Improving High-Frequency Soft Magnetic Performance of Fe-Si-B-Cu-Nb Nanocrystalline Magnetic Powder Cores by Phosphating Treatment
摘要
The effects of phosphating treatment and annealing conditions on the static and high-frequency magnetic properties of Fe73.5Si13.5B9Cu1Nb3 nanocrystalline soft magnetic powder cores (NMPCs) were systematically investigated. Phosphating with 0.3 wt.% phosphoric acid forms a uniform and continuous insulating layer on the atomized alloy powders, effectively increasing core resistivity and suppressing eddy current loss, resulting in a 23.4% reduction in total core loss (Pcv) compared with the unphosphated sample, while maintaining high saturation magnetization (Ms), effective permeability (μe), and DC bias performance. Excessive phosphoric acid (0.6-0.9 wt.%) produces rough and inhomogeneous layers, increases hysteresis loss (Ph) and hence Pcv, and deteriorates both Ms and μe. Prolonging annealing at 813 K from 1 to 2 h promotes α-Fe nanograin precipitation without significant grain coarsening, leading to further reduction in Pcv due to decreased Ph, together with increased Ms and μe. Elevating the annealing temperature to 873 K deteriorates the high-frequency performance due to coarsened nanostructure and degraded phosphate layer. Combining 0.3 wt.% phosphating with 813 K/2 h annealing achieves optimal comprehensive soft magnetic performance, with Ms of 127 emu/g, μe of 36.2 at 200 kHz, %μ of 71% at 100 Oe, and Pcv of 299 mW/cm3 at 50 mT/200 kHz and 2771 mW/cm3 at 50 mT/1 MHz. Compared with unphosphated NMPCs, the optimized Pcv decreases by 49.6% at 50 mT/200 kHz and 42.6% at 50 mT/1 MHz, respectively.