Effect of Phosphate Treatment on Corrosion Resistance of Nd-Fe-B Anisotropic Magnetic Powder

Anisotropic Nd-Fe-B hydrogenation disproportionation desorption recombination (HDDR) powder with a high corrosion resistance was prepared by phosphoric acid treatment. The treated samples baked at temperatures higher than 250°C exhibited a high corrosion resistance; the change ratio of the coercivity (ΔH
cj
) before and after the anticorrosion test was within 5%. Microstructural observations indicated that a uniform layer of phosphate with a small amount of Nd oxide could be formed at a high baking temperature.