Effect of the initial state on nanostructuring and strengthening of middle- and high-strength age-hardenable aluminum alloys under severe plastic deformation (Review)

Abstract

General requirements to the initial structure and phase composition of commercial middle- and high-strength age-hardenable aluminum alloys, especially to the parameters of precipitates of main strengthening phases and transition metals aluminides, which are important for nanostructuring of the alloys matrix under processing, involving severe plastic deformation (SPD), preliminary and post-SPD heat treatment, are reviewed. The data on the structure, hardness and tensile strength found in disc-shape samples severely deformed via room temperature high pressure torsion (HPT) are analyzed. The role of precipitates in grain refinement down to nanoscale sizes is demonstrated. Influence of the origin, morphology and densities of precipitates on the efficiency of nanostructuring and strengthening of the alloys is analyzed. Structure-strength relations, evolution of grain and second phase structure parameters prior to, during, and after SPD are discussed. It is concluded that in order to obtain high-strength nanostructured states, the alloys should be deformed in a preliminarily quenched state. Post-SPD aging of preliminarily quenched and underaged alloys can provide them extra hardening up to 15 %. A contribution of the SPD-induced formation of nanosized subgrain / grain boundary networks on the strength of alloys does not exceed that of dispersion hardening by conventional aging.