To resist serious electrochemical corrosion, various anti-corrosion surface treatment technologies are utilized to isolate the base of sintered Neodymium magnets and environmental substances. Magnet base itself must be strong enough even magnets have already coated. Both weight increase method and weight loss method can be used to test corrosion rate of the magnet. Then the concept and products of low weight loss Neodymium magnets emerged. Low weight loss Neodymium magnets are essentially high corrosion resistance Neodymium magnets. From the viewpoint of material science, poor corrosion resistance of Neodymium magnets is stem from the below reasons:
- Material structure. Sintered Neodymium magnets have multi-phase structure, then each phase certainly has different antioxidant ability. Nd-rich phase and B-rich phase will be firstly oxidized and directly cause intergranular corrosion.
- Impurities, especially chloride, will accelerate the oxidation process.
- Working conditions.
Source power of this intergranular corrosion originates from the potential difference between Nd2Fe14B main phase, Nd-rich phase, and B-rich phase, therefore, minimize potential difference between relevant grain boundary phases can decrease intergranular corrosion to some extent.
Along with the deepening research regard to the coercivity mechanism of sintered Neodymium magnets, dual-alloy technology, dual-main phase technology, and grain boundary diffusion technology has allowed manufacturers adding new phase, such as sub-alloy, nano-metal/alloy, and micro-size oxide during powder making or molding process.