Galvanneering

Galvanneering is a finishing process applied to steel that involves coating it with a zinc-iron alloy. This coating is created by heating a galvanized steel sheet to a high temperature, typically between 500 and 700 degrees Celsius, in a controlled atmosphere. During this heating, the zinc coating diffuses into the steel substrate, forming a brittle, intermetallic layer of zinc-iron. This layer is harder and more brittle than the pure zinc coating found on galvanized steel.

The primary advantage of galvannealing is the enhanced paint adhesion and weldability it offers. The alloy layer provides a surface that is more receptive to paint, leading to better corrosion resistance and a more durable finish when the steel is subsequently painted. Furthermore, the iron content in the alloy layer reduces the spattering that can occur during welding operations on galvanized steel, making it a preferred choice for applications requiring both good paintability and ease of welding.

The galvannealed coating typically consists of distinct phases of zinc-iron alloys, such as gamma, delta, and zeta phases, depending on the annealing temperature and time. This process is commonly used in the automotive industry, construction, and appliance manufacturing where a combination of corrosion protection, aesthetic appeal through painting, and ease of fabrication is required. While it offers benefits in adhesion and weldability, the brittleness of the alloy layer can make it less suitable for applications involving significant post-forming deformation compared to standard galvanized steel.