Equal channel angular pressing of pure aluminium - an analysis

Equal channel angular pressing (ECAP) is a novel technique for producing ultra fine grain structures in submicron level by introducing a large amount of shear strain into the materials without changing the billet shape or dimensions. This process is well suited for aluminium alloys and is capable of producing ultra fine grain structures with grain sizes falling between 200 and 500 nm. The present study attempts to apply ECAP technique to 99.5% pure aluminium and characterize the resulting aluminium by optical metallography, atomic force microscopy (AFM) and hardness measurement. ECAP of 99.5% pure aluminium produces ultrafine grain structure of about 620 nm after 8 passes. Despite an increase in the hardness from 23 to 47 BHN up to 6 passes, it decreases slightly for seventh and eighth passes. The results are compared with the already existing results available on pure aluminium. Analysis of the results of this investigation with those available in the literature has revealed that the number of passes essential to achieve a homogeneous microstructure in pure Al increases, while the ultimate equilibrium grain size obtained becomes finer with decreasing purity.