Effect of short-time thermal oxidation on the surface of Al−Li−Cu−Mg alloy (8090) sheet

Abstract

The oxidation behaviour of 8090 AI-Li alloy sheet was studied after exposure for short times (<5 min) in laboratory air, moist air, moist argon and hydrogen at 530 ° C. Oxidation was greater at grain boundaries in hydrogen but not in air. Sites of rapid local oxidation (number density 9 to 8 x 103 cm -2) were associated with insoluble particles. Four types of growth morphology were identified with these sites. Some growths believed to be spinel, were 10 to 25/~m diameter and grew to ~ 1 mm in height at 2 #m sec -1 . Pits beneath these growths were 25#m diameter and 10 to 20#m deep. A qualitative model is proposed for rapid oxidation in AI-Li alloys and the effect of these sites on weight gain measurements, surface contamination and mechanical properties is discussed.

Effect of heat treatment environment on Li depletion and on mechanical properties in Al-Li alloy sheets

“…This points out the fact that diffusion of Li from thebulk to the surface and its loss to the environment, either by oxidation or sublimation (in inert environments or under vacuum), is not influenced much by the composition of the surface layers and is primarily controlled by the concentration gradient alone. The depth of Li depletion after the heat treatments varied from 100 to 150 ~tm in all the alloy systems that were tested and is in good agreement with earlier studies by various investigators [4][5][6][7]11]. In 8090 series alloys there is a small but appreciable change in the amount of Li lost to different environments used for the solution heat treatment.…”

“…Using Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) techniques, Ahmed [-6] has shown that the rate of oxidation in these alloys is controlled by bulk diffision of Li in the A1 alloy matrix. The oxidation products of A1-Li alloys are permeable to Li, leading to its unhindered loss with time at high temperatures [7]. It has also been shown that Li is lost to the environment at-the free surface by sublimation in vacuum and in inert gas environments [7].…”

“…The oxidation products of A1-Li alloys are permeable to Li, leading to its unhindered loss with time at high temperatures [7]. It has also been shown that Li is lost to the environment at-the free surface by sublimation in vacuum and in inert gas environments [7]. In the early stages of oxidation, significant variations in the amount of oxidation has been found between the grain boundary regions and the grain interiors and has been attributed to the greater rates of diffusion in the grain boundaries [7].…”

“…It has also been shown that Li is lost to the environment at-the free surface by sublimation in vacuum and in inert gas environments [7]. In the early stages of oxidation, significant variations in the amount of oxidation has been found between the grain boundary regions and the grain interiors and has been attributed to the greater rates of diffusion in the grain boundaries [7]. Although, lithium depletion from the surface of A1-Li alloys at high temperatures is controlled by the diffusion of Li in the bulk of the material [6], it also depends on the rate at which it is removed from the free surface.…”

27Al and 7Li spin‐echo and spin‐echo double resonance NMR applications to the study of lithium depletion and surface oxidation in Al–Li alloy

“…10 Scanning electron microscopy was used to observe the morphology of the oxide surface. 11 Detailed descriptions of these techniques and experimental results can be found in the publications cited, and the results related to this paper will be discussed in the text.…”