In this research work, characterization of a broad area zone with ultra fine grain size of 7075-T6 grade aluminum sheets with the thickness of 8 mm was carried out using friction stir processing (FSP) and quenching by liquid nitrogen on both, i.e. upper and lower, surfaces. In the first step, ability and competence of two tools with different designs in creating a stir zone without any defects were examined; selected samples were exposed to FSP by efficient tools and in a highly extensive quenching media. Friction stir processing was carried out on the samples in three different rates (fast, medium and slow), the mechanism of ultra fine grain size as well as the creation of dislocation in thermo-mechanical affected zone was evaluated. Micro structural evaluation using transmission electron microscopy showed that the samples exposed to FSP in slow manner, had the finest grain size (20 nm) in the stir zone, and the lowest amount of dislocation in the thermo-mechanical affected zone. More details are discussed in the presented results.