The Study Of Preparation And Coercivity Enhancement Of Co-based Permanent Magnets(Co-Zr,Co-Y)

The development of rare earth-free or high abundance rare earth permanent magnets?with high concentrated Y,La or Ce?has attracted the extensive attention due to the rapid consumption of heavy rare earth resources and the serious environmental pollution caused by their exploitation.Co-Zr and Co-Y based permanent magnetic alloy is representative alloys.However,the coercive force of a pure binary Co-Zr permanent magnet alloy is low,and further enhancement of the coercivity is the key for the practical application of the Co-Zr-based permanent magnetic alloy.In this paper,the less expensive high-abundance rare earth elements La and Y were used to replace the Zr of Co-Zr-based alloys.The Co-Zr-La and Co-Zr-Y series permanent magnets were prepared by ball milling,and the evolution of its magnetic properties and physical mechanisms were studied in detail.The magnetic properties of Co-Y permanent magnetic alloys were compared between the two cases using YH₂ or pure metal Y as the element sources in terms of the results of Co-Zr-Y series permanent magnetic alloys.The permanent magnetic properties of Co-Y permanent magnets were significantly improved by introducing the highly active element Ca.The main experimental results are as follows:The Co₈₀Zr₂₀ permanent magnet alloy was prepared by ball milling followed by annealing at different temperatures?550?,600?,650?,and 700??.It was found that the coercive force reached a maximum value of 95 Oe at the annealing temperature of 600°C.The Co₈₀Zr_20-xLa_x?x=1,2,3,4,5?series and Co₈₀Zr_20-xY_x?x=0,2,4,6?series permanent magnets alloy were prepared with the substitute elements of La and Y respectively.The results show that the annealed sample with 4%La content has the maximum coercive force of 994 Oe at 600?,one order higher than the Co₈₀Zr₂₀ alloy without addition of elements.And in the Co₈₀Zr_20-xY_x?x=0,2,4,6?series,the sample with 4%Y annealed at 600°C has the maximum coercive force of 1558 Oe with the remanence of only 3.94 kG.The coercive force of Co₈₀Zr₁₆Y₄ sample annealing at 700°C is 1483 Oe and the remanence increased to 6.13 kG,which is 2.19 kG higher than the value at 600°C.The phase analyses show that the formation of Co₁₁Zr₂ hard magnetic phase was promoted by La and Y addition.Based on the results of Y additions in Co₈₀Zr_20-xY_x permanent magnet alloys,Co-Y permanent magnetic alloy was studied.Co₈₀Y₂₀ and Co₈₀?YH₂?₂₀ permanent magnetic alloy were prepared by ball milling accompanied with the annealing within the temperature range from 550°C to 750°C.The results show that the coercive force of Co₈₀?YH₂?₂₀ permanent magnet is about 1045 Oe,which is 416 Oe higher than the value of 629 Oe for Co₈₀Y₂₀permanent magnet.XRD analyses indicate that the Y element,decomposed fromYH₂ during ball milling and annealing,is more active to form the YCo₅ hard magnetic phase.On the other hand,the highly reducing Ca element was added to reduce CoO and Y₂O₃.The highest coercivity of 8643 Oe was achieved at an annealing temperature of 750 ^oC?Limited temperature of experimental facility?.It was deduced that the reduced Y and Co is favorable to form the hard magnetic phase YCo₅,enhancing the coercivity.