Friction stir welding by using counter-rotating twin tool

A twin-tool setup has been designed and fabricated to make a comparative study between twin tool and single tool using double pass in a friction stir welding process. Twin tool helps in generating high heat causing intense plastic deformation in the processed zone. Defect free weld depends not only on the rotational speed, but also on the combined effect of welding speed and rotational speed. Higher hardness profile is observed with higher welding and rotational speeds; defect-free joints are also observed in this combination. Further, SEM results confirm the existence of ductile failure with microscopic voids of different shapes and sizes.