How to deal with the electroplating problem of neodymium magnets?

NdFeB magnetic materials are made by mixing, pressing and sintering ultrafine powders of praseodymium, neodymium, iron and boron after sieving. According to the needs of the product, it can be machined into different shapes. Since NdFeB materials have relatively vivid chemical properties and are easily oxidized, their finished products need to be electroplated and coated. However, the quality of electroplating coating is closely related to its pretreatment. This kind of pre-treatment process generally includes degreasing, rust removal, activation and other processes.If one part of this pre-treatment process is not cleanly handled, it will bring latent defects to the final electroplated product, causing problems such as blistering and peeling of the electroplated layer. Defective magnetic data parts will lose market value and be scrapped. If magnetic data parts with concealed defects are applied to the equipment, the whole machine may be defective due to such unqualified parts being put on the machine. It even has serious consequences.NdFeB magnetic materials are not as dense as forged metal materials. It is a microporous material. Its porosity brings many difficulties and troubles to the pretreatment of electroplating. In addition to removing the alkaline and acidic substances on the surface of the workpiece and the dirt brought by the processing process, the difficulty is how to remove the dirt in the micropores
Regarding generally low-level low-magnetic materials, the pre-treatment process used for neodymium iron shed magnets in the past is: alkaline degreasing-water washing-acid washing-water washing-surface activation-electroplating. Although this process is simple, it has high requirements for degreasing agents. It requires a special NdFeB degreasing degreasing agent. The formula of this degreasing degreasing agent is complicated and requires a large variety of raw materials. The user’s manufacturing process is very troublesome. Moreover, once the ratio is improper, it will fail, and the practicability will be poor. The electroplating process is to connect the magnet to the cathode of the DC power supply and immerse it in a solution containing cations of the coating material. The cations will migrate to the cathode under the action of an electric field and be transformed into metal atoms to crystallize on the surface of the magnet.Sintered NdFeB commonly used zinc plating and nickel plating, and nickel-copper-nickel composite plating.Zinc is relatively stable in dry air, and a zinc carbonate film is formed in moist air or oxygen-containing water, which can delay the corrosion rate of zinc, but it has better corrosion resistance in acid-base salt solutions, marine atmosphere, and high-temperature and high-humidity air. Poor, passivation treatment can significantly improve the corrosion resistance of the zinc coating. Nickel easily forms a very thin passivation film with oxygen in the air, and has good corrosion resistance to the atmosphere, alkalis and some acids at room temperature. Therefore, nickel plating has become the most common electroplating method for sintered NdFeB. However, nickel is an excellent soft magnetic material, which will form a shield to the magnetism of the substrate. The shielding is especially obvious when the magnet is small or very thin. The corrosion risk of single-layer nickel is relatively high, and multi-layer plating or composite plating can solve this problem well. Copper has a lively chemical nature and is easy to rust, so it is generally not used alone, but as a bottom coating or an intermediate layer to improve the bonding force between the substrate and the surface coating. Click to learn more about electroplating related knowledge (use scenarios of different coatings, corrosion resistance, etc.) Corrosion resistance of different coatings of sintered NdFeB (salt spray test and PTC)3. Electroless plating
Electroless plating is the same as electroplating. It is also through oxidation-reduction reaction. The metal ions in the plating solution are reduced to atoms and adhere to the surface of the magnet. The difference is that there is no current to attract ions and enhance the adhesion of atoms. Therefore, a reducing agent is required to coexist in the plating solution. , The surface of the substrate also needs catalysis. No power supply is the biggest advantage of electroless plating. It can form a coating with uniform thickness on the surface of a magnet with complex shapes. The coating has high hardness, small voids and high chemical stability.
4. Electrophoresis Different from phosphating and electroplating, the surface protective layer formed by electrophoresis, spraying and dipping is organic. Electrophoresis is a phenomenon in which the charged colloidal particles in the conductive dispersion medium move towards the opposite electrode under the action of an external electric field. Electrophoretic coating uses this feature to make the charged organic paint molecules (usually epoxy resin) firmly adsorb on the opposite electrode. The surface of the magnet, the magnet is taken out from the electrophoresis tank and then cured to form a dense protective film.

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