Influence of Shoulder Diameter, Plunge Depth, Welding Speed, Rotational Speed on the Tensile Behavior of Friction Stir Welded AA 6061-T6 Sheets

In the present work, the effect of a few important process parameters like shoulder diameter, plunge depth, welding speed, rotational speed on the tensile behavior, namely flow strength, elongation, and hardness are studied. The relation between the thickness gradient of friction stir welded (FSW) sheets developed during the forming and strain hardening exponent of weld zone and elongation improvement has been explored. Micro-hardness showed a decreasing trend, from the base material to the centre of the nugget zone, except near the transition zone. With increase in shoulder diameter and welding speed, hardness has increased. However, with increase in plunge depth and rotational speed, hardness has decreased. The plunge depth effect on hardness distribution is negligible. The FSW sheets showed a decreased flow stress and improved elongation when compared to base material. The overall elongation of FSW sheets and weld zone has improved with increase in plunge depth, shoulder diameter, and rotational speed in most of the cases, while welding speed has shown insignificant effect. The thickness gradient is found to be severe in un-welded blanks as compared to FSW blanks. With increase in shoulder diameter, plunge depth, and rotation speed, the thickness gradient is found to decrease, while welding speed showed negligible effect. With improvement in strain hardening exponent of FSW sheets and weld zone with respect to changing welding conditions, the thinning gradient has reduced improving the overall elongation of welded sheets in most of the cases.