Fabrication and characterization of an actively protective Mg-Al LDHs/Al2O3 composite coating on magnesium alloy AZ31

A magnesium-aluminum layered-double-hydroxides (Mg-Al LDHs) coating was fabricated on the surface of Mg alloy AZ31, followed by electrophoretic deposition of an Al2O3 nanoparticles layer. The morphology, structure and composition of the composite coatings were investigated by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and energy dispersive spectrometry (EDS). Ball on disc tests were carried out for measurements of the friction coefficient, wear loss and morphology of worn surfaces. Corrosion behavior of the coatings was investigated using potentiodynamic polarization curves and electrochemical impedance spectroscopy. Results indicate that the LDHs/Al2O3 composite coatings fabricated with 2.5 g/L Al2O3 nanoparticles solution exhibited best wear resistance, while best corrosion resistance was associated with the composite coating fabricated with 0.5 g/L Al2O3 nanoparticle solution. A sound mechanism for improving wear-resistance of the resulting coatings was proposed.