Acoustic emission during magetization in 3％ Si-Fe and mild steel

Abstract

The motion of magnetic domain walls in ferromagnetic material produces acoustic emission, named ``MAE``, through magnetoelastic coupling between spin motion in domain wall and internal lattice strain. The rms value and the waveform of MAE of 3% Si-Fe and mild steel have been measured in each cold-rolled and annealed condition with various frequency and intensity of magnetic field. The magnetization was alternated by solenoid and the maximum frequency and intensity of magnetic field was 70Hz and 30 Oe respectively. A resonant type AE transducer, having 175KHz nominal center frequency was used with a band pass filter (125KHz-250KHz) and the total amplification was 80dB. It was found that the intensity of MAE signal was active at nearby coercive force and the rms value increases linearly with the increase of magnetizing frequency or magnetic field intensity. These results indicated that the MAE is caused by mainly domain wall displacement rather than rotation in magnetizing process and the intensity of MAE increases with the increase of domain wall velocity. The MAE of annealed state shows a higher response than cold-rolled state. The effects of rolling texture on MAE have been investigated in annealed 3% Si-Fe with the angle to the rolling direction. Also the effects of plastic deformation produced by tensile stress on MAE have been investigated in annealed mild steel. It was found that the rms value of MAE decreases with plastic deformation gradually, and then increase slightly at fracture. Compared these behaviors of MAE with the conventional magnetic properties obtained by hysteresis loop measurements in each case, the intensity of MAE increases with the saturation induction and decreases with the coersive force. As a result, it seems that the amount of prior cold work, the difference in heat treatment, and the presence of rolling texture can be determined by monitoring this MAE phenomenon in ferromagnetic materials.