Effect of secondary phases on nanostructuring and hardness of severely deformed high-strength aluminum alloy

M.V. Markushev, Y.L. Burdastykh Yulia, S.V. Krymskiy, O.S. Sitdikov show affiliations and emails
Received: 10 February 2017; Revised: 21 March 2017; Accepted: 29 March 2017
Citation: M.V. Markushev, Y.L. Burdastykh Yulia, S.V. Krymskiy, O.S. Sitdikov. Effect of secondary phases on nanostructuring and hardness of severely deformed high-strength aluminum alloy. Lett. Mater., 2017, 7(2) 101-104
BibTex   https://doi.org/10.22226/2410-3535-2017-2-101-104


Influence of precipitates, formed upon preliminary heat treatment, on development under severe straining of nanocrystalline (NC) structure and hardness of 7xxx - type aluminum alloy with Zr and Sc additions was investigated. The samples cut from homogenized ingot were processed by high-pressure torsion (HPT) via 10 revolutions under 6 GPa at room temperature. Prior HPT, the alloy was solution treated, water quenched and annealed for 5 hours in the temperature range of 170-250 0C to change its structural heterogeneity - size and density of precipitates of different origin. In addition to coherent disk-type aluminides of transition metals ~25 nm in diameter (so-called dispersoids), that were in pre-quenched alloy, annealing led to precipitation of the main strengthening  (MgZn) - type phases with equivalent diameter from ~10 to 200 nm. Most highly developed NC structure with a (sub)grain size of ~80 nm was processed in the pre-quenched alloy and resulted in its abnormally high hardness. HPT of the pre-annealed at 170 0C alloy with -phase precipitates of less size and one order higher densities than that of dispersoids, on the opposite, produced completely non-recrystallized structure with near 15% reduced hardness owing to the grain refinement suppression. Increasing the temperature of annealing led to coarsening and less densities of - phases, intensifying nanostructuring. However, all pre-annealed NC states demonstrated minimum hardness as their work hardening did not compensate the softening due to -phase coagulation.

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