Galvannealed

Galvannealed refers to steel that has been hot-dip galvanized and then subjected to an additional annealing step in a reducing atmosphere, causing iron from the steel to diffuse into the zinc coating. This diffusion forms a zinc–iron alloy coating (an alloy layer beneath a zinc-rich surface) and gives the coating a characteristic dull, matte appearance compared with bright galvanization. The resulting surface is known for improved paint adhesion and certain forming benefits.

Process and composition: After conventional hot-dip galvanizing, the strip is passed through an in-line annealing furnace. The elevated temperature promotes diffusion between iron and zinc, producing an iron-rich alloy layer integrated with zinc. The surface coating is typically described as galvanneal or a zinc–iron alloy coating, with a mixture of intermetallic phases that influence adhesion, formability, and corrosion behavior. The coating adheres well to paints and primers, making it suitable for pre-painted products.

Applications and properties: Galvannealed steel is widely used for automotive body panels, appliances, and other pre-painted metal components where paint adhesion and formability are important. Compared with standard hot-dip galvanization, galvannealed coatings offer improved paint bonding and surface uniformity, which can enhance production efficiency and finish quality. However, the corrosion resistance profile differs due to the zinc–iron alloy content, and performance can vary with environment and coating thickness. The coating can be more prone to certain forms of corrosion in aggressive atmospheres, depending on process conditions.

Variations and terminology: The term galvannealed (or galvanneal) is used in industry to describe this annealed, iron-enriched zinc coating. It is distinct from conventional electrogalvanized or hot-dip galvanized coatings, though all are used as protective surfaces on steel.