Long-term localized corrosion behaviors of 5A06 aluminum alloys exposed in the natural deep-sea environment of South China Sea

Abstract

The deep-sea field exposure experiment of 5A06 aluminum alloy was carried out successfully in the South China Sea with the sea depths of 1200 m, 2000 m, and 3000 m for one year. Corrosion morphologies show that pitting corrosion and crevice corrosion as the main corrosion types occur on the specimen surface, and that the crevice corrosion makes more contributions. The corrosion data results show that average corrosion rate, maximum pitting depth and corrosion area ratio reduce with the sea depth increasing and that the highest values are 13.8 μm a−1, 87.2 μm and 18.32% for 1200 m specimen. XPS results show that the oxygen content decreases with the sea depth increasing while the magnesium content increases. Comparing with 1200 m specimen, 2000 m and 3000 m specimens display higher ratios of Al2O3: Al(OH)3 and MgO: Mg(OH)2, which may be ascribed to the slightly higher oxygen concentration. Mott–Schottky results show that donor densities and acceptor densities are 1.14 × 1024 cm−3 and 9.16 × 1023 cm−3 for 1200 m, 2.82 × 1023 cm−3 and 2.10 × 1023 cm−3 for 1200 m, and 3.11 × 1023 cm−3 and 4.05 × 1023 cm−3 for 3000 m, respectively.