纯铝等径角挤技术(Ⅱ)--变形行为模拟

通过有限元模拟和坐标网格，对纯铝等径角挤过程的变形行为进行了模拟和试验。结果表明，纯铝在单道次等径角挤压过程中所需的载荷随着样品位移的增加大致可分为快速增加、缓慢增加、快速增加、载荷值趋于稳定、载荷下降5个阶段。由于样品外部在主要变形区的流动速率比样品内部的快，因而样品在等径角挤压过程中会出现不均匀变形，样品底部沿宽度方向的塑性变形量明显少于样品顶部和中部的，坐标网格法实验结果也证明了这一点。在等径角挤压过程中，样品不同部位的应力状态不一致，样品内部存在压应力→拉应力的转变，样品外部存在压应力→拉应力→压应力的转变。摩擦消除后，有效应变有所增加，但并不能降低样品变形的不均匀性；采用尖角模具既能产生更大的剪切应变，又能提高变形的均匀性。

Equal channel angular pressing process of pure aluminum(Ⅱ)--Simulation of deformation behavior

The computer simulation and experiments for the deformation behavior of pure Al in equal channel angular pressing (ECAP) process were conducted by finite element method (FEM) and coordinate network. The results show that the load required to drive the deformation varies with increasing the displacement, according to the following five steps: rapid increase, slowly increase, another rapid increase, stabilizing and decrease. Inhomogeneous deformation exists in the width direction of the sample, and the plastic deformation in the end of the sample is smaller than that in the top and that in the center. The coordinate network experiment verifies this phenomenon. This inhomogeneity is attributed to the fact that the strain rate in the outer side of the sample is faster than that in the inner side. During ECAP process, the stress state in different positions of the sample is different. In the inner side of the sample, there is a stress transition from compressive to tensile state; while in the outer side there is a transition from compressive to tensile and finally to compressive state. The simulation also indicates that elimination of abrasion can not ameliorate the deformation inhomogeneity, but can increase the effective strain; with closed mould, lager and more homogeneous shear deformation can be obtained.