Source: https://lettersonmaterials.com/en/Readers/Article.aspx?aid=1361
Timestamp: 2019-04-23 16:26:59+00:00

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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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