Corrosion Behavior of Al-Cr Hot-Dip Coated Steel Sheet in NaCl Solution

摘要

The microstructure and the corrosion behavior of aluminized steel sheet and hot-dipped Al-Cr steel sheet were investigated. The EPMA, GDLS and XRD measurements of the Al-Cr coated layer showed that the coating layer was characterized by three phases. The surface layer was Al, the middle layer was Al_(13)Cr_2, and the interfacial layer between the Fe substrate and the coated layer was composed of Al_(13)Fe_4 and Al_5Fe_2. The polalization curve indicates that the corrosion behavior of Al-Cr coated layer was different from that of Al coated layer. For the Al coated layer, porosities in the Al-oxide film on the surface layer lead to preferential corrosion. Alter the Al coated layer was completely removed, the Al_5Fe_2 layer was selectively corroded and then, the steel substrate was exposed to the corrosion medium. In case of the Al-Cr coated layer, the Al_(13)Cr_2 layer became a barrier against further corrosion after the Al layer was removed. In this case, corrosion was not proceeded even through the same current density. The high corrosion resistance was due to the existence of the Al_(13)Cr_2 layer.