Study Of Surface Modification For Enhanced Self-healing Anti-corrosion Property Of Magnesium And Aluminum

Light metal and their alloys have been widely used in national defense, aerospace, automobiles, electronics, instrumentation and other areas for its excellent properties such as high strength/weight ratio, easy to process, good physical and chemical performance and so on. However, the corrosion resistant of light metal and their alloy is poor, the corresponding corrosion protection measures should be taken to solve the corrosion problem. At present, the coating protection is the most common, most effective and most economic anticorrosion measure. However, due to the inherent porosity and defects of the traditional coating, it is easy to accelerate coating failure which limiting the widely used of the coating. Therefore, how to give the coating good self-healing protection performance has become an urgent problem to be solved. This paper introduce a new method to prepare high corrosion resistance, high service life and self-healing coating for magnesium and aluminum light metal alloy, mainly based on chemical dissolution equilibrium principle. The corresponding growth mechanism and corrosion protection mechanism of the coating is explored. The research work provides a new thought and theoretical basis for the development of efficient anticorrosion materials and the study of atmospheric corrosion.Firstly, the dense, uniform and stable Mg(HQ)2 and Al(HQ)3 coatings are prepared on the surface of AZ91D magnesium and aluminum substrate through the corrosion induced deposition techonogy. The polarization curve and EIS test results show that the corrosion current of magnesium and aluminum metal with coatings is decreased one order of magnitude than that without coatings. Meanwhile, the impedance value is increased by nearly two orders of magnitude than that without coatings, which largely improves the corrosion resistance of the pure metal.Secondly, the corrosion protection mechanism of the conversion coating is deeply explored. The results show that the conversion coating not only effectively retarding the corrosion attack of aggressive species, but also provides a long-term barrier by its dissolution-redeposition and self-healing behavior based on the chemical equilibrium principle of coating. Once the coating suffers from corrosion defect, the released metal ions and 8-hydroxyquinoline anions tend to recrystallize on the defect, thus effectively inhibits the further development of local corrosion.Finally, based on the above work, the 8-hydroxyquinoline anion is further used for modification treatment of LDH coating on aluminum surface. Results show that the chemical modification treatment induces the phase conversion of hydrotalcite coating to Mg(HQ)2 and Al(HQ)3 compound by the intercalation of corrosion inhibitor into the coating, which enhanced the corrosion resistance of the coating. The hydrotalcite coating with unique layer micro/nanostructure not only effectively blocks the corrosive medium, but also spontaneous and oriented releases the accommodated corrosion inhibitor HQ- when it suffers from local corrosion attack in aggressive environments. The released 8HQ- activator may accelerate the deposition of more stable and compact passive alumina layer by actively inducing the corrosion of the defected and scratched region in the coating, thus further strengthening the corrosion protection performance of the coating.