Sintered Nd2Fe14B tends to be vulnerable to corrosion. In particular, corrosion along grain boundaries may cause deterioration of a sintered magnet. This problem is addressed in many commercial products by adding a protective coating. Nickel plating or two-layered copper-nickel plating are the standard methods, although plating with other metals or polymer and lacquer protective coatings is also in use.
There are two principal neodymium magnet manufacturing routes:
The classical powder metallurgy or sintered magnet process
The rapid solidification or bonded magnet process
Sintered Nd-magnets are prepared by the raw materials being melted in a furnace, cast into a mold and cooled to form ingots. The ingots are pulverized and milled to tiny particles. This undergoes a process of liquid-phase sintering whereby the powder is magnetically aligned into dense blocks which are then heat-treated, cut to shape, surface treated and magnetized.