Computational Study of Metal Flow Behavior of AA 6061 in Friction Stir Processing with Twin Tools

In order to tackle the growing demand of low weight to strength ratio materials in shipbuilding, trains, and aerospace applications, high strength aluminum alloys have shown good promise. Fabrication of parts with aluminum alloys has always been a challenge as conventional welding processes, which are basically fusion welding techniques, are not able to provide enough joint strength against impact. Friction stir welding (FSW) that generates heat from friction between a rotating tool and work-pieces to be welded, has shown promise to provide better strength. One of the important parameters that dictate the strength of joints produced by friction stir welding is the amount of mixing. Research has been carried out to improve mixing by modifying the tool geometry by several scholars. The present work is focused on improving mixing using twin tools instead of a conventional single tool. Numerical analysis is carried out using a finite volume method based computational fluid dynamics (CFD) solver. The result reveals that twin tools in linear alignment in the direction of welding with the rear/follower tool rotating in a direction counter to the front one can improve mixing as well as even distribution of material, leading to stronger joining.