Preparation and Electrochemical Behavior of Graphene-Oxide/Zinc-Phosphate Composite Coatings on as-Cast Al-Zn (5.0 wt.%)-Mg (2.5 wt.%) Alloy

Graphene-oxide/zinc-phosphate composite coatings (GO/ZP) have been synthesized on as-cast Al-Zn (5.0 wt. %)-Mg (2.5 wt.%) alloy substrate using the chemical conversion coatings technique. X-ray diffraction (XRD), electron microscopy (SEM) associated with energy-dispersive X-ray spectroscopy unit (EDX) and X-ray photoelectron spectroscopy (XPS) were utilized for characterizing the microstructure of GO/ZP composite coating films. The electrochemical behavior of GO/ZP composite coatings was studied using potentiodynamic polarization and potentiostatic techniques. The results revealed that the incorporation of GO sheets in the ZP coating bath up to 1.0 g/L led to increasing the coating weight (g/m(2)) and the corrosion protection efficiency (%). The improvement of corrosion resistance could be attributed to the regular distribution of GO which closed up the free spaces in coating films and inhibited the penetration of corrosive ions into alloy substrate. Nevertheless, a further incorporating of GO (1.25 and 1.5 g/L) gave an adverse effect on the coating weight and the corrosion resistance.