A Comparative Study on the Corrosion Resistance of Cerium-Based Conversion Coatings on AZ91D and AZ31B Magnesium Alloys

In the present work a comparative study has been carried out on the surface morphology, electrochemical properties and corrosion performance of cerium-based conversion coatings (CeCCs) on AZ91D and AZ31B magnesium alloys. The as-deposited coatings consisted of a two layer structure: a continuous Mg/Al oxide transition layer of ~ 50 nm thick and a CeCC layer of ~ 400 nm thick. Potentiodynamic polarization and impedance spectroscopy results using a 0.6 wt% NaCl and 0.6 wt% (NH4)2SO4 electrolyte showed that cerium-based conversion coatings enhanced the corrosion resistance of AZ91D and AZ31B magnesium alloys compared to polished uncoated samples. Good correlation of electrochemical test and ASTM B117 salt spray was realized.