The impurity in the alloy and material structure are poor corrosion resistance causes of Sintered magnesy neodymowe

　　The impurity in the alloy:

　　Contamination that may exist in sintered magnesy neodymowe permanent magnetic alloy mainly has O, H, N, C, Si, Cl and chloride and so on, among which, the most serious corrosion damage is oxygen, chlorine and chloride. Magnet's corrosion is mainly for the oxidation process, and chlorine, chloride and especially sodium chloride pollution will accelerate the oxidation process of the magnesy neodymowe magnet.

　　Material structure:

　　Sintered magnesy neodymowe permanent magnetic alloy has multiphase microstructures, and the oxidation capacity of phases is different, distributed at the grain boundaries of rich Nd phase and the B rich phase easily occurs preferentially oxidation, forming intergranular corrosion.

　　In addition the magnet density is not high, and the oxide is loose, and porosity is large, the magnet surface is difficult to form a protective oxide film, once causing the oxidation, it will lead to a chain reaction, and accelerate oxidation. And because the magnet's main phase volume fraction of magnesy neodymowe phase is generally above ninety percent, When the electrochemical local corrosion cell is formed, it has the anode and cathode characteristics,the corrosion current density of riching in Nd and B phasein grain boundary is high, accelerating the intergranular corrosion and damage.