大应变冷轧工业纯铝的强度与应变的关系研究

Correlation Between Strength and Strain in Heavily Cold-rolled Commercial Purity Aluminum

工业纯铝在冷轧大变形过程中,屈服强度随应变量的增加先上升后降低。强度在等效应变为3.3时(εvM=3.3)达到峰值,之后随着压下量进一步增加,其强度反而下降,即出现了变形致软化的现象。透射电子显微镜观测两种样品(εvM=3.3和εvM=4.1)发现,造成这一现象的主要原因是材料内部微观结构不同。εvM=4.1的样品微观结构为冷轧大变形之后典型的层状结构;而εvM=3.3的样品中除含有典型层状结构之外,还包含近似等轴晶的区域,该区域中小角度晶界比例以及位错密度较高。通过理论计算位错强化与细晶强化的贡献,发现εvM=3.3的样品强度高于εvM=4.1的样品,与实验结果一致。

The yield strength of heavily cold rolled commercial purity aluminum increases first and then decreases as reduction in the thickness increasing. Such softening by further deformation phenomenon indicate that the yield strength reaches a peak at εvM=3.3 （εvM is the von Mises equivalent strain） and then decrease when εvM is furtherly increased. A typical lamellar structure resulted from cold rolling process was observed in the εvM=4.1 sample. However, approximately equiaxial grains with higher density of dislocation and higher fraction of low angle grain boundaries are found in addition to the lamellar structure in the εvM=3.3 sample. Theoretical calculation with dislocation strengthening and grain boundary strengthening mechanism show that the yield strength of the εvM=3.3 sample is higher than that of the εvM=4.1 sample, which is in accordance with the experimental results.