Large batch recycling of waste Nd-Fe-B magnets to manufacture sintered magnets with improved magnetic properties

The waste Nd-Fe-B sintered magnets up to 500 kg per batch were recycled to manufacture anisotropic sintered magnets by combination of hydrogen decrepitation (HD) and alloying technique. Magnetic properties and thermal stability of both the waste magnets and recycled magnets were investigated. The recycled magnet exhibits magnetic properties with remanence (Br) of 12.38 kGs, coercivity (Hci) of 24.89 kOe, and maximum energy product [(BH)max] of 36.51 MGOe, respectively, which restores 99.20% of Br, 105.65% of Hci, and 98.65% of (BH)max of the waste magnets, respectively. The volume fraction of Nd-rich phase in the recycled magnets is about 10.1 vol.%, which is bigger than that of the waste magnets due to the additive of Nd3PrFe14B alloy containing more rare earth. The remanence temperature coefficient (α) and coercivity temperature coefficient (β) of the recycled magnets are −0.1155%/K and −0.5099%/K in the range of 288-423 K, respectively, which are comparative to those of the waste magnets.