Strain Mode Dependence of Deformation Texture Developments: Microstructural Origin

Fully recrystallized commercial-purity aluminum sheets were deformed by limiting dome height tests, the following strain modes: uniaxial tension (US), near plane strain tension (PS), and equibiaxial tension (BS) were identified using standard procedure. The deformation texture developments differed significantly depending on the strain mode. Although the full constraints Taylor (FCT) model captured the texture developments in US, it failed to reproduce deformation textures in PS and especially in BS. The Advanced LAMEL (ALAMEL) model and the crystal plasticity finite element method (CPFEM) were, however, successful with respect to all three strain modes. Microtexture data brought out interesting observations of orientation gradients. First, the orientation gradients increased from US to PS to BS. Second, such gradients were mostly around initial (or prior deformation) grain boundary regions. A simple algorithm, and an associated computer program, was developed to demarcate such near boundary gradient zones (NBGZs). The area fraction and severity of NBGZ seemed to affect the texture development; FCT was reasonably successful at low NBGZ, whereas high NBGZ required the ALAMEL and the CPFEM models that are capable of addressing strain heterogeneity and grain interactions.     

Effect of Strain Rate on Deformation Behavior of Semi-Solid Dendritic Alloys

The behavior of semi-solid Sn-Pb alloys was studied in compression between two parallel plates. Small dendritic samples were deformed at cross-head speeds leading to initial strain rates ranging from 1.3 × 10^-3 s^-1 to 1.2 × 10³ s^-1 in the semi-solid state at a temperature just above the eutectic. At the lower rates of deformation, breakdown of the dendrite structure occurs, at strains of 0.2 to 0.4, and a high degree of segregation of the liquid phase occurs. For higher rates the segregation no longer occurs to such a great extent and the alloy deforms more homogeneously. Some related experiments involving compression over a filter are presented to obtain stress-strain relations in bulk compression for later analysis. The behavior in compression of alloys in the semi-solid state may be used as a refining process in the low strain-rate range where segregation of the liquid is large. It may also prove useful in the high strain-rate range as a forming method. M. SUERY, formerly Visiting Scientist, Materials Processing Center, Massachusetts Institute of Technology.     

板带热轧变形过程中的非均匀应变问题分析

 采用有限元分析软件ANSYS/LS DYNA模拟板带轧制过程,分析了轧辊直径、轧件温度、轧件入口厚度和接触摩擦对变形区等效塑性应变的影响。结果表明：轧辊直径、轧件入口厚度和接触摩擦显著影响应变分布的不均匀性,应变的不均匀会导致再结晶晶粒的不均匀分布,而轧件温度对应变分布的影响规律不十分明显。该研究结果将为组织性能预报提供基础数据。