Zinc flake coatings can also be applied to high-strength materials without process risks, such as hydrogen-induced brittle fracture. Zinc flake systems are similar to paints and contain pigments and metallic platelets/flakes dispersed in special binders, which can be composed of different alloy components. Even very thin layer thicknesses ensure the highest protection. Depending on requirements, layer thicknesses of 7 - 25 µm are applied. Many delivery specifications require a minimum proportion of 70% zinc and 10% aluminum, but today, in systems of the latest generation, further alloy components are added in order to further increase corrosion protection and significantly reduce coating corrosion/white rust formation. The high proportion of metallic pigments in platelet form (flakes) and the presence of conductive binders guarantee a very good cathodic protection and classify the layer as an inorganic coating. Most zinc flake systems have to be crosslinked under heat, depending on the requirements and the product, usually at temperatures between 170 - 250°C. Meanwhile, high-performance air-drying systems are also available, which are particularly suitable for spray application. Depending on the product, operating temperature resistance of up to 300°C can be achieved without losing corrosion protection.
The variety of demands requires the zinc flake coatings to be supplemented with topcoats or sealants. The pure zinc flake coating can already ensure a very high level of corrosion protection, but as soon as chemical resistance or aggressive climatic change tests are required, the surfaces must be supplemented with an additional covering layer. Specified systems are available in order to meet the wide range of requirements, including the different specifications for friction coefficients for threaded parts.
The great advantage of this technology also lies in the possible combinations of characteristics, such as classic duplex layer structures, e.g. ZnNi + topcoat, in order to achieve greater durability in corrosion protection, to guarantee better friction properties or to avoid contact corrosion. Non-ferrous metals can be coated with topcoats to ensure better media resistance or, for example, to protect high-strength aluminum alloys from inter-crystalline attack.