Study of High Corrosion Resistant Zinc-Aluminum Composite Electroplated Steel Sheet

Abstract

Significant improvement of corrosion resistance of electrogalvanized steel sheet has been accomplished by codepositing particles (-250 mesh) of metallic aluminum in zinc layer. The composite coating is obtained electrolytically using a new plating bath containing zinc ion and aluminum particles dispersed.
The properties of Zn-Al composite electroplated steel sheet depend on the content of aluminum particles and the distribution of them in the plated layer. It has been found that the corrosion resistance by salt spray test is significantly improved with an increase of aluminum content in the plated layer.
Drawability, spot weldability and ED paint adhesion are also superior to those of electrogalvanized steel.
The corrosion mechanism of composite electroplated steel sheet has been studied by using electro-chemical methods. It becomes clear that the codeposited aluminum particles in plated layer act as cathodes and the cathodic reaction is suppressed by the existence of some resistive film on aluminum surface, and, as a result, anodic dissolution of zinc in plated layer is remarkably decreased.