Galvanic zinc alloy plating has for years been established as a high-quality corrosion-control measure for iron and steel products.
In the salt spray test a zinc/iron alloy is distinguished by 4-5 times higher endurance until the onset of coating corrosion (white rust) than conventional zinc plating (see also graph). Black chromating (Mark ”F” concerning DIN 50961) is a prerequisite here however as zinc/iron yellow chromating only gives about the same degree of protection as a zinc yellow chromating.
Comprison of corrosion in the neutral salt spray test as per DIN 50021-SS between electroplated zinc coating- black cromated and black cormated zinc-iron alloy coatings
As in the case of the standard galvanisation, here too a CrVI black chromation can be replaced by a CrVI-free black passivation with additional sealing, without compromising corrosion resistance.
Attaining the required coating properties also requires exact compliance with all bath parameters, which is only possible in on-line operation.
Zinc/iron alloy depositing is resistant up to 100 °C (VW regulations TL 153 require tempering for 24 h at 100 °C before the corrosion test). For higher temperature ranges of 120-150 °C – e.g. in a car’s engine compartment – a zinc/nickel coating is generally used. As this is usually reserved for that specific utilisation because of its high cost in terms of environmental technology and the coating price is 1.6 to 1.8 times higher, we do not offer this process at present.
Zinc/iron alloy plating is possible on all standard types of steel and usually on cast iron also. Depending on the type of cast iron, an intermediate layer of pure zinc may be necessary.
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