Galvanizing can considerably improve the anti-corrosion properties of steel. Furthermore, applying coating over it can significantly increase the corrosion resistance, while improving the appearance.
The coated steel sheets are also referred to as pre-coated steel sheets. ("Pre-coated" means coating applied prior to molding as opposed to "post-coating" that refers to coating applied after molding.) Pre-coated steel sheets used to be made of hot-dip galvanized steel sheets, but recently, they are made of various materials including electro-galvanized and alloyed zinc-coated steel sheets as well.
[Table 1] shows the surface-coated steel sheets.

[Table 1] Surface-coated steel sheets

The organic films used for the paint film applied on the steel sheets listed in the table are made of polyester, acrylic resin, vinyl chloride, silicone polyester, urethane, and fluorine-based resins.
Zinc-rich paint film is a high molecular epoxy polymer-based organic film in which fine zinc particles are dispersed. It is known to have excellent corrosion resistance. However, due to the drawbacks of workability and weldability, organic composite plated steel sheets were developed.
Organic composite plated films are made by applying a composite of acrylic resin, epoxy resin, and silica sol to form an approx. 1 µm film thickness onto electroplated Zn-Ni alloyed steel sheets through a chromate layer. They are known to have enhanced formability and weldability.