Surface Treatment of Neodymium Magnets

Neodymium permanent magnets have strong chemical activity and are very easy to be corroded and oxidized, so surface treatment is generally required. Conventional surface treatment methods include nickel plating, zinc plating, etc. Coating with different materials, the corrosion resistance of NdFeB magnets is completely different.

The following lists some conventional surface treatment methods of Neodymium magnets:

Coating chemical symbol Coating thickness (μm) Color PCT/Hast(hours) Neutral salt spray resistance(hours)
Zinc Zn 10-15 Light blue 16 24
Color -Zinc Color-Zn 10-15 Colorful 24 72
Nickel Ni 10-20 Silver 16 4
Double Nickel Double-Ni 15-20 Silver 16 24
Nickel Copper Nickel Ni-Cu-Ni 15-30 Silver 42 48
Electroless Nickel Electroless Ni <1 Silver 24 72
Epoxy Epoxy 10-50 Black 24 300
Zinc-Nickel Zn-Ni 10-20 Colorful 72 720
Nickel-Tin Ni-Sn 10-30 Silver 96 96
Nickel-Gold Ni-Au 10-30 Gold 96 96
Nickel-Silver Ni-Ag 10-30 Silver 48 96

The difference between electroplated nickel and electroless nickel

The principle difference between electroless plating and electroplating is that electroplating requires an external current and anode, while electroless plating relies on the autocatalytic reaction that occurs on the metal surface.

The electroless nickel plating layer is extremely uniform. As long as the plating solution can be soaked and the solute exchange is sufficient, the plating layer will be very uniform and can almost achieve the effect of profiling.

Electroplating cannot coat the full surface of some complex-shaped workpieces, but electroless plating can be used to coat workpieces of any shape. The electroless nickel plating layer with high phosphorus is amorphous, and there is no crystal gap on the surface of the plating layer, while the electroplating layer is a typical crystalline plating layer. Because electroplating has an applied current, the plating speed is much faster than that of electroless plating, and the plating of the same thickness is completed earlier than electroless plating.

The bonding force of electroless plating is generally higher than that of electroplating. Since most of the electroless plating uses food-grade additives and does not use harmful substances such as cyanide, electroless plating is more environmentally friendly than electroplating. Electroless plating currently has only one color of pure nickel-phosphorus alloy on the market, while electroplating can achieve many colors.

Nickel Plating Plating

Nickel plating consists of three layers of nickel, copper and nickel. This type of coating is the most widely used and protects magnets from corrosion in most environments. Nickel-copper-nickel plated magnets can be used in motors, generators, medical equipment, sensors, and more.

NdFeB salt spray test

Salt spray test is an important indicator to detect the corrosion resistance of magnet coating. The graph lists some of the coating salt spray test times. For more information of the salt spray test, please check the article The Salt Spray Test of Neodymium Magnets.

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