Neodymium Magnet - History and Manufacturing Techniques

History and Manufacturing Techniques

In 1982, General Motors (GM) and Sumitomo Special Metals discovered the Nd₂Fe₁₄B compound. The effort was principally driven by the high material cost of the SmCo permanent magnets, which had been developed earlier. GM focused on the development of melt-spun nanocrystalline Nd₂Fe₁₄B magnets, while Sumitomo developed full-density sintered Nd₂Fe₁₄B magnets. GM commercialized its inventions of isotropic Neo powder, bonded Neo magnets, and the related production processes by founding Magnequench in 1986. Magnequench, now part of the Neo Materials Technology, Inc., supplies melt-spun Nd₂Fe₁₄B powder to bonded magnet manufacturers. The Sumitomo facility has become part of the Hitachi Corporation and currently manufactures and licenses other companies to produce sintered Nd₂Fe₁₄B magnets. Hitachi holds more than 600 patents covering Neodymium magnets.

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.