Effect of Annealing Temperature on Corrosion Resistance of Rapidly Solidified Nd-Fe-B Powders and Their Bonded Magnets

The objective of this work is to investigate the feasibility of improving corrosion resistance of solidified Nd-Fe-B powders and their bonded magnets by optimizing crystallization conditions. Anodic potentiodynamic polarization experiments were carried out for the determination of electrochemical corrosion rate. Measurements of open circuit magnetic flux were performed with a Helmholtz coil and a flux meter to determine the irreversible flux loss after aging at elevated temperature. The average grain sizes of powders were obtained from broadening of the XRD peaks. Thermal magnetic analysis (TMA) of annealed powders was conducted in argon. Magnetic properties of powders were measured by a vibration sample magnetometer (VSM). It is suggested that the improvement of corrosion resistance may be due to a formation of uniform Nd₂Fe₁₄B grain structure.