Study Of The Controllable Fabrication Of Regional Hydrophilic/super Hydrophobic Composite Coating On Magnesium Alloy

Based on the combination of the phosphate conversion treatment with plasma chemical vapor deposition technique,multi-element phosphate/plasma.chemical vapor deposition composite coatings have been fabricated on magnesium alloy in this article.Specifically,multi-elements phosphate/silicon nitride and multi-elements phosphate/silicon oxide composite coatings were prepared on AZ31 magnesium alloy and comparison study were carried out.Multi-elements phosphate/silicon nitride and multi-elements phosphate/silicon oxide composite coatings were fabricated on AZ31 magnesium alloy via CCT(chemical conversion treatment)/PECVD(plasma enhanced chemical vapor deposition)composite technology.The morphologies and structures of those composite coatings were investigated,and their anti-corrosion performances were comparatively analysed based on the results of corrosion experiment.XRD(X-ray diffraction)results show that the silicon nitride and silicon oxide layer deposited on the surface of multi-elements phosphate prepared by chemical conversion treatment is amorphous.The infrared absorption spectra of those composite coatings show that there are obvious Si-O-Si and Si-N absorption peak respectively,indicating that deposit layer are silicon oxide and silicon nitride structure respectively.SEM(Scanning electron microscopy)results show that after chemical vapor deposition,there are transparent silicon oxide and silicon nitride layers formed on multi-elements phosphate conversion layer,respectively.Immersion tests demonstrate that those composite coatings exhibit better anti-corrosion performance than solitary multi-elements phosphate layer after the short period of HC1 immersion.With the immersion time extending,the corrosion rate of multi-elements phosphate/silicon oxide composite coating is obviously lower than that of multi-elements phosphate/silicon nitride coating,exhibiting excellent anti-corrosion performance.Furthermore,combined with the phosphate conversion treatment,PECVD technique,etching process ande lectro chemical deposition,a regional hydrophilic/super hydrophobic composite coating can be formed on AZ31 magnesium alloy.The process is as follows:first,multi-elements phosphate conversion layer was prepared on AZ31 magnesium,then fabricating local hydrophilic SiO2 layer and super-hydrophobic layer on multi-elements phosphate conversion layer.,It was validated that this regional hydrophilic/super hydrophobic composite coating has unique droplet adhesive performance and excellent corrosion resistance.The morphology,structure and wettability of the regional hydrophilic/super hydrophobic composite coating were investigated by scanning electron microscopy(SEM),infrared spectrometer(IR),polarization curve and contact angle meter.Scanning electron microscope(SEM)results demonstrated that the boundaries of hydrophilic area and super hydrophobic area are very obvious,and via surface elements distribution of field emission scanning electron microscopy(SEM)also confirmed the results,the morphology of super hydrophobic coatings is similar to clusters structure of mastoid structure on lotus leaf surface.The average size of the structure is 1～2μm,the average spacing is 3～5μm.The infrared absorption spectra results demonstrated the composition of regional hydrophilic/super hydrophobic composite coating,which is composed of SiO2 deposition and cerium salt.The corrosion resistance of the composite coating was measured via electrochemical workstation.Its contact angle is more than 150°,demonstrating the super hydrophobic performance.This study provides the demonstration of location-selective pinning of a sliding water droplet on regional hydrophilic/super hydrophobic comosite coating having a gradient in the adhesive force that acts on the water droplet,that means it can select different mass droplets.