AA6082-T6 joints were produced using a trigonal shape pin. The influence of Friction Stir Welding (FSW) process parameters on the formation of banded structures was predicted using numerical modeling and then experimentally validated by optical and electron microscopy. Special attention was paid to the formation and evolution of banded structures observed in the plane of the welded sheets. A finite element (FE) analysis based on the Coupled Eulerian-Lagrangian formulation was developed to predict and quantify the influence of FSW process parameters on the formation and extent of the banded structures. The combination of the experimental and numerical analyses showed that the formation of the banded structures is mainly related to the geometry of the pin whereas the friction conditions have a much smaller effect.