Friction stir welding of T-joints in dissimilar materials: Influence of tool geometry and materials properties

The aim of this work is to investigate the influence of the materials properties, process parameters and tool geometry on the formation of defects and mechanical strength of Friction Stir Welding (FSW) of dissimilar T joints. The 3 mm thick aluminium plates of AA5083-H111 and AA6082-T6 alloys were arranged in a T- geometry, using the AA6082 alloy as the skin or as the stringer. An additional 1 mm thick plate overlaps the skin to provide material to fill the fillets. Two tool geometries were analysed. The geometry of the variable section pin of the tool allied to the setup dies constrains the formation of two independent material pin driven flows whose morphology depends also on the processed base material properties. Thus, the formation of weld defects is greatly affected by the tool geometry, the materials and the process parameters. AA 5083 requires low tool rotation (w) and traverse (v) speeds but w/v ratio above 16 to avoid defects. The oxides in the nugget, produced for very high w/v ratio, reduce the mechanical strength of the welds. The welds with AA 5083 skin exhibit similar fatigue strength to those with AA 6082 as skin, although the latter alloy has higher fatigue strength than the former.