Corrosion Protection Coatings

Zinc Electroplating with Blue / Yellow / Thick Layer Passivation (CrVI)-free

Electroplated coating systems ISO 4042

In the zinc electroplating process zinc ions are deposited from an electrolyte by applying electrical voltage. This creates a thin coating of zinc on the surface.

Post-plating treatments: Passivations are processes by which metal surfaces are made more resistant to corrosion by generating non-metallic protective layers, so-called conversion layers. The various passivation processes – blue passivation, thicklayer passivation, black passivation, yellow passivation, etc. – differ in terms of corrosion protection, appearance, colouring and passivation layer thickness.

Mitigating the risk of hydrogen embrittlement

Heat treatment (baking) after plating reduces the risk of possible parts failure. However, if your goal is to eliminate the risk of hydrogen embrittlement completely, other coating processes like mechanical plating or zinc flake coating should be considered.

Learn more about Hydrogen Embrittlement

Mechanical Zinc Plating with Blue / Yellow / Thick Layer Passivation (CrVI)-free

Mechanically deposited coatings of zinc ISO12683

The mechanical zinc plating method is used to prevent hydrogen embrittlement in steel fasteners with high strength / hardness. The parts to be coated are loaded in a barrel with proprietary chemicals, glass beads and zinc powder and tumbled. During tumbling, the glass beads peen zinc powder onto the part.

Generally, this method is suitable for fasteners with a simple geometry, which ensures zinc coating to all surfaces.

Post-plating treatments: Post-treatments of mechanical plating are similar to those used in electroplating.

Zinc Flake Coating (CrVI)-free

Non-electrolytically applied zinc flake coating systems ISO 10683

Zinc flake coatings are non-electrolytically applied coatings to prevent hydrogen embrittlement in high strength / hardness steels. These coatings typically contain a mix of zinc and aluminium flakes in a binder. The coating is applied as a liquid material in the same way as conventional paint, generally using a dipping process, then centrifuged and baked.

Zinc flake coatings have excellent corrosion protection properties. This kind of coating is less recommended for threaded parts ≤M5 and for fasteners with small internal drives.

Additional topcoats: To increase the corrosion protection further, an inorganic or organic topcoat can be applied. These topcoats not only provide even higher corrosion protection, but also a more uniform appearance.

Hot Dip Galvanizing

Hot dip galvanized coatings ISO10684

Hot-dip galvanizing is carried out by dipping the parts in molten zinc at temperatures of over 530°C. Immediately after dipping, a centrifugal process is used to remove the excess zinc, reducing the thickness of the zinc layer to values around 40 - 60 µm.

The corrosion protection from hot-dip galvanizing lasts much longer than electroplating zinc due to the greater coating thickness. However, the resulting zinc layer thickness requires special thread dimensions / tolerances, and is only feasible starting from thread size M8 and up.

Corrosion Protection Coatings: Evaluation

The corrosion resistance of a coating is strongly dependent on the type of plating or coating applied, the passivation products used, the use of additional topcoats and sealants as well as the applied thicknesses of the individual layers.

To support you in choosing the right method for you, we have created an interactive online tool:

Selection of Material and Coatings for Corrosion Protection