| Magnesium（Mg）alloys are widely used owning to their excellent physical and mechanical properties.However,high chemical activity makes them easy to be corroded.The air layer formed by the micro-nano structure on superhydrophobic coating can hinder the contact between the corrosive medium and the metal substrate,and effectively improve the corrosion resistance of the magnesium alloys.Polypropylene（PP）and polyvinylidene fluoride（PVDF）are a class of polymer materials with stable chemical properties and low surface energy.The preparation of superhydrophobic PP or PVDF coatings on Mg alloys are expected to improve the corrosion resistance of magnesium alloys.In this paper,the porous oxide transition layer was grown on AZ31 magnesium alloys by micro-arc oxidation（MAO）firstly,and then the superhydrophobic PP/MAO and PVDF-SiO2/MAO composite coatings were deposited on MAO Mg alloys by the impregnation method,which significantly improved the corrosion resistance of Mg alloys.The specific work content was as follows:（1）Hard porous MgO ceramic coating was prepared on magnesium alloys by MAO,and its surface morphology,roughness,wettability and corrosion resistance were characterized.The results showed that the water contact angle（WCA）on MAO coating was 18°,which was hydrophilic.Compared with the magnesium alloys substrate,the charge transfer resistance（Rct）value of the MAO coating was improved one order of magnitude.（2）PP polymer solution was prepared by utilizing the PP as a solute,the PP-g-MAH as a compatibilizer and the xylene as a solvent.PP/MAO composite coating was deposited on magnesium alloys by impregnation method by taking MAO coating as transition layer.The effects of PP impregnation solution concentration on the wettability and corrosion resistance of PP/MAO composite coating were studied.The results showed that the corrosion resistance of PP/MAO composite coatings increased firstly and then decreased with the increase of PP impregnation solution concentration.When the concentration of PP impregnating solution is 2.0%,the WCA of coating is 153°,showing good superhydrophobicity.the corrosion current density（icorr=6.59×10-7 A/cm2）is the smallest.In addition,the friction and wear test and acid-base salt immersion test showed that the superhydrophobic coating had good chemical stability and mechanical stability.（3）PVDF impregnating solution was prepared by using the PVDF as a solute and the N,N-dimethylformamide（DMF）as a solvent.PVDF/MAO coatings were deposited on magnesium alloys by MAO process and impregnation method.The microstructure and properties of PVDF/MAO coating were investigated by similar methods as PP/MAO coating.The results showed that the corrosion resistance of the coating increased firstly and then decreased with the increase of PVDF concentration.When the concentration of PVDF impregnating solution was 5.0%,the sealing effect of PVDF on MAO coating was the best,and the WCA of the coating was 108°,which achieves the hydrophobic effect and enhances the corrosion resistance of the magnesium alloys.（4）PVDF-SiO2 solution was obtained by adding SiO2 nanoparticles into PVDF solution.PVDF-SiO2/MAO composite coating was prepared on magnesium alloys by the above process.The surface morphology,wettability and corrosion resistance of PVDF-SiO2/MAO composite coatings with different SiO2 additions were investigated.The results showed that the corrosion resistance of the coating increased firstly and then decreased with the increase of SiO2 content When the addition amount of SiO2 was 1.5%,the particles on the coating were evenly distributed,and the maximum WCA is 162°,which had excellent superhydrophobicity.The icorr（6.69×10-9 A/cm2）of the coating was the smallest.The prepared coating has good chemical stability and mechanical stability.Compared with PVDF/MAO coating,the Rct value of superhydrophobic PVDF-SiO2/MAO coating was increased 2 orders of magnitude,which is more conducive to the long-term protection of magnesium alloys. |
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