Numéro
J. Phys. Colloques
Volume 48, Numéro C3, Septembre 1987
4th International Aluminium Lithium Conference
Page(s) C3-729 - C3-735
DOI https://doi.org/10.1051/jphyscol:1987385
4th International Aluminium Lithium Conference

J. Phys. Colloques 48 (1987) C3-729-C3-735

DOI: 10.1051/jphyscol:1987385

THE PHENOMENON OF STRESS INSTABILITIES IN Al-Li BINARY ALLOYS AND MICROSCOPIC MECHANISMS CONNECTED

J.M. GENTZBITTEL, G. VIGIER et R. FOUGERES

Groupe d'Etudes de Métallurgie Physique et Physique des Matériaux, INSA, CNRS-UA 341, 20, Avenue Albert Einstein, F-69621 Villeurbanne Cedex, France


Abstract
For several years it has been well established that aluminium alloys with lithium additions are very attractive for aerospace applications, since they offer interesting combinations of high specific strength and high specific modulus /1/, /2/. Numerous studies were carried out in order to obtain optimum mechanical properties by modifying suitably microstructures /3/, /4/, /5/. Mechanical properties are mainly dependent on interactions between dislocations and precipitates, especially δ' (Al3Li) precipitates. Fundamental studies were carried out on Al-Li binary alloys exhibiting only δ' precipitates /6/. We have entered upon a study concerning the identification of microscopic mechanisms which control the cyclic deformation of Al-Li binary alloys. During fatigue tests, we have discovered an interesting substructure in hysteresis loops corresponding to stress instabilities in fatigue behaviour which are rigorously coupled with a strain age hardening phenomenon. The aim of this paper is to describe this phenomenon which is typical of the fatigue behaviour of Al-Li binary alloys with small δ' precipitates. In the last part of this paper, this unstable behaviour is compared to the PORTEVIN-LE CHATELIER (PLC) phenomenon. In addition, microscopic mechanism that control stress instabilities and strain age hardening are analysed in terms of interactions between dislocations and δ' precipitates.