The role of back pressure in the processing of pure aluminum by equal-channel angular pressing

Samples of pure Al with a purity of 99.65% were processed by equal-channel angular pressing for up to four passes using different back pressures. Microhardness measurements were taken on cross-sectional planes and these data were supplemented by microstructural observations. The results show that the application of a back pressure leads to reasonable homogeneity within the billet except only in a narrow region of lower hardness lying adjacent to the bottom edge. For a constant number of passes through the die, the hardness distributions are independent of the magnitude of the imposed back pressure. It is shown that these results are consistent with theoretical predictions using finite element analysis. There is also evidence that the hardness values increase slightly when the pressing speed is increased by one order of magnitude.