Kurchatov Institute National Research Centre – VIAM, Moscow, Russia

A. V. Zavodov, Category 2 Engineer, Candidate of Technical Sciences, e-mail: zavodovad@gmail.com
E. A. Lukina, Head of Laboratory, Candidate of Technical Sciences, e-mail: evaluk69@gmail.com
T. A. Shlyapnikova, Deputy Head of Laboratory, Candidate of Technical Sciences, e-mail: tanusha1607@yandex.ru

This study compared the effects of one-, two- and three-step ageing of aluminium alloy V-1977 on the mechanical and corrosion properties, as well as on the characteristics of metastable strengthening T′ and η′ precipitates. With the help of scanning electron microscopy and quantitative analysis, it is shown that the maximum strengthening effect (720 MPa) can be reached after applying a one-step ageing mode T1 at the temperature of 120 ^oC in the course of 24 hours. This effect becomes the result of type I Guinier–Preston zones forming simultaneously with lamellar metastable η′ precipitate having the respective sizes of 3.2 and 4.0 nm. Application of a three-step ageing mode T12 brings the strength of the alloy down to 680 MPa due to the coarsening of the η′ precipitate grain from 4.0 to 5.7 nm, a double growth of the η precipitate at the grain boundaries and the formation of the second metastable spherical T' precipitate with the size of 3.3 nm instead of type I Guinier–Preston zones. It is shown that the presence of zirconium intermetallides Al3Zr, which have a completely coherent interface, does not affect the nucleation of the metastable η′ precipitate. It is highlighted that the application of the three-step ageing mode T12 helps maintain the high strength properties in V-1977 alloy by weakening its proneness to layer corrosion from 7–8 to 4–5 points.

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