ABSTRACT
Soft magnetic powder cores have a wide range of applications in various inductor devices, power transformers and other fields. In this dissertation, the current research status of magnetic powder cores and its applications in the world were summarized. Fe and FeSiB based soft magnetic cores were prepared. The effects of processing on the magnetic properties were investigated in detail.
After completion of the market research for different soft magnetic materials companies,some representative corporations were selected to analyze the type, performance, applications,and development of their magnetic core products. Especially, based on the author's engineering practical experience in Guangzhou Deloop Electronic Device Co. Ltd, the preparation process of soft magnetic powder cores and production process of electronic devices were introduced. The current development in soft magnetic powder cores industry was discussed. In addition, the faced problems and the future trends of domestic powder cores industry were analyzed.
On the basis of the investigations on the research and development of soft magnetic cores, iron powder cores and iron-based amorphous powder cores (Fe78Si9B13) were fabricated by powder metallurgy method. X-ray diffractometer (XRD), differential Scanning Calorimeter (DSC), scanning electronic microscopy (SEM), vibrating sample magnetometer (VSM), AC and DC soft magnetometers and other devices were employed to characterize the micro-structure and properties of the samples. The effects of pre-treatment for raw powders and core preparation parameters on the permeability, power loss, coercivity, quality factor of the soft magnetic cores were investigated. The main research scope and the conclusions are as follows:
(1) Magnetic powder cores prepared by different processes have the constant permeability between the frequencies of 1kHz and 100kHz. The soft magnetic properties are influenced by powder type, powder size, kind and quantity of coating agent, compaction pressure and annealing temperature.
(2) For iron powder cores synthesis, adding 2wt.% epoxy resin E-12 as insulating binder can lead to excellent magnetic properties. For the amorphous powder cores synthesis,increased magnetic permeability and reduced power loss can be obtained by employing SH-201 high temperature silicone resin as the binder, and passivation treatment in the phosphate-acetone solution to form a uniform and dense passive film on the powders.
(3) Different types of powders require different compaction pressures for core consolidation. Generally, a large pressure is necessary. Iron powders are relatively soft and easy deformed. The optimized molding pressure is 400MPa. For amorphous powders, a compaction pressure of 1200MPa can lead to a density up to 5.42g/cm3. The coercivity can reach the lowest value of 73.7A/m.
(4) The cores prepared using the SH-201 high temperature resistant silicone resin as the binder can be heat treated at relatively high temperatures. It was found that heat treatment can increase permeability and reduce core loss. Reasonably set heat treatment temperature for the amorphous powder cores can lead to high permeability, large quality factor, low coercivity and low core loss.
(5) Through gradual optimization of the process conditions, the best preparation process conditions for the iron powder core include using 2wt.% epoxy E-12 as binder, particle size 50μm-75μm, and molding pressure of 400MPa. The initial permeability can reach 83.1 under 50mT/50kHz. The effective permeability reaches approximately 105, and unit mass loss is 75w/kg. The optimal preparation conditions for amorphous FeSiB powder cores include passivation in 2wt.% phosphoric acid acetone solution, use of 2wt.% organic SH-201 silicone resin as binder, compaction pressure of 1200MPa, heat treatment at 400℃ for 30min. The soft core exhibits an optimum permeability of 26, minimum core loss of 11.1W/kg at 50mT/50kHz.
Key words: iron powder core, Fe-based amorphous powder core, insulation coating,annealing, soft magnetic properties
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