溶融Zn-6%Al-3%Mg合金めっき鋼板の大気暴露腐食生成物

抄録

Atmospheric corrosion of hot-dip Zn-6%Al-3%Mg alloy coated steel sheet after 5 years of exposure in a severe marine and a rural sites have been investigated compared with Zn-0.2%Al and Zn-4.5%Al-0.1%Mg alloy coated steel sheets.
The corrosion resistance of Zn-6%Al-3%Mg alloy coated steel sheet is more superior than that of Zn-4.5%Al-0.1%Mg alloy coated steel sheet in both exposure sites. An extensive study using XRD and TEM revealed that the corrosion products consisting of amorphous, finecrystal Zn₅(OH)₈Cl₂·H₂O and Zn₆Al₂(OH)₁₆CO₃·4H₂O are formed on Zn-6%Al-3%Mg alloy coated steel sheet after 1 year of exposure in a severe marine site. Even after 5 years of exposure the formation of zinc oxide, which have little protective action for coatings, is suppressed on Zn-6%Al-3%Mg alloy coated steel sheet.
It is concluded that the surface of Zn-6%Al-3%Mg alloy coated steel sheet is covered with the protective corrosion products in the early stage of exposure, resulting in the remarkably improvement of atmospheric corrosion resistance.