Effect of pH, Chloride Ion Concentration and Immersion Time on the Microstructural and Corrosion Properties of Atmospheric Plasma Sprayed Alumina Coatings on AZ31B Magnesium Alloy Under Immersion Environment

The corrosion deterioration process of plasma sprayed alumina coatings on AZ31B magnesium alloy was investigated using immersion corrosion test in NaCl solution at different chloride ion concentrations, pH value and immersion time. The experiments were conducted based on a three factor, five level, central composite rotatable design matrix with full replications technique. Response surface methodology was used to develop the relationship. The developed relationship can be effectively used to predict the corrosion rate of plasma sprayed alumina coatings on AZ31B magnesium alloy at 95% confidence level. The results showed that the corrosion deterioration of alumina coated magnesium alloy in NaCl solutions was significantly influenced by chloride ion concentration and pH value. The alumina coatings were found to be highly susceptible to localized damage, and could not provide an effective corrosion protection to Mg alloy substrate in solutions containing acidic environments (pH3), higher chloride concentrations and immersion time.