Pulse electrodeposition of Zn-Co alloy coatings obtained from an alkaline bath

摘要

Zn-Co alloy coatings were electrodeposited on steel substrate using a cyanide-free alkaline bath containing glycine as a complexing agent. The effect of pulse current parameters, such as current-on time (Ton), current-off time (T_(off)) and peak current density (I_p) on the surface morphology, chemical composition and phase distribution of coatings were investigated using SEM, EDS and XRD. Also, the corrosion behavior of the coatings was studied by using potentiodynamic polarization test in 3.5 wt.% NaCl solution. The results showed that I_p and T_(on) had a significant effect whereas T_(off) had a slight effect on chemical composition and surface morphology of the deposits. It was also shown that increasing peak current density, up to 220 mAcm~(-2), decreases the grain size and further increase in current density increases the grain size of the deposit. The corrosion resistance of the deposits was also highly influenced by the composition and morphology of the coatings. On the whole, Zn-Co deposit containing 2.35 wt.% Co showed the highest corrosion resistance among the coatings due to its single phase structure and its fine morphology.