Comparison of corrosion-resistance and hydrogen permeation properties of Zn–Ni, Zn–Ni–Cd and Cd coatings on low-carbon steel

Abstract

Zn–Ni–Cd alloy was electroplated from an alkaline sulfate bath under potentiostatic conditions. The corrosion and hydrogen permeation characteristics of Zn–Ni–Cd alloy coatings electrodeposited from alkaline bath were studied and compared with those of Cd and Zn–Ni coatings obtained using commercial baths. Zn–Ni–Cd alloy was electroplated from an alkaline sulfate bath under potentiostatic conditions. The corrosion potential of this Zn–Ni–Cd coating was −0.62 V vs. SCE, which is still negative potential compared to iron. The corrosion rate of Zn–Ni–Cd coated steel was 0.073 mm y −1, which is estimated in a 0.5 M Na 2 SO 4+0.5 M H 3 BO 3 solution at a pH of 7. This value is much lower than the corrosion rate of Zn–Ni alloy (0.502 mm y −1) and Cd (0.306 mm y −1) coatings deposited from commercial baths. Zn–Ni–Cd alloys are also demonstrated to have superior hydrogen permeation inhibition properties compared to Cd and Zn–Ni coatings. Kinetic parameters of hydrogen permeation such as the transfer coefficient, α, the modified exchange current density, i 0 ′, thickness dependent adsorption–absorption rate constant, k ″, recombination rate constant, k 3, surface hydrogen coverage, θ s, were evaluated by applying a mathematical model to analyze experimental results.