Abstract
In the present review, the role of Cl－ions, Cu2+ ions, dissolved oxygen and an inhibitor in the corrosion of pure aluminum and 1050‐, 3003‐, and 4043‐aluminum alloys is described on the basis of immersion tests in hot aqueous solutions and dry/wet repeating tests. Chloride ions in solutions make the oxide films on Al phase, Fe‐, and Si‐enriched areas unstable, and enable them to work as local cathodes, leading to the enhancement of the corrosion. In Cu2+-containing solutions, copper particles are deposited on Al-phase and Fe‐enriched areas by the reduction of cupric ions, and the Cu particles deposited work as local cathodes to enhance the corrosion. In both Cl－- and Cu2+-containing solutions, copper particles are deposited on Si‐enriched areas as well as Al‐phase and Fe‐enriched areas, and the corrosion is enhanced vigorously, showing a synergistic effect.
Addition of an inhibitor to Cu2+-containing solution protects corrosion very effectively by the formation of a thin SiO2 layer, preventing copper particles from being deposited, while the addition to Cl－-containing solution inhibits corrosion less effectively, due to a high pH of the solution. Dry/wet repeating tests with a droplet of Cl－-containing solution show that large pits are formed at the outer parts of the droplet, and that the corrosion at the central parts is similar to that in Cl－-containing solution. The corrosion behavior at the central parts can be explained in terms of the contact with highly concentrated NaCl solution for long periods with a quick oxygen supply through a thin water membrane.
