Galvanneal is an alloy coating made with 90% zinc and 10% iron. This coating will have an alloying reaction that will result in a hard and brittle finish that will eventually flake. Galvanneal is used and designed for applications of post fabrication painting such as automotive. When unpainted and exposed to earth elements a red color will appear due to the corrosion of the Iron in the coating.
AmeriTrellis does not advise any grower to use Galvanneal coated post.
Below are examples of cracked and exposed edges on a competing stake with a Galvanneal coating.