| FeSiBNbCu nanocrystalline soft magnetic alloys have excellent soft magnetic properties,such as high permeability(?),low coercive force(Hc)and low loss.They are mainly used in new energy vehicles,transformers,high-precision transformers,wireless charging and so on.In recent years,the explosion of wireless charging market has promoted the development of wireless charging equipment towards miniaturization,high efficiency and high power.There is a higher demand for the performance of nanocrystalline soft magnetic materials used for wireless charging magnetic shielding pieces.At present,the commercial magnetic shielding pieces is Finemet(FeSiBNbCu)alloy,but its saturation magnetic induction strength(Bs)is only 1.24 T,which can't satisfy the development requirements of miniaturization and high power.Therefore,improving the Bs of nanocrystalline FeSiBNbCu alloy without deteriorating the soft magnetic properties has become a research hotspot.In this work,the nanocrystalline FeSiBNbCu soft magnetic alloy with good comprehensive magnetic properties was obtained by microalloying Al and P elements and appropriate heat treatment process.By using vibrating sample magnetometer(VSM),differential scanning calorimetry(DSC),X-ray diffraction(XRD),transmission election microscopy(TEM),magneto-optical Kerr microscope and M(?)ssbauer spectroscopy,the relationship among the composition,heat treatment process,microstructure,domain morphology,electromagnetic parameters and magnetic properties of the alloys was studied,and the mechanism of the change of magnetic properties was revealed.The results provide a reference for the development of nanocrystalline soft magnetic materials used for wireless charging system.The main results are as follows:1.On the basis of nanocrystalline Fe76Si13B8Cu1Nb2 alloy developed by our group,Fe76Si13B8Cu1Nb1.5Al0.5 alloy was developed by replacing Nb with Al.Al microalloying has little effect on the thermal stability of the alloy,but the soft magnetic properties of the alloy decrease slightly.By increasing the Fe content and replacing B with 1 at% Al,the ? of Fe77Si12B7Nb2Cu1Al1 alloy is 23900 at 1 k Hz,and the Hc,Bs and heat treatment range are 1.24 A/m,1.4 T and 193 K,respectively.2.The magnetic properties of nanocrystalline Fe77Si10B9Cu1Nb3-x Alx(x = 0 and 1)alloys have been investigated and their structural and electromagnetic parameters have been quantitatively studied by XRD,TEM and M(?)ssbauer spectra under one-step and two-step annealing processes.Both Bs and ? of the nanocrystalline alloys are increased by substituting 1 at% Al for Nb and one-step annealing,from Bs = 1.41 T to 1.47 T and from ? = 18000 to 23000 at 1 k Hz,respectively.The two-step annealing has little effect on the Bs,Hc and grain size of the nanocrystalline alloys,but greatly improves the ? of the Al-doped alloy,reaching up to 28000 at 1 k Hz.The improved ? can be attributed to the increased magnetic moment and exchange stiffness constant,homogeneous chemical structure and reduced magnetostriction.The Al-doped nanocrystalline alloy has high Bs,high ?,low Hc and good frequency stability,which makes it a potential application in the field of wireless charging.3.Nanocrystalline Fe77.8Si10B9Cu0.6Nb2.6 alloy was obtained by further increasing Fe content and decreasing Cu content.The ?,Bs and Hc are 28000 at 1 k Hz and 15000 at 100 k Hz,1.46 T and 2.5 A/m,respectively.When 1 at% P replaces B,the magnetic properties are almost unchanged,i.e.,?=27200(1 k Hz),?=14400(100 k Hz),and Bs = 1.44 T.However,Hc decreases and remains about 2 A/m in a large temperature range.The decrease of Hc is mainly due to the precipitation of smaller nanocrystalline particles.From the view of crystallization kinetics,the addition of P element results in the increase of activation energy of crystallization.In addition,it can be seen from the domain structure that the number of pinning points is less and the magnetocrystalline anisotropy is smaller than those of P-free alloy,so the Hc is reduced.At the same time,the amorphous forming ability of the nanocrystalline alloy with P addition is higher and the high temperature stability is better,which is more suitable for industrial production. |
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