Galvannealed coated steels are made by running a steel coil through a continuous hot-dip zinc bath and then heat treating the steel inline to diffuse iron from the substrate into the zinc layer. ZF-coated steel provides excellent paintability and unbeatable weldability due to the coating’s iron content.
Galvannealed is designated by GA in the VDA 239-100 standard, ZF (for EN 10346:2015 standard) and A (for ASTM standards), and is informally known as a zinc-iron or hot-dip galvannealed (HDGA) coating.
During its heat treatment process, iron from the steel reacts with hot-dipped zinc and forms zinc-iron compounds. With an iron content of approximately 10%, galvannealed coating delivers exceptional resistance weldability for coated steel, with low electrode galling for longer electrode life.
Galvannealing produces a finely structured matte surface that paints readily adhere to. GA-coated steel that have been painted has excellent corrosion resistance, even under demanding application conditions.
Because of the sacrificial nature of the Galvannealed coating, it provides a level of corrosion resistance for areas that have been exposed: for example, cut edges, scratches, dents, etc.
SSAB offers Galvannealed coatings with different coating thicknesses, surface qualities and surface treatments to meet the demands of various applications.
*In triple spot test.
In addition to meeting these EN10346:2015 specifications, we offer coatings with guaranteed coating mass on both surfaces (Bill asks: How is this different from what is listed above?), as well as the ability to meet other OEM specifications upon request.
Typical forming methods like bending, stretching, and drawing are suitable for galvannealed coated steels when using the proper forming parameters. Galvannealed coatings have a higher hardness than traditional zinc (GI) coatings, providing increased scratch protection during forming. GA coatings can lead to powdering during drawing, which can be minimized or eliminated by the proper forming set-up and by specifying thin galvannealed coatings. Galvannealed coatings have good laser-cutting properties, which can reduce your laser cutting costs.
In general, galvannealed coated steels are considered optimal for the resistance welding of corrosion-resistance steels. Compared to traditional zinc (GI) coatings, galvannealed coatings allow a much larger range in welding currents. With lower welding currents, GA coatings enable longer electrode service life. And with the correct welding parameters, galvannealed welded joints are comparable to those on uncoated steel.
Conventionally applied paint readily adheres to galvanneal’s finely structured matte surface. As with all painting, any oils or impurities must be fully removed prior to painting. To further improve coating adhesion, you can use pretreatments in the receiving plant that are suitable for zinc-based coated steels, such as zinc-phosphating. When requested, improved surface quality B is obtained by skin passing.
Contact our corrosion resistance steel coating experts.
