Research On Preparation And Corrosion Resistance Of Layered Double Hydroxide Steam Coating And Composite Coating On AZ31 Magnesium Alloy Surface

Magnesium alloys have the advantages of low density,excellent mechanical properties and good biocompatibility,which make them widely used in various fields.However,their application is greatly limited due to their defects such as active chemical properties,poor corrosion resistance and short product life.Therefore,how to improve the corrosion resistance of magnesium alloys is an urgent problem to be solved.In this paper,layered double hydroxide(LDH)steam coating and its composite coatings were prepared by various surface modification technologies.They can make up for the defects of the magnesium alloy,and improve its functional characteristics.Firstly,the in-situ steam method was used to prepare the LDH steam coating.Secondly,on the surface of the LDH steam coating,a myristic acid(MA)composite coating and a silane/Ce(NO3)3 composite coating were prepared on the surface.Its role is to seal the LDH coating and improve its performance.Subsequently,the best conditions for the preparation of LDH steam coatings by in-situ steam method were investigated by acid pretreatment experiments.Finally,the film-forming mechanism and corrosion mechanism of LDH steam coating,myristic acid modified LDH composite coating and silane/cerium nitrate modified LDH composite coating are proposed.The results show that the amount of MA affected the morphologies and compactness of the composite coating.When the amount of MA is 0.4 M,the coating is the densest and the self-corrosion current density of the composite coating is the smallest,indicating that the coating has the best corrosion resistance.In addition,the MA modified LDH coating has a hydrophobic function,and its maximum contact angle can reach 129°±3.5°.The morphologies of BTESPT silane and silane/cerium nitrate modified coating changed significantly.The silane-modified LDH coating has good corrosion resistance.The addition of a trace amount of Ce(NO3)3 effectively improves the corrosion resistance of the coating.This is based on the fact that cerium nitrate can promote the hydrolysis and agglomeration of silane,leading to its network structure decomposition.The morphology of the LDH steam coating prepared after pretreatment with a certain concentration of hydrochloric acid and citric acid solution has changed,and the content of LDH in the coating has increased.Different acid pretreatments affect the compactness of the coating.The morphology of the LDH steam coating prepared after citric acid pretreatment is denser,and the self-corrosion current density of the coating is smaller,indicating that the coating has better corrosion resistance.