Effect Of Graphene Oxide Additive On The Corrosion Resistance Of The Plasma Electrolytic Oxidation Coating Of The AZ31 Magnesium Alloy

Magnesium alloys are widely used in aerospace industry, automobile manufacturing, and electronic devices, due to their superior physical and mechanical properties, such as low densities and high specific strengths. However, the poor corrosion resistance of magnesium alloys significantly limits the application of these materials under corrosive environments. As a surface treatment technology, micro-arc oxidation (MAO) can provide a layer of oxide coating covering the metal matrix such as magnesium, aluminum and titanium. The oxide coatings usually exhibit high corrosion resistance and wear resistance.In this study, graphene oxide (GO) parpered by Hummers method was added into the electrolyte during the preparation of oxide coating on AZ31 magnesium alloy by MAO and its influences on the thickness, microstructure, and corrosion resistance of the coating were studied. The main studies are as follows:(1) The particle size and zeta potential of GO sample parpered by Hummers method were measured, and it were characterized using XRD GO were 1.14μm and-63.5mV (pH=7, deionized water). The XRD and UV-Vis spectrum results show that the oxygen-containing functional groups such as hydroxyl formed on the GO sheets.(2) The MAO layer was fabricated by a two-step PEO process, first in a phosphate alkaline electrolyte and subsequently in a disodium hydrogen phosphate electrolyte with different concentrate of GO. The influences of GO on the thickness and corrosion resistance of the MAO coating were studied. It could be summarized that the added of GO in the electrolyte could reduce the thickness of the MAO coating. Compared with coating formed in the electrolyte without GO, the corrosion resistance of coating formed in the electrolyte with 1 g/1 was improved. With the concentration of the GO increased in 2 g/1, the corrosion resistance of coating was decreased.(3) The MAO layer was fabricated by a similar two-step PEO process, firstly in alkaline phosphate electrolyte after in acid electrolyte with GO. The influences of GO on the thickness, microstructure, and corrosion resistance of the coating were studied. The thickness and surface porosity of the MAO coating formed in electrolyte with the addition of GO was decreased. The results of XPS and EDS demonstrated that GO was partly reduced to rGO during MAO and it was successfully incorporated into the MAO coating. Moreover, the results of electrochemical test revealed that the corrosion resistance of the MAO coating was markedly improved.