Aluminum alloys processed by severe plastic deformation (SPD) usually exhibit a significant increase of the mechanical strength and even superplasticity due to the strong grain size reduction. The 6061 commercial aluminum alloy is heat treatable and its remarkably high hardness after aging is due to a fine distribution of nanoscaled precipitates containing Mg and Si. It was shown however that its hardness could be significantly increased thanks to equal channel angular pressure (ECAP) processing before the aging treatment. The aim of this work is to investigate such nanostructure resulting from SPD to understand these unusual mechanical properties. A solutionized 6061 aluminum alloy was processed by ECAP and aged. Then, the distribution of alloying elements (Mg and Si) was mapped out in 3D at the atomic scale thanks to the three-dimensional atom probe (3D-AP) technique. In this paper, we discuss the precipitation kinetics induced by SPD and deformation mechanisms leading to high mechanical properties of these alloys.