Influence of pH, chloride ion concentration and spraying time on the corrosion behaviour of atmospheric plasma sprayed alumina coatings

The corrosion behaviour of the plasma sprayed alumina coatings was evaluated by conducting salt fog test in NaCl solution at different chloride ion concentrations, pH value and spraying time. Empirical relationship was developed to predict the corrosion rate of alumina coatings by incorporating the corrosion process parameters. The corroded surface was characterised by scanning electron microscopy (SEM) and X-ray diffraction. The results showed that the corrosion deterioration of alumina coating was significantly influenced by chloride ion concentration and pH value. The alumina coatings were found to be highly susceptible to localised damage. It could not provide an effective corrosion protection to Mg alloy substrate in solutions containing acidic environments (pH 3), higher chloride concentrations and spraying time.