Microstructural evolution over a large strain range in aluminium deformed by cyclic-extrusion-compression

Polycrystalline pure aluminium (99.99%) has been deformed at room temperatu re by the Cyclic-Extrusion-Compression (CEC)-method to strains in the range 0.9-60 (1-67 cycles). At different strains, the microstructure and local c rystallography have been characterised in particular by transmission electr on microscopy. It has been found that the microstructure develops from a ce ll block structure into an almost equiaxed structure of cells and subgrains , that the spacing between the boundaries subdividing the structure is almo st unaffected by the strain and that the misorientation across these bounda ries increases with the strain over the whole strain range. At the largest strain, the average misorientation across the deformation induced boundarie s is similar to 25 degrees. The flow stress in compression is measured afte r the cyclic deformation and it is found that the flow stress increases wit h strain towards a saturation level which is reached at a relatively low st rain. The discussion comprises the effect of deformation mode and plastic s train over a large strain range on the microstructural evolution and mechan ical behaviour of aluminium. (C) 1999 Elsevier Science S.A. All rights rese rved.