What is the difference between galvanized and galvannealed steel?

Resolution:

Galvannealed and galvanized steel are zinc coated at the steel mills and are designed for rust and corrosion resistance. Both steels are passed through a hot dip coating process for rust prevention. Galvannealed steel goes through and additional annealing process which vastly improves the formability and paint adhesion. Galvanneaed or galvanized steel is always recommended:

1. Exterior applications
2. Interior applications where rust and/or corrosion may be a factor

Galvannealed Steel - zinc-iron alloy-coated by the hot-dip process followed by heating the steel to induce diffusion alloying between the molten zinc coating and the steel. The resulting finish is a dull matte surface.

1. Galvannealed steel is very conducive to forming, welding and allows for excellent paint adhesion. Galvannealed steel is the preferred coated steel for use in architectural applications.
2. Specification - ASTM A 653/A 653M, coating designation “A” (A60, A40)

Galvanized Steel - zinc-coated by the hot-dip process, resulting in a full spangled finish

1. Galvanized steel is less conducive to forming, welding and painting
2. Specification - ASTM A 653/A 653M, coating designation “G” series (G90)