Preparation And Magnetic Properties Of Fe-Si Alloy Powder Cores

Fe-6.5%Si alloy powder cores have been widely used in high-frequency circuits owing to their high saturation magnetic flux density,excellent DC-Bias characteristics and relatively low cost. In thispaper,the effects of particle size,surface insulation of powder, density,heat treatment on the magnetic performances, i.e. effective magnetic permeability, DC-bias characteristic and core loss,have been investigated. Furthermore, a choke in switching power supplies with powder cores was designed by the method of area product(AP).The results show that gas-atomized Fe-6.5%Si alloy powderspossess a relatively low loss and better DC-Bias characteristics.With decreasing particle size,permeability of the core is correspondingly reducing; quality factor is significantly increasing;smaller particle size can improve DC performance.With the increasing of the amount of coating liquid,permeability of the cores is correspondingly reduceing;under DC-Bias field,percent of permeability is increasing, however, the core loss first decreases and then increases. The sample corresponging to powders treated with 1.0 wt% of solution possesses a stable permeability of 78, a core loss of 170 m W/cm3 at frequency of 50 k Hz under induction of 500 Gs, and 55% permeability at 100 Oe of DC-bias field.Molding pressure within 1287Mpa~1931Mpa can increase the effective permeability of the core and reduce the loss;but if the pressure is too large,the insulating layer causes destruction of the particle surface,even a deformed spherical particles,so that the performance of the core deteriorates.With the increasing annealing temperature,effective permeability first increases and then decreases,and when the annealing temperature exceeds the critical value,the frequency characteristics of the effective permeability is worsening.with the increasing of the heat treatment temperature,DC-bias characteristics worse before getting better again worse.When the heat treatment temperature is 500?,the core has the best DC bias characterisitics.The core loss decreases and then increases,and the opposite variation of Q value;when the heat treatment is 500?,the core loss is minimized.It is found that a composite insulating layers can be formed on the particle surfance through multi-coating process. As a result, the magnetic performance of the Fe-Si powder cores can be greatly improved, i.e., the effective permeability maintains at ~57, core loss is 186.44 m W/mm3 at 50 k Hz/500 Gs, and 73.57 % permeability at 10 m T of DC-bias field.Finally, the specifications of candidate powder cores and coil winding parameters were obatined for the detailed applications.