Study On Preparation And Properties Of Amorphous FeSiB Magnetic Powder Cores

Metal magnetic powder core is one of soft magnetic materials, which is compressed by magnetic powder mixed with insulation medium, its special properties can't be compared by the other materials. In the 21th century, scientific and technological progress needs high performance electronic devices,which put forward higher requirements for magnetic powder cores. Amorphous Fe78Si9B13 magnetic powder core has high quality factor, low loss in high frequency and low price, Which is hope to be widely used as inductor cores in high frequency.In this experiment, amorphous Fe78Si9B13 strip used as raw materials was broken into amorphous powder by mechanical and airflow mill separately, then compressed into magnetic powder cores applying powder metallurgy technology. Effects of process parameters on the permeability, quality factor, and loss of Fe78Si9B13 magnetic powder cores were investigated by modern analysis techniques including x-ray diffraction analysis(XRD), scanning electron microscopy(SEM) and differential scanning calorimeters (DSC). The main conclusions are listed as follows:Powders broken by mechanical mill are flake, mostly polygon and strip, and there are a lot of sharp corners. But the powders broken by airflow mill are round flake mostly, and the edges are smooth. Airflow mill is the more suitable breaking method for amorphous powders.The magnetic powder core prepared by the airflow mill powder has better performance.Magnetic powder has a layer of phosphate coating after passivation. The addition of passivant can improve the frequency character, reduce the magnetic loss and increase the quality factor of amorphous magnetic powder cores.Insulation treating is the most key procedure for the prepatation of magnetic powder core. Increasing insulating compound content can reduce eddy current loss and promote frequency character. but excessive insulating compound can increase the proportion of non-magnetic material of magnetic powder core, and then reduce the permeability. The best binding admixture content is 3.5%.The proper particle ratio can effectively reduce loss of magnetic powder core and promote the permeability. It was found that the optimum particle ratio of Fe78Si9B13 magnetic powder is 60% of -100% of +150 mesh, 10% of -150~ +200 mesh, 10% of -200~ +250 mesh, 20% of -250~+320 mesh.Heat treatment is the most important factor of affecting magnetic performance. Increasing annealing temperature can effectively reduce loss of magnetic powder core and promote the permeability. Over annealing temperature can deteriorate magnetic properties due to the crystallization of amorphous power, the forming of nonmagnetic phase, and the damage of coating insulation. The optimum annealing temperature is 400℃, the time is 1 hour.Shaping pressure is the basis for magnetic powder cores to obtain high magnetic property. Adding pressure can increase the density of the sample and promote the permeability. But much too big pressure will destroy the insulating coating of magnetic powder cores and reduce the magnetic properties. The optimum comprehensive magnetic properties can be obtained when the shaping pressure is 1800MPa(1 minute the pressure).