Microstructure evolution, lattice rotation retardation and grain orientation fragmentation in commercial purity aluminium deformed by high pressure torsion

Abstract

The behaviour of commercial purity aluminium processed by high pressure torsion is studied for a wide range of strains. The microstructure and texture are used to characterise the HPT deformation. Two different stages of microstructure evolution, i.e. grain fragmentation and grain elongation, are first found before attainment of steady state during HPT deformation. The grain fragmentation is not a linear function of shear strain in HPT. Significant grain refinement mainly occurs in the equivalent strain ranges of ∼0 to 1 and ∼11 to 32. Preferred simple shear orientations appear and vanish periodically due to the intrinsic instability of the shear direction in HPT. The lattice rotation of ultra-fine grain material is related to the grain size in the steady state. The strong ideal components have larger grain size than weak ideal components and non-ideal components. But the sensitivity of fragmentation to grain orientation tends to disappear as the steady state is attained.

Keywords

• High pressure torsion
• Aluminium
• Microstructure evolution
• Lattice rotation retardation
• Grain orientation fragmentation.