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.
A base material, a welding sample and the welding samples treated shot-peening were prepared from wrought non-combustible magnesium alloy (AMX602) used for a welding structure, in order to reduce stress corrosion cracking at welding parts in the magnesium alloys. The samples were examined by 400 hours corrosion test at 35°C and 100% humidity with preload of 80% angle of break point. The results were as follows. (1) The pitting corrosion without the stress corrosion cracking was observed on the base material. (2) The welding sample was observed the stress corrosion cracking in 200 hours corrosion test. (3) 0.2% proof stress of the welding sample was showed 12% decrease in comparison with that of the base material. (4) Stress corrosion cracking was suppressed by shot peening process to impart compression residual stress deeper than 100 μm. In this time, 0.2% proof stress of the species peened by shot was more than or equal to that of base material.
Corrosion behavior of 13%Cr SS and modified 13Cr martensitic stainless steels were investigated in CO2 solution with trace amounts of H2S in presence of acetic acid. Conventional 13%Cr SS observed pitting corrosion in 2.0 MPa CO2 with 20,000 ppm chloride solution at 40°C. However, pitting corrosion of 13%Cr SS was inhibited by presence of trace amounts of H2S. The pitting corrosion was initiated on modified 13Cr SS in CO2 solution with 0.002 MPa H2S and number of pits was increasing with increasing acetic acid concentration. At 180°C, maximum corrosion rate of 13%Cr SS was observed in presence of 0.0005 MPa H2S and decreased corrosion rate in higher H2S partial pressure with 7.8 MPa CO2 solution. Corrosion rate of modified 13Cr SS was independent of acetic acid concentration without H2S partial pressure however, corrosion rate was increased with increasing acetic acid concentration with trace amount of H2S. Effect of acetic acid was concluded that, decreasing pH, increasing solubility of Fe2+ and weaken passivation film and significantly affected corrosion behavior by coexistence of H2S and acetic acid in CO2 solution.