电塑性效应中的磁场对金属流动应力的影响

Influence of magnetic field on metal flow stress in electroplastic effect

电塑性效应是指在金属塑性变形过程中向其塑性变形区通电导致的金属变形抗力急剧下降、塑性显著提高的现象。虽然目前金属的电塑性加工技术已取得较好的实验研究成果,但对电塑性效应的作用机理的研究一直处在探索之中,其中比较关键的问题是电流在材料中产生电塑性效应的机理和电塑性效应中材料的各塑性相关量(变形抗力、延伸率)的理论计算方法。本文从电流引起的磁塑性效应的角度解释了电塑性效应,认为金属塑性的提高是由于电流产生的磁场促进位错从顺磁性障碍物中脱钉。将位错滑移热激活理论与磁场引起的位错滑移激活面积增大理论相结合,得到了电流密度和电流作用下金属拉伸应变速率之间的关系,然后将所得结论代入到金属的本构方程中,得到了电塑性成形过程中流动应力的解析表达式。最后,对铜丝进行了电塑性拉伸实验,实验结果表明在0~2000 A/mm^(2)电流密度范围内,电流作用下的金属流动应力理论计算结果与实验结果相符合。

The electroplastic effect refers to the phenomenon that the resistance to metal deformation decreases sharply and the plasticity increases significantly when the electric current is applied to the plastic deformation zone during the metal plastic deformation.Although the current electroplastic processing technology of metals has achieved good experimental results,the mechanism of the electroplastic effect has been a subject.Among them,the key problems are the mechanism of electroplastic effect produced by electric current in materials and the theoretical calculation method of various plasticity correlations(deformation resistance,elongation)in the electroplastic effect.In this paper,the electroplastic effect of metal is explained from the view of magnetoplastic effect caused by electric current.It is considered that the improvement of metal plasticity is due to the magnetic field produced by electric current promoting dislocation depinning from paramagnetic obstacles.The relationship between the current density and the tensile strain rate is obtained by combining the theory of dislocation slip thermal activation with the theory of dislocation slip activation area increasing caused by magnetic field.Then the results are substituted into the constitutive equation of metals,producing the analytical expression of flow stress in the process of electroplastic forming.Finally,the electroplastic tensile test was carried out on the copper wire.It is observed that the theoretical calculation results of the metal flow stress under the action of current agree with the experimental results in the range of 0~2000 A/mm^(2) current density.