60 Years’ marine corrosion of aluminium alloy 24S (2024) from an historic aircraft wreck site: Implications for conservation

Abstract

Aluminium alloys forming the remnants of Lockheed P38 of Antoine de Saint-Exupéry was identified as the 24S aluminium alloy developed in 1930s. After 60 years in sea water, thick corrosion layers composed of aluminium hydroxide, copper salts and nanometre pure copper particles. In addition, the ancient aluminium alloy has undergone a very important intergranular corrosion. After the synthesis of Al₂Cu, Al₇Cu₂Fe and Al₂CuMg intermetallic phases, the study of their electrochemical behaviour in NaCl medium explains the significant presence of pure copper, because all the phases undergo a dealloying process. Electrochemical impedance spectroscopy measurements show that the kinetic of dealloying is constant versus immersion time, and is not limited by diffusion which explains the complete formation of copper sponge in NaCl medium in the conditions of long-term corrosion on aluminium artefacts.