A Qualitative and Quantitative Evaluation of Zn+Cr-CrO _x Multilayer Coating Compared to Other Coated Steel Sheets

A study has been made of corrosion resistance and material processability of Zn+Cr-CrO_x (ZCC) compared with electrogalvanized (E2) and Zn-Ni (ZN) or Zn-Fe (ZF) coated sheets. It has been found that ZCC and ZN have better perforating corrosion than ZF and EZ. Cosmetic corrosion resistance of the three alloy coatings is almost the same; ZCC is slightly better also after deformation; EZ has the worst behavior. All the coated products take the phosphate coating except for ZCC which is inert to phosphating baths. Its paint adhesion is ensured by the CC top layer. In painting ZCC has the least tendency to cratering due to the presence of metallic chromium on its surface. In spot weld-ability the special coatings require electrode dressing and replacing 3-4 times less frequently than EZ. An economic study has also been made based on the N. Italsider electrogalvanizing line showing that production of ZCC is clearly more profitable than EZ, ZN and ZF.