Effect of solution pH value on the corrosion resistance of Co-Fe LDHs coating developed on MAO treated magnesium alloy AZ31

Abstract

As a post-treatment method of MAO coating, layered doubled hydroxides (LDHs) can improve the corrosion/degradation resistance of magnesium (Mg) alloys. This study innovatively prepared Co-Fe LDHs coatings on MAO treated Mg alloy AZ31, and investigated the effect of pH value on the corrosion/degradation resistance of the coatings. The results indicate that the corrosion/degradation resistance of LDHs coatings first increase and then decrease with the increase of pH. The best corrosion/degradation resistance occurred for pH = 12, with a corrosion current density (icorr) of 5.18×10–8 A∙cm–2. The icorr after immersing in NaCl solution for 14 days was 1.65×10–6 A∙cm–2. The Co-Fe LDHs nanosheets (pH = 12) effectively sealed the pores of the MAO coating, resulting in increased coating density and hindering the diffusion of corrosive media, thereby effectively protecting the Mg alloy. This study is of great significance for the corrosion protection and rapid degradation prevention of Mg alloys and other alloys.