| Magnetic powder cores is a kind of soft magnetic composites, which is manufactured by the conventional PM process, it can be described as ferromagnetic powder particles coated by an electrical insulating film. Thanks to the good insulation between magnetic particles, the resistivity of particles is increased and the core loss is reduced greatly, and thereby ensures the steady permeability in wide frequency. The above is the best advantage of powder cores. Its special soft magnetic properties bring it many advantages that are hardly comparable by other magnetic materials. It was widely applied in many fields such as telecommunications, radar, television, power, solar power, etc.The study of thispaper is based on powder metallurgy production process, and consult a traditional the industrial production process of magnetic powder core. The paper systematically studied the effect of powder pattern, grain size, insulation coating, pressing process and annealing on properties of amorphous Fe7gSi9Bj3magnetic powder core and water atomization Fe73.5Cu1Nb3Si15.5B7nanocrystalline magnetic powder core, and the magnetic powder core with high performance were prepared. Mpp magnetic powder core with high performance were prepared by improved process. On this basis, we investigated the effect of magnetic annealing on properties of the three kinds of magnetic powder core. The main conclusions are listed as following:(1) The magnetic performance of amorphous Fe78Si9B13magnetic powder core was closed to powder pattern. Powders broken by mechanical mill were flake, mostly polygon and strip, and there were a lot of sharp corners. But the powders broken by airflow mill were round flake mostly, and the edges were smooth. Airflow mill was more suitable for insulation coating and the performance of powder core was better. The magnetic powder core with bigger particle size had a higher permeability and loss. The proper particle ratio could effectively decrease loss of magnetic powder core and promote the frequency characteristic. It was found that the optimum particle ratio of Fe78Si9B13magnetic powder is70%of75～100μm,10%of61～75μm,20%of45～61μm.(2) Magnetic powder had a layer of phosphate coating after passivation. The addition of passivant could improve the frequency characteristic, reduce the core loss and increase the quality factor of amorphous magnetic powder cores.(3) Organic and inorganic insulation coating method was suitable for preparation of high performance magnetic powder core. Accession of insulating medium could increase the resistivity of magnetic powder core, reduce eddy current loss and improve the quality factor, over insulation would reduce magnetic permeability. Increasing forming pressure could increase radial crushing strength (RCS), density and permeability of amorphous Fe78Si9B13magnetic powder core and reduce loss and coercivity, but over pressure would injury mould. Increasing annealing temperature could effectively increase permeability and reduce core loss and coercivity, but over-annealing could deterioration magnetic properties.(4) Compared to ordinary annealing, both longitudinal and transverse magnetic field annealing could increase permeability and qality factor and decrease loss and coercivity of amorphous Fe78Si9B13magnetic powder core. The magnetic powder core had a better magnetic property after annealing in longitudinal magnetic field. The optimum process parameters are listed as following:insulation content is4%, forming pressure is1800MPa, annealing temperature is350℃and annealing in longitudinal field1h. The corresponding magnetic properties of magnetic magnetic core show:at1000kHz,3mT, the magnetic permeability is50.6, loss is52.31kW·m-3.(5) The powder pattern of Fe73.5Cu1Nb3Si15.5B7nanocrystalline could be improved by ball milling technology. With milling2hours magnetic properties of powder core were best enhanced. It was found that the optimum particle ratio of Fe73.5Cu1Nb3Si15.5B7nanocrystalline magnetic powder core is10%of154～224μm,10%of75～154μm,10%of45～75μm,70%of30.8～45μm.(6) The core loss of nanocrystalline magnetic powder core was decreased with increasing insulation content, but over high of insulation content would decrease the permeability of nanocrystalline magnetic powder core. Increasing forming pressure could effectively increase permeability and density and decrease core loss and coercivity of nanocrystalline magnetic powder core, but over pressure would reduce magnetic property due to plenty of dislocation in nanocrystalline. Increasing annealing temperature could effectively promote magnetic permeability and quality factor, decrease core loss and coercivity of nanocrystalline magnetic powder core because of better release of innerstress. But over-annealing could destroy inner structure of nanocrystalline magnetic powder core and make the crystal grain growth, and then decreased magnetic property by increasing the magnetic anisotropy.(7) It was found the optimum process parameters of Fe73.5CuiNb3Si15.5B7nanocrystalline magnetic powder core are:insulation content is3%, forming pressure is1800MPa, annealing temperature is500℃, annealing time is1h. The corresponding magnetic properties of magnetic magnetic core show:at1000kHz,20A·m-1, the magnetic permeability is42.5, loss is12.25kW·m-3.(8) The improved fabrication process of Fe17Ni81Mo2magnetic powder core could effectively increase permeability and quality factor, and decrease core loss. Meanwhile, the work efficiency was enhanced, the energy sources was saved. Annealing process could remove innerstress and enhance magnetic properties. For Fe17Ni81Mo2magnetic powder core, the best annealing condition was650℃×1h.(9) The Fe17Ni81Mo2magnetic powder core with bigger particle size displayed a high permeability but low quality factor. The proper particle ratio could improve the magnetic properties. It was found that the optimum particle ratio of Fe17Ni81Mo2magnetic powder is80%of above75μm,20%of61～75μm.(10) The results of researching on magnetic annealing of Fe17Ni81Mo2magnetic powder core showed:the effect of magnetic annealing on permeability was little. Both longitudinal and transverse magnetic annealing could decrease core loss and increase quality factor. Compared with transverse magnetic annealing, Fe17Ni81Mo2magnetic powder core had a better comprehensive magnetic property after annealing in longitudinal magnetic field. And the corresponding magnetic properties of magnetic magnetic core show:at3000kHz,20A·m-1, the magnetic permeability is59.2,loss is28.69kW·m-3. |
PDF Full Text Request