Equal-channel angular pressing: influence of die design on pressure forces, strain homogeneity, and corner gap formation

The results of experiments directed to the optimization of Equal-channel angular pressing (ECAP) die design can be affected by the material response to deformation, thus making difficult to isolate the die performance, particularly with respect to the assessment of strain homogeneity. In the present work, a completely “inert” material was employed for the physical simulation of the ECAP deformation, thus permitting an unequivocal analysis of the die performance. Such material is the Pb–62 %Sn alloy, of which absence of strain hardening, that is, full recrystallization during or after equal-channel angular pressing, was here ascertained. As a consequence, the corner gap effect, a phenomenon known to decrease strain homogeneity, will depend only on die geometry. The study was extended to the case in which the strain distribution depends on both outer (R) and inner (r) curvature radii. Results show that the size of the corner gap is related to the deformation homogeneity of the billet, and the pressing forces are reduced for large outer radii. Emphasis was given to the quantitative measurement of the corner gap size, its relationship with the von Mises strain, and its distribution within the ECAP-processed billet, for different R–r combinations.