Study On Corrosion Resistance Of Superhydrophobic Polypropylene Composite Coatings On Magnesium Alloy

Magnesium(Mg)alloy has attracted more and more scholars' attention because of its unique properties such as low density,good rigidity,high conductivity,and has been applied in electronic equipments,automobile accessories,and aviation fields.However,the high chemical activity indicates that Mg alloy is easy to be corroded.Therefore,it has far-reaching significance to reduce the corrosion rate of Mg alloy for promoting its wide range application.Constructing the superhydrophobic coating on the Mg alloy can greatly extend its service life.However,the low adhesion and mechanical properties of superhydrophobic polymer coating restrict its further application.In this study,three different bottom coatings were prepared on the surface of Mg alloy,and then the integrated superhydrophobic polypropylene(PP)coatings were constructed on the surface of pretreated Mg alloy.The aim of the study is to investigate the hydrophobicity,adhesion and corrosion resistance of silane/polypropylene(PAPTMS/PP),magnesium hydroxide/polypropylene(Mg(OH)2/PP),and micro arc oxidation/polypropylene(MAO/PP)composite coating.Results show that the three superhydrophobic composite coatings modified by polypropylene possess spherical or granular structure of micron scale;the wettability results found that the PAPTMS/PP,Mg(OH)2/PP,and MAO/PP coatings have excellent superhydrophobic properties,and the superhydrophobic properties of prepared composite coatings gradually increase;nano scratch tests indicate that the three composite coatings show the strong adhesion to AZ31 Mg substrate,the surface of MAO possesses the best adhesion;electrochemical polarization curve shows that the corrosion current density(Lcorr)of three polypropylene composite coatings is reduced by three,four and four orders of magnitude compared with Mg alloy substrate;hydrogen evolution tests show that the surface morphologies of polypropylene composite coatings remain intact after 248-250 h of immersion,indicating that the three hydrophobic coatings have stable structures.Electrochemical and immersion tests confirm that the three superhydrophobic coatings prepared can protect the Mg alloy matrix for a long time.Fianlly,the preparation and corrosion mechanism of superhydrophobic coatings are proposed.