Surface modification by multilayered Zn-Co alloy coatings

Nanostructured multilayer alloy or composition modulated multilayer alloy coatings of Zn-Co have been developed, and their corrosion behaviours were studied by potentiodynamic polarisation and electrochemical impedance spectroscopy methods. The coatings were developed galvanostatically using square, triangular and sawtooth current pulses through single bath technique. The cyclic cathode current density and the numbers of layers have been optimised for peak performance of the coatings against corrosion. Under optimal conditions, the coatings developed using square, triangular and sawtooth current pulses were found to be respectively similar to 100, 80 and 90 times more corrosion resistant than monolithic alloy of same thickness. The better corrosion resistances of the composition modulated multilayer alloy coatings were attributed to the dielectric barrier at the interface, as evidenced by dielectric spectroscopy. Surface morphology, multilayer formation and surface after corrosion tests were examined by scanning electron microscopy.