Effect of the First Tempering on Microstructure and Properties of Sintered Nd-Fe-B Magnets

The effect of tempering process on the microstructure and magnetic properties of sintered Nd-Fe-B magnets were investigated.It was manifested that when the tempering temperature was below 910℃, the Nd-rich phase on grain boundary gathered and a wide band of the Nd-rich phase formed, the volume fraction of matrix phase was small and so the magnetic properties of the magnets were low.When the temperature was above 930℃, the grain size became coarse, the grain boundary area became smaller, the band of the Nd-rich phase on grain boundary became wider and the magnetic properties of the magnets were deteriorated.When the temperature is between 910℃ and 930℃, the grain size was inclined to be uniform, the content of clustered Nd-rich phase reduced, the magnetic properties of magnets were optimized.So the proper temperature for the first tempering of Nd30Dy3.5Al0.2B1 alloy shall be from 910℃ to 930℃.