Preparation And Corrosion Resistance Of Graphene Oxide Based Composite Coating On Magnesium Alloy

Magnesium and its alloys have attracted wide attention in electronic communications,automotive industry,aerospace and other industrial fields due to their low density,high specific strength and specific stiffness,good machinability and recycling.But the corrosion resistance of magnesium alloys is poor,which greatly limits their large-scale application.Therefore,it is very necessary to explore effective methods for surface protection of magnesium alloys.In this paper,first of all,raphene oxide?GO?was prepared by improved Hummers method.Then,two kinds of composite coatings of APTES/GO and MAO?GO?were prepared on the surface of AZ31B magnesium alloy by using3-aminopropyltriethoxysilane?APTES?coupling agent and micro arc oxidation?MAO?method.The morphologies and composition of the GO and two composite coatings of APTES/GO and MAO?GO?were analyzed by scanning electron microscopy?SEM?,energy spectrum analysis?EDS?,infrared spectrum analysis?FTIR?,X-ray photoelectron spectroscopy?XPS?and Raman spectroscopy.The corrosion behavior of the two composite coatings in 3.5wt%NaCl neutral solution was studied by measuring the potentiodynamic polarization curves and AC impedance spectra.?1?The optimal preparation parameters of APTES/GO composite coating are:APTES content:5%;alcohol water ratio:1:18;soaking time:30 min;GO:2 g/L.The morphology of the coating is uniform and dense,and the thickness of the coating is1?m.The XPS,FTIR and Raman measurements showed that silane layer of APTES bonds precisely with the AZ31B substrate through Si-O-Mg bonds.And graphene oxide was successfully grafted onto the substrate surface via amide reaction employing3-aminopropyltriethoxysilane?APTES?as an intermediate layer.The electrochemical test showed that the corrosion current density of the APTES/GO coating decreased by three orders of magnitude compared with the blank sample,and the corrosion potential of the coating increased by 0.11 V,and the protective effect on the matrix was obviously higher than that of the single silane coating.?2?The optimal process parameters for the preparation of MAO?GO?composite coating are:electrolyte composition:Na₂SiO₃ 7 g/L,NaP₂O₇·10H₂O 3 g/L,NaOH 5g/L;GO:0.5 g/L;current density:6 A/dm²,oxidation time:5 min.SEM analysis shows that GO has a sealing and covering effect in the ceramic layer,which reduces the number and size of micropores on the surface of carbon containing ceramic.The coatings with the thickness of about 4⁵?m is more compact and smooth,which is well adhesive to the substrate.The electrochemical test and total corrosion test show that the carbon containing ceramic layer has the highest corrosion potential and the lowest corrosion current density compared with other samples,and it can effectively protect the AZ31B magnesium alloy substrate for a long time.