ATMOSPHERIC CORROSION BEHAVIOR OF HOT-DIP ZINC ALLOY COATED STEEL SHEET SUBJECTED TO FORMING(IL02)

摘要

The atmospheric corrosion behavior of hot-dip Zn-alloy coated steel sheets [hot-dip Zn-5%Al alloycoated steel sheet (GF), hot-dip Zn-6%Al-3%Mg alloy coated steel sheet (Zn-Al-Mg) and hot-dipZn-55%Al-1.6%Si alloy coated steel sheet (GL)] subjected to bend-forming have been investigatedand compared with a hot-dip Zn-0.2%Al coated steel sheet (GI) after five years of exposure incoastal and rural environments.In the coastal environment, each coated steel sheet exhibited more advanced corrosion in bentportions than in flat portions. Upon comparing the bent portions of various types of sheets,numerous cracks were generated in the coating layer on the Zn-Al-Mg specimen, but bettercorrosion resistance than that of the GI and GF specimens was still exhibited. As the exposure timeelapsed, the entire bent portions of the Zn-Al-Mg specimen were considered to be covered by fineand dense zinc corrosion products containing Mg and/or Al, resulting in better corrosion resistance.In the GL specimen, it was recognized a considerable reduction of corrosion resistance in the bentportions as compared to the flat portions. Fe rust (red rust) was formed on cracked parts of thecoating layer due to corrosion of the steel substrate underneath, which is likely to have facilitatedcorrosion of the coating layer.