Improving the electrochemical stability of AZ31 Mg alloy in a 3.5wt.% NaCl solution via the surface functionalization of plasma electrolytic oxidation coating

The unique interactions between hexadecanoic acid (HA) and albumin (ALB) molecules on the surface of the porous layer of AZ31 Mg alloy were exploited to fabricate a novel hybrid composite film with excellent electrochemical stability in a 3.5 wt.% NaCl solution. Herein, the inorganic layer (IL) obtained by plasma electrolytic oxidation of AZ31 Mg alloy in an alkaline-phosphate-WO 3 electrolyte was soaked in an organic solution composed of ALB and HA for 10 and 24 h at 60 ??C. Although albumin and HA may coexist on the same surface of IL, the higher reactivity of ALB molecules would prevent the formation of a thick layer of HA. The donor-acceptor complexes formed due to the unique interactions between ALB and/or HA and IL surface would reduce the area exposed to the corrosive species which in turn would efficiently protect the substrate from corrosion. The porous structure of the IL would provide preferable sites for the physical and chemical locking triggered by charge-transfer phenomena, leading to the inhomogeneous nucleation and crystal growth of a flowery flakes-like organic layer. DFT calculations were performed to reveal the primary bonding modes between the ALB, HA, and IL and to assess the mechanistic insights into the formation of such novel hybrid composites. (C) 2021 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd.

Automated summary

The unique interactions between HA and ALB molecules on the surface of the porous layer of AZ31 Mg alloy were utilized to fabricate a novel hybrid composite film with excellent electrochemical stability. The interaction between ALB and HA molecules can effectively reduce the exposed area to corrosive species, protecting the substrate from corrosion. The porous structure of the IL facilitates the formation of physical and chemical locking, leading to the heterogeneous nucleation and crystal growth of the organic layer.