Evaluation of sintered and reground Nd-Fe-B alloys with Co, Dy and Al substitutions for use in bonded magnets

Crushing sintered Nd‐Fe‐B into coarse powders quickly destroys their coercivity and alignability in a magnetic field, making them useless for bonded magnets. But a double anneal of 890 °C/1 h plus 570 °C/1 h can largely restore these properties for particles ≳200 μm. Alloys modified with two or more of Co, Dy, and Al additions suffer much lower Hci and Hk losses during grinding. They also respond favorably to annealing, but less than the ternary alloy. Sintered magnets of four compositions were prepared in many size fractions between ∼50 and 1600 μm and demagnetization curves measured as‐crushed, after single and double anneals. Powders of alloys (Nd0.88Dy0.12)(Fe0.8−xCo0.12B0.08 Alx)5.5, where x=0.012 and 0.036, retain Hci values above 10 kOe down to ∼200 μm and could be quite useful in bonded magnet fabrication. This paper reports detailed results for two selected compositions: the six‐component alloy with x=0.012 and ternary Nd‐Fe‐B.