What is it?

This defect looks like the galvanized coating is peeling after forming, due to poor adhesion to steel. It is also called adherence failure or peeling galvanize. The defect can be caused by either overheating the zinc in the galvanizing pot, entering a strip that is too hot into the galvanizing pot, or low levels of aluminium in the galvanizing bath. All of these instances can accelerate the formation of the zinc/iron alloy layer between the steel and molten zinc. This layer is brittle and causes flaking when the layer is too thick. Atmosphere problems in the heating furnace can also result in flaking by the formation of an oxidized layer on the steel and slowing or preventing the formation of the zinc/iron alloy layer.

Flaking