Temporary Corrosion Protection of Galvanised Steel by Coatings Containing Cerium, Yttrium and Lanthanum

The temporary corrosion protection of continuously galvanised steel by rare earth metal containing salts has been investigated. The qualitative surface property, corrosion performance and adhesive feature of galvanised steel treated by immersion in cerium nitrate, cerium chloride, yttrium chloride and lanthanum chloride has been studied by surface analytical methods and electrochemical techniques. The surface film consists of Ce(III) from cerium nitrate solution using short (10 s and 60 s) immersion time occurs as an inhomogeneous layer on zinc coating. Applying long-term immersion period (30 min) the developed layer becomes more homogeneous from all of the solutions used. On EDS spectra oxygen peak appears when the time of film growth increases. This phenomenon indicates the oxide containing film development on the galvanised surface. The presence of protective film on the surface decreases the corrosion rate due to the anodic protection. Concerning the adhesive properties of the films testing by blending method, it can be established that acrylic paint covers the surface evenly without any cracks across the bending line. Based on the obtained results we can conclude that treatment in lanthanum- and yttrium-chloride solutions provides the most promising protective film properties on the galvanised surface.