STUDY OF Zn-Fe AND Zn-Fe-Co ALLOYS COATINGS OBTAINED BY ELECTRODEPOSITION FROM ACID BATHS CONTAINING CITRATE IONS

摘要

Zinc alloy coatings have attracted great interest in industry due to the characteristics of ductility, weldability, adhesion to paint and corrosion resistance in comparison with pure zinc. In this work, Zn-Fe alloy and Zn-Co-Fe were obtained on copper from acid baths containing citrate. The electrochemical experiments were performed on 0.5 mol/L Na_2SO_4 + 0.05 mol/L EDTA solution. Results of anodic dissolution voltammetry and galvanostatic dissolution showed that the decrease in [Zn~(+2)] in the bath results in electrodeposited Zn-Fe with higher Fe content (1.2 - 60%) when the ratio [Zn~(2+)]:[Fe~(2+)] change from 1:1 to 1:4. Analysis of scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) and X-ray diffraction showed refinement of the structure up to loss of crystallinity in alloys with high Fe content and the presence of ZnFe r|-phase in alloys with low Fe content. Addition of 0.05 mol/L Co~(2+) bath for different [Zn~(+2)] and [Fe ] favored the incorporation of Fe in the Zn-Fe-Co alloy. It was also observed that increasing the current density of -5 to -30 mA/cm~2 contributed to the increasing content of Fe in the alloy.