Study On Preparation And Corrosion Resistance Of Self-lubricating Micro-arc Oxidation Coating On The Surface Of 10B21 Steel

Automobile lightweight is to reduce the quality of the whole vehicle equipment as much as possible under the premise of ensuring the strength and safety performance.Therefore,the magnesium alloy with light weight and higher specific strength than elastic modulus shows broad application prospects.In order to solve the problem of contact corrosion between magnesium alloy auto parts and steel rivets during cold connection,this paper uses micro arc oxidation（MAO）technology to prepare MAO-PTFE self-lubricating high corrosion resistance composite coating on the surface of 10B21 rivet steel.First,study and select the optimal negative voltage parameters by the controlled variable method to prepare the MAO ceramic coating based onα-Al2O3,and on this basis,directly add polytetrafluoroethylene（PTFE）dispersion to the electrolyte system Preparation of MAO-PTFE self-lubricating composite coating.On the one hand,PTFE particles can be directly deposited on the surface of the coating to improve the wear resistance and hydrophobicity of the coating.On the other hand,it can fill the holes of the MAO coating to make the coating denser.At the same time,explore the effect of PTFE dispersion concentration on the performance of the coating.In order to further improve the corrosion resistance of the composite coating,continue to add glycerin to the electrolyte for optimization.Glycerin can effectively inhibit the tip discharge,enhance the oxidation reaction of the MAO process,and significantly improve the corrosion resistance of the MAO-PTFE composite coating.By testing the composition,morphology and performance of the coating,the best high corrosion resistance self-lubricating composite coating was obtained.The research results are as follows:1)The influence of negative voltage on the composition,surface morphology and bonding strength of MAO coating is significant.When the negative voltage is-100 V,the coating has the best compactness and the porosity drops to 7.4%.The thickness of the coating is increased to 34μm,and the bonding strength reaches 118.2MPa.The electrochemical self-corrosion potential increased from-0.713 V to-0.488V,and the corrosion current density decreased from 161μA·cm^-2 to 3.64μA·cm^-2.The corrosion rate dropped to 2.26 g·m^-2·h^-1 after 72 hours of salt spray corrosion,indicating that the coating also has excellent corrosion resistance.In addition,the negative voltage has a direct effect on the formation ofα-Al₂O₃ in the oxide coating and the distribution of the Fe-Al transition zone at the interface between the coating and the substrate.It provides a way to further improve the corrosion resistance of the micro-arc oxidation coating on the surface of low carbon steel.2)Under negative voltage-100 V,prepare MAO-PTFE self-lubricating coating and explore the influence of PTFE dispersion concentration on the performance of composite coating.It is found that when the concentration is 6 g/L,most of the coating holes It has been filled with PTFE,the inner layer structure is dense,the thickness is increased to 37μm,and the porosity is reduced to 3%.At this time,the bonding ability of the coating is also better than other coatings,and the bonding strength is 128.5 MPa.At the same time,the corrosion resistance of the coating is significantly improved compared to the substrate.In the friction and wear test,the average friction coefficient of the N2 coating is only 0.28,and the amount of wear is5.01×10^-5 mm³·N^-1·m^-1.This is due to the uniform self-lubricating phase PTFE deposited on the surface,filling the holes in the coating and forming a dense structure,which greatly increases the wear resistance of the coating.3)Continue to add glycerin to improve the corrosion resistance of the composite coating.As a result,it is found that when the glycerin concentration is 2ml/L,the PTFE on the surface of the coating and theα-Al₂O₃ inside the coating are more evenly distributed,and it has excellent resistance to electrochemical corrosion and High insulation capacity.And the ability to protect magnesium alloy from salt spray corrosion is the strongest.The corrosion rate of AZ91D alloy is only 0.53g·m^-2·h^-1 at 72 h.Effectively solve the corrosion problem of the cold joint of steel and magnesium alloy.