Abstract
By successive deposition from dual baths containing Zn sulfate electrolyte and Ni sulfate–chloride electrolyte, smooth and bright compositionally modulated multilayered (CMM) coatings with different number, thickness and sequence of the sublayers were obtained. The corrosion resistance of the coatings was studied by anode potentiodynamic dissolution and by corrosion potential measurement. With increase in the number of sublayers, regardless of their individual thickness, the correlation between the quantity of Zn, dissolved at more negative potentials (between −1.250 and −0.750 V vs SSE), and the whole quantity of the metal in the coating, decreases. This correlation is smaller in CMM coatings ending with a Ni oversublayer compared to CMM coatings ending with a Zn oversublayer. The corrosion potentials of CMM coatings ending with a Zn oversublayer composed of a great number thin (0.7 μm) sublayers, are more positive (0.150/0.200 V) than the potentials of CMM coatings composed of a few thick (3.0 μm) sublayers. The most positive corrosion potentials (−0.750/−0.800 V vs SSE) have the CMM coatings ending with a Ni oversublayer; i.e. these multilayered coatings are the most corrosion resistant.
Published Version
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