Electrodeposition and characterization of thin layers of Zn-Co alloys obtained from glycinate baths

An alkaline bath containing CoSO4 . 7H(2)O, ZnSO4 . 7H(2)O, Na2SO4 and NH2CH2COOH is proposed for the deposition of thin layers of Zn - Co alloys onto steel substrates. Electrodeposition was carried out at 0.216-1.080 A dm(-2), pH 10 and 10 - 55 degreesC. The influence of bath composition, current density and temperature on galvanostatic cathodic polarization, cathodic current efficiency and alloy composition was studied. Different proportions of the two metals were obtained by using different deposition parameters, but at all Zn(II)/ Co( II) ratios studied, preferential deposition of zinc occurred and anomalous codeposition took place. Increasing the bath temperature enhanced the cobalt content in the deposit. X-ray diffraction measurements indicated that the phase structure of the deposits was controlled by the applied current density. The Co5Zn21 phase was formed at low current density, while the CoZn13 phase was formed at high current density. The potentiodynamic dissolution of the coatings showed that they contained Zn - Co alloy of different content and structure.