Study On Microstructures And Magnetic Properties Of Y-substituted Rare-earth Permanent Magnets

To alleviate unbalanced consumption of rare earth resources,high-abundance rare-earth is applied to Nd-Fe-B permanent magnet.The early research on high-abundance rare-earth permanent magnetic materials mainly focused on the R₂Fe₁₄B containing La and Ce,which has poor phase structure stability and is difficult to control microstructures.Because in the R₂Fe₁₄B phase containing high-abundance elements Y,La and Ce,Y₂Fe₁₄B has the advantages of the highest integrated magnetic properties and stable phase structure,the Y-substitution R₂Fe₁₄B permanent magnetic materials are gradually becoming a research hotspot.On the one hand,due to the strong magnetic dilution effect of Y concentrating on the main phase,it is necessary to optimize the element distribution of Y-substitution R₂Fe₁₄B permanent magnets.In this paper,the distribution of high-abundance elements in the magnets was regulated by the synergistic effect of Y/Ce,and the Nd-Fe-B permanent magnet with high Y substitution were prepared.On the other hand,because Y₂Fe₁₄B possesses the high temperature stability of coercivity,preparing high temperature stability of Y-substitution rare earth magnets is one of the important research direction.In this paper,Dy element distribution on the surface of the grain of the Y-substitution magnet was regulated by using double alloy method and grain boundary diffusion,and high temperature stability of low heavy-rare-earth containing Y-substitution R₂Fe₁₄B permanent magnets were developed.Main research contents and results are as follows:（1）Taking advantage of the core-shell structure of Y element in the main phase and Ce element entering in grain boundary,the distribution of high-abundance elements in the（PrNd）-（YCe）-Fe-B magnets were adjusted,and the correlation among the microstructure,element distribution and magnetic properties of the（PrNd）-（YCe）-Fe-B magnets were analyzed under different Y/Ce ratios.With the decrease of Y/Ce ratio,the core-shell structure of Y element can still be maintained in the magnets.Meanwhile,the high-abundance elements in the main phase grain decrease,which weakens the magnetic dilution effect and effectively improves the coercivity of the magnets.On this basis,the element distribution optimization model of Y-substitution R₂Fe₁₄B permanent magnets is established.（2）The effects of adding DyH_xto Y-substitution R₂Fe₁₄B permanent magnets by double alloy method and grain boundary diffusion method on Dy element distribution,microstructure and magnetic properties were systematically studied,and the correlation between Dy element distribution and temperature stability was analyzed.By enhancing the magnetic hardness of grain surface,the improvement efficiency of Dy element to coercivity in double alloy method is about2.8 k Oe/wt%.Compared with the double alloy method,the Dy-rich shell formed by diffusion is thinner,the Dy element concentration in the shell is higher,and the grain boundary structure is better.Therefore,in the grain boundary diffusion method,the improvement efficiency of Dy element on coercivity reaches the highest to 13.42 k Oe/wt%.The coercivity temperature coefficient of the magnets prepared by grain boundary diffusion and double alloy are obviously better than that of ordinary commercial magnets without Y.In addition,due to the"self-compensation effect"of Dy element gradient distribution in the grain boundary diffusion magnet,the irreversible flux loss of the magnet prepared by grain boundary diffusion is lower than that of the magnet prepared double alloys.