Mechanism of Corrosion Protection at Cut Edge of Zn-11%A1-3%Mg-0.2%Si Coated Steel Sheets

Zinc and zinc alloy coated steel is widely utilized for home appliance, construction, automobile, and so on for its high corrosion resistance. In this work, corrosion behavior at cut edges of Zn-11%A1-3%Mg-0.2%Si alloy coated steel sheets (SD) was investigated with cyclic wet-dry corrosion test. The result showed that SD have the superior anti-corrosive property to zinc coated steel sheets (GI) at early period of corrosion. GI produced red rust, whereas SD produced no red rust. After the cyclic wet-dry corrosion test, zinc-containing white rust deposited on steel substrate. In the case of SD, magnesium reached the center of cut edge and larger area on the steel was covered with white rust. With polarization measurements of steel substrate on which white rust deposited, it was clarified that white rust of SD reduced both anodic and cathodic current density of steel substrate more largely than that of GI. In the case of SD, galvanic current between steel substrate with white rust and coating layer was small compared with GI. It was suggested this anti-corrosive property of SD is due to magnesium-containing white rust.