Dopamine self-polymerized sol-gel coating for corrosion protection of AZ31 Mg Alloy

Mg alloys have excellent mechanical and physical properties. Unfortunately, the poor corrosion resistance becomes the main disadvantage of the application of such materials in aqueous and atmospheric media. Although the sol-gel-based coating has attracted significant attention for alloys in corrosion protection, most of the existing sol-gel coatings are unable to give a long-term protection for the substrate against corrosion in saline solutions due to micro-/ nano-pores contained in its glassy sol-gel networks. To address this issue, a new sol-gel coating was prepared by utilizing the strong adhesion property of polydopamine (PDA) to provide a highly condensed sol-gel-based coating (PDA@sol-gel) on Mg alloy AZ31. Long-term corrosion testing by electrochemical impedance spectroscopy in aqueous 0.1 M NaCl indicated that the prepared PDA@sol-gel coating exhibited a substantially improved corrosion protection performance with a test duration of over 20 days. In comparison, the unmodified coating failed after 3 days of immersion in aqueous NaCl. The improved anti-corrosion performance may be attributed to the self-polymerized PDA filling the micro-/ nano defects in the cross-linked network of the SiO 2 sol-gel, which greatly improves the compactness of the coating. This work presented a new approach to significantly improve the corrosion protection performance of magnesium alloys by dopamine-modified sol-gel coating, which can find ample applications in a wide range of industries.