1. Fundamental reason: The neodymium element in the Sintered NdFeB block magnet material is very chemically active, and its standard electrode potential is EO (Nd3+/Nd)=-2.431 V. The Sintered NdFeB block magnet itself has a multi-phase structure, in which The Nd-rich phase is the most chemically active, and there is a large electrochemical potential difference between the phases within the material. In an electrochemical environment, electrochemical corrosion is prone to occur. The grain boundary phase (Nd-rich phase) as the anode will bear a larger corrosion current, and the main phase (Nd2Fe14B phase) as the cathode will bear a smaller current, eventually forming The corrosion characteristics of the small anode and cathode accelerate the corrosion of the intergranular phase, eventually leading to the destruction of the entire magnet due to corrosion.

2. The structure of the Sintered NdFeB block magnet itself: The density of the sintered NdFeB magnet produced by the powder metallurgy method is low, the porosity inside the magnet is high, and a dense oxide film cannot be formed on the surface of the magnet. Once oxidation occurs, the inside of the magnet will The pores will become fast corrosion channels for the rapid diffusion of corrosive media such as oxygen, which can cause a chain reaction inside the magnet, causing oxidation corrosion of the magnet itself.

3. Other added elements: Other added elements in NdFeB materials may have adverse effects on corrosion resistance. For example, although some commonly used added elements such as cobalt and copper can improve the magnetic properties or thermal stability of the material, they may also have a negative impact on the corrosion resistance of the material.