| Fe Si Al magnetic cores can be widely used in the electrical motors with low prices and excellent soft magnetic properties, which include switching electrical supply technologies, filters, chokes and other electronic components. However, Fe Si Al magnetic cores with relatively high total core loss at high frequencies which limited its applications in the advanced technologies. Lots of factors have a great effect on the performance of Fe Si Al magnetic cores. In general, those factors are classified into four main categories:powder microstructures, insulating coatings, compaction conditions and annealing treatment. We explored powder morphologies and obtained the best ratio of powder with different sizes in order to solve the problems of Fe Si Al magnetic cores and reduced total core losses at high frequencies. We also researched the influence of binders on the performance of Fe Si Al magnetic cores on the basis of the best ratio of different sizes of powder. Besdie, it intended to find suitable compaction conditions and annealing treatment to prepare Fe Si Al magnetic cores with relatively high permeability and quality factor at high frequencies. We used scanning electron microscopy, X-ray diffraction, Soft AC measuring instrument, PPMS to analyze the properties of Fe Si Al magnetic cores in this paper. Furthermore, it explored mechanisms which influence the performance of Fe Si Al magnetic cores.We prepared Fe Si Al magnetic cores with different morphologies of flat shape and flocculent. It discovered that magnetic cores which prepared with flat shape of powder showed good soft magnetic properties. Then we carried out experiments with 33.3%, 50%, 66.7%, 75% and 100% of powder with flat shape. It was found that with increasing flat shape powder of Fe Si Al magnetic cores, the core losses decreased and permeability increased.It was chosen flat shape powder with mesh numbers 120, 200, 300 and 400 to prepared Fe Si Al magnetic cores, We found that with increasing particle size, the core losses and permeability of Fe Si Al magnetic cores increased. The magnetic cores showed a core loss of 80W/kg, the permeability value is 42.4 and the quality factor is 8.7 at 65 k Hz for Bm=50m T when were annealed at 500℃ for 0.5h in vacaum atmosphere.Powder with sizes of mesh numbers 120 and 200 were mixed to prepared Fe Si Al magnetic cores. It was found that with 33.3% of 120 mesh and 66.7% of 200 mesh exhibited the best performance. Then the particle size of 300 mesh powder were added in the mixture of mesh numbers 120 and 200 with the percentage of 33.3% and 66.7%. It showed that the core losses increased and permeability decreased compared with previously experiments.It has a great influence on the properties of sample of binders. We used silicone resin, sodium silicate, DC-805 high temperature resistant silicone resin as binders to prepared magnetic cores. It exhibited that DC-805 high temperature resistant silicone showed the best soft magnetic properties among binders in the experiments. With increasing the content of DC-805, Fe Si Al magnetic cores with lower core losses, higher quality factor and lower permeability. It obtained highest quality factor when the content of the binder is 7%.We investigated the effect of compaction pressure, dwelling time and rate of pressure rised on the properties of Fe Si Al magnetic power cores. The permeability of cores increased with increasing compaction pressure and decreased when compaction pressure exceed 1200 MPa. Furthermore, the change of core losses in contrast with permeability. It exhibited the highest permeability and lowest core losses under compaction pressure of 1200 MPa. It discovered that dwelling time has no great influence on the magnetic properties of cores.Annealing is an effective way to decreased core losses and improved permeability of Fe Si Al magnetic cores. We investigated annealing temperature on the performance of cores in this thesis. The samples were annealed at 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ and 800℃ for 0.5h. We discovered that with increasing annealing temperature, the core losses decreased and permeability increased. The magnetic cores showed a lowest core loss of 14.6W/kg, the highest permeability value of 90 and the highest quality factor of 65 at 65 k Hz for Bm=50m T when were annealed at 700℃ for 0.5h in vacaum atmosphere. It was also found that with the testing temperature increased, the magnetic permeability of cores could be decreased but with a smaller changes. It indicated that the cores has a constant magnetic permeability. |
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