Localized corrosion at nm-scale hardening precipitates in Al-Cu-Li alloys

The localized corrosion of Li-containing nm hardening precipitates in the 3rd generation of Al-Cu-Li alloys was investigated based on a quasi in situ approach by sequentially exposing the material to NaCl solution and characterizing the structural, chemical, and electrochemical evolution at atomic scale using electron microscopy, spectroscopy, 3D tomography, electrochemical measurements, and DFT calculations. Localized corrosion of Al7.5Cu4Li (T-B phase) initiated along {001} family of planes through the dealloying of Al and Li due to a low surface work function. Cu was enriched along the Cu (110) // T-B (011) Al (100) orientations on and around corroded T-B precipitates. No strong galvanic interactions were observed at the T-B and Al matrix interface due to the formation of a Li-C-O rich passivation layer during electrolyte exposure. Similarities and differences between T-B and other common Al-Cu-Li precipitates (Al2CuLi, Al6CuLi3, and Al3Li) with respect to corrosion are discussed. The reported corrosion mechanism can assist in the assessment of the localized corrosion susceptibility of precipitation-hardened Al alloys and assist in the design of new alloys. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.