Pulse DC electrodeposition of Zn-Ni-Co coatings

Anomalous co-deposition of Zn-Ni-Co ternary alloy on carbon steel and copper substrates was attempted using pulse direct current electrodeposition technique. The obtained coatings were characterised for their crystal structure, chemical composition and surface morphology by X-ray diffractometry, energy dispersive X-ray spectroscopy and scanning electron microscopy, respectively. X-ray diffraction measurement showed peaks for Zn, Ni and Co. The concentration of Ni and Co in the ternary alloy increased with decrease in pulse frequency as confirmed by energy dispersive X-ray measurement. Scanning electron microscopy revealed uniform morphology of the coating surface with an average grain size of 1 mu m. Potentiodynamic polarisation and electrochemical impedance spectroscopy tests conducted in 3% NaCl solution confirmed improved corrosion behaviour of the coatings deposited at lower current pulse frequencies.