In this post, we’ll explore nickel plating for magnets.
We’ll discuss its benefits, key specifications, common issues, quality control methods.
And we’ll cover important considerations when deciding whether to use it for your magnet applications.
Let’s get started!
What is Nickel Plating?
Nickel plating is a common protective coating.
It is applied to magnets, especially neodymium magnets.
The purpose is to prevent corrosion and extend their lifespan.
- The process involves thoroughly cleaning the magnet’s surface.
- Then dipping it into a nickel plating solution, rinsing, and drying.
- The most common type of nickel plating for neodymium magnets is a three-layer coating.
- It consists of nickel-copper-nickel (Ni-Cu-Ni).
Nickel platings have some features that make them suitable for certain applications.
- Nickel plating is the most frequently used surface treatment for iron and steel products.
- It accounts for 50% of the global nickel production.
Why Nickel Platings for Magnets?
Corrosion & Oxidation Resistance
Nickel acts as a barrier against moisture, oxygen, and corrosive elements.
It protects the underlying magnet material from oxidation and rust.
This is especially important for neodymium magnets.
Enhanced Durability
The nickel layer increases surface hardness and wear resistance.
It protects the magnet from scratches, chips, and physical damage.
This protection is useful during handling and use.
Improved Appearance
Nickel plating provides a smooth, shiny, and polished finish to the magnet.
This enhances its aesthetic appeal.
Cost-Effectiveness
Nickel plating is relatively inexpensive compared to premium coatings.
Premium coatings include gold or plastics.
Yet nickel still provides effective protection and durability.
Specifications & Parameters
Plating Composition
- The most common nickel plating for neodymium magnets is a three-layer Ni-Cu-Ni coating.
- Each layer is typically 5-7 μm thick.
Overall Plating Thickness
- The total Ni-Cu-Ni plating thickness ranges from 15-21 μm.
- Thicker coatings like nickel-copper-nickel with epoxy are 20-28 μm thick.
Corrosion Resistance
- Ni-Cu-Ni plated magnets typically withstand 24 hours in a salt spray test.
- And 48 hours in a pressure cooker test.
Adhesion
Proper pre-treatment of the magnet surface is crucial.
It is important for good adhesion of the nickel plating.
Types
Nickel coatings are thin layers of nickel that are applied to metal objects for various purposes, such as decoration, corrosion resistance, wear resistance, or electrical conductivity. Nickel coatings can be produced by different methods, such as electroplating, electroless plating, or spraying. There are different types of nickel coatings that have different characteristics and applications. Some of the most common types are:
Bright nickel plating
This is a type of electroplating that uses an aqueous electrolyte solution and an electric current to deposit a shiny layer of nickel onto a metal object. Bright nickel plating is typically used for decorative purposes and corrosion protection. It can also be combined with other metals, such as chromium or gold, to form a more attractive finish.
Electroless nickel plating
This is a type of plating that uses a chemical reaction to deposit a uniform layer of nickel onto a metal object without using an electric current. Electroless nickel plating is more resistant to corrosion and wear than electroplated nickel. It can also cover complex shapes and hard-to-reach areas. Electroless nickel plating can be further classified into different subtypes, such as nickel-phosphorus, nickel-boron, or composite coatings, depending on the composition and properties of the coating.
Dull nickel plating
This is a type of electroplating that uses an aqueous electrolyte solution and an electric current to deposit a matte layer of nickel onto a metal object. Dull nickel plating is usually used for engineering applications where high corrosion resistance, ductility, or electrical conductivity is important, and a high luster is not required. Dull nickel plating can also be used as an undercoat for other metals, such as chromium or silver, to improve their adhesion and durability.
Potential Quality Issues
Hydrogen Embrittlement
During the plating process, hydrogen can diffuse into the magnet.
This causes embrittlement and makes the magnet more prone to cracking or shattering.
You may need a hydrogen embrittlement relief bake after plating to mitigate this issue.
Inconsistent Plating Thickness
Achieving uniform plating thickness can be challenging.
Especially with complex magnet shapes.
Variations in thickness can affect corrosion resistance and performance.
Passivation
The nickel surface can become passive during the plating process.
If left in the solution too long before applying current.
This causes cosmetic defects and makes subsequent plating difficult.
How to verify
One way to tell whether the protective film on a magnet is nickel or not is to:
- Use a spot test with dimethylglyoxime and ammonium hydroxide.
This is a chemical test that can detect the presence of nickel ions in a solution.
- If the coating is nickel, it will react with these chemicals and turn pink.
- This test is quick, easy, and inexpensive.
To perform this test, you will need the following materials:
- A drop of 1% dimethylglyoxime solution
- A drop of 10% ammonium hydroxide solution
- A cotton swab or a small brush
- A clean and dry metal object with the coating you want to test
The steps are as follows:
- Apply a drop of dimethylglyoxime solution to the cotton swab or brush.
- Rub the swab or brush gently on the coated surface of the metal object. You may need to scratch the surface slightly to expose the coating.
- Apply a drop of ammonium hydroxide solution to the same spot where you applied the dimethylglyoxime solution.
- Observe the color change. If the spot turns pink, it means that the coating is nickel. If there is no color change, it means that the coating is not nickel.
Measuring Nickel Plating Quality
It’s good to pay attention to their finished results on neodymium magnets.
There are several methods that can be used to verify the quality of nickel platings.
Visual inspection
This is a simple and quick method that involves visual inspections on the surfaces of the nickel coatings on neodymium magnets to ensure that they don’t have defects. Usually, quality engineers can do it with their naked eyes.
Microscopic examination
This method involves using a microscope to inspect the surface of the nickel coating at a higher magnification. This can help to identify any defects or imperfections in the coating that may not be visible to the naked eye.
Surface roughness measurement
We measure surface roughness using a device such as a profilometer. This can help to ensure that the nickel coating has a smooth and even finish, which is important for many applications.
Adhesion testing
Adhesion testing involves applying a force to the nickel coating to see how well it sticks to the neodymium magnets. We use a cross-cut tester or a scratch tester to do this test.
Salt spray testing
This method involves exposing the nickel coating to a salt spray environment for a period of time and then examining the surface for signs of corrosion or other damage. Usually, the duration time depends on specific applications.
Thickness measurement
We use a thickness gauge to measure the thickness of the nickel coating. This can help to ensure that the coating is applied to the correct thickness for the specific application.
Hardness testing
It will need a Rockwell hardness tester to obtain the hardness of the nickel coating. This can help to ensure that the coating has the required level of hardness for the specific application.
Types of Nickel Platings
Electroplated nickel
This type of nickel coating is applied using an electrolytic process, in which a current is used to deposit a layer of nickel onto the surface of a substrate. Substrates can benefit from electroplated nickel coatings thanks to better wear resistance, corrosion resistance, and aesthetics.
This is the most common technique that we use to apply nickel coatings onto neodymium magnets. Many coating technique suppliers use it for various products every day. It is fully optimized and less likely to have quality issues. Meanwhile, they can offer excellent cost-effectiveness, thanks to their wide applications.
Electroless nickel
This is a type of nickel coating that is applied using an autocatalytic chemical process rather than an electrolytic process. It offers an evenly distributed, robust, and corrosion-resistant coating that can be used on a range of substrate materials. This is one of the best surface treatment techniques in the world.
Nickel-chrome
This is a type of nickel coating that is applied over a layer of chromium. In applications where high temperatures and harsh conditions are a concern, nickel and chromium work together to provide a strong, corrosion-resistant coating.
Nickel-phosphorus
This is a type of nickel coating that is alloyed with phosphorus to improve its corrosion resistance and wear resistance. We usually use it in situations that need a lot of lubricities, like bearings and gears.
Nickel-tungsten
This is a type of nickel coating that is alloyed with tungsten to improve its hardness and wear resistance. We typically use it in applications requiring great wear resistance, including cutting tools and dies.
Initially, magnets were coated with a single layer of nickel, but this approach had its limitations.
- The single-layer nickel plating had high porosity, making it inadequate for effectively safeguarding the NdFeB substrate.
- Additionally, this plating method was cathodic in nature, meaning it posed challenges unless the nickel layer was exceptionally thick, typically reaching 20 to 25 micrometers.
However, an excessively thick nickel layer, being ferromagnetic, adversely affected the magnetic properties of the NdFeB magnets.
As a result, NdFeB single-layer nickel plating was not considered an ideal choice.
And then, a vast majority of magnet manufacturers have shifted to a more effective solution:
- Double-layer nickel plating, specifically nickel-copper-nickel plating.
Wrap Up
Now you’ve finished reading about the key benefits, specifications, common issues, quality control methods, and performance implications.
You can make an informed decision on whether nickel plating is the right choice.
If you are looking for nickel-plated neodymium magnets, consider dropping Osenc a line.