Effect of tool geometry on mechanical and microstructural behaviours in dissimilar friction stir welding of AA 5086-AA 6061

The aim of this investigation is to study the effect of geometric tool parameters on mechanical and microstructural behaviours during dissimilar friction stir welding of 5 mm thick plates of AA 5086-O and AA 6061-T6. Three tool geometries were used, including a tool with a concave shoulder and a conical probe with three grooves, flat shoulder and threadless cylindrical probe, and a tool with a flat shoulder and a threaded cylindrical probe. It was found that the tool with a concave shoulder and a conical probe with three grooves produces higher heat input and temperatures that provides more homogeneous stir zones than the other tools. In addition, the grain sizes of the stir zone in the AA 6061 side of all the welds are finer than those produced in the AA 5086 side, and decreasing the weld pitch, i.e. a ratio of welding to rotational speed, results in coarser grain structures in the stir zone.