Not every corrosion-protection job is the same and in many cases the use of a coating to prevent corrosion will save a part from early failure and potentially a whole batch of them from non-compliance with regulations. The use of zinc nickel coating is no exception and is best used in specific circumstances.
Harsh or Corrosive Environments
Plating plain zinc onto components destined for use in salt-laden environments, which are exposed to moisture and subject to high temperatures, can result in very short service life. As an example, under-bonnet car components, offshore plant equipment and coastal-based factory equipment all require a coating that is superior to zinc in salt-spray tests. Zinc nickel plating, which resists red rust up to 1,000 hours or more in such tests, is often the preferred coating.
High-Strength Steel and Embrittlement Risk
The risk of hydrogen embrittlement is a serious consideration when surface treating high strength steel (over approximately 1,000MPa). Zinc nickel plating using an alkaline process is less harmful than zinc plating using an acid process. Proper baking of the plated part after plating will also drive off any hydrogen that has been absorbed. High-tensile fasteners, springs and other safety critical steel parts need to be surface treated with care.
Replacing Cadmium on Regulated Parts
Cadmium coating has long been used for the protection of parts intended for use in the aerospace and defence industries. While the coating provides good sacrificial protection it is increasingly being restricted in industrial use. Zinc nickel coating provides similar protection and is an approved alternative to cadmium coated parts in many industries where cadmium coating is now either restricted or banned.
Close Dimensional Tolerances
Hot-dip galvanising forms a large uneven layer of zinc on the steel component. For applications requiring parts with close dimensional tolerances, such as threaded parts and components with precise bores, the thin consistent layer produced by the zinc nickel process is far more suitable.
If you want Zinc Nickel Coating, www.poeton.co.uk/surface-treatments/plating/zinc-nickel-plating is a good place to start.
Mixed-Metal Assemblies
In mixed metal assemblies where contact corrosion between steel fasteners and aluminium parts could compromise service life of the part, the less aggressive nature of Zinc Nickel to aluminium over zinc coated parts makes it an attractive alternative.
So, there are plenty of scenarios in which using a zinc nickel coating is simply better than using other corrosion coatings.
