7068 welded joints

Friction stir welding (FSW) is presently a significant process still underway of research owing to its dynamic behavior of the process. The process is still in its developing stage for the reason that every change in tool dimensions can lead to a different result altogether. In this present work, one such attempt to redesign the tool geometry is experimented for joining AA7068-T6. The specimens were fabricated with the experimentation matrix developed, using a central composite design. The input parameters particularly Rotation Speed (RS), Transverse speed (TS), Pin Profile (PP) and Axial Load (AL) of the tool have been considered for experimentation. To enhance the mechanical properties of FSW joints regression equation is developed and Response Surface Methodology (RSM) is used to optimize the process parameters. A total of 30 sets of experimental runs and three confirmatory experiments were conducted for prediction and validation purposes. The experimental results illustrated that to improve the tensile and hardness property of the joint, the optimum values of process parameters should be fixed at 1515 rpm, 57.3 mm/min, 10.4 kN, and the welding to be carried out with a tool straight pentagon. The statistical analysis showed that, as compared with the geometry of the tool profile and TS, the parameters RS and the AL influence the tensile and Hardness of FSW joints. A joint efficiency of 88% was found to be achievable when the right combination of process parameters is applied.