Research On Surface Modification Of Fe-Si-Cr Magnetic Powder Cores

As an important part of electronic devices,metallic magnetic cores are widely used in industrial automation,transportation system,power supply system,electronic information products,environmental pollution control and many other fields.With the development of electronic technology,the higher requests for metallic magnetic cores are put forward such as the higher effective permeability,resistivity as well as saturation induction density and the lower coercive force,core loss,as well as magnetocrystalline anisotropy.For the reason of Fe-Si-Cr magnetic powder cores with excellent DC-bias,good plasticity,low core loss in high frequency,strong ageing resistance and high permeability,the magnetic powder cores made of Fe-Si-Cr have wide application fields.This paper has mainly studied the influence of insulation coating,pressing and annealing on the properties of Fe-Si-Cr magnetic powder cores.Firstly,we explored the effect of phosphate treatment on the properties of Fe-Si-Cr magnetic powder cores.The result shows that with the increase of the concentration of phosphoric acid,the loss of magnetic power cores firstly decreases and then increases.Fe-Si-Cr has the lowest power loss when the concentration of phosphoric acid is 1.5wt%.If we increase the concentration of phosphoric acid,the cut-off frequency and DC-superposition will increase but the density,permeability,saturation magnetization and quality factor will decrease.The increase of the phosphating temperature will reduce the density,core loss,permeability,saturation magnetization and quality factor but improve the cut-off frequency and DC-bias of Fe-Si-Cr magnetic core.The core loss is the lowest when phosphating time is one hour.Increasing phosphating time will reduce the density,permeability,saturation magnetization and quality factor but improve its cut-off frequency and DC-bias.Secondly,we used SiO₂ to coat Fe-Si-Cr magnetic powder and found that increasing SiO₂ content could improve the resistivity,cut-off frequency and DC-bias but decrease the density,permeability,saturation magnetization and quality factor of Fe-Si-Cr magnetic powder cores.In addition,if we use SiO₂ to coat Fe-Si-Cr magnetic powder after the phosphorization of it,the power loss characteristics,cut-off frequency and DC-bias of the powder cores would be better when compared with those samples which are only phosphorized or coated with SiO₂,but the core loss,density,permeability,saturation magnetization and quality factor would be worse.Then,the effect of compaction pressure on the performance of Fe-Si-Cr magnetic powder cores was discussed in this paper.The result shows that the powder core has the lowest core loss when the compaction pressure is 7MPa and the permeability,quality factor,saturation magnetization will be improved by increasing the compaction pressure,which at the same time leads to the reduction of the DC-bias and cut-off frequency.In the end,the influence of annealing temperature and annealing time on the performance of Fe-Si-Cr magnetic core was discussed.The experiment shows that,the magnetic core has the lowest core loss when the annealing temperature is 500?.The raise of the annealing temperature can improve the magnetic permeability and the saturation magnetization but reduce the DC-bias,the cut-off frequency and the constant band of permeability's frequency.In the experiment,the annealing time of the sample was one to four hours and it was found that prolonging the annealing time is beneficial to reduce the core loss of the magnetic core and increase its magnetic properties.However,if the annealing time is long enough,the improvement of magnetic properties will not be obvious.