Galvannealed coating (ZF) is a zinc-iron alloy coating featuring excellent resistance welding properties and paint adhesion. It is ideal coating for spot welding and high-end painting applications.
The Galvannealed coating provides first-class painted surfaces that last under demanding conditions. The surface of the Galvannealed coating is finely structured, providing an attractive appearance to the painted surface wherein the paint firmly adheres to the product. Therefore painted Galvannealed surfaces also feature excellent corrosion resistance.
Galvannealed coating can be recognized by its typically grayish, matte surface. The coating is produced by heat treatment after continuous hot-dip coating. In this heat treatment process, iron from steel reacts with zinc and forms zinc-iron compounds. The iron content of the coating is approximately 10%. Consequently, the coating provides unbeatable resistance weldability for coated steel, meaning longer electrode life and low galling on electrodes.
Because of the sacrificial nature of the Galvannealed coating, it provides corrosion protection for areas of exposed steel surfaces, such as cutting edges and possible areas where coating has damaged (scratches, impacts, etc.).
SSAB offers Galvannealed coatings with different coating thicknesses, surface qualities and surface treatments to meet the demands of various applications.
| Coating designation | Minimum total coating mass, | Guidance value for coating thickness per surface, |
| both surfaces (g/m2) * | typically (μm) | |
| ZF080 | 80 | 6 |
| ZF100 | 100 | 7 |
| ZF120 | 120 | 8 |
| ZF140 | 140 | 10 |
* in triple spot test
In addition to these coating quantities defined according to EN10346:2015, the offering contains coatings with guaranteed coating mass on both surfaces, and other OEM specifications that are available upon request.
Typical forming methods like bending, stretching and drawing are applicable for Galvannealed coated steels when correct forming parameters are used. Galvannealed coating is not easily scratched during handling because the coating has higher hardness as compared to traditional zinc coating (Z). Possible powdering in drawing can be eliminated or minimized by proper setup of drawing process and also by using thin Galvannealed coatings available in the offering.
In general, Galvannealed coated steels are best choice for different resistance welding processes. They are more robust to use in the welding process due to the much larger welding current range as compared to traditional zinc (Z) coated steels. By enabling lower welding current Galvannealed coating also provides long electrode service life. Consequently it has superior behavior in resistance welding process. If welding recommendations or welding method test results are observed, the mechanical properties of welded joints are comparable to those in non-coated sheet.
The matt looking Galvannealed surface having finely structured surface provides excellent adhesion for painting by using conventional painting methods. In order to ensure good adhesion, any oils or impurities should be carefully removed from the surfaces to be painted. The product can be pre-treated by zinc-phosphating or alternative pretreatment suitable for zinc-based coated steels in receiving plant to further improve the coating adhesion.
If a high surface quality for the painted surface is required, the skin passed surface quality B is recommended.
