HDG Hot Dip Galvanized Coating Structure

Galvanizing forms a metallurgical bond between the zinc and the underlying steel or iron, creating a barrier that is part of the metal itself. During galvanizing, the molten zinc reacts with the surface of the steel or iron article to form a series of zinc/iron alloy layers. The figure below is a photomicrograph of a galvanized steel coating cross-section and shows a typical coating microstructure consisting of three alloy layers and a layer of pure metallic zinc.

Progressing from the underlying steel surface outward, these are:

• The thin Gamma layer composed of an alloy that is 75% zinc and 25% iron
• The Delta layer composed of an alloy that is 90% zinc and 10% iron
• The Zeta layer composed of an alloy that is 94% zinc and 6% iron
• The outer Eta layer that is composed of pure zinc