All-Russian Scientific Research Institute of Aviation Materials “VIAM”, Moscow, Russia

N. I. Kolobnev, Chief Researcher, e-mail: olanko@bk.ru
L. B. Khokhlatova, Head of Department
M. S. Oglodkov, Leading Engineer
Yu. Yu. Klochkova, Leading Engineer

This paper shows an overview of publications and some results of research of phase composition, grain structure and properties of semi-finished products, made of aluminium-lithium alloys of Al – Cu – Li system, which were additionally alloyed with Zn, Ag, Zr, Sc and Mg. There is considered an offer to divide the aluminum-lithium alloys in two groups:
— 2.0–3.0% of Cu with 1.2–1.8% of Li;
— 3.5–4.5% of Cu with 0.6–1.3% of Li.
V-1461 (В-1461) alloy and similar 2099 (2199) alloys belong to the first group. At the same time, V-1469 (В-1469) and 2060 alloys belong to the second group. It should be taken into account that V-1461 and V-1469 alloys were developed in Russia, when 2099 (2199) and 2060 alloys were developed abroad. Depending on the content of Cu and Li as basic alloying elements, the following phases may precipitate: δ'(Al₃Li), θ'(Al₂Cu), T_B (Al₇Cu₄Li), Т₁(Т'1) (Al₂CuLi) and T₂ (Al₆CuLi₃). Diagrams of phase transformations at aging of V-1461 and V-1469 alloys within a wide “temperature – time” range are presented along with the phase areas, providing the maximum strength. Similar results were obtained according to the phase composition of foreign 2199 (2099) and 2060 alloys. There is given the strengthening degree, provided by each strengthening phase. The causes of decreasing of ductility and fracture toughness of aluminum-lithium alloys were analyzed along with the description of their resolving ways. The following factors may be considered as a basic cause of lowered ductility, fracture toughness, sharp strain texture and considerable anisotropy of mechanical properties:
— the strain localization near the grain boundaries, caused by cutting of particles of the main strengthening phase (δ') by dislocations;
— strong texturing of the fibrous structure.
Conditions, which eliminate the strain localization and decrease the texture sharpness, were created in the new generation alloys due to some decreasing of lithium content, addition alloying with Zr, Sc and Mg and application of multi-step aging. Chemical compositions of alloys and conditions of semi-finished products manufacturing were adjusted using the foregoing factors, including thermal and mechanical treatment. Conditions of multi-step aging were developed for the purpose of provision of increased fracture toughness level. There are given the properties of V-1461, V-1469, 2199 (2099) and 2060 alloys with rather high characteristics of fracture toughness.

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