Anticorrosive passivating conversion coatings containing rare-earth metals for galvanized surfaces

• A.A. Abrashov¹, A.V. Kolesnikova¹, V.A. Sukhorukova¹, N.S. Grigoryan¹, N.A. Asnis¹, O.Yu. Grafov² and T.A. Vagramyan¹

¹ Mendeleev University of Chemical Technology, Russia, Moscow, Miusskaya sq., 9, 125047 Moscow, Russian Federation
² A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation

Abstract: The paper deals with chromate-free protective conversion coatings based on rare-earth metals (REM) for galvanized steel. Solutions containing three kinds of layer-forming REM cations have been developed. The physicochemical and mechanical properties of REM-based protective coatings on zinc have been studied as an alternative to environmentally hazardous chromate coatings. Addition of the third type of REM layer-forming cation (La³⁺, Nd³⁺, Y³⁺) and citrate anion to the converting solution results in an increase in the thickness of the coatings formed, more homogeneous appearance, more uniform thickness, along with an increase in the protective ability, abrasion resistance, frost and heat resistance compared to coatings formed in solutions containing one or two types of layer-forming cations. The coatings are resistant to temperature fluctuations and withstand multiple cyclic tests at high (120°C) and low (–30°C) temperatures without deterioration of their protective characteristics. It has been found that the coatings developed are close to rainbow chromate coatings in terms of protective ability, despite their smaller thickness (180–230 nm vs. 800–1000 nm).

Keywords: surface treatment, chromate-free passivation, rare-earth metals, corrosion protection, conversion coatings

Int. J. Corros. Scale Inhib., 2025, 14, no. 1, 179-193
doi: 10.17675/2305-6894-2025-14-1-11

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