Research On Preparation And Corrosion-resistance Of Super-hydrophobic Mg Alloys

Magnesium alloy has attracted widespread concern because of its excellent characteristics such as good high strength-to-weight ratio and structural performance, while poor corrosion resistance has limited its development; preparing super-hydrophobic coating on magnesium alloy surface is an important means to improve its corrosion resistance. Since the super-hydrophobic surface holds properties like anti-infection, anti-pollution and self-cleaning, it therefore has increasingly caused people’s attention. Electro-deposition in ionic liquid and surface modification method are two simple, efficient and low-cost methods for fabricating super-hydrophobic surface. After being treated, magnesium alloy surface can achieve super-hydrophobicity, the corrosion resistance is also greatly improved.In this paper, two methods were used for fabricating super-hydrophobic layer on magnesium alloy surface, the surface microstructure of the treated sample were tested and characterized by XRD and SEM; moreover, some performance of super-hydrophobic surface were researched through electrochemical test, contact angle measurements and adhesion test. To electro-deposition method for fabricating super-hydrophobic layer, the author explored the influence of current density and additives on the surface structure and super-hydrophobic properties of the magnesium alloy.The following conclusions can be researched through study:(1) In electrodeposition method, super-hydrophobic surface on magnesium alloy can be built successfully by adjusting the current density. When the current density was turned to around 0.25 mA/cm2, the surface, which resembles the structure of water strider’s leg, was super-hydrophobic with water contact angle 161 ± 4° and sliding angle almost 2°.(2) Preparation of super-hydrophobic surface with electrodeposition method under the effect of additives. Results show that with addition of PEG-800, magnesium alloy surface shows super-hydrophobicity when current density is adjusted to 1 mA/cm2. The contact angle can be reached 162 ± 2°. The coating is well adhered with the substrate and even has reached the highest level of 0. The corrosion resistance of the sample is significantly improved.(3) Two kinds of etchant CuCl2 and ZnSO4 were used respectively for etching the surface to construct a rough surface, and then low surface energy materials, stearic acid and oleic acid, were used as modifier to conduct surface modification to obtain the super-hydrophobic surface on Mg alloy. As observed from SEM, the sample surface was consisted of petal-shaped ridges; these sheets are nano-scale and form three-dimensional porous structure. Air trapped in these voids can form a cushion that prevents water droplets from infiltrating the surface, so as to create an structural advantage for the formation of a super-hydrophobic surface; after modification, FTIR analysis showed that both methyl(CH3–) and methylene(–CH2–) groups from stearic acid and oleic acid have been successfully grafted onto the sample surface, which is another important reason attributed to the super-hydrophobicity of surface. After being etched by CuCl2 and then modified with oleic acid and stearic acid, the resulted two kinds of samples both obtained super-hydrophobic properties. Compared with the bare Mg alloy, one can find that the electrochemical performance of the treated one was much better and the corrosion potential was significantly improved, while the corrosion potential of stearic acid modified sample showed the highest. The corrosion resistance principle of super-hydrophobic sample was also discussed. The resulted samples after being treated by two modifiers showed better stability in air, and the super-hydrophobic coating was also well bonded with the matrix.(4) After being etched by ZnSO4 and then modified with oleic acid and stearic acid, the resulted two kinds of samples both obtained super-hydrophobic properties. The sample surface structure was similar to water strider’s leg. Moreover, the modified super-hydrophobic sample showed better corrosion resistance when compared with the bare sample, the The corrosion potential of stearic acid modified sample was much higher than that of oleic acid modified sample, which indicated that the corrosion resistance of stearic acid modified sample was better.(5) When compared with the influence of CuCl2 and ZnSO4 to corrosion resistance of sample, one can find that the corrosion resistance of CuCl2 etched sample is better than ZnSO4 etched sample; in view of hydrophobic property, the contact angle of CuCl2 etched sample is also greater than that of ZnSO4.