Preparation And Properties Of Fe-based Soft Magnetic Composites By Diffusion Method

Soft magnetic composites（SMCs）are soft magnetic materials that coat the surface of ferromagnetic particles with insulating substances to increase resistivity and reduce losses.Due to the advantages of low magnetic loss of ferrite and high saturation magnetic flux density of metal soft magnetic,SMCs are often used as an essential medium for magnetoelectric transformations such as power conversion,signal transmission and electromagnetic compatibility.With the rapid development of power electronics technology,people start to put forward higher requirements for the performance of SMCs.How to maintain low loss and good magnetic permeability of SMCs at medium and high frequencies through effective interface design and insulating coating has become the focus and difficulty of soft magnetic composite development.In this thesis,the spherical Fe powder is used as the matrix to prepare the magnetic ring,and B₂O₃,Sb₂O₃,and Al-Si alloy are used as the diffusion sources,respectively,and three kinds of soft magnetic composite materials are obtained by means of high-temperature interfacial diffusion.The effects of diffusion medium,diffusion temperature,diffusion time and other parameters on the microstructure and properties of soft magnetic composites are systematically studied in this thesis.The main research contents and conclusions are as follows:（1）Preparation and properties of B₂O₃/Fe SMCs were studied when B₂O₃ was used as the diffusion source.The magnetic ring was coated,and B₂O₃/Fe SMCs were obtained after diffusion annealing.It was found that with the increase of annealing temperature,the density and effective permeability of SMCs increased,the loss first increased and then decreased,and the magnetic performance was the best at 750°C:at 500 k Hz and 5 m T,the magnetic loss was 4047 k W/m³.At 600°C,with the prolongation of annealing time,the density increased slightly,the effective permeability decreased,the loss first decreased and then increased,and the magnetic properties were the best at 0.5 h:at 500 k Hz and 5 m T,the magnetic loss was 923.4k W/m³.The results show that the interfacial diffusion of B₂O₃ can effectively enhance the magnetic properties of Fe-based SMCs:the magnetic loss was reduced and the DC bias characteristics are improved.（2）Preparation and properties of Sb₂O₃/Fe SMCs.Using Sb₂O₃ as the diffusion source,the magnetic ring was coated,and Sb₂O₃/Fe SMCs were obtained after diffusion annealing.The study found that with the increase of annealing temperature,the density of SMCs increased,the effective permeability first increased and then decreased,and the loss first decreased and then increased,and the magnetic performance was the best at 800℃:500 k Hz,5 m T,the magnetic loss was 2935.7k W/m³.At 900°C,with the prolongation of annealing time,the density of SMCs remained basically constant,the effective permeability first increased and then decreased,and the loss first decreased and then increased,and the magnetic properties were the best at 4 h:500 k Hz,5 m T,the magnetic loss was 3050.9 k W/m³.The results show that the interfacial diffusion of Sb₂O₃ can effectively enhance the magnetic properties of iron-based SMCs:the magnetic permeability is increased,the magnetic loss is reduced,and the DC bias characteristics are also improved.（3）Preparation and properties of Al-Si/Fe SMCs.Using Al-Si alloy as the diffusion source,the magnetic ring was coated,and Al-Si/Fe SMCs were obtained after diffusion annealing.The study found that with the increase of annealing temperature,the density and effective permeability of SMCs increased,the loss decreased,and the magnetic performance was the best at 900°C:at 500 k Hz,5 m T,the magnetic loss was 4149 k W/m³.At 900°C,with the prolongation of annealing time,the density and effective permeability first increased and then decreased,and the loss first decreased and then increased,and the magnetic performance was the best at 2 h:at 500 k Hz and 5 m T,the magnetic loss was 3769.6 k W/m³.The results show that the interfacial diffusion of Al-Si alloy can effectively improve the magnetic properties of Fe-based SMCs:the magnetic permeability is increased,the magnetic loss is decreased,and the DC bias characteristics are also improved.