| Recent years, with the rapid development of industry and cities, metallic engineering materials are increasing in many industrial fields. Among them, magnesium alloys have received much more attention in recent years because of their attractive properties, including low density, high strength-to-weight ratio, excellent machinability, good damping properties, fine electromagnetic interference shielding properties and easy recyclability. These properties make them ideal candidates for automobile, aircraft and aerospace industries. And magnesium is called one of "the green engineering materials" in 21st century. But its low potential and poor corrosion resistance in humid environment limit its wide application. So finding a method of simple, low-cost, easy to be carried out to make superhydrophobic surface on magnesium surface for improving the corrosion resistance is very important.In recent decades the famous lotus effect, which is called superhydrophobic property with a water contact angle (CA) greater than 150° and a sliding angle (SA) less than 10°, was popularly reported. Then the study of superhydrophobic materials has been received considerable attention for their special functions, such as water-repellency, self-cleaning, anti-icing and anti-corrosion. In the humid environment, humid air canbe easily liquefied on the material surface to form electrolyte membrane layer by dissolving CO2 et.al in water layer. The electrolyte membrane layer can accelerate the corrosion rate on material surface. In corrosive solution, corrosive solution can directly interact with the substrate or penetrates into inside though the apertures of defects/damages and rough surface. The prepared superhydrophobic surface can trap air to form an air film on the surface, which can keep corrosive solution penetrating into inside. Therefore, fabricating a superhydrophobic coating on magnesium surface can improve corrosion resistance effectively.In this dissertation, we prepared superhydrophobic coating on magnesium surface with different composition and excellent corrosion resistance by suing conversion treatment, phase separation and dip-coating methods:(1) Preparing superhydrophobic surface based on self-healing mechanism. In the study of preparing superhydrophobic coating based on self-healing mechanism, we obtained cubic magnesium stannate coating on magnesium alloy surface and researched the self-healing mechanism in neutral 3.5 wt.%NaCl solution. The SEM method was used to study the morphology of magnesium stannate coating after being self-healed in neutral 3.5 wt.% NaCl solution for different time. The results of potentiodynamic polarization indicate that the coating being self-healed for 4 h possessed the best corrosion resistance. We first proposed the mechanism of solving-reprecipitation based on these research results. And superhydrophobic coating with a water contact angle value of 157.8° was successfully fabricated on the magnesium stannate coating with a 4 h self-healing process. Furthermore, the stimulated acid rain dropping test indicate that the surface possesses strong superhydrophobicity after dipping with 1000 mL stimulate acid rain and it behaves excellent corrosion resistance in stimulate acid rain with a pH value of 2.5.(2) Preparing highly anticorrosion superhydrophobic PVC film. In the following study about superhydrophobic PVC film with highly corrosion resistance, we prepared superhydrophobic PVC film by suing phase separation method. SEM technique was used to study the relationship among superhydrophobicity, structure and nonsolvent. The obtained superhydrophobic PVC film was first successfully applied to AZ91D magnesium surface. And the research results indicate that the as-prepared superhydrophobic PVC coating on magnesium alloy surface behaved highly superhydrophobicity and excellent anti-corrosion effect in acid, alkali and salt corrosive solution. It is a straightforward and simple route to fabricate low-cost and anti-corrosion coating on various substrate materials. Moreover, this one step process may find potential application in the field of industry because its simplicity and universality. |
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