Research On Anti-corrosion Performance Of Graphene Modified Coating On AZ31 Magnesium Alloy

The low density,high specific strength and rigidity of magnesium alloy play an important role in the design of lightweight and emission reduction.However,magnesium alloy is easily corroded,which reduces the use time of magnesium alloy products and hinders its promotion and application in real life.Surface anti-corrosion technology can solve this problem well.Among them,organic coating is the most economical method.However,due to the cross-linking and curing of coatings,organic coatings are more prone to defects such as holes.Therefore,this article chooses to add graphene corrosion inhibitor filler to the coating to improve the coating corrosion resistance.The specific operation method is as follows:epoxy resin coating and epoxy/polyurethane composite coating modified with different graphene addition amount are prepared on the surface of AZ31 magnesium alloy.Through scanning electron microscope microscopic observation(SEM),X-ray diffractometer phase detection(XRD),fourier infrared spectroscopy and raman spectroscopy and other characterization methods and test methods,the effect of different graphene content on the microscopic shape of the coating was studied.The influence of appearance and composition structure.Then,an electrochemical workstation was used to explore the influence of different graphene content on the corrosion resistance of the coating,and combined with SEM to observe the microscopic morphology of the magnesium alloy substrate and coating after electrochemical corrosion,and comprehensively analyze the corrosion of the coating by graphene.The impact of the mechanism.Mainly get the following research results and conclusions:(1)Using brush coating technology,successfully coated epoxy resin coating and epoxy/polyurethane composite coating modified with different graphene content on the surface of AZ31 magnesium alloy.The thickness of the epoxy resin coating is200±20?m,The thickness of the epoxy/polyurethane coating is 450±20?m.(2)Through the characterization of the microstructure and composition structure of graphene and coatings,it is found that the surface structure of graphene has relatively low defects,the size is below 20?m,the number of stacked layers is about four,and there is no excessive polymerization that affects its performance.The structural study found that the graphene inside the oily epoxy resin coating on the surface of the AZ31magnesium alloy would attract each other with the benzene ring in the resin structure,resulting in a decrease in the curing quality of the coating.Both oil-based and water-based epoxy resin coatings have the best surface quality when the graphene content is 0.3%by weight;the oil-based epoxy/polyurethane coating has the best surface quality when the graphene content is 0.3%by weight,while the water-based epoxy resin coating has the best surface quality when the graphene content is 0.3%by weight.Oxygen/polyurethane composite coating will decrease the surface quality of the polyurethane topcoat as the graphene content in the primer increases.(3)Electrochemical testing shows that the coating can provide good corrosion protection for the magnesium alloy substrate.When the graphene content is 0.6wt%and0.3wt%,oily and water-based epoxy resin coatings show the best corrosion resistance.Performance,corrosion current density is reduced from 6.20×10^-7A/cm²to 6.96×10^-12A/cm²and 2.79×10^-11A/cm²;when graphene content is 0.3wt%and 0wt%,oily and water-based the epoxy/polyurethane composite coating has higher corrosion resistance,and the self-corrosion current density is 1.81×10^-12A/cm²and 5.07×10^-12A/cm².(4)Observation of the micro morphology after corrosion revealed that the surface of magnesium alloy is corroded seriously,and the expansion of pitting corrosion caused corrosion pits and cracks;graphene can improve the shielding ability of epoxy resin coating to corrosive medium and reduce defects generated during the curing process of the coating,so the damage caused by corrosion is significantly reduced,and the corrosion resistance of the magnesium alloy matrix is improved;for the oily epoxy/polyurethane composite coating,graphene can improve the surface quality of the oily epoxy primer and promote the oiliness The polyurethane topcoat cures well and improves the corrosion resistance of magnesium alloys.For the waterborne epoxy/polyurethane composite coating,the addition of graphene leads to an increase in the hydrophobicity of the waterborne epoxy primer surface,and the polyurethane topcoat cannot be cured well on its surface.Therefore,it accelerates the damage of the corrosive medium to the surface structure of the coating,resulting in poor shielding performance of the coating against the corrosive medium,and reducing the corrosion resistance of the magnesium alloy substrate.