Study On Preparation And Magnetic Properties Of Soft Magnetic Powder Core Synthesized By A Surface Modification Method

Soft magnetic powder core is a new composite material prepared using the ferromagnetic alloy particles coated with an insulation layer through the compaction and the annealing process.It possesses high saturation flux density,low eddy-current loss and good DC-bias performance due to the high filling ratio of the magnetic alloy powders and the existences of the insulation layer with a large resistance on the powder’s surface and the distributed gaps between the powder particles.This makes it widely used in various power electronic devices.In this dissertation,the Fe-Si-Al soft magnetic powder cores were prepared by using the Fe-Si-Al soft magnetic powder insulated with silica powder and epoxy resin.The influences of the contents of the silica and the resin,the compaction pressure and the annealing temperature on the core’s magnetic and electrical properties were studied in detail.The main results are listed as follows:(1)The appropriate increase of the contents of the silica and the resin can decrease the effective permeability and the eddy-current loss of the cores,improve the DC-bias performance,and make the quality factor decrease at low frequency and increase at high frequency.But the excessive addition of the resin can lead to the contrary results.(2)The appropriate increase of the compaction pressure can achieve a high effective permeability,a low loss and a high quality factor at low frequency.But meanwhile,the core’s DC-bias performance and the quality factor at low frequency deteriorate.If too high compaction pressure is adopted,the core loss at high frequency may increases abnormally due to the destruction of some insulation layers.(3)The appropriate increase of the annealing temperature can improve the effective permeability,the quality factor at low frequency,and the core loss.But the core’s DC-bias performance decreases accordingly.Too high annealing temperature can result in the remarkable increase of the core loss,which causes the decrease of the quality factor at high frequency.(4)The demagnetization field,the hysteresis and the eddy current within the powder core are believed to be the physical origins affecting the core’s magnetic and electrical properties.Both the large inner stress and the high demagnetization field caused by the low density can result in the large hysteresis,which lead to the decrease of the effective permeability,the improvement of the DC-bias performance,and the deterioration of the core loss at low frequency.The thickening of the insulation layer can reduce the eddy current within the powder core and thus results in the effective decrease of the core loss at high frequency.