Kimio Uchida

High performance Nd–Fe–B sintered magnets made by the wet process

The wet process for the fabrication of Nd–Fe–B sintered magnets has been developed on the mass production scale. In this process, mineral oil is used as a solvent to prevent the milled powder and green bodies from oxidation. It is removed before sintering. As a result, the oxygen uptake during storage is less than 0.01 wt %/day. By reducing the oxygen content and the total rare earth (TRE) content in sintered magnets to less than 0.2 and 29.3 wt %, respectively, magnets with (BH)max/iHc greater than 50 MGOe/10 kOe, 45 MGOe/15 kOe, and 32 MGOe/32 kOe were obtained with high reliability. The magnets produced by this wet process also show better corrosion resistance and 20% higher mechanical strength than those made by conventional methods. These characteristics may be explained by a smaller grain size, smaller TRE content, and higher density produced by the wet process.