Research On Heat Treatment Process And Performance Of Fe-based Amorphous/Nanocrystalline Core

The residual internal stress during the production of Fe-based amorphous/nanocrystalline alloys will affect its soft magnetic properties.During production,the heat treatment process is often adjusted to effectively eliminate internal stress or promote the precipitation of nanocrystalline grains.However,when the laminated amorphous strips or wound amorphous strips is annealed as a whole,the effective thermal conductivity of the laminated sheets is lower than Original material’s,leading to uneven internal and external temperature fields,which further lead in low annealing efficiency,reduced soft magnetic performance,and brittle amorphous core Problems.such as are not only unfavorable for subsequent processing,but also increase the scrap rate.In order to optimize the performance of the magnetic core and improve the efficiency of heat treatment,this thesis first uses ANSYS software to establish a heat transfer model to study the distribution of temperature and stress fields during heat treatment,and conduct temperature test of laminated stainless steel to verify the simulation conclusions;In this thesis,in exploring the annealing process of amorphous/nanocrystalline magnetic cores,a method that can promote the uniform annealing of the magnetic core is carried out.The magnetic cores made of Fe80Si9B11 alloy and Fe73.5Cu1Nb3Si13.5B9 alloy are subjected to ordinary heat treatment and copper-wrapped heat treatment.The changes of the soft magnetic properties and inductance characteristics of the core under two annealing systems are studied,and further,the magnetic properties and structural changes of the strips at different positions of the annealed core are analyzed.Through simulation heat transfer analysis,it can be known that wrapping copper around the amorphous magnetic core can increase the overall thermal conductivity of the material,enhance heat conduction,effectively reduce the temperature difference between the inner and outer parts of the magnetic core,and improve the uniformity of the temperature field distribution.Comparing the heat transfer rate of the magnetic core and the overall temperature rise,it can be seen that with the increase of the copper/amorphous thickness ratio,the heat conduction effect gradually increases and the temperature difference decreases.At the same time,the radiation effect of the furnace wall on the outer surface of the magnetic core is weakened,causing the overall temperature response of the magnetic core to lag.And because the thermal expansion coefficient of copper is much higher than that of amorphous materials,during the heat treatment process,the thermal expansion of copper will cause a certain pressure on the amorphous material,which will cause stress and deformation of the amorphous material.The stress action varies with temperature,time and the copper/amorphous ratio.When the copper is set in a spiral shape,the stress effect is obviously reduced.It is preliminarily speculated that in the heat treatment process,the copper strip is wrapped inside and outside the magnetic core to achieve copper wrapping heat treatment.During the stress relief annealing process,the optimal ratio of Copper/amorphous is about 1/1～2/1;during crystallization annealing,it can be appropriately reduce the proportion of copper.By comparing and analyzing the performance analysis of annealed cores,it can be known that the best heat treatment process for the amorphous alloy core Fe80Si9B11 is 693 K-40 min,and the saturation magnetic induction intensity(Bs)is 1.535T(External magnetic field H=2000 A/m),the coercivity(Hc)is 6.077 A/m,and the specific total loss value(Ps)is 0.209 W/kg(f=50 Hz,working magnetic flux Bm=1 T)under this condition.The best heat treatment process for nanocrystalline alloy core Fe73.5Cu1Nb3Si13.5B9 is 798K-60 min,Hc is 1.297 A/m,initial permeability(μi)is 105.520 K,Ps is 23.3 W/kg(f=20 kHz,Bm=0.5 T),the inductance LS is 11.774 μH/N2(f=20 kHz,U=1 V),and the effective permeability μe is 124.194 K(f=20 kHz,U=1 V).Based on the results of conventional heat treatment experiments,this thesis further studies the effect of the performance of the magnetic core after the copper-wrapped annealing in the heat treatment process,and hopes to improve the heat treatment efficiency under the premise of ensuring the performance of the magnetic core.The results show that compared with ordinary heat treatment,the performance of the magnetic core obtained after the copper-wrapped heat treatment is improved,and the annealing time is greatly shortened,energy consumption is saved,and the heat treatment efficiency is improved.Among them,for the amorphous magnetic core,heat preservation at 693K for 15 minutes,when the Copper/amorphous thickness ratio is 3/2,μi increases by 8.7%and Ps decreases by 6.4%(f=50Hz,Bm=1T);its best heat preservation time is changed from 40min to 15min;For nanocrystalline cores,four heat treatment conditions of 798 K-5 min,785 K-7 min,773 K-20 min and 748 K-25 min are selected for experimental research,corresponding to Copper/amorphous thickness ratio is 1/4,1/4,1/4 and 1/1,all of which can improve the magnetic properties.The choice of copper-wrapped heat treatment process can be summarized as low temperature,long time,and larger Copper/amorphous thickness ratio;high temperature,short time,and smaller Copper/amorphous thickness ratio.Further analysis of the properties of the strips at different positions of the annealed core shows that the copper-wrapped heat treatment can promote the uniformity of the stress relief of the amorphous core,delay the heating rate of the outer strip of the core,and shorten its holding time at high temperatures to prevent it from crystallization;it can also promote the simultaneous crystallization of the strips in the inner and outer positions of the nanocrystalline magnetic core,and the coercive force of the strips at different positions is reduced,and the fluctuation range of the crystal grain size is reduced,thereby improving the overall performance of the magnetic core.