Corrosion properties and surface free energy of the Zn Al LDH/rGO coating on MAO pretreated AZ31 magnesium alloy

Micro-arc oxidation (MAO) is one of the promising surface treatment methods that can enhance the corrosion resistance of magnesium alloys. However, the existence of pores and microcracks significantly restricts the further advancement of corrosion resistance. In this study, effective and environmentally friendly materials, layered double hydroxides (LDH), with and without combination of rGO (reduced graphene oxide) nanosheets, were employed to seal the pores and micro-cracks in order to enhance the anti-corrosion and degradation performance of the MAO coating on AZ31. Microstructural morphologies and crystallography of the coatings were characterized using scanning electron microscopy (SEM), and X-ray diffraction (XRD). The corrosion performances of coatings were investigated by an electrochemical workstation. Moreover, hydrophobicity and surface free energy of the synthesized coatings were measured by sessile drop method. The characterization results demonstrated that incorporation of the GO sheet with ZnAl LDH flakes could effectively enhance the anti-corrosion properties (iCorr = 5 nA/cm2) and long-term degradation of the MAO coating. Furthermore, the GO plates were reduced to rGO during the hydrothermal process, which further improves the hydrophilicity and lowers the surface free energy of the coatings, i.e. γMAO−LDH/rGOs=17.8mNm<γMAO−LDHs=24.7mNm<γMAOs=43.1mNm.