Activation volume and the role of solute atoms in Al-Mg-Si alloy processed by equal channel angular extrusion

•Al-Mg-Si alloy was processed by ECAE.•TEM and ASTAR show that grain size is reduced to 100 nm.•SRS experiments show that activation volume V is reduced to 70b3.•Constant V is leveled by solute atoms effects.•GBS contribution is clearer after ageing. [Display omitted] Grain refinement to the sub-micron scale was found to enhance both strength and plasticity. In this size range, the micro-mechanisms of deformation are not yet sufficiently specified. In the present work, strain rate sensitivity was investigated in an Al-Mg-Si alloy processed by equal-channel angular extrusion. The microstructure was controlled by conventional transmission electron microscopy and orientation imaging-ASTAR. In the as-quenched state, deformation produces grains below 100 nm in size. The activation volume V was reduced to 70b3. Based on published theoretical models, we have shown that in such alloy, pure grain boundary sliding cannot be revealed in the low-stress range, due to the intervention of solute atoms. Beyond, the stress-dependence of V consists with an inverse Cottrell-Stokes behavior. This trend was confirmed by TEM which revealed dislocation activity and grain boundary emission. Ageing at 150 °C increases the contribution of GBS whereas the residual activation volume continues to be leveled.