Effect of Silicate Treatment on The Corrosion Behavior of Hot-Dip Galvanized Steel

Document Type : Original research papers

Authors

1 Tabbin Institute for Metallurgical Studies (TIMS), Tabbin, Helwan 109, Cairo 11421, Egypt.

2 Chemistry Dept., Fac. of Science, Ain Shams Univ., Abbasiya, Cairo, Egypt, 11566.

Abstract

Passivation treatment by Potassium silicate solution is considered as an alternative to Chromate conversion treatment to improve the corrosion resistance of hot-dip galvanized steel. One of the main objectives of this study is to evaluate the viability of a simple and industrially easy-to-implement substitute to the widely employed chromate coatings. In this paper, silicate conversion coatings were prepared by immersing hot dip galvanized steel sheets immediately upon removing from the molten zinc in potassium silicate solution bath with chemical composition: 25% SiOR2R, 12% KR2RO and 63% water, at metal immersion temperatures in excess of about 150°C or higher, the immersion time was constant about 30 s. After optimization of silicate immersion bath concentration and immersion temperature of hot-dip galvanized steel, the corrosion behavior of hot-dip galvanized steel was evaluated by means of electrochemical impedance spectroscopy measurements and Potentiodynamic polarization. The morphology and the phase analysis of zinc-silicate coating were observed by scanning electron microscopy and X-rays diffraction, respectively. The results showed that: the corrosion resistance increased with increasing silicate ions concentration up to 6%, also corrosion resistance increased as temperature of galvanized steel sheet increased up to 250°C. This can be related to the addition of the silicon ions in the zinc coating to form a zinc-silicate complex, which is highly resistant to corrosion.
 

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The Bulletin Tabbin Institute for Metallurgical Studies (TIMS)
Volume 106, Issue 1
September 2017
Pages 24-37

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