Enhance the Magnetic Properties of Fe-Si-Al-Cr Flaky Particles by Annealing

摘要

Fe-Si-Al-Cr flaky particles were used as microwave absorbing material. Iron-Silicon-Aluminum-Chromium ingots with nominal compositions Fe73Sii5AlioCr2 were produced by alloying the pure elements in an induction melting furnace under argon atmosphere at 0.03 MPa, and then the ingots were crushed into irregular shaped particles. As-crushed alloy had been milled by planetary miller for 32 h. In order to increase the effective permeability, the material was annealed under different conditions. The morphology of the powders was characterized by scanning electron microscope (SEM). The phases of powders were estimated by X-ray diffract ometer (XRD). The microwave permeability dispersion spectra of annealed powders within a frequency range of 0.5-8 GHz was measured. The SEM results showed that particles had been successfully transformed into the flaky shape. The average diameter of flakes is about 43 μm. The average aspect ratio (width/thickness) of flakes is about 28. The XRD results showed that the D03 ordered phase coexisted with a-Fe(Si,Al,Cr) matrix phase by annealing above 500°C. When the annealing temperature increased from room temperature to 800°C, the grain size grown from 10.4 nm to its maximum 29.8 nm and part of a-Fe(Si,Al,Cr) matrix phase translated into D03. The imaginary part of the effective permeability increased with the annealing temperature, and decreased when the temperature was above 500°C. The resonance frequency decreased with the annealing temperature, and increased when the temperature was above 400°C. The effective permeability of the powders, obtained by 500°C annealing, had a maximum value of 6.0 at 2.5 GHz.