A Study On Anticorrosion Mechanism Of Arc-sprayed Zn And Al Coatings

Zn and Al coatings can be used as the long-lasting anticorrosion coating because of its merits such as the low potential and the anticorrosion performance is caused by corrosion products film. At present, the research scope of the Zn and Al coatings mostly concentrates on the physical properties, the spraying process and the practical application effect. But using electrochemical method to make further research on the anticorrosion performance of Zn and Al coatings is also quite rare.This paper applies some common methods such as the corrosion potential duration curve method, the polarization resistance duration curve method, the polarization curve method and the more advanced electrochemical impedance spectroscopy (EIS) method in the coatings anticorrosion performance research, in view of influencing factors which are the soaking time, the medium temperature, the closed level and the electrode potential, key research the factors that have influence on the anticorrosion performance of the Zn and Al coatings. In addition, according to various stages in different EIS tests, established its own equivalent circuit of each stage. Though the fitting EIS with ZView software, we can be obtain the evolution laws from parameters of the equivalent circuits, and summarized the anticorrosion mechanism of Zn and Al coatings.On the basis of anticorrosion experiments above, the anticorrosion mechanisms of Zn and Al coatings are as follows:1. The potential of the Zn and Al coatings lower than the full protective potential of steel of -0.85V in soaking time, it proves that coatings have the role of sacrificial anode.2. Both Zn and Al coatings are have the self-sealing effect to corrosion medium,that is the buffer function of the corrosion products increasing with soaking time.3. In the temperature changing process, the buffer function of Zn and Al coatings were weaken with temperature increasing,the reasons for this phenomenon due to the solubility of oxygen reduction and the state of corrosion products change from the ability of jellylike adhesion to the ability of granular non-adhesion, those reasons mentioned above lead to the corrosion products left the porosity and surface of coatings into the the electrolyte solution and prompte the buffer function of coatings against the electrolyte solution obviously weakened.4. The EIS of pure zinc and pure Al show that the Zn coatings have the role of sacrificial anode and better than Al coatings.5. The rule of the EIS of Zn and Al coatings in the closed condition in the soaking time is as follows: Zn and Al coatings can produce the synergistic effect with sealing coating, so that the impedance of composite coating which is Zn or Al coatings closed with sealing coating increasing with soaking time.