Fabrication Of Superhydrophobic Coating On Mg-Zn-Ca Alloy And Its Corrosion Resistance

Magnesium and its alloys have been available to military,aerospace,automobile and electronic industries owing to their excellent physical and mechanical properties.Nevertheless,magnesium alloys are very active and easily corroded in aggressive environments,which intensely impedes their application range.In recent years,the fabrication of superhydrophobic surfaces has become one of the main research fields for corrosion protection of magnesium alloys.This article selected Mg-5Zn-1.5Ca die-casting magnesium alloy as the substrate,using chemical conversion method and laser processing technology combined with surface modification successfully prepared the superhydrophobic surface on the magnesium alloy.Different methods were employed to characterize the surface morphology,chemical composition,surface wettability,mechanical stability as well as corrosion resistance of the coating.The main contents are as follows:A calcium phosphate coating with typical biological surface characteristics of micro/nanoscale hierarchical structure was prepared by a simple and highly effective chemical conversion method.After stearic acid modification,the static contact angle of the surface was as high as 159°.The formation mechanism of the coating was discussed.The XRD and XPS results showed that the main components of the conversion coating were Ca HPO4·2H2O and Ca3(PO4)2,also contained a small amount of Mg3(PO4)2.After fluoride treatment,the calcium phosphate coating appeared denser and better adhered onto the substrate.The electrochemical measurements revealed that the corrosion resistance of the superhydrophobic calcium phosphate coating was significantly improved as compared with that of the substrate,the corrosion current density of the superhydrophobic coating decreased from 1.29×10-4 to 1.3×10-6 A/cm2,and its corrosion potential increased from-1.56 to-1.36 V.The anti-corrosion mechanism of the superhydrophobic coating was also discussed.It can be indicated that the corrosion inhibitive properties of the coating are in accordance with its hydrophobicity,which is owing to the presence of a protective layer of air trapped in the grooves of the coating surface to isolate the underlying materials from the external environment,providing good anti-corrosion effect.Selecting the structural features of rose petals as a bionic basis,using laser pr ocessing technology to prepare a periodic laser-induced groove structure surface.After stearic acid modification,the static contact angle of the surface reached 153°.Surface morphology analysis and contact angle measurement results showed that with the change of processing parameters such as scanning space and laser power,the surface microstructure and wetting properties have obviously changed.With the increase of laser scanning space,the hydrophobicity gradually weakened;with the increase of laser power,the hydrophobicity gradually increased.Electrochemical measurements revealed that the superhydrophobic surface could effectively improve the corrosion resistance of magnesium alloys and protect the substrate from corrosive media.