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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.

A galvannealed steel sheet (GA) with a Ni-base inorganic lubricant film has been developed to meet the needs of the automotive industry, especially for improved press formability. This paper describes the results of tests performed to evaluate formability, spot weldability, phosphatability, paintability and corrosion resistance of the GA with the Ni-base lubricant film. The coefficient of friction as measured by flat sliding test decreases with increasing Ni content in the lubricant film. The spot weldability evaluated by electrode tip life test is slightly improved after the application of the lubricant film. Phosphatability, paintability and corrosion resistance of the GA with the lubricant film are equivalent to those of GA without the lubricant film.