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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.

The formability of electrodeposited Zn-SiO2 composite coating has been studied. Flaking of the coating and die pick-up were hardly observed during the draw bead simulation test. Powdering resistance of the coating were also better than that of galvannealed steel. Good formability of Zn-SiO2 composite coatings is attributed, primarily to the low friction coefficient of the coating, and secondly to the microcracking effect which release the forming stress.