Novel self-healing glass-like CexOY film on a Flash-PEO coated AZ31B Mg alloy

Abstract

The aim of this work is to develop a glass-like CexOy coating to seal the pores of a Flash-PEO coated AZ31B Mg alloy and simultaneously provide smart self-healing corrosion protection. The cerium sol was synthesized using cerium acetate as main precursor by sol-gel method. SEM micrographs revealed that upon cerium sol deposition, the pores of the oxide coating were effectively sealed, resulting in a double-layer coating system and thereby in a big reservoir of cerium ions (Ce3+/Ce4+). The glassy character of the cerium coating, confirmed by X-Ray diffraction, implies that cerium exists in Ce3+ and Ce4+ ionic states enclosed in a high internal energy structure which facilitate the diffusion of cerium ions to active cathodic zone. Electrochemical Impedance Spectroscopy (EIS), X-Ray Diffraction (XRD), and Raman spectroscopy were used to explore the active corrosion protection of the CexOy sol-gel coating. The corrosion inhibition mechanism involves the migration of cerium ions and the precipitation of insoluble-crystalline cerium compounds (CeO2). The coating demonstrated self-healing properties, presenting a promising alternative to traditional chrome conversion coatings (CCC).

Keywords

• Glass-like CexOy
• Flash-PEO
• Mg alloy
• Self-healing
• Active corrosion protection
• Free-chromate coating