What is Zinc Nickel Plating?
Zinc-nickel plating involves zinc and nickel being co-electrodeposited on to components. Zinc-nickel plating can be passivated to further improve its corrosion resistance. The plated coating generally consists of 11 to 16% nickel and the remainder as zinc (many specifications allow a larger range, but best performance is usually found in this range).
Why Zinc Nickel?
For many applications zinc-nickel alloy plating is superior to standard zinc plating. Due to the complexity of zinc-nickel plating, it has only become cost effective in recent years as technology has improved. Zinc-nickel is now seen by many as an improvement on zinc plating and as an alternative to toxic cadmium plating.
Metal Finishings Ltd offer zinc-nickel plating at a variety of thicknesses. Unpassivated, clear passivated or black passivated finishes are available. Topcoats are also available.
Zinc nickel bridges the galvanic gap between steel and aluminium, reducing the risk and rate of galvanic corrosion. In this way, it works similarly to cadmium. Zinc-nickel is still sacrificial and so provides some protection to the steel even in the event of small scratches, cracks etc.
More Corrosion Resistant Than Zinc
Standards for zinc-nickel plating typically require unpassivated parts coated with 10µm of zinc-nickel to withstand 500 hours or more of neutral salt spray testing before red corrosion. For comparison zinc plated and passivated parts of a similar thickness are expected to achieve only 120 hours - considerably less.
Zinc-nickel has good unpassivated corrosion resistance, although it can be improved even further with passivates and top coats. By comparison zinc plating is very reliant on the passivation and topcoating for protection. In this way, zinc nickel may perform much better than zinc for higher temperature applications (passivates lose this effectiveness at elevated temperature).
Use Metal Finishings Ltd for Zinc Nickel
As a reputable surface treatment company, our zinc-nickel coatings are checked for composition and thickness on every production batch by XRF. This is critical to ensure parts perform as designed in service, but not offered as standard by all companies. Additionally, our coatings are backed by monthly salt spray testing to check corrosion resistance (per ASTM B117).
We can work to many other specifications, but the above are our most popular. Please contact us with your requirements.
Information for Designers
Thickness and Growth
Zinc-nickel plating is deposited on the surface of the component. So the growth per surface will be equal to the thickness per surface. Thicknesses for zinc-nickel plating are generally specified as minima, although control within a range is possible.
A coating of zinc-nickel on steel acts as a sacrificial anode because of its position in the galvanic series. This is very useful because even if the coating is scratched or damaged, the zinc-nickel will provide protection to the base metal by sacrificing itself.
Base Material Condition
The base material is very important to the quality of the plating. Best results will be obtained by using clean steel (as opposed to black steel). It is recommended that you ensure that material is not porous or pitted, because these will be corrosion sites despite the zinc-nickel plating.
Tensile Strength of Base Metal
Components with a tensile strength of over 1000 MPa are liable to hydrogen embrittlement and require de-embrittlement and stress relief. It is essential that parts that are high tensile strength and will require de-embrittlement and/or stress relief are clearly marked as requiring this when sent to us.
This is not a concern for the majority of parts. The geometry of parts may make it difficult for the zinc-nickel to “throw” into certain areas (usually insides of tubes and the corners of deep boxes). For situations like this we can usually have an internal anode manufactured (for all over coverage).