Research On The Magnetic Field Induced Formation And Properties Of Soft Magnetic Powder Cores With Fe Based Alloy

Soft magnetic powder core with iron based alloys is one of soft magnetic devices highly valuable in the field of electronic components due to its good soft magnetic properties, high strength, high corrosion resistance and high thermal stability, etc. In this thesis, the effects of process parameters and ordering of powders on magnetic properties such as the permeability and the quality factor of Fe₇₈Si₉B₁₃ amorphous powder cores and composite powder cores were investigated systematically by using the amorphous powders prepared by crushing Fe₇₈Si₉B₁₃ amorphous ribbons and the reduced iron powders as the raw materials and a magnetic field as an external field to induce the structure ordering.Effects of the ratio of particle size, the concentration of the passivator, the insulating agent content, the forming pressure and the annealing temperature on the magnetic properties of Fe₇₈Si₉B₁₃ amorphous powder cores were firstly investigated. The smaller the particle size is, the lower the effective magnetic permeability is and the higher the quality factor is. With the increase of phosphoric acid mass fraction（between 0.5% 1.5%） and insulation agent mass fraction（between 0.5% 2.0%）,the effective permeability of the magnetic cores decreases and the quality factor increases. With the increase of molding pressure（between 1000 MPa 1300MPa）, the density, the effective permeability and the quality factor of the magnetic cores all increase. With the increase of heat treatment temperature（between573K⁷23K）, the effective permeability and the quality factor of the magnetic cores increase first and then decrease.The effect of the structural orientation on soft magnetic properties of Fe₇₈Si₉B₁₃ amorphous cores was then investigated. It appears that the properties of Fe₇₈Si₉B₁₃ amorphous cores depend strongly on their shape anisotropy of magnetic powders and the powders parallel to the external magnetic field is beneficial for achieving the excellent performance of the cores. The circular orientation structure of powders is helpful to improve the effective magnetic permeability and the quality factor. Below 100 kHz the effective permeability of the circularly orientated amorphous magnetic powder core increases by 7.5% and 16.6%, and the product of the effective permeability and the quality factor of the circularly orientated amorphous magnetic powder core increases by 9.1% and 21.2% compared to those of the disordered and the radially orientated amorphous magnetic powder cores, respectively.Finally, the effect of the circular orientation of magnetic powders on magnetic properties of the cores composited with Fe₇₈Si₉B₁₃ amorphous and pure iron powder were investigated. The resultsindicate that the density, the effective permeability and the initial permeability of circularly orientated composite powder cores are better than those of non-oriented composite powder cores with the same mixture ratio. On account of the flakes of pure iron powders have been broken, both the degree of orientation of the circularly orientated composite powder cores and the optimization effect of the circular orientation of magnetic powders on magnetic properties of the composite cores weaken gradually as the content of pure iron powder increases.