Enhancing corrosion resistance of magnesium alloys via combining green chicory extracts and metal cations as organic-inorganic composite inhibitor

Organic inhibitors provide advantages for corrosion protection through formation of chelation layers. However, individual inhibitors have weak inhibition efficiency when they are exposed to neutral media containing chloride ions. In this study, corrosion resistance of Mg alloy AZ91D is synergistically enhanced by combining green chicory (CA) extracts with metal cations (Ca2+, Fe3+, Fe2+, and Ni2+). The Mg(OH)2 and MgO corrosion products are porous in the early stages of immersion. The main organic compounds in CA including caffeic acid (Caf) and chicoric acid (Chi), which combine with inorganic cations via chelation reaction, are adsorbed on the corroded area. The large Bader charge and adsorption energies of Chi-Calcium-Chi (CaChi) complexes determined through density functional theory calculations suggest that CaChi interacts strongly with inorganic cations. The combined organic–inorganic inhibitors can therefore be absorbed firmly on the Mg substrate to form an active inhibitory layer. Among the various investigated CA-cation mixtures, CA-Ca2+ exhibited the highest anti-corrosion effect after immersion for 120 h and a corrosion current density (icorr), corrosion potential (Ecorr), and inhibition efficiency (η) of 0.09 ± 0.03 μA·cm−2, –0.87 ± 0.03 V (vs. SCE), and 92%, respectively. This work provides an effective approach for corrosion protection through combination of organic and inorganic inhibitors.