Microstructural Evolution of a Strain-Hardened, Ultra-Fine Grained Al-Mg Alloy

摘要

A high strength, ultra-fine grain (UFG) aluminum alloy plate of (~62 cm diameter x 1. 9 cm thick) has been produced using cryomilled powders, consolidated by quasi-isostatic (QI) forging and rolling. To recover strength losses attributable to grain growth during thermo-mechanical processing (TMP), sections of the plate were cold-rolled to reductions of 20, 30, 40 and 50 %. Trends in dislocation densities and grain sizes were quantified by transmission electron microscopy (TEM) to provide insight into the mechanisms responsible for strengthening the UFG plate. After annealing, the cold-rolled material, some strength loss was documented, but notable improvements in tensile ductility were also seen. To better understand the mechanisms, electron backscatter diffracton (EBSD) was used to carefully characterize the strain-hardened microstructure before and after annealing. The EBSD analysis shows the effect of cold work and subsequent annealing on grain boundary angles, grain size, texture and accumulated strain in the plate.