PEO Treatment for Improved Corrosion Resistance in a Zn-Mg Alloy: Electrochemical and Structural Analysis

Zinc-based alloys have been extensively studied for their potential applications in biodegradable materials, yet their corrosion behaviour necessitates the development of effective surface treatments. In this study, a ZnMg alloy was developed by casting in an inert medium and subsequently treating it with Plasma Electrolytic Oxidation (PEO). The corrosion behaviour was characterised in a 0.9% NaCl solution through Tafel polarisation, cyclic polarisation, and electrochemical impedance spectroscopy (EIS). Additionally, the surface morphology was investigated using scanning electron microscopy (SEM) and EDX analysis. The structure and phases of the oxide layer and of the corrosion products were investigated through X-ray diffraction (XRD). The electrochemical results demonstrated a substantial decrease in the corrosion current density and an increase in the polarisation resistance for the treated samples. Electrical Impedance Spectroscopy (EIS) modelling revealed the formation of a layer exhibiting distinct capacitive behaviour, comprising two distinct regions. XRD analysis confirmed evidence of corrosion compounds characteristic of chlorinated media on the surface. The findings indicated that PEO treatment enhanced the corrosion resistance of the ZnMg alloy, suggesting its suitability for biomedical applications or exposure to marine environments characterised by high levels of corrosion.