12th International Conference on Zinc & Zinc Alloy Coated Steel Sheet - GALVATECH 2021

Electro-galvanizing of steel strip represents an important industrial process of corrosion protection and surface finishing. Electro-galvanized steel sheets are used e.g. in the automotive industry, for household appliances, and in the electronics industry. The zinc coatings show a very homogenous microstructure, a good spot weldability, as well as excellent surface appearance and painting adhesion properties. However, the demand for electric energy in the electro-galvanizing process is high. High current densities of up to 200 A/dm² are needed to enable fast and economical production. Because of the high current densities, a sufficient electrolyte flow is needed to avoid current densities close to the limiting current density and thus preventing formation of dendrites or powdery zinc deposits. This can be achieved by different cell designs with forced electrolyte flow. In order to be able to optimize the energy demand, a basic understanding of the underlying principles is needed. The energy demand for the zinc deposition is mainly composed of the cell voltage and the cathodic current efficiency. The influence of electrolyte composition and temperature on current efficiency and energy demand has been investigated in literature for low current densities of up to 5 A/dm². However, there are only a few studies on the behavior of current efficiency with higher current densities. In this contribution, the influence of the electrolyte composition and temperature on cathodic current efficiency and cell voltage for relevant current densities are investigated. For this purpose, laboratory tests are carried out in a flow cell. The results are translated into an overall model that allows to predict the total energy consumption. Furthermore, the resulting zinc coatings are analyzed in terms of zinc adhesion, morphology, and zinc crystallography.