Influence of Metallic Complexes on Electrodeposition Process of Zn-Fe Alloy Coatings

摘要

Electrodeposited Zn-Fe alloy coating has good anti-corrosion performance and has been widely applied to protect steel materials from corrosion. Metallic complexes in plating bath play important role during alloy electrodeposition. In this paper, Zn-Fe alloy coatings were plated from acidic sulphate bath, and the relationship between real concentration of metallic complexes ([ZnL~+] and [FeL~+]) in the bath and component of alloy coating was studied. Concentration of metallic complexes was calculated through solving nonlinear equations by MET-LAB software. When ZnSO_4·7H_2O added in plating bath increases from 10 g/L to 50 g/L, the ratio of ferrous complex to total complex decreases from 81.96% to 46.76%, simultaneously the iron content in Zn-Fe alloy coatings decreases from 26.82% to 6.32%. When ZnSO_4·7H_2O added in the bath increases from 40 g/L to 80 g/L, the ratio of ferrous complex to total complex increases from 50.02% to 66.23%, simultaneously the iron content in coatings increases from 8.26% to 13.77%. When (NH_4)_2SO_4 added in the bath increases from 40 g/L to 80 g/L, ratio of ferrous complex to total complex increases from 58.65% to 60.37%, simultaneously the iron content in coating increases from 9.28% to 11.92%. The results show that, in the process of alloy deposition, variation of concentration ratio of different metallic complexes in the bath can lead to variation of component of alloy coating proportionally. Accordingly, the variation trend of component of alloy coating can be approximately deduced by calculating concentration of metallic complexes.