Self-degradation of micro-arc oxidation/chitosan composite coating on Mg-4Li-1Ca alloy

The degradation of micro-arc oxidation coating (MAO)/chitosan (CS) coating decreases solution pH value at lower level (≤8.25) in comparison to MAO coating. A self-degradation mechanism of CS-based materials is proposed. And the degradation process experiences three stages: (1) initial water diffusion, absorption and hydration of CS coatings; (2) gradual decrease in molecular weight; and (3) scission and dissolution of oligomers and monomers. Thus, the degraded CS releases -NH3+ ions, which react with MgO of MAO coating and lead to the formation of Mg2+ ions and water along with the micro-cracks and pores of the MAO coating.272