HEAVY RARE EARTH FREE SINTERED ND-FE-B MAGNETS AND MANUFACTURING PROCESS THEREOF

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The present invention relates to sintered Nd-Fe-B magnets, which are free of any heavy rare earth elements. The present invention further relates to corresponding manufacturing process thereof. The process comprises the steps of : a) providing an alloy sheet made of a Nd-Fe-B magnet composition, wherein Pr and Nd are present in a combined amount of 31 wt.% ≤ Pr and Nd ≤ 34wt.%; B is present in an amount of 0.8 wt.% ≤ B ≤ 1.2 wt%; Al is present in an amount of 0.4 wt.% ≤ Al ≤ 0.8 wt.%; Co is present in an amount of 0.6 wt.% ≤ Co ≤ 1.2 wt.%; Cu is present in an amount of 0.2 wt.% ≤ Cu ≤ 0.5 wt.%; Ga is present in an amount of 0.1 wt.% ≤ Ga ≤ 0.4 wt.%; and wherein the balance element is Fe; b) the alloy sheet is broken into alloy pieces by a decrepitation process; c) an amount of 0.05 to 0.5 wt.% lubricant is added to the alloy powder and then the mixture is milled by a jet mill process until an average particle size D50 of the resulting alloy powder ranges from 2.0 µm to 3.0 µm; d) another amount of 0.03 to 0.2 wt.% lubricant is added to the alloy powder after milling and mixed, then the alloy powder is compressed into compacts while applying an orienting magnetic field of 2.0 to 2.5T; and e) the compacts are sintered in a vacuum furnace, wherein a pressure within the furnace during the sintering step is equal to or less than 5x10-2 Pa.