Hardness inhomogeneity and local strengthening mechanisms of an Al1050 aluminium alloy after one pass of equal channel angular pressing

Samples of an Al1050 aluminium alloy (99.5% Al) were subjected to an equal channel angular pressing (ECAP) at room temperature for one pass. The microhardness is highest at the centre of the cross-section of the billet, and the grain size is smallest at the edges, which rules out grain size strengthening as the dominant hardening mechanism. On isochronal ageing at temperatures between 200 °C and 375 °C, low angle grain boundaries disappear, the hardness gradually decreases, and hardness differences gradually disappear. A model is described that captures the strengthening mechanisms and model results fit the experimental results well. Analysis of recovery behaviour and strength modelling indicates that the contribution of the dislocations to the strength is higher than that of grain size.