(2) Properties of plating film

(1) Film composition

The plating film consists of the aluminum layer composed of the same materials as the plating bath over the Fe-Al alloy layer generated by a reaction of molten aluminum and a steel substrate. Additional processing is required for post-plating treatment since the alloy layer Fe₂AL₅ (52 to 55% of aluminum) is extremely hard but fragile.
For steel plates requiring drawability, Al-Si alloy bath with 2 to 3% silicon (Si) is used for inhibiting the development of Fe-Al alloy layer.

(2) Corrosion resistance

Molten aluminum plating has superior resistance to climate conditions than hot dip galvanizing, especially in coastal areas or in the atmosphere with high content of sulfur dioxide. If they are exposed for a long period, they may be discolored. However, the corrosion will not progress further because the corrosion products are not soluble.

(3) Heat resistance

[Fig.] shows the increasing amount of oxidization measured at certain temperatures after heating the various types of steel plates.

Up to the relatively low temperature of around 500°C, the dense alumina layer formed by oxidation occurred on an aluminum surface layer inhibits the diffusive intrusion of oxygen. For temperature higher than this, the Fe-Al alloy exerts the superior resistance to oxidation when the aluminum diffuses into the steel substrate.

(3) Major applications

[Table] Major applications of molten aluminum plating