An Examination of Anisotropic Void Evolution in Aluminum Alloy 7075

Abstract

This paper investigates the anisotropy of void evolution and its relation with ductility in the high strength rolled aluminum alloy 7075-T7351. Smooth tension specimens are extracted from three principal material orientations, i.e. rolling (R), transverse (T), and short transverse (S). The mechanical behavior of these specimens is characterized and the varying ductility in the three orientations is clearly observed. Electron Backscattered Diffraction (EBSD), optical microscopy, and Scanning Electron Microscopy (SEM) are employed to characterize the grain structure and the size, location, and chemical composition of the intermetallic particles. In-situ X-ray Tomography (XCT) experiments are performed to obtain tomographic images of the specimens at critical loading steps. The radiographs acquired during the tensile test are then reconstructed and examined through quantitative analysis to partition particles and voids. These tomographic images enable us to visualize void evolution as the specimens are loaded along material orientations. The tomographic images clearly illustrate anisotropy in the void evolution and highlight the importance of local coalescence in developing 1D and 2D void structures prior to global coalescence. Fractography confirms tomography. These findings motivate model forms with appropriate internal variables to adequately describe the dominant mechanisms which govern anisotropic void evolution.