Design of self-healing PEO-based protective layers containing in-situ grown LDH loaded with inhibitor on the MA8 magnesium alloy

Abstract

The high corrosion rate of magnesium and its alloys in chloride-containing solution significantly reduces the potential of this material for diverse applications. Therefore, the formation of a smart protective coating was achieved in this work to prevent degradation of the MA8 magnesium alloy. A porous ceramic-like matrix was obtained on the material by plasma electrolytic oxidation (PEO). Further surface functionalization was performed using layered double hydroxides (LDH) served as nanocontainers for the corrosion inhibitor. Several methods of LDH intercalation with benzotriazole (BTA) were proposed. The composition and morphology of the formed coating were studied using SEM-EDX analysis, XRD, XPS, and Raman microspectroscopy. The corrosion behavior of the coated samples was evaluated using electrochemical impedance spectroscopy and potentiodynamic polarization. The corrosion rate was estimated using volumetry and gravimetry methods. The formed composite coating provides the Mg alloy with the lowest corrosion activity (|Z|f = 0.1 Hz = 8.48·105 Ω·cm2, Ic = 1.4·10−8 A/cm2, PH = 0.21 mm/year) and improves the protective properties of the PEO-coated sample (|Z|f = 0.1 Hz = 8.37·103 Ω·cm2, Ic = 4.1·10−7 A/cm2, PH = 0.31 mm/year). The realization of the self-healing effect of the inhibitor-containing LDH/PEO-coated system was studied using localized electrochemical methods (SVET and SIET) with two artificial defects on the surface. A mechanism involving three stages for the active corrosion protection of the alloy was proposed. These findings contribute to the follow-up work of developing modified LDH/PEO-based structures that promote the Mg alloy with high corrosion resistance, superior electrochemical performance for applications in various fields of industry and medicine.

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