The effect of calcination temperature on microstructure and properties of FeNiMo@Al2O3 soft magnetic composites prepared by sol-gel method

Abstract The effect of calcination temperature on the coating layer and the phase of the alloy matrix is the main problem to improve the heat treatment process of SMCs and obtain excellent magnetic properties. In this study, FeNiMo@Al2O3 powders which were coated by sol-gel and calcined at 900–1300 °C were prepared and these powders were pressed into SMCs. The results showed that the surface of the powder was uniformly coated with Al2O3. As the heat treatment temperature increases, the phase of the coating changed from AlOOH to γ-Al2O3, δ-Al2O3, θ-Al2O3, and α-Al2O3. Meanwhile, the new phase γ-Fe, Ni appeared in the alloy matrix. The magnetic permeability of the sample is very stable in the frequency range of 10–500 kHz. The magnetic loss decreases first and then increases, with a minimum at 1100 °C. The permeability and magnetic loss of the sample pressed from the powder obtained by calcination at 1100 °C are 321.78 mw/cm3 and 87.61 (50 kHz, 100 mT) at the typical industrial application conditions of Iron–Nickel SMCs. The microstructure and the magnetic properties show that the obtained α-Al2O3 have excellent insulation and heat resistance. This resulted in a significant reduction in core losses of FeNiMo SMCs.