Lithium depletion during heat treatment of aluminum-lithium alloys

Oxidation induced void formation in TEM specimens of Al–Cu–Li alloy

“…Although our alloy was not deliberately oxidized at such a high temperature, a low-temperature oxidation process could occur during and after the 150 or 160˚C aging. If such an oxidation was possible in our ACL alloy, voids could have originated by the same mechanism as that proposed for the high-temperature oxidation (8) . According to observations by Papazian et al (8) , fast-moving lithium atoms are preferentially oxidized, creating a lithium-denuted zone near the alloy surface.…”

“…If such an oxidation was possible in our ACL alloy, voids could have originated by the same mechanism as that proposed for the high-temperature oxidation (8) . According to observations by Papazian et al (8) , fast-moving lithium atoms are preferentially oxidized, creating a lithium-denuted zone near the alloy surface. The lithium-denuted zone is not replenished fast enough by slow-moving aluminium atoms, thus leaving excess vacancies inside the zone.…”

“…In fact there is one previous paper that reported (8) observations of large ( > 1 µm) voids in a Al-Lirelated alloy (Al-2.58%Li-1.06%Cu-0.56%Mg-0.07%Fe-0.02%Si-0.021%Ti-0.08%Zr in weight %) after high-temperature (~500ºC) oxidation in air. Although our alloy was not deliberately oxidized at such a high temperature, a low-temperature oxidation process could occur during and after the 150 or 160˚C aging.…”

“…The formation mechanism of these voids was thought to be similar to that of the hollow-core oxide particles, because a TEM specimen has some geometrical resemblance in such a way to trap oxidation-induced excess vacancies between two surface oxide films. There is only one report on voids in this class of alloy system by Papazian et al (8) , who found much larger (> 1 µm) voids as a result of high-temperature (~500ºC) oxidation, but the voids in this small size range (~3 nm) have never been reported previously.…”

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

“…These factors and the occurrence of all the oxidation products together in surface films, preclude the use of gravimetric data for determining oxidation rates for A1-Li alloys [1,2,10], nor can the depth of the lithiumdepleted layer be used to predict oxide layer thickness as suggested elsewhere [14]. Furthermore the use of X-ray diffraction data to relate the amount of each oxidation product to the oxidation conditions is made difficult by the lack of sensitivity at low volume fractions [12], by the variety of oxidation products, by the 8090, A1-2.5 Li-l,4 Cu-0.65 Mg-0.14 Zr, 8091, A1-2.47 Li-2.0 Cu-0.58 Mg-0.12 Zr, 2090, A1-2.7 CU-I.9 Li-0.16 Zr (wt %).…”