| Magnesium alloy, the lightest metallic construction material with high strength/weight ratio, high thermal conductivity, good machinability and recyclability, is considered as the most promising green engineering material in the 21 st century. Therefore, magnesium and its alloys are attracting great interest as they have enormous promising potential applications in the automotive, aircraft, aerospace, electronic industries, biomedical materials and so on. However, due to its high chemical activity, magnesium alloy is easily oxidized and corroded in an aqueous solution or a humid atmosphere, which seriously hinder its large-scale use. Therefore, it is of great significance to make great efforts to improve the corrosion resistance of magnesium alloys for their large-scale application. Surface treatment is a simple, efficient and easily carried out method to protect magnesium alloy from corrosion.Superhydrophobic surfaces have attracted tremendous interest in both fundamental research and industrial application due to their special functions, such as corrosion resistance, self-cleaning, anti-icing, and oil/water separation. Superhydrophobic surface can avoid the direct contact between the substrate and corrosive medium by preventing the wetting of substrate surface, so that superhydrophobic surface can avoid the corrosion on substrate surface. Therefore, fabricating a superhydrophobic surface on magnesium alloy is a quite effective method to improve corrosion resistance and solve the corrosion problem of magnesium alloy. Besides, the other special functions of superhydrophobic surface could further expand the application scope of magnesium alloy.In this dissertation, three different kinds of superhydrophobic surfaces on magnesium alloys have been successfully fabricated by using simple, effective method and environmentfriendly, low-cost low surface energy materials. The chemical composition, structures and wettability of as-prepared surfaces were investigated. We also analyzed the corrosion resistance, self-cleaning performance, chemical stability and mechanical stability of superhydrophobic surfaces. These methods for fabricating superhydrophobic surface on magnesium alloy could effectively improve the properties and expand application scale of magnesium alloy.(1) A stable corrosion resistant superhydrophobic surface with self-cleaning property was obtained on AZ31 magnesium alloy via a process combining electroless Ni-P, electrodeposition Co and post-modification with stearic acid. Surface morphology could be controlled by adjusting electrodeposition current density. Then, we successfully fabricated high adhesive superhydrophobic surface and low adhesive superhydrophobic surface on magnesium alloy. The high adhesive superhydrophobic surface with granular structure had a static water contact angle of 152.9°, the water droplet could stick to surface even inverted 180°. The low adhesive superhydrophobic surface with leaf-like and cotton-like structures possessed a water contact angle of 156.2° and a sliding angle of 1°. The polarization and impedance tests in 3.5 wt.% Na Cl solution showed that the corrosion potential of superhydrophobic surface is 1079 m V more positive than the bare AZ31, the corrosion current density of superhydrophobic surface(2.08 × 10-7 A/cm2) decrease by more than 2 orders of magnitude as compared to that of bare AZ31 and the module value increase by more than 2 orders of magnitude, demonstrating that the superhydrophobic surface significantly improves the corrosion resistance of magnesium alloys. Abrasion test showed that the superhydrophobic surface still maintained superhydrophobicity after abrasion 900 mm, suggesting good mechanical stability. Besides, the as-prepared superhydrophobic surface possessed self-cleaning effect and good chemical stability.(2) A highly anticorrosion superhydrophobic surface with self-cleaning property was obtained on AZ31 magnesium alloy via a process combining electroless and electrodeposition. The superhydrophobic surface had a water contact angle of 158.6° and a sliding angle of 1°. The polarization tests in 3.5 wt.% Na Cl solution showed that the corrosion potential of superhydrophobic surface is 1120 m V more positive than the bare AZ31, the corrosion current density of superhydrophobic surface(1.12 × 10-9 A/cm2) decrease by more than 4 orders of magnitude as compared to that of bare AZ31. The impedance tests illustrated the module value of superhydrophobic surface increase by more than 4 orders of magnitude and value of resistance is 3.3 × 104 times of bare AZ31, demonstrating that the superhydrophobic surface can significantly improve the corrosion resistance of magnesium alloys. Besides, the contact model in corrosive medium and anticorrosion mechanism of the superhydrophobic surface were proposed. The superhydrophobic surface still maintained the contact angle above 150° after abrasion 500 mm, suggesting good mechanical durability. Furthermore, the obtained superhydrophobic surface possessed self-cleaning effect and good chemical stability.(3) A rapid one-step process was developed to fabricate superhydrophobic surface on magnesium alloy by electrodeposition method. The formation mechanism of the superhydrophobicity and the process of electrodeposition were studied. The incorporation of low surface energy cerium stearate during the creation of surface roughness resulted in superhydrophobic surfaces through one-step method, which simplified the conventional complex multi-step procedures, and shorten the fabrication process, the shortest electrodeposition time for fabricating a superhydrophobic surface was about 1 min. The optimal processing parameter was 30 V and 10 min. The as-prepared superhydrophobic surface with nodular-like structures had a static water contact angle of 158.4° and a sliding angle as low as 2°. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements demonstrated that the superhydrophobic surface greatly improved the corrosion resistance of magnesium alloy in 3.5 wt.% Na Cl solution. The superhydrophobic surfaces showed good selfcleaning performance and chemical stability. The presented method is of significant value for the industrial fabrication of corrosion resistant superhydrophobic surfaces. Furthermore, this approach is easy, low-cost and effective, and it can be easily extended to other metallic materials. |
PDF Full Text Request