Adverse effect of 2,5PDC corrosion inhibitor on PEO coated magnesium.

Besides their noteworthy tribological and corrosion protection properties, Plasma Electrolytic Oxidation (PEO) coatings feature a porous microstructure that is able to host corrosion inhibitors. This study reveals that although 2,5pyridindicarboxylate (2,5PDC) shows a remarkable corrosion inhibition effect for bare AZ21 Mg alloy, it can extensively deteriorate a PEO coating on the same Mg substrate, resulting in an overall accelerated failure of the PEO-coated AZ21 alloy. The deteriorative behavior of 2,5PDC towards PEO-coated AZ21 is explained based on the characterization of the bare and PEO-coated AZ21 exposed to the NaCl electrolyte with and without inhibitor using EIS, SEM, STEM and ToF-SIMS. • 2,5PDC could effectively inhibit the corrosion of AZ21 in 3.5 wt% NaCl. • 2,5PDC could accelerate the degradation of AZ21 coated with the phosphate-based PEO. • The inhibition/adverse effect of 2,5PDC on bare/coated AZ21 is intensified with its concentration. • Formation of a soluble complex between Mg2+ and 2,5PDC destabilizes the PEO layer. • Formation of a relatively thick corrosion layer on AZ21 accelerates the failure of PEO coating. [ABSTRACT FROM AUTHOR]