An Industrial Perspective on Electrolytic Zinc Phosphating

Abstract

Electrolytic zinc phosphating is an emerging wet surface treatment undergoing early adoption in the wire drawing industry. Zinc phosphate coatings are in fact excellent lubricant carriers due to their intrinsic porous nature and good adhesion with metallic substrates. For this reason, they are often employed in combination with stearate lubricants in wire drawing lines as means to reduce the wear of the expensive drawing dies. [1] Electrolytic phosphate deposition is carried out in a two-electrode system, where a cathodic polarization is applied to the steel wire in order to promote either hydrogen evolution or nitrate reduction, leading to the formation of a local increase in pH and the formation of the phosphate layers. [2] In this presentation we will show the application of electrolytic phosphating for the deposition of zinc phosphate coatings in a continuous wire drawing line. The high current densities at which electrolytic phosphating can operate are in fact a perfect fit for a high-throughput process such as wire drawing. Moreover, the relatively simple geometry of the phosphating tank allows the possibility of attaining a uniform current distribution and thus an homogeneous coating thickness, which is the main drawback of electrolytic phosphate deposition. The data shown in this talk will focus on the comparison between continuous and pulsed polarization modes, highlighting the advantages of the latter over the former. The presentation will discuss the scale-up of the technology from the laboratory scale up to a full-size phosphating plant, comparing the results obtained in the two cases. References [1] M. Suliga, P. Szota, M. Gwoździk, J. Kulasa, A. Brudny, The Influence of Temperature in the Wire Drawing Process on the Wear of Drawing Dies, Materials 17 (2024) 4949. https://doi.org/10.3390/ma17204949. [2] F. Lissandrello, L. Magagnin, Tailoring surface sensitivity towards nitrate reduction for enhanced electrolytic zinc phosphate deposition, Surf. Coat. Technol. 505 (2025) 132073. https://doi.org/10.1016/j.surfcoat.2025.132073.