How Zinc Nickel Plating Performs in Salt Spray

How Zinc Nickel Plating Performs in Salt Spray

Salt spray testing is a typical test to compare corrosion resistance of coatings. The higher the hour rating the better the coating resists corrosion before it starts to rust.

What the Hour Ratings Mean

Results are recorded as hours to white rust (surface oxidation) and hours to red rust (base metal corrosion). The results can also be stated in terms of hours to the first sign of failure. The test can also be run so that the parts are immersed in the salt spray fog, such as in B235/ISO 3576 test for atmospheric corrosion resistance of powder coated steel.

Typical Zinc Nickel Results

12% to 15% nickel bearing Zinc Nickel Plating solutions typically provide 500 to 1000 hours to white rust and in excess of 1000 hours to red rust. In comparison, pure zinc plating usually lasts around 200 to 300 hours to red rust, whilst cadmium again lasts for a similar period.

Which Industries Specify These Figures

The automotive, aerospace and defence industries include the salt spray hours in component specifications. These can be fasteners, brackets and other items which are used on the road and are exposed to road salt or in coastal areas.

How Thickness and Nickel Content Affect Results

A thicker coating, typically in the range of 8-12 μm, will provide better corrosion protection and therefore higher hour ratings. Also the higher the nickel content, typically above 10%, will provide better corrosion protection than lower nickel contents below 10%. A nickel content of 12-15% is typical for corrosion resistant zinc-nickel coatings.

There is more on Zinc Nickel Plating at swmf.co.uk/surface-coatings/zinc-nickel-alloy-plating/.

Salt spray figures provide consistent and measurable numbers to compare various coatings before agreeing on a specification.