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/phase state of the commercial middle- and high-strength age-hardenable aluminum alloys, especially to precipitates of aluminides of transition metals and main strengthening phases, under thermomechanical processing, involving severe plastic deformation (SPD), preliminary aging and re-aging, and aiming at nanostructuring the alloy matrix, are reviewed. The data on the alloy structure, hardness and tensile strength, realized in disc-shape samples severely deformed via room temperature high pressure torsion (HPT), have been taken into consideration. Influence of the nature, morphology and densities of secondary phases on efficiency of the alloys nanostructuring and strengthening are analyzed. The role of main strengthening phases in the alloys (sub)grain refinement to nano sizes, as well as in complete suppression of the matrix nanostructuring, are discussed. Nature of the alloys structure transformations and structure-strength relations owing to evolution of the grain and second phase structures due to SPD, preliminary and post-SPD heat treatment are considered. It was concluded that the «direct» impact of the formation of nanosized net of grain boundaries on the alloys strength is not exceeding the impact of its dispersion hardening under conventional aging. The main alloy hardening effect under HPT is due to an increasing the crystal defects densities, predominantly of dislocations.