Springback and Formability Studies on Friction Stir Welded Sheets

In the present work, the effect of selected welding conditions on the temperature evolution, springback behaviour and formability of friction-stir welding (FSW) sheets is investigated. The Al6061T6-Al6061T6 combination is used for temperature evolution studies, while dissimilar Al combination made of Al6061T6 and Al5052H32 is used in springback and formability tests. The springback experiments are performed with a V-bending set-up without tension, and formability experiments are conducted using a limiting dome height (LDH) set-up. By increasing the shoulder diameter, plunge depth and tool rotation speed, the peak temperature is increased, and it is vice versa for welding speed. In the case of springback, the performance of FSW sheets is in between that of Al6061T6 and Al5052H32 base materials. Reduction in springback of FSW sheets is observed at higher rotational speed and welding speed, and this is correlating well with the modifications in tensile properties such as yield strength to elastic modulus ratio and strain hardening exponent of the weld zone (WZ) with varying FSW conditions. Three different modes of failures, normal and parallel to the WZ, are observed during formability testing of FSW sheets made of dissimilar Al grades at two different strain-paths. It is better to evaluate the forming limit of FSW sheets at individual strain-paths, rather than in all the strain-paths using a forming limit curve (FLC), because of changing failure pattern with changing strain-paths.