Investigations Of Magnetic Properties And Microstructure Of The Die-upset Magnets With The High Abundance Rare Earths

We prepared the hot-deformed NdFeB magnets with the high-abundance rare earth by the dual main phase technology, which was proposed by China Iron & Steel Research Institute Group (CISRI). At the final, the dual main phase hot-deformed magnets’magnetic properties were better than that of the magnets which were prepared by the single alloy method. In this way, it can be decreased the cost of preparation of magnets and got the balanced use of rare earth resources. In this thesis, we have done a lot of work about the melt-spinning. And the model of the numerical simulation analysis of the melt-spinning solidification process was established. These principal conclusions of the thesis obtained as follows:(1) In the melt-spinning process, with the Nd content increases in the composition of ingot casting, it will promote the melt crystallization of solidification of nano-crystalline. Under the optimum technological preparation of melt-spinning, the isotropy ribbons will not been the further treatment of crystallization annealing. And the anisotropic HD magnets with the highest magnetic properties are produced from the maximum particle fraction of 200～300μm:Br=14.46kGs, Hcj=15.24kOe, (BH)max=52.4 MGOe.(2) The uniformity of phase distribution was improved significantly after the high temperature diffusion annealing. It is revealed that Ce-rich phase, Nd-rich phase and a-Fe were reduce, the proportion of the main phase raise. The grain size increases with increasing Ce content and the dendrite shape of a-Fe phase has slowly evolved into dot diffuse distribution. The date shows that:each adding 20% more Ce in the amount of rare earth in the ingot composition, the melting point of the ingot reduces nearly 10℃. The content of Ce increases in the ingot, diminishing the melt-spun ribbons" magnetic performance substantially.(3) From the numerical simulation model of the melt-spinning process, we can get that the thickness of the ribbons decreases with the increase of roller-speed. The dates of simulation calculation and actual thickness changes of the ribbons show the tendency of evolutionary processes compatibly. We can explain that we get the performance difference ribbons in one experiment of melt spinning by the model. We can use the temperature field cloud picture to explain the different grain growth of the ribbons which were prepared by the different roll speed. We got the roller speed of 25-30m/s is suit to prepare the high performance ribbons. The results from the test and calculation of are in agreement and the modeling and the simulation method is validated.(4) The hot-deformed magnets, which were prepared by double main phase technology, have reached the standard of the multiple brands of the permanent magnet in the market; The nominal composition of the ingots is (CexNd1-x)30FebalCo4Ga0.2B0.92 The smaller of the value of X, the more addition of the Ce based magnetic powder. Then it is bad for the hot deformation process and the grain orientation. This will deteriorate the performance of the magnets. With the addition increases, the Hcj of the magnets increased first and then decreased and the Br and (BH)max of magnets almost reduced in linear trend. Because there are two different nature of the grain in the magnets, in the process of hot-deforming, the two kinds of grains growing up will restrain each other. The grain size of final state magnet is significantly smaller than that of the single alloy preparation.(5) The data shows that the dual main phase hot-deformed magnets’ magnetic properties were better than that of the magnets which were prepared by the single alloy method. The coercive force significantly higher than that of single alloy prepared magnet. But adopting the double main phase method significantly than the single alloy method means the degree of deterioration of magnet is small.