| Magnesium alloys which are compared as the 21st Green Engineering Material possess a unique set of properties such as light weight, high strength-to-weight ratio, high thermal conductivity, dimensional stability and damping characteristics, good electromagnetic shielding and machinability as well as recyclability. However, magnesium alloys have a number of undesirable properties including high chemical reactivity and poor corrosion resistance that have hindered its widespread use in many applications. Therefore, it is of great significance to study the surface treatment technology of magnesium alloy.Based on the review of corrosion mechanism of magnesium alloys and the current study advancement in the whole world, Si sol-gel and polyaniline hybrid coating were directly prepared on the magnesium alloy surface via sol-gel method. The primary research of healing for Si sol-gel coating was also carried out due to the lack of self-healing functionality. Meanwhile, the corrosion behiviour of polyaniline hybrid coating was also investigated. Electrochemistry impedance spectroscopy (EIS), potentiodynamic polarization tests. X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and viscosity measurements were employed to character the properties of the prepared coatings including the corrosion resistance, surface morphology and composition.It is not possible to apply the inhibitor directly on the magnesium alloy surface for some inhibitors because the high chemical activities may cause the subsequent corrosion of substrate. However, Sol-gel coatings cannot provide adequate corrosion protection for metal/alloys in the corrosive environments due to their high crack-forming potential. Therefore, the possibility to employ cerium nitrate as inhibitor to decrease the corrosion development of sol-gel based silane coating on the magnesium alloy in NaCl solution was demonstrated. Cerium nitrate was added into the NaCl solution where the silane coating coated magnesium alloy was immersed. Scanning electron microcopy (SEM) was used to examine surface morphology of the silane coating coated magnesium alloy immersed in NaCl solutions doped and undoped with cerium nitrate. The corrosion electrochemical behaviors were investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. The results showed that the introduction of cerium nitrate into NaCl solution could effectively inhibit the corrosion of the silane coating coated magnesium alloy. Moreover, the influence of concentration of cerium nitrate on the corrosion inhibition and the possible inhibiting mechanism were also discussed in detail.To study the inhibition for sol-gel coating deeply, we researched the effects of KMnO4 as the inhibitor. The inhibitor was added to 0.05 M NaCl solution directly which the AZ91D magnesium alloy coated with silane films immersed. The results from electrochemistry measurements showed that the KMnO4 could prolong the protection time of silane films. EDS analysis demonstrated the present of MnO2, which the inhibiting mechanism would be related to. The efficient inhibition may attribute to the oxidation of KMnO4 then the undissolved production healed the defects to stop the corrosion process.Polyaniline is a conductive polymer and also owns a normal good corrosion resistance. We use chemical synthesis legal prepared conductive state polyaniline successfully. N-methylpyrrole (NMP) and polyethylene pyrrole silane K30 (PVP) were selected as the appropriate solvent and into film-former, respectively. Electrochemical test was carried out in 0.005 M NaCl solution. The results showed that the long-term corrosion resistant performance of a single polyaniline layer is poor. On the country, Composite layer after long-term immersion still had good corrosion resistance. Moreover, the corrosion mechanism of polyaniline was also discussed in detail. |
PDF Full Text Request