Neodymium Iron Boron Magnets require a protective coating / surface finish to prevent corrosion of the magnet. Moisture in the atmosphere is potentially enough to cause an uncoated NdFeB magnet to show signs of corrosion. Marine environments are particularly effective at making NdFeB magnets corrode.
The plating process is carried out on magnets that have been thoroughly cleaned and dried. The standard coating is a triple layer plating of Nickel-Copper-Nickel (Ni-Cu-Ni). Unless otherwise requested, Ni-Cu-Ni coating is always applied to the magnets. It should be noted that the level of protection given by any coating depends on the environment that the magnet will be subjected to and how the coating is looked after. If the coating is scratched or broken, it will not offer protection from moisture.
The current range of coatings available is as follows:
|Passivation||N/A||1||Silver grey||Temporary Protection|
|Nickel||Ni+Ni||10-20||Bright Silver||Excellent against Humidity|
|Zinc||Zn||8-20||Bright||Good against salt spray|
|Cr-Zn||Shiny Color||Excellent against salt spray|
|Tin||Ni+Cu+Sn||15-20||Silver||Superior against Humidity|
|Gold||Ni+Cu+Au||10-20||Gold||Superior against Humidity|
|Epoxy||Epoxy||15-25||Black, Red, Grey||Excellent against Humidity & salt spray|
The corrosion resistance offered depends on the grades of AlNiCo and the chemicals it is exposed to.Protective coating / surface finish is not needed when AlNiCo Magnets are used in following applications:
- Motor oil ●Organic solvents ●Petrol and alcohol
AlNiCo materials show signs of corrosion over time when exposed to salt water, strong alkali solution and inorganic acids. It is possible to put a protective layer over the AlNiCo e.g. Ni, Zn, paint, epoxy Coated etc.
The color of the coating is almost always red. This is why AlNiCo magnets are often known as Red Magnets, Other colors are also available in AlNiCo Magnets, such as black.
Samarium cobalt magnets are resistance to corrosion and oxidation resistance, generally do not need protective coating.
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