The Research Of Corrosion Resistance About Rich Aluminum-magnesium-alloys Coating Brushed On Aluminum Alloys In Mimetic Ocean-atmosphere Environment

Rich magnesium coating could carry on the effective protection to the aluminum alloy,because its good corrosion resistance and the characteristics of non-toxic and environmental protection, it has gradually become containing chromium-pretreatment coating and chromium coating the best replacement. However, due to coating using pure magnesium granules as filler, and chemical properties of pure magnesium granules is very lively and autolyzing tendency is big, lead to the time of coating's cathodic protection is very small, protective life of coating greatly reduced.This thesis for problems that the protection time of rich magnesium coating in mimetic ocean-atmosphere environment(salt fog environment) is small and the coating is easy to fail, in order to improve the corrosion resistance of magnesium coating in the high temperature, high humidity and high salt environment, organic rich aluminum-magnesium alloy coating was prepared with aluminum-magnesium alloy particles, then the corrosion resistance of rich aluminum- magnesium alloy in the salt fog environment were studied.Using Al instead of parts of Mg in rich pure magnesium coating has not a harmful effect for the cathodic protection of rich pure magnesium coating, on the contrary, it has a great extent improvement on the protection of aluminum alloy base. Experimental research shows that the PVC for 50% of the rich aluminum-magnesium alloy coating on the cathode protection of aluminum alloy is better. The addition of Al, reduced the Mg content and distribution in the coating, decreased the activity of the filler metal and the effects of the current produced in the reaction, so as to make the coating aging and degradation speed is reduced and improve the corrosion resistance of coating.The contrast research of scratch samples' corrosion resistance for organic rich pure magnesium coating, organic rich AZ91 D magnesium alloys coating and organic rich aluminum-magnesium alloy coating in the environment of salt fog was done, and the results showed that: After salt spray test 1440 h, nearly 50% of the surface of the rich magnesium coating produced bubbling phenomenon, the enrichment phenomenon for corrosion products was found around fork place of organic rich AZ91 D magnesium alloy coating and the surface of organic rich aluminum-magnesium alloy coating is neither a bubbling phenomenon, nor the enrichment phenomenon for corrosion products also was found, which shows that the corrosion resistant properties of organic rich aluminum-magnesium alloy coating is better than the other two coatings. Based on three different filler metal coating in the mass fraction of 3.5% sodium chloride solution for open circuit potential monitoring,we found that using the aluminum-magnesium alloy powder made from Al and Mg instead of pure magnesium powder reduces the content of Mg in the coating, which did not affect the effect of cathodic protection, but reduces the reaction intensity in the process of coating protection and the damage to the coating, to extend the time of protection and enhance the corrosion resistance of coating. By observing variation about the three coating for impedance modulus of electrochemical impedance spectrum,we found that the shielding performance of rich aluminum-magnesium alloy coating is better than rich pure magnesium coating and rich AZ91 D magnesium alloy coating. By comparing the potentiodynamic scanning results and polarization curve fitting result of three different filler metal coating sample and aluminum alloy substrate in the mass fraction of 3.5% sodium chloride solution, we can conclude: Three kinds of coating can make the aluminum alloy substrate's potential to cathodic polarization, which have the effect of cathodic protection; Three kinds of coating corrosion rate is below the corrosion rate of the aluminum alloy substrate, among them, the corrosion rate of rich aluminummagnesium alloy coating is lowest and the corrosion resistance is best. Through three different filler metal coating samples were scanned by electron microscope, we found that the defects on the surface of the rich aluminum-magnesium alloy coating is very few,almost no, metal particles and resin combined with close, which shows that corrosion resistant performance is good.Research on the corrosion resistance mechanism of the organic rich aluminummagnesium alloy coating was done by using electrochemical impedance spectroscopy, and it is concluded that the failure process of the organic rich aluminum-magnesium alloy coating is divided into four stages: The first stage, the stage of shielding before coating corrosion, coating shielding effect; The second stage, coating activation stage, corrosion electrolyte comes into the coating, and aluminum-magnesium alloy particles in coating react with it, then coating impedance modulus is decreased; The third stage, aluminummagnesium alloy provides cathodic protection to aluminum alloy substrate, corrosion products in coating began to accumulate and spread in this stage, diffusion tail appear on the low-frequency end of the Nyquist figure obviously; The fourth stage, the failure stage,a double arc appears on Nyqusit figure,and aluminum-magnesium alloy particles in coating were depleted, which leads to coating failure at last.