Abstract
The adhesion of the hot-dip galvanized coating of high-strength steel sheet was studied in connection with the Al and Pb content of the Zn bath.
Coating adhesion, as evaluated by Gardner impact test, 0t-bending test and U-shaped bending test, differed, the Gardner impact test being the most severe.
Coating adhesion depended on the structure of the alloy layer formed between the substrate and the coating (η-Zn), which was changed by the Al and Pb contents in the coating bath. In a 0.05% Al-0.20% Pb-Zn bath, an alloy layer consisting of coarsely developed Fe-Zn intermetallic compounds made coating adhesion poor. In a 0.15%Al-0.20%Pb-Zn bath, the poor adhesion of the coating was considered to be due to the alloy layer consisting of fine Al-Fe-Zn intermetallic compounds and locally developed Fe-Zn intermetallic compounds. The addition of Pb to the coating bath facilitated the local formation of Fe-Zn intermetallic compounds.
