Corrosion Behavior of Oxyacetylene Flame Sprayed Zn-Ni Composites Coating with Spray-dried Agglomerating Powders in Natural Seawater

摘要

In this paper, three different nickel content agglomerated Zn-Ni powders were prepared by spray-driedmethod, then Zn-Ni composites coating was deposited by oxyacetylene flame spraying method. Theanti-corrosion performance of Zn-Ni composites coating in seawater was examined bypotentiodynamic polarization and electrochemical impedance methods, together with the analysis ofSEM, EDS and XRD. The results show that the thickness of Zn-Ni composite coatings prepared bythermal spraying process is about 300m. Zinc was consumed first as it is immersed in seawater. Theattachment of corrosion products on the coating surface and the formation of nickel-rich layer belowthe product film can slow down the corrosion rate of coating. With the nickel content increasing, thecorrosion potential Ecorr of coating becomes more positive. When the nickel content is too high, micro- cell corrosion will occur and have a negative influence on the coating. The corrosion products,accumulated within the coating, have a significant impact on the anti-corrosion performance of coatingand decrease the corrosion current continuously. The presence of nickel can prevent the denseZn(OH)2 from being converted into the loose ZnO. The anti-corrosion performance of the coating with2 20wt% Ni is the best. The stable corrosion current Icorr of the coatings range from 1.24A/cm to2 1.87A/cm , while the stable corrosion potential Ecorr range from -0.98V to -0.95V. The Zn-Nicoatings meet the requirements of the cathodic protection. It can be concluded from above analysis thatZn-Ni coating can serve as low potential cathodic coating for steel substrate and has a long life period.