The plasticity of material is associated closely with the movement and proliferation of dislocation. Therefore, in the deformation and plasticity theory the dislocation kinetics is an important topic. In the case of no magnetic field, the conventional dislocation kinetics normally focuses on the dislocation microstructure, nucleation and mobility, and the inherent relationship between electron spin and plasticity is seldom concerned. As a matter of fact, the electron rotation is directionless and unordered in the absence of magnetic field, so the electron behavior will not take an apparent effect on the microstructure and properties of material. Nevertheless, in the presence of magnetic field the case is different. The magnetic field will influence the electron spin and, therefore, atomic rearrangement. The dislocation behavior and plasticity will also be affected by the magnetic field, which is called the magnetoplastic effect. In this paper, on the basis of magnetoplastic effect the dislocation kinetics involving dislocation stress, mobility and others is discussed both qualitatively and quantitatively. It has rarely reported currently in the literature. The pulsed magnetic field is first utilized to process solid nanometer alumina particulates reinforced aluminum matrix composites. The experimental results demonstrate that the dislocation density increases with magnetic induction intensity increasing from zero to 3 T. The phenomenon reveals the characteristic of plastic deformation in a processed sample. The further theoretical analysis displays that the generated magnetic force is not large enough to activate the dislocation movement. The fundamental reason lies in the magnetoplastic effect, that is, the magnetic field brings about the transition of electron spin in the radical pairs between paramagnetic dislocation cores and obstacles. The radical pairs tend to be conversed from the singlet state with high bonding energy to the triplet state with low bonding energy, therefore, the prerequisite energy for dislocation to surmount the obstacles will be lowed and the depinning tendency will be apparent. In a period of dislocation movement, the rate limiting consists in the dislocation stopping at the obstacle;on the contrary, the electron excitation and atomic arrangement governed by the magnetic field take negligible time. Hence, it can be seen that the performance of magnetic field is highly efficient. The critical magnetic induction intensity is calculated to be 3 T. That is, when the intensity is lower than 3 T, the magnetoplastic effect becomes strong with the increase of magnetic induction intensity and action time;when the intensity is higher than 3 T, the effect changes gently. Under this critical magnetic induction intensity, the dislocation velocity is deduced to be on the order of 10−3 m/s. Moreover, the dislocation length will be increased by two orders of magnitude. The displacement of dislocation is proportional to the square of magnetic induction intensity and action time of magnetic field. To sum up, the magnetic field treatment has been proved to be an efficient approach to improve the plasticity of material. The prospective research will focus on the mechanical properties of alloys or composites subjected to magnetic field, together with tensile stress so as to acquire the effect of magnetic field parameters of macro plasticity of materials.%基于磁致塑性效应探讨了磁场作用下位错受力和运动机制,对磁场下的位错动力学机制进行了定性和定量分析。选择氧化铝纳米颗粒强化铝基复合材料为实验对象,在不同磁感应强度下(0—3 T范围)对试样进行磁场处理。结果表明,随着磁感应强度增加,位错密度提高,表现出塑性变形特征。分析认为,磁场力不足以驱动位错运动,位错增殖诱因在于磁致塑性效应,即磁场改变了顺磁性位错芯与障碍间自由基对中的电子自旋状态,促使自由基对从强键结合单线态向弱键结合三重态转化,位错穿越障碍时所需能量减小,退钉扎趋势明显；位错运动中的限速环节是位错在障碍处的停留,磁场诱发的电子激发和原子重排速度很快,表现出磁场作用的高效性。磁场起作用的临界磁感应强度约为3 T,低于3 T时磁场作用随磁场强度增加而变得明显,高于3 T后磁场效果会减小。计算得到3 T时位错运动速度是10−3 m/s,位错线长度比未加磁场时增加两个数量级,位移与磁感应强度平方和磁场作用时间成正比。实验和理论研究表明磁场具有改善材料塑性变形能力的显著作用。
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