Studies On Preparation And Magnetic Characteristics Of FeSiCr Alloy Powders

FeSi alloy powder, due to its the high resistivity and low magnetic anisotropy constant and magnetostrictive coefficient, can possess high microwave permeability in gigahertz microwave frequencies and have a broad application in the magnetic core material, radar absorbing material. Cr is a typical element which can improve the ability of oxidation resistance, corrosion resistance, resistivity, ductility, and inhibiter the grain growth, reduce the magnetic anisotropy in Fe-based alloy. Adding a certain amount of Cr element in FeSi alloys can not only greatly enhance the practical performance of the alloy, but also reinforce their plastic which can improve the aspect ratio of flaky powders. Thus, FeSiCr alloy powder may have a high permeability and permeability loss, and could become a new kind of microwave absorbing material within 500M~5G range.FeSiCr alloy powders of different Si / Cr content were prepared by wet milling and heat treatment method. Through studying the role of ball milling time, annealing temperature, different compositions in morphology, structure and static magnetic properties, we analyze the main reasons for variation of the microwave permeability, and finally find the optimum composition which have the maximum permeability.Results show that: In the ball milling process, with the milling increased, the shape of powders gradually turn form irregular to flat and small. The real part ?’ and the imaginary part ?" of complex permeability of samples increase firstly and then decrease, reach the maximum at milling time 48 h, meanwhile, the resonance peak gradually moved to the higher frequency. The variation of permeability can be attributed to the change of the aspect ratio of flaky powders. In order to obtain high magnetic permeability, the flaky powder should have a high aspect ratio under the premise of small particle size.In the heat treatment process, with the annealing temperature increased, the real part ?’ of complex permeability of samples increase firstly and then decrease before 1GHz, decrease after 2GHz. The imaginary part ?" increase firstly and then decrease, reach the maximum at annealing temperature 350℃. The main reason for the variation of permeability is attributed to the combined effect of grain size and internal strain. In order to obtain high magnetic permeability, grain size should be controlled to prevent excessive grain growth.Cr element replace Si element in the sample can enlarge the particle size, but can not improve the aspect ratio of the sample. Cr element replace Si element can reduce the real part ?’ and the imaginary part ?" of complex permeability of sample. Considering Cr element substitute Fe element can lower the dielectric constant of the sample, the substitution of Cr should be maintained less than 2%.Fe element replace Si element in the sample can enlarge the particle size, and can increase the aspect ratio of the sample in a certain range. With decreasing Si element content, the real part of complex permeability samples increase firstly and then decline before 1GHz, decrease all the time after the frequency 2GHz. The imaginary part ? " of permeability increase firstly and then decrease, reach the maximum at Si = 13at%. The resonance peak shifted to low frequencie. Substituted with increasing dielectric constant of the sample amount is increased. Reducing the amount of Si should be adjusted according to the actual application. The powders-paraffin composites which formulation is Fe86.4Si13Cr1.6, the mass ratio of powders and paraffin 2:1, in the frequency range from 500 M to 5G, have the highest real part ?’ = 6, imaginary part ?" = 4.7.