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Cross-sectional characterization of the conversion layer formed on AA2024-T3 by a lithium-leaching coating

Journal Article (2020)
Author(s)

A. Kosari (TU Delft - (OLD) MSE-6)

P. Visser (Akzo Nobel)

F. Tichelaar (Kavli institute of nanoscience Delft, TU Delft - QN/Afdelingsbureau)

S. Eswara (Luxembourg Institute of Science and Technology)

J. N. Audinot (Luxembourg Institute of Science and Technology)

T. Wirtz (Luxembourg Institute of Science and Technology)

H. Zandbergen (Kavli institute of nanoscience Delft, TU Delft - QN/Zandbergen Lab)

H. Terryn (TU Delft - (OLD) MSE-6, Vrije Universiteit Brussel)

J. M.C. Mol (TU Delft - (OLD) MSE-6)

DOI related publication
https://doi.org/10.1016/j.apsusc.2020.145665 Final published version
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Publication Year
2020
Language
English
Volume number
512
Article number
145665
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350
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Abstract

This work focuses on the cross-sectional characterization of the protective conversion layer formed on AA2024-T3 by lithium-leaching from a polyurethane coating in a corrosive environment. The layer shows a multi-layered arrangement comprising nanoscopic local phases. Transmission electron microscopy (TEM) and complementary high-resolution secondary ion mass spectroscopy (SIMS) were employed to observe the cross-sections of the entire layer formed at different locations of a 1-mm-wide scribe, in terms of morphology, structure and chemical composition. The conversion layer was comprised of two ubiquitous sublayers; a thin dense layer (i.e. 150 nm) adjacent the alloy substrate and a porous layer. The former represents an amorphous lithium-containing pseudoboehmite phase, Li-pseudoboehmite, whereas the latter is composed of amorphous and crystalline products; an outer columnar layer merely seen on the peripheral region is also crystalline. Through a sandwich structure and the d(003) basal spacing, the crystalline phases were identified as Li-Al layered double hydroxide. Although lithium was found uniformly spread within different regions, the local phases with no/low concentration of lithium were revealed with energy filtered TEM and confirmed with SIMS analysis.