Carbon steel is inherently susceptible to corrosion, which means it must be protected by some other metallic coating that is less corrosive. Carbon steel sheet is called “galvanized” when coated with a thin layer of commercially pure zinc.
This coating provides two types of corrosion protection for the steel: “barrier protection” (sealing the surface from air and water) and “sacrificial protection” or “galvanic” protection—especially at scratches and cut edges. This is an electrolytic process whereby the base metal is protected, but at the expense of the coating. The zinc “sacrifices” itself to protect the underlying layer of steel.
The most popular carbon steel coating is now aluminum/zinc alloy (55% AlZn). Known as Galvalume®, by most US domestic producers, it combines the superior barrier protection of aluminum with the sacrificial properties of zinc. Galvalume offers superb weathering protection while still providing galvanic protection from corrosion. Scratch and cut-edge protection of Galvalume is also very good – preventing or retarding exposed-edge and scratch corrosion and progression.
The trade name “Galvalume®” combines the words galvanized (zinc) and aluminum. This coating for steel combines the corrosion-resistance of aluminized steel with the benefits of galvanized steel. It is applied by the same “continuous hot-dip” method as galvanized, but at higher temperatures (above 1200ºF). The specific make-up consists of 55% Aluminum, 43.4% zinc and 1.6% silicon (percentages by weight). By volume, the coating is about 80% aluminum. The addition of the silicon serves to assist with coating adhesion to the steel during application, roll-forming and other fabrication activities. Click to read more.