Zinc coating (Z) produced on both sides by hot-dip galvanizing extends the service life of the end product by protecting the steel from corrosion.
The continuous hot-dip galvanizing process offers a wide protection range from Z100 to Z600 in addition to a tight bond between the coating and the steel. These properties make zinc coatings well suitable to forming and demanding corrosive atmospheres.
Because of the sacrificial nature of the zinc, the coating provides corrosion protection for areas of exposed steel surfaces, such as cutting edges and areas where coating has damaged (scratches, impacts, etc.). Full corrosion protection is also achieved in areas that have been heavily formed because the peeling tendency of low-friction and tightly bonded coating is low.
SSAB offers zinc coatings with different coating thicknesses, surface qualities and surface treatments to meet the demands of various applications.
Minimum total coating mass, both surfaces (g/m 2) *
Guidance value for coating thickness per surface, typically (μm)
* in triple spot test
In addition to these Zinc coating thicknesses defined according to EN10346:2015, the offering contains different asymmetric coatings, coatings with equal coating minimum mass per surface, and other OEM specifications that are available upon request.
Processing of zinc coated steel
The successful forming of metal coated steels depends on selections made regarding the geometry of component, steel grade, metal coating type and thickness, surface quality and protection, and a tool used in the forming.
Metal coated steels can be welded by various welding techniques including different methods of resistance welding, laser welding and arc welding. When welding recommendations are followed, the mechanical properties of welded joints are equal to those of non-coated steels.
Resistance welding methods, like spot welding, are most common and give excellent results with metal coated steels. Advantageous anticorrosion properties of the zinc-based coating mainly remain in the area of the properly made spot weld. Spot welding of metal coated material requires slightly higher current and electrode force than for uncoated steels due to the lower contact resistance of the coating. Similarly the increase in coating thickness increases slightly the required welding current. Therefore, in order improve weldability and achieve longer service life of welding electrodes, it is recommended to avoid unnecessarily thick coatings in welding applications. Galvannealed (ZF) coating is recommended for resistance welding applications with numerous welds.
Laser welding is also ideal for metal coated materials thanks to the narrow (only few mm) weld and low heat input. When any fusion welding methods are used, the heat input must be as minimal as possible in order to limit the heated zone in the metal coated sheet. Similar to scratched areas of the coating, also in the narrow weld the sacrificial effect of the zinc-based coating provides cathodic corrosion protection. However, the weld area is recommended to be painted or protected by other appropriate coating after the fusion welding process.
Ventilation of the workplace must be arranged properly because welding of zinc-based coated steels produces welding fumes containing zinc oxide.
In addition of providing the desired color for the final product, painting also further improves the corrosion protection of the final product. The skin-passed surface quality B is recommended when high surface quality for the painted surface is required.
Zinc coating provides a good substrate for painting when the surface is prepared correctly and right paints are used. In order to ensure good adhesion, any oils or impurities should be carefully removed from the surfaces to be painted. The product can be pretreated by zinc-phosphating or alternative pretreatment suitable for zinc-based coated steel in receiving plant to improve the coating adhesion.