The Research On The Magnetic Performance Of Micro-alloying Fe-6.5wt.%Si Powders

Fe-6.5wt.%Si alloy is an excellent soft magnetic material, with good DCbias characteristics, low magnetic loss and low cost, which is widely used in switching power supplies, electric cars, and photovoltaic industry. However, high Si content leads to the brittleness of the alloy, and the alloy cannot be processed by conventional methods like cold-rolled and hot-rolled. Generally, the alloy is broken into powders and then pressed into magnetic cores with powder metallurgy technology. Gas-atomized powders have high sphericity, smooth surface and low oxygen content, which are easy for coating processing and is used for powder processing in this article. Ni is a magnetic element, and the addition of Ni can improve the magnetic properties, like permeability, coercive force and magnetic core loss. However, excessive Ni element can also cause the increase of the melt viscosity, which hinders atomization process.Based on a number of studies on the optimization method of Fe-6.5wt.%Si, gas-atomization and micro-alloying are determined. Fe-6.5wt.%Sixwt.%Ni(x=0, 0.2, 0.5, 0.8, 1.0) alloy powder are prepared, and the relationship between Ni element and the performance of powders are studied, like physical and magnetic properties. Research has shown that a moderate amount of Ni element addition can improve the performance of the alloy powder.The physical properties analysis of the powders show that, the powder particle is unimodal and approximate normal distribution. The oxygen content is below 250 ppm. The addition of Ni element can increase the metal melt viscosity and surface tension, which can prolong the atomization time and increase the particle size. The median diameter increases from 21.04μm to 38.62μm. The smoothness of powder surface decreases and the amount of irregular particles and satellite balls increases.With the increase of frequency, magnetic permeability remains unchanged, coercive force has an approximate linear rise, magnetic loss has an approximate parabola rise, and quality factor has an approximate parabola reduction. With the increase of Ni element content, magnetic permeability, coercive force, magnetic loss and quality factor get worse and then turn better, and the optimum performance is acquired when Ni content is 1.0%, with the coercive force of 307.9A/m and the magnetic loss of 4595mW/cm3 at 100 k Hz, 50 mT.Take Fe-6.5wt.%Si-1.0wt.%Ni magnetic powder core as an example to study the relationship between annealing temperature and magnetic properties of magnetic cores. At 773 K, the internal stress cannot be completely removed, which prevents the rotation of the magnetic domain. At 973 K, the insulating coating layer is partly damaged, and oxide forms, and the magnetic properties worsen. When annealed at 873 K, optimal magnetic properties can be achieved.Powder particle size can affect the magnetic properties. Magnetic permeability increases and coercive force decreases with the decrease of the particle size, while magnetic core loss decreases and quality factor increase. So, in industrial production, reasonable particle size ratio can improve the performance of magnetic cores.