Magnetoplastic Effects In Pure Metals Under Action Of Alternating Magnetic Field

As an important means of material preparation and performance regulation,alternating magnetic field(AMF)has been widely used in industrial production.In recent years,the plasticity change of materials under the action of magnetic field,namely: magneto-plastic effects(MPE),has become an emerging research field and has attracted wide attention.At present,the existing research is mainly limited to the related research on the steady state and the dislocation motion under the pulsed magnetic field.However,the research on the MPE under AMF has rarely been reported,and the change of dislocation density under the action of magnetic field is rarely studied.Therefore,this work is based on different magnetic pure metals(Ni,Al and Cu),with the help of metallography,X-ray diffraction,microhardness,electron backscatter diffraction(EBSD)and other technical means.The variation of dislocation density and hardness of deformed pure metal under variable magnetic field,and the mechanism of plasticity change of material under AMF.The main conclusions are as follows:1)The effect of AMF on the dislocation density and microhardness of paramagnetic pure metal was studied.After the paramagnetic polymorphic pure Al and single crystal deformed Ni samples were annealed by AMF,the HWFM of the diffraction peak increases,the dislocation density of the sample increases,and the microhardness increases compared with the absence of the magnetic field,but is still lower than the hardness of the unannealed sample.The magnetic harden effects of the paramagnetic material are lower than the annealing soften effects in the same time.The AMF causes the spin state between the dislocation core and the obstacles between the paramagnetic metal to change from the singlet S state to the triplet T state,and the system energy increases and the stability decreases,which is beneficial to the dislocation being weak.The pinning at the particle point promotes dislocation motion,which helps to increase the dislocation density and the microhardness.2)The effect of AMF on the dislocation density and microhardness of ferromagnetic pure Ni was studied.The ferromagnetic single crystal deformed pure Ni sample was annealed under AMF of different strengths,and the XRD diffraction peak of the sample changed significantly.the decrease of the HWFM of the diffraction peak,and the decrease of microhardness and dislocation density.The EBSD test results show that the application of AMF,the KAM value in the sample area changes significantly,the average dislocation density decreases,and the dislocations tend to be uniform in the crystal,and the microhardness of the sample decreases.The AMF causes the magnetic domain domain wall of the ferromagnetic material to move and the magnetic moment rotates,which changes the stress distribution inside the material and promotes the dislocation source to start.At the same time,the periodic magneto-induced vibration effect makes the impurity elements and vacancies more easily diffuse,which is beneficial to the position.Mis-distribution,reducing material dislocation density and microhardness.3)The effect of AMF on the dislocation density and microhardness of diamagnetic pure Cu was studied.Applying different strength AMF to the same annealed diamagnetic polymorphic pure Cu sample,it was found that as the magnetic field strength increased,the HWFM of the peak decreases,and the dislocation density and microhardness of the sample also decrease.On the one hand,the AMF increases the viscosity of the electron inside the diamagnetic Cu,and the friction of the electron-dislocation system increases.On the other hand,the magnetic field is favorable for the triplet T state with higher electron energy.The mechanism is activated to reduce the internal friction of the dislocation.The combination of the two mechanisms results in a decrease in dislocation density and a decrease in microhardness.