Structure of ultrafine grained alloy A2024 after combined heat-deformation treatment

A. Petrova, I.G. Shirinkina, I.G. Brodova, L. Kaczmarek, M. Stenglinski


This work presents the results of the effect of preliminary heat treatment on the features of the formation of ultra fine-grained  structure of Al-Cu-Mg alloy obtained by means of high pressure torsion in Bridgman anvils. It was established the nature of grain refinement and hardening in the aged or quenched alloys.The present work studies the effect of preliminary heat treatment on the features of ultra fine-grained (UFG) structure formation in Al-Cu-Mg alloy by means of high pressure torsion in Bridgman anvils. Heat treatment was carried out following two regimes: regime 1 included heating to a temperature of 500°C, 16 hours and quenching in water, and regime 2 additionally included two-stage T6I6 aging: 120°C, 1.5 hours and 160°C, 6 hours, after quenching with water quenching after each stage. The number of revolutions of the anvil was n = 5, 10, which, according to the calculation, corresponded to the true logarithmic strain e ≈ 5.5, 6.5. It is shown that after the preliminary two-stage aging T6I6 of coarse-grained alloy fragmented grain / subgrain structure with high dislocation density was formed at e = 5.5. The relaxation processes were suppressed by blocking of the grain boundaries by dispersed particles of the strengthening S phase. It was shown that at e = 6.5 alloy structure is refined to the nanolevel, and the process of dynamic dissolution of S phase precipitates started parallel. It is accompanied by the appearance of defect-free grains and a mixed structure was formed. In the case of the torsion of hardened coarse-grained alloy, the main mechanism of grain refinement to 450 nm is dynamic recrystallization. At e = 6.5 the dynamic aging of the supersaturated Al solid solution becomes the additional relaxation channel of the elastic energy and the hardness of the UFG alloy increases up to 3000 MPa.

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