Marine Corrosion and Protection of Aluminum Alloys According to Their Composition and Structure

Abstract

Based on long-term tests of aluminum alloys in seawater of various climatic zones from the Arctic to the tropics, the peculiarities of their corrosion behavior are revealed. In contrast to other alloys, hydrogen sulfide has a beneficial effect on their corrosion resistance due to the passivation. However, deep in the Black Sea, the alloys, which are susceptible to structural types of corrosion, were subjected to strong exfoliation corrosion, because hydrogen sulfide excluded fouling with microorganisms that inhibits exfoliation corrosion. Alloys of the Al-Mg system exhibit the highest corrosion resistance in seawater. Alloy of an AMr61 type (σul = 340 MPa, σ0.2 = 180–210 MPa, δ = 11–15%) has shown a good performance. Alloying with scandium and thermomechanical treatment make possible further simultaneous improvement of mechanical properties and corrosion resistance. It is shown that crevice corrosion is more typical of corrosion-resistant low aluminum alloys possessing lower free-corrosion and pitting potentials compared to high alloys, which are susceptible to structural types of corrosion, in particular, exfoliation corrosion. The methods of the aluminum alloys protection against marine corrosion are considered. It is shown that, in contrast to carbon steels, the anodic-cathodic protection is used for aluminum alloys.