Why are NdFeB magnets plated with three layers (nickel-copper-nickel)?
The nickel-plated layer has high stability in the air. Due to the strong passivation ability of metallic nickel, a passivation film can be rapidly formed on the surface, which can resist the corrosion of the atmosphere, alkali and certain acids. Nickel electroplating is in an electrolyte composed of nickel salt (called main salt), conductive salt, pH buffer, and wetting agent. The anode is made of metallic nickel, and the cathode is a plated piece. Direct current is applied to the cathode (plated piece). Deposit a uniform, dense nickel coating. Bright nickel is obtained from the bath with brightener, and dark nickel is obtained from the electrolyte without brightener.
The era of NdFeB magnets with a layer of nickel was around 1995. After 2000, it was withdrawn from the stage of history. That is to say, almost all nickel-plated products after 2000 are nickel-copper-nickel. The first three layers are anti-corrosion. If the ability is enough, then two layers or direct copper-nickel plating is not possible because direct copper plating of NdFeB was still a big problem at that time, and it was difficult to ensure the bonding force, because the NdFeB matrix would replace copper in the copper plating solution. , the copper plating layer does not have enough bonding force, and the NdFeB after nickel plating has a good bonding force, and there is no need to worry about the bonding force of nickel plating and copper plating, so it is still necessary to plate a layer of nickel to ensure the NdFeB matrix. The advantages of copper plating are that the coating has fewer defects, no shielding effect on the magnetism, good uniform plating, low corner effect, and the coating has little change in the shape of the workpiece.
Now it has broken through the technical difficulties of direct copper plating of NdFeB components. Direct copper plating followed by nickel plating is the development trend. Such a coating design is more conducive to the achievement of customer needs for thermal demagnetization of NdFeB components. Generally, the harsh thermal demagnetization index of 1.5%-4.0% can be achieved.
Conventional nickel-copper-nickel plating thickness is 12 microns, nickel thickness is 4-5 microns, and copper thickness is 8 microns.
NdFeB magnets can be divided into two types: bonded NdFeB and sintered NdFeB. Bonding is actually injection molding, and sintering is vacuuming and heating at high temperature! NdFeB magnets are by far the strongest permanent magnets. Material grades are N35-N52; various shapes can be processed according to specific requirements: round, square, perforated, magnetic tile, magnetic rod, convex, trapezoidal, etc.; despite these advantages, the surface is easy to rust, so it is usually necessary to Do some protective surface treatment: nickel plating, zinc plating, gold plating, epoxy plating, etc. The applicable ambient temperature of ordinary NdFeB magnets is below 80 degrees, but there are also several types that can withstand high temperatures of 200 degrees. Mainly used in electronics, electrical appliances, packaging, motors, toys, leather goods, automotive machinery, etc.