Zinc Electroplating with Blue / Yellow / Thick-Layer Passivation, Cr(VI)-free
Electroplated coating systems, ISO 4042
In the zinc electroplating process, zinc ions are deposited from an electrolyte when electrical voltage is applied. This creates a thin coating of zinc on the surface.
Post-plating treatments: Passivation is a process 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, thick-layer, black, or yellow passivation, etc. – differ in terms of corrosion protection, appearance, coloring, and passivation layer thickness.
Mitigating the Risk of Hydrogen Embrittlement: Heat treatment after plating reduces the risk of part failure. However, if your goal is to eliminate hydrogen embrittlement completely, other coating processes should be considered (see below).
Mechanical Zinc Plating with Blue / Yellow / Thick-Layer Passivation, Cr(VI)-free
Mechanically deposited coatings of zinc, ISO 12683
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 are then 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 on all surfaces.
Post-plating treatments: Post-treatments of mechanical plating are similar to those used in electroplating.
Zinc Flake Coating, Cr(VI)-free
Non-electrolytically applied zinc flake coating systems, ISO 10683
Zinc flake coatings are non-electrolytically applied coatings that prevent hydrogen embrittlement in high strength / hardness steels. These coatings typically contain a mixture of zinc and aluminum flakes in a binder. The coating is applied as a liquid material in the same way as conventional paint, generally using a dipping process, and are 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 provide a more uniform appearance in addition to higher corrosion protection.
Hot Dip Galvanizing
Hot dip galvanized coatings, ISO 10684
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.
