Self-healing effect by phosphoric zinc and calcium silicate included in organic-inorganic composite coating on 55%Al-Zn coated steel sheet

Akira Matsuzaki, Masayasu Nagoshi, Hisato Noro, Masaaki Yamashita, Nobuyoshi Hara

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Recently, it has become necessary to improve the corrosion resistance of zinciferous coated steel sheets, especially 55% Al-Zn alloy coated steel sheets. However, it is known that cracks are easily generated on the surface of 55% Al-Zn alloy coated steel sheet during production processes. This is due to the hardness of the metallic coating. We studied non-chromate corrosion-preventive compounds for organic-inorganic composite coatings and found that the composite coating containing both Zn 3(PO 4) 2 and CaSiO 3 had the highest corrosion resistance among all the additives tested. The corrosion mechanism was investigated by the analysis of the specimens after corrosion test using SEM, AFM, TEM and EDX. It was found that the amorphous surface layer, which was approximately 30 nm in thickness and contained Ca, Cr, P, Si, C, and O, was newly formed on the steel surface exposed after deformation of the coating. It is presumed that Ca 2+ and HPO 4 2- are formed by dissolution of the CaO component in CaSiO 3 and hydrolysis of ZnO 3(PO 4) 2, respectively, and they react each other to form an insoluble Ca-phosphoric compound, which might inhibit the corrosion of metals exposed in the cracks.

Original languageEnglish
Pages (from-to)862-869
Number of pages8
JournalNippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals
Volume73
Issue number11
DOIs
Publication statusPublished - 2009 Nov 1

Keywords

  • 55% aluminun-zinc alloy
  • Chromate
  • Chromate-free
  • Coated steel sheet
  • Corrosion
  • Cross-sectional analysis
  • Inhibitor
  • Microstructure
  • Self-healing

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Metals and Alloys
  • Materials Chemistry

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