Rare-Earth Fe-B powder coating for improvements in corrosion resistance, flux aging loss, and mechanical strength of bonded magnets

Coating formulations have been investigated for rare-earth Fe-B (RE Fe-B) type melt spun magnetic powders, to provide them with enhanced corrosion and oxidation resistance when exposed to aggressive environments. The coating formulations consist of an epoxy binder-based system and specialty additives. Results with two RE Fe-B powder types using these new formulations show between 19°C and 26°C enhancements in their operating temperatures for comparable flux aging loss, but now with better magnetic property retention at high temperatures and better adhesion between powder and organic coating. Optimal flux aging loss was found to result after curing the compacts within 180°C to 200°C for 30 to 60 min at a compaction pressure of 690 MPa (7 tons cm^-2), although higher pressures resulted in more severe magnetic losses but higher bending strengths. The new formulations yield magnets whose magnetic properties are less affected by curing at these typical high temperatures.