Effect of grain boundary addition of PrNd and Pr75Al15Cu10 on magnetic and mechanical properties of fine-grained heavy-rare-earth-free sintered Nd-Fe-B magnets
Fine-grained heavy-rare-earth-free sintered NdFeB magnets were prepared by adding 1％(mass fraction)Pr25Nd75 and 2％(mass fraction)Pr75Al15Cu10.Furthermore,addition of 1％(mass fraction)PrNd was utilized by oxygen controling and adding oxygen during the jet-milling process.The average grain size of the magnets was 3.5-4.2 μm.Magnetic and mechanical properties of the investigated magnets were analyzed and compared.The co-ercivity of the magnets with 1％PrNd(mass fraction)addition by oxygen controling was 18.46 kOe and the bending strength was 492 MPa,which was basically the same as the magnets by adding oxygen in coercivity,and 65 MPa higher than the magnets by adding oxygen in bending strength.The coercivity of the magnets with addition of 2％(mass fraction)Pr75Al15Cu10 reached 19.04 kOe,which was 0.58 kOe higher than the magnets with addition of 1％PrNd by oxygen controling.The bending strength of the magnets with addition of 2％(mass fraction)Pr75Al15Cu10 reached 506 MPa,which was 14 MPa higher than the magnets with addition of 1％(mass fraction)PrNd by oxygen controling.The results showed that the oxygen content in the magnets with fine-grained controlled oxygen process was 134 × 10-6 lower than the magnets with oxygen added during the jet-milling process.Pr and Cu elements were congregated the grain boundary via the addition of 2％(mass fraction)Pr75Al15Cu10,which resulted in uniform and continuous distribution of the grain boundary.The optimized grain boundary improved the coercivity of the mag-nets.Meanwhile,the addition of 2％(mass fraction)Pr75Al15Cu10 alloy effectively enhanced the proportion and dis-tribution of the grain boundary phase,which could effectively hinder the propagation and expansion of cracks,there-by improving the bending strength of the magnets.
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