Galvannealing steel takes place immediately after the zinc bath for galvanizing. While the zinc is still liquid, the steel goes into an annealing furnace to fuse the zinc and alloy layers together.
While this is a thinner layer of zinc than galvanizing, and therefore less resistant to corrosion, the surface because very smooth and works well for painting. The galvannealed steel surface is slightly more absorbent, so paint adheres better. This finish is popular for outdoor uses requiring both rust-resistance and painting.