Study On The Interaction Mechanisms Of Si And Al Co-diffusion Into Silicon Steel Sheets In Preparing High Silicon Steel By PVD Method

Silicon steel sheet is currently the most widely used core material in the electrical and electronic industries.Due to the intrinsic properties of the material,silicon steel sheets used as iron core materials will inevitably generate energy loss during the working process.At present,the general silicon content of silicon steel sheets is generally below 3.5%?mass percent,the same below?.When the Si content in the silicon steel matrix reaches 6.5%Si,the alloy has the lowest AC iron loss,the minimum coercive force and almost zero hysteresis.Therefore,6.5%Si high silicon steel is considered to be the most ideal core material.However,since the content of Si in silicon steel exceeds 4%,the hardness and brittleness of the alloy increase sharply,making it difficult to mass-produce by conventional rolling process,which severely limits the application of the alloy in engineering practice.The research on the preparation process of 6.5%Si high silicon steel has great economic benefits and far-reaching social significance for energy saving and consumption reduction in China and the world.The preparation of 6.5%Si high silicon steel by PVD method has proved to be an energy-saving and environmentally friendly and effective process.The basic idea is to deposit a Si-rich film on the surface of a low-silicon steel sheet by a magnetron sputtering coating technique and perform high-temperature diffusion treatment to infiltrate Si into the low-silicon steel matrix until the Si content reaches 6.5%.It is difficult to perform subsequent punching since the prepared 6.5%Si high silicon steel still has the problem of room temperature brittleness.The results show that adding appropriate Al element to 6.5%Si high silicon steel can improve its plastic toughness.Therefore,the silicon-aluminum co-infiltration process is studied based on the PVD method to prepare 6.5%Si high silicon steel process.Firstly,the Si-rich?Al?film is deposited on the surface of the low-silicon steel sheet,and then subjected to high-temperature vacuum diffusion treatment to make Si and Al atoms.The low-silicon steel matrix is infiltrated in order to obtain 6.5%Si high-silicon steel containing a certain concentration of Al,and it is expected that the alloy has excellent soft magnetic properties and good mechanical processing properties.It is necessary to carry out systematic research on the preparation process and diffusion treatment process of Si?Al?film deposited by PVD method,and explore the interaction mechanism of silicon-aluminum co-infiltration of low silicon steel matrix.Firstly,the DICTRA software was used to simulate the diffusion behavior of diffusion couples composed of different Si,Al content films and low silicon steel substrates at different temperatures and at different times.It is found that the diffusion rate of Al in?-Fe is lower than that of Si.When high concentration of Si and Al are simultaneously present in the diffusion source,they mutually promote the diffusion of each other.It causes the other element to spread uphill,when the concentration of one element is in a gradient distribution,and the phenomenon disappears as the diffusion time increases and the concentration gradient disappears.Substituting an equal amount of Al for the same amount of Si in the diffusion source material deteriorates the overall diffusion effect.Firstly,the fabrication process of Fe₅Si₃ and pure Al films deposited by magnetron sputtering technology was studied.It was found that the deposition rates of both films increased linearly with sputtering power,but increased first and then decreased with working pressure.The deposition rate of the film is the highest,when the working pressure is 0.8 Pa,and the Fe₅Si₃ and Al films are columnar crystal structure,the film is compact and has good bonding properties with the matrix.On this basis,the effect of diffusion treatment on the diffusion behavior of Si and Al in pure iron substrates and low silicon steel samples deposited with Si?Al?rich films was studied.The results show that increasing diffusion temperature,prolonging diffusion time and increasing the content of diffusive source materials in pure iron and low silicon steel matrix contribute to the diffusion of Si and Al.The optimum diffusion temperature is 1180?.In the process of co-permeation of Si and Al,the presence of high concentration gradient Si or Al will lead to the uphill diffusion of Al or Si elements which are uniformly distributed.The reason is that there is strong mutual exclusion between Si and Al.Pre-infiltration of Al in low silicon steel matrix hinders the subsequent Si-increasing treatment.Finally,it was studied that the microstructures,physical properties,soft magnetic properties and machinability of Al-containing high silicon steel.It is found that Al penetrates into the Fe-3%Si low-silicon steel matrix and the?110?diffraction peak position shifts to the left,indicating that Al infiltration leads to an increase in the lattice constant of the alloy.As the concentration of infiltrated Al increasing,the electrical resistivity of the alloy increases and the microhardness increases simultaneously.However,when the same amount of Al is substituted for the equivalent amount of Si,the microhardness of the alloy is low,which proves that the infiltration of Al element in the preparation of high silicon steel can improve the processing performance to some extent.With the increase of the concentration of Si and Al in the silicon steel matrix,the high-frequency iron loss of the alloy is significantly reduced.