Corrosion Resistance of Electrodeposited Zinc-Silica Composite Coated Steel

Corrosion resistance of Zn-SiO₂ composite coated steel has been investigated both in the wet/dry cyclic corrosion test and in the accelerated atmospheric corrosion test (modified Volvo test). In this investigation, perforation corrosion test were carried out using cathodic electrocoated lapped-panel models. Zn-SiO₂ composite coated steel has shown good perforation resistance as well as good cosmetic corrosion resistance. Polarization measurements for the Zn-SiO₂ composite coating have indicated the inhibition of both anodic and cathodic reaction. The inhibition of these reactions becomes more marked as corrosion of the coating progresses. From the microstructural analysis of the coating after the corrosion tests, excellent corrosion resistance of Zn-SiO₂ composite coated steel is attributed to the chemically stable corrosion product consisting of zinc hydroxide and SiO₂ particles.