What is the difference between "Galvanized" steel and "Galvalume" steel?

Galvanized steel is steel with a zinc coating applied at the steel mill through a hot-dipped process. Galvalume coated steel is applied similarly via a hot-dipped process except the metallic coating is more than just zinc.

Galvanized steel is steel with a zinc coating applied at the steel mill through a hot-dipped process (the steel strip is passed through a bath of molten zinc). Galvalume, a.k.a. Acrylume, or, aluminum-zinc-alloy coated steel is applied similarly via a hot-dipped process except the metallic coating is more than just zinc. The Galvalume coating is made up of 55% aluminum, 43.4% zinc, and 1.6% Silicone. Galvalume provides the best of both worlds through aluminums' excellent barrier protection and zincs' excellent sacrificial protection. Bare Galvalume will last significantly longer than bare Galvanized in normal atmospheric conditions.