Structure and Corrosion Resistance of Hot Dip Aluminized Zinc Silicon Coating

The galvanized layer and the aluminized layer each have their advantages and disadvantages, and the 55% Al-Zn-Si plated layer can be said to combine the advantages of both, and overcome the disadvantages of both. This is determined by its special plating structure. The microstructure of the hot-dip 55% Al-Zn-Si alloy coating is shown in Fig. 1, which is also divided into two parts, the outer layer and the inner layer. Because of the greater mass ratio and volume ratio of Al than Zn, this coating is closer to the aluminum plating layer than Al, but is more complicated than the zinc plating layer and the aluminum plating layer.

The inner layer, that is, the compound layer has the Al-Fe diffusion formed Al-Fe compound layer as well as the aluminized layer. Since a certain amount of Si is added, Si preferentially forms the Fe-Si compound layer on the surface of the steel substrate. The AbFe compound layer becomes very thin, thereby improving its processability.

The outer layer of this coating is also very complex and just right. A large amount of aluminum crystallized to form a very fine aluminum-rich dendritic crystal, accounting for about 80% of the volume, forming a fine network skeleton in the entire coating layer, and in the remaining only about 20% of the intercrystalline gap is zinc-rich The eutectic structure. The organic combination of these two kinds of organizations makes the coating have a good overall performance. The aluminum-rich dendritic network lays a good corrosion resistance and heat-resistant oxidation performance of the aluminum-plated coating, and the zinc-rich intergranular structure makes the coating have the same cathodic protection as the galvanized sheet in the scratched environmental medium. The product film produced by the corrosion and corrosion is retained by the aluminum-rich phase network and filled in the gap between the dendrites. A protective film with a protective effect is formed on the surface of the plating layer, so that the corrosion rate is slowed down. Corrosion resistance is greatly improved over galvanized layers of the same thickness.