Quantitative phase analysis of Al-Cu-Li-Mg system alloys

Аuthors

Betsofen S. Y.^*, Osintsev O. E.^**, Knyazev M. I.^***, Dolgova M. I.^****, Kabanova Y. A.^*****

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: s.betsofen@gmail.com
**e-mail: osintcevoe@mati.ru
***e-mail: kniazevmk@bk.ru
****e-mail: dolgowami@gmail.com
*****e-mail: djulia.kbz@yandex.ru

Abstract

The authors have developed a method for computing a number of intermetallic phases (T₁ and δ′- phase) of Al-Cu-Li-Mg system alloys based on measuring α-solid solution lattice periods; Vegard’s law, linking up solid solution lattice period value with alloying ingredients content in it, as well as chemical and phase content equations. Lithium content in solid solution serves herewith as variable parameter. Quaternary Al-Cu-Li-Mg system alloys quantitative phase analysis method is based on the assumption that all magnesium resides in the solid solution. This fact is considered by introducing the relevant term into equation for calculating the solid solution lattice period. This is the only difference fr om the previously developed similar method for ternary alloys Al-Cu-Li. The paper shows that the developed method can be effectively used for quantitative interpretation of thermal and thermomechanical processing impact on alloys’ phase content study results, as well as while Al-Cu-Li-Mg system alloys content optimization. This method allowed us to compute the relation between periods of solid solution lattice and the amount of intermetallic phases for 29 Russian and foreign industrial alloys of various generations. The paper reveals the existence of linear dependence of relative quantity of intermetallic phases in alloys  from the atomic concentrations of lithium and copper (magnesium)  in these alloys. It shows also, that relation between δ′-phase and ternary phases is determined by the atomic concentration of lithium and copper. The authors suggested new Al-Cu-Li-Mg — alloys classification, wh ere all alloys should be divided into five groups, differing from each other by the double δ’-phase and ternary phase shares , or  ratio.

According to this classification, all the alloys are divided into five groups. The first group includes Al-Mg-Li alloys, for which the phases ratio . For the second group the ratio  varies from 2 to 3; for the 3rd group — from 5 to 7; for the fourth group — from 7 to 8, and the fifth group — from 11 to 17.

Keywords:

Al-Li alloys, quantitative phase analysis, δ′-phase

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