Electrochemical Corrosion Behavior of Atmospheric Plasma Sprayed Alumina Coatings
Alumina-based coatings are employed in many industrial applications, in order to protect the surface of metal components against high temperature, wear, corrosion and erosion. The corrosion deterioration process of plasma sprayed alumina coatings on AZ31B magnesium alloy was investigated using potentiodynamic polarization test in NaCl solution at different chloride ion concentrations, pH value and exposure time. Furthermore, an attempt was made to develop an empirical relationship to predict the effect of pH value, chloride ion concentration and exposure time on corrosion rate of plasma sprayed alumina coatings. The corroded surface was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). 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 exposure time.