| Magnesium alloy has advantages of low density,high specific strength and specific rigidity,good cutting performance,easy recycling and so on.It has been widely used in aerospace,rail transition,3C products,medical and other aspects,but its poor corrosion resistance is one of fatal disadvantages for its application in industry.The hydrophobic/super-hydrophobic coating reduces or even isolates the contact between the magnesium alloy and the corrosive medium,which can effectively improve the corrosion resistance of the magnesium alloy.In this paper,three methods were used to prepare hydrophobic/superhydrophobic coatings on the surface of AZ81 magnesium alloys:low-energy modification combined etching,low-energy modification combined hydrothermal synthesis,and one-step hydrothermal synthesis.Using XRD,FTIR,SEM,etc.to characterize the phases composition and microstructure of the hydrophobic/hydrophobic coatings,the hydrophobic angles,and electrochemical performance of the uncoated and coated AZ81 magnesium alloys.The fitted equivalent circuit according to the impedance spectrum were used to study the optimization of the parameters of the prepare processes,improvement of the hydrophobicity,the corrosion resistance of the magnesium alloys surface,and the improvement mechanism.The specific research content was as follows:（1）Use zinc sulfate solution etching to construct a rough surface and stearic acid ethanol solution（concentration of 14 g/L）for low-energy modification（modification time is 1 h）to prepare hydrophobic coatings on magnesium alloys.The effects of etching time,temperature and ZnSO4 concentration on the hydrophobic surface were investigated.It is found that when the etching time is 6 min,the etching temperature is 20℃and the concentration of zinc sulfate is 42.5 g/L,the contact angle of hydrophobic coating on magnesium alloy surface is the largest,which is 149.02°;When the etching time is 6 min,the etching temperature is 80℃and the concentration of zinc sulfate is 42.5 g/L,the corrosion resistance of the hydrophobic coating is the best,and the corrosion current density is 4.83×10-7A/cm2,which is three orders of magnitude lower than that of the substrate.（2）Using zinc sulfate solution hydrothermal synthesis method to construct a rough surface and stearic acid ethanol solution（concentration of 14 g/L）for low-energy modification（modification time is 1 h）can prepare hydrophobic coatings on magnesium alloys.The effects of hydrothermal time,hydrothermal temperature and ZnSO4 concentration on hydrophobic surface were investigated.The results show that the superhydrophobic coating with contact angle of 151.58°is obtained under the conditions of hydrothermal time of 1 h,hydrothermal temperature of 80℃,ZnSO4 concentration of 25.5 g/L;the corrosion resistance of the coating is the best under the conditions of hydrothermal time of 2 h,hydrothermal temperature of 80℃,ZnSO4 concentration of 17 g/L,and the corrosion current density is 6.37×10-6 A/cm2,which is two orders of magnitude lower than that of the matrix.（3）Using zinc sulfate solution and stearic acid ethanol solution to prepare hydrophobic coatings on magnesium alloys by one-step hydrothermal synthesis method.The effects of reaction time and temperature on the surface hydrophobic coating of AZ81 magnesium alloy were investigated.Research shows,When the reaction time was 7 h and the reaction temperature was 150℃,a super-hydrophobic coating with a maximum value of 155.03°of contact angle was gained.At the same time,this super-hydrophobic coating had the best corrosion resistance owing to its lowest corrosion current density of 2.86×10-8 A/cm2（4 orders of magnitude lower than that of the magnesium alloy matrix）.The research results showed that the one-step hydrothermal synthesis method was the most effective among these three methods to improve the surface hydrophobicity and corrosion resistance of magnesium alloy surface. |
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