Different Underlying Corrosion Mechanism for Mg Bulk Alloys and Mg Thin Films

The influence of microstructure on the corrosion resistance of magnesium alloys was studied by comparing standard cast alloys with thin-film alloys (solid solution) of the same nominal composition. Latter were deposited on Si by means of magnetron sputtering. Results from potentiodynamic polarisation measurements, electrochemical impedance spectroscopy (EIS) and immersion tests with inductively coupled plasma (ICP) spectroscopy of the aqueous NaCl solution prove that beside lower corrosion rates for the thin films, a different corrosion mechanism is active in both systems, due to the dissimilar microstructure. Localised or pitting corrosion is dominating for the bulk alloys and uniform corrosion (on a much lower level) for the coatings.