Effect of annealing on microhardness and electrical resistivity of nanostructured SPD aluminium

- Increase of microhardness and electrical conductivity of nanostructured Al by annealing.
- The strengthening is associated with high angle grain boundaries in the microstructure.
- Contribution of grain boundary non-equilibrium state to electrical resistivity is analyzed.
- The average width of potential barriers at grain boundaries for electrons was estimated.

The influence of microstructure evolution on microhardness and electrical resistivity of ultrafine grained (UFG) commercial purity Al under annealing at different temperatures within a range of 363-673 K was studied. The initially coarse grained Al was processed by high pressure torsion (HPT) technique for the formation of UFG structure. The microstructure was characterized by electron backscattering diffraction and X-Ray diffraction. It was shown that annealing of UFG Al at temperatures within a range of 363-473 K leads to simultaneous increase of microhardness (by 6-13%) and electrical conductivity (by 4-8% at 300 K). The correlation between microstructural features and the resulting properties were analyzed. The average width s of potential barriers at grain boundaries (GBs) in HPT-processed Al was estimated in the frame of a tunnel model. The obtained large value of s compared with the GB crystallographic width is associated with elastically distorted lattice near GBs. The obtained results suggest a new way to increase simultaneously strength and electrical conductivity of UFG Al alloys by an appropriate annealing.