Development of layered Zn-Fe coatings for better corrosion protection

In this research, the Zn-Fe coating having successive layers of alloys of two different compositions were developed alternatively on mild steel for better corrosion protection. The multilayer coatings, or alternatively, composition modulated alloy (CMA) coatings of different configurations have been developed, and their corrosion behaviors were evaluated by electrochemical DC and AC methods. The cyclic cathode current densities and numbers of layers have been optimised for peak corrosion stability of the coatings. Under optimal condition, the CMA coating having 300 layers, having about 67 nm average thickness was found to be approximately six times higher corrosion resistant than monolayer coating of same thickness. The better corrosion resistance was attributed to the changed dielectric property, consequent to difference in phase structure of alloys in alternate layers, evidenced by dielectric spectroscopy and X-ray diffraction (XRD) study, respectively. Layers formation and corrosion mechanisms were examined using Scanning Electron Microscopy (SEM).