How to protect neodymium magnets from corrosion?
Wondering do neodymium magnets rust? The answer is yes because neodymium magnets are famous for their poor corrosion resistance. They may corrode badly from the inside-out if you fail to follow the pre-treatment process. To avoid corrosion, multi-layer (nickel, copper, nickel) is required, but it is not sufficient for several applications.
Every magnet has an iron form, and iron is responsible for dramatic ferromagnetic properties. It is available in every powerful magnet. Iron is reactive to liquid; therefore, high iron content can make a magnet susceptible to rust. Usually, magnets have numerous ferromagnetic elements, such as cobalt, dysprosium, gadolinium, and nickel. These have a heavy impact on the resistance and strength of a magnet.
Strongest Permanent Magnet Neodymium
Neodymium magnets are the strongest magnets, with 64% to 68% iron content. For this reason, these are highly vulnerable to corrosion in a damp environment. Modern techniques prefer the use of dysprosium to neo alloy for better resistance to deterioration. Moreover, it will increase magnetic properties in neodymium magnet. A triple-layer (nickel, copper, nickel) is a typical coating.
Corrosion Mechanism
A dense neodymium magnet is designed through a powdered metal procedure. The high-quality powder can improve the magnetic performance and environmental tolerance of neo magnet. Well-designed, appropriately sized powder grains with limited un-reacted integral elements may result in top-rated magnets.
Remember, magnets designed with the best powder will have un-reacted components that may rust. If you have a poorly designed magnet, it will rust from inside out. Typically, a preventive plating or coating is necessary to avoid corrosion. Adhesion of plating and coating is a major concern. Neo magnets do not have plating or coating to a specific ASM, ASTM, etc.
The coating performance is evaluated using an SST (Salt Fog/Salt Spray Test). It is executed in ASTM B117 accordance.
The coating to resist corrosion, magnet geometry and neo alloy works to increase the operational life of magnets. Salt fog testing can evaluate neo magnets with a layer to avoid corrosion. In this test, neodymium magnets without any plating or coating fail instantly.
Salt Fog Testing
Salt fog testing is helpful to evaluate coating or plating performance. This test is not suitable to evaluate the quality of the neodymium magnet. Several humidity tests and elevated temperature may be appropriate to find the quality of neodymium magnet alloy. The efficient volume loss of gauged neo magnet proves helpful to check the quality of neo magnet.
It is beneficial to evaluate effective mass after and before the atmosphere testing exposure. The lost volume represents the portion of neodymium alloy that reacted during the testing and corrode. Finally, the oxidation or rust is detached from the given sample, and the resulting difference in mass between the early states is calculated.
Safety for Commercial Uses
Remember, the application of perfect rust-inhibiting coating is necessary. For commercial application, manufacturers often encapsulate neo magnet. Undoubtedly, iron content in magnets can impact their corrosion resistance. Unfortunately, you will not get any magnet immune from corrosion. You have to work in a controlled environment with neodymium magnets to decrease the chances of corrosion.