Corrosion Resistance of Cerium-Conversion Coated AZ31 Magnesium Alloys in Cerium Nitrate Solutions

Cerium conversion coatings are a potential alternative to chromium conversion coatings for improving the corrosion resistance of magnesium alloys. This study detailed the microstructure and corrosion resistance of cerium conversion coatings on AZ31 magnesium plates treated in 0.05 kmol m^-3 cerium nitrate solution, with and without 0.25 kmol m^-3 hydrogen peroxide. The results indicate that the corrosion resistance of the coating was related to the microstructure of the major overlay, and to the defects of the coating. The major overlay changed from a fibrous structure to a compact layer, as hydrogen peroxide was added to a cerium nitrate solution. Meanwhile, severely-damaged areas were observed on the coating formed in the presence of hydrogen peroxide. Although the compact coating displayed better corrosion resistance than its fibrous counterpart, both coatings were locally corroded during the polarization test.