Study On Preparation And Coating Thermostability Of Iron-based Soft Magnetic Composite Materials

Soft magnetic composite (SMC) materials refers to that use pure iron powders asraw material, with appropriate methods, coating the iron powder with an insulating layer,and compacted at900MPa then heated under selected atmospheres and pre-settemperatures then still shows excellent thermal stability. Because of this isotropiccharacteristics of soft magnetic powder, it can greatly reduce eddy-loss-energy in thehigh-frequency application. However, due to the poor thermal stability of the insulatinglayer, it largely limits the application of SMC.Two kinds coating materials were prepared by hydrothermal synthesis and theirproperties were characterized by different methods. We coat iron powders by differentways such as wet evaporation coating method and dry grinded coating method, thencompacted at900MPa and heated under700℃and900℃. Of course, the resistivity anddensity of the SMC samples were measured before and after heat treatment.It shows that the Si-Al-B-K kind coating material has very small particle size, evento nano-level, its resistivity can reach to1100×10-4Ω cm when coating iron powders,shows great insulate performance, it contains lots of Si-O-Al band in the coating powders.But when heated after700℃and900℃, the SMC samples resistivity sharply decreaseto8×10-4Ω cm, it occur restructuring and recrystallization process shows from theDTA/DSC.The other coating material is Si-B-K kind of insulating layer, we find that the KOHcontent has a great influence to melting point of this insulating layer. Although the thermalstability is poor, when it is melting in heat treated process, it can coating iron powdertightly. Because of its low viscosity, it can separate from iron powder, so its resistivityalso decrease after heating. Specially, at the same time, when we use the heated powdersafter700℃heating, the SMC materials samples resistivity has improved, it can reach to50×10-4Ω cm after900℃heating treatment, also its density is7.26g cm-3, it is a greatimprovement to the coating powders materials.