Formation of ultrafine scale structures in aluminium containing small amounts of particles by conventional rolling deformation

The development of deformation microstructures during rolling has been studied in polycrystalline aluminium containing 0.8 vol.% of small Al2O3 particles and 2 vol.% of SiC whiskers. The morphology, size and misorientation of the ultrafine scale structures as a function of the imposed strain were characterised using transmission electron microscopy (TEM) technique.

The observations were compared to those of cold rolled particle-free pure aluminium reported in the literature. The presence of particles enhances the rate and changes the nature of the development of the overall microstructure in comparison with pure aluminium. With the addition of second phase to pure aluminium, the ultrafine scale microstructure with its size less than 0.5 μm and a fraction of high angle boundaries greater than 30% can be obtained at a comparatively low strain of 2.7.

In contrast, complicated processes or severe deformation with a strain of more than 5 are required for obtaining such structures in pure aluminium. The results indicate that there is a considerable potential for extending the present investigation to other particle-containing materials. By selecting second phases with suitable particle size and volume fraction and deformation processes one can expect to develop composites with ultrafine scale microstructure at a comparatively low strain.