Study on the self-healing mechanism of corrosion product film on EW75 Mg alloy

Abstract

A compact corrosion product film can be spontaneously formed on the surface of EW75 Mg alloy in NaCl solution. In particular, this corrosion product film can realize self-healing after scratched. The self-healing mechanism was investigated by Scanning Electron Microscope (SEM), electrochemical tests and local pH measurements. The results show that self-healing is attributed to the formation of micro-galvanic cell between the scratched anodic area and unscratched cathodic area, which promotes the rapid regeneration of the corrosion product film in the damaged regions. Moreover, the local pH and Rare Earth (RE) ion concentrations at the scratch edge are higher than those in other regions, which results in a higher regeneration rate. As the scratch widths increase, the cathode/anode area ratios decrease, and the galvanic effect weakens, resulting in the slower self-healing rate and the prolonged time for achieving self-healing, but all samples with different scratch widths can still realize self-healing.