Chemisorption-dominated organic–silicate hybrid anchoring on porous MgO for durable corrosion protection of AZ31 Mg alloy

Abstract

A chemically and electronically driven surface engineering strategy is presented to enhance the corrosion resistance of AZ31 Mg alloy through interfacial hybridization within a porous oxide framework. A porous MgO layer was first generated via anodic plasma-assisted oxidation, producing a chemically active surface enriched with Mg²⁺ sites. Subsequent hydrothermal functionalization with L-tryptophan and a silane precursor yielded a consolidated Trp–siloxane hybrid coating (Hyb@MgO) that infiltrates and seals the intrinsic porosity of the oxide layer. Structural and surface characterizations confirm the formation of a chemically integrated network rather than a discrete overlayer. Electrochemical evaluation in chloride-containing media shows that Hyb@MgO exhibits a markedly ennobled corrosion potential, an ultralow corrosion current density on the order of 10⁻⁹ A·cm⁻², and a low-frequency impedance modulus approaching 5 × 10⁷ Ω·cm², indicating robust barrier performance under the applied test conditions. In contrast, applying the same Trp–TEOS treatment directly to bare AZ31 produces a weak, discontinuous surface film with only marginal corrosion improvement, highlighting the essential role of the porous MgO interlayer. DFT and Monte Carlo simulations further demonstrate that Trp–TEOS co-condensation forms an electronically activated Trp–Si(OH)₃ hybrid that enables chemisorption-dominated anchoring on MgO, accounting for the enhanced interfacial stability and corrosion resistance beyond simple physical pore sealing.