Galvannealed Steel (GA) is coated with zinc using the hot-dipped process that goes through an extra processing step. Once the raw steel is coated in the molten bath of zinc, and right after the air knives remove the excess zinc, it is passed through an annealing furnace. The annealing process pulls the iron from the steel, causing it to mix with the zinc coating creating a new finish that is 90% zinc and 10% iron.
This process causes the coating to become harder, more scratch-resistant, and more uniform in appearance.
The Galvanneal process also vastly improves formability, paint adhesion, and corrosion resistance, but leaves it with a duller matte surface compared to the spangle finish achieved with hot-dipped Galvanized.
Galvannealed coating is designated with an “A” (A40, A60). The number is the weight of the coating in ounces per square foot. A60, for example, is 0.60 ounces per square foot. (Which adds an ‘average’ thickness of about 0.0005 inches to the steel.).