Microstructural misorientations in extruded aluminium

Abstract Aluminium billets of two purities (99.999 and 99.7%) were extruded at 250°C using commercial equipment to produce 10 mm rod (extrusion ratio, 25:1). On air cooling, the resulting microstructures were investigated using optical and transmission electron microscopy, including Kikuchi line analysis. Thefine microstructure of the lower purity extrusion consisted of subgrains of about 2μm dia., formed by dynamic recovery. Although the microstructure of the higher purity extrusion appeared to be similar both in morphology and size, the misorientation measurements revealed that this extrusion was composed of small high-angle grains. These recrystallized grains were found to be stable and resulted in an associatedflow strength of50-62 MN/m2