Magnesium alloys are excellent candidates for applications involving weight savings in structure, transportation, electronics, and biomedical systems; however, their applicability in chloride-containing environment has been limited due to rapid localized corrosion, unstable film formation, and under-coating propagation following exposure to defects in the magnesium alloy substrate. PEO can produce an adhering, ceramic-like layer on magnesium alloys; nevertheless, the same microdischarge processes responsible for creating the layer also result in formation of pores, cracks, and microchannels associated with these discharges. The critical factor in the performance of the coating system is the existence of inhibitor reservoirs adjacent to possible electrolyte routes and not just coating thickness. The classification of coating systems based on AZ31, AZ31B, AZ91D, AM50, AM60, MA8, and Mg--Li alloys is done in terms of substrate, chemical nature of inhibitor, integration strategy, and corrosion inhibition response. Five weighted parameters are used to classify the layer systems based on proximity of inhibitor, healing potential, barrier reinforcement, quantifiable improvement in corrosion resistance, and durability. The calculation of impedance retention value is applied separately to defected triplex PEO/silane/epoxy coated samples with cerium and organic inhibitors. PEO/MSNTs@MN on AZ31B, ZnG@ZIF-8/MAO on AZ31, and Triplex-Ce-HQ on AZ31 provide the best protection classes due to active species in proximity of interface, quantifiable improvement in corrosion resistance and barrier moderation. In the defect-impedance retention subset, Triplex-Ce-HQ provides a low-frequency impedance value of 6.168, retention ratio of 0.954 after 48 h, and defect-impedance value of 5.883. The durable protection of magnesium alloys can be provided if the PEO layer is designed as an active reservoir.

magnesium alloy,plasma electrolytic oxidation,self-healing coating,corrosion inhibitor,active reservoir,electrochemical impedance spectroscopy,chloride corrosion,nanocontainer