Influence of ultra-high strains at elevated temperatures on the microstructure of aluminium. Part I

Abstract

A1 (purity, 99·7%) with 0·1 or 2 mm grains was torsionally deformed at 400°C and 0·2s-1 up to equivalent strains of 60. Tangential sections were examined by polarized light, transmission electron microscopy and scanning electron microscopy. The grains wound into helicoids with an axial thickness varying inversely with the strain. Subgrains persisted at a constant size (about 7 μm) and equiaxed throughout the straining from 0·5 to 60. Relative misorientations, of structural units were determined by scanning transmission electron microscopy channelling patterns, which confirmed the X-ray diffraction textures. The grains, with their boundaries strongly serrated, retained their distinctness up to strains of 10 for 0·1 mm grains and up to 60 for 2 mm grains, while their thickness was greater than the subgrain diameter. For the former at strains of 20-60, the microstructure consists of subgrains having a mixture of small- and large-angle boundaries; this development is called geometric dynamic recrystallization.