Electron Microscopy Analysis of Grain Boundary Structure and Composition in Superplastically Deformed Al-Mg Alloys

Abstract

Evaluation of grain boundary composition and structure in superplastically deformed AA5083-based alloys (AI-4.5Mg-1.6Mn-0.2Zr) was carried out in a field-emission gun transmission electron microscope (FEG-TEM). During superplastic deformation at high homologous temperatures materials undergo extensive grain boundary sliding (GBS) which creates a flow of defects in the near-boundary region. Recent literature has shown that the grain-boundary composition in Al-Mg alloys is not necessarily the same as the matrix, and that these differences can have an effect on GBS.Two alloy conditions were tested, with slightly different particulate content and superplastic deformability. Samples were tested at temperatures of 400°C and 450°C and a strain rate of 1x10-−3s−1 to vary the degree of grain boundary sliding, then quenched under load to preserve as much of the high-temperature structure as possible. TEM samples were prepared by carefully punching disks from the gage section of the deformed sample and electropolishing. Additionally, one sample was brought up to temperature and quenched but not deformed.