The role of backpressure during large scale Equal-Channel Angular Pressing

In this study we investigate the influence of various magnitudes of backpressure (0 to 200 MPa) during large scale (cross-section 50x50 mm2) equal-channel angular pressing (ECAP). We focus on the homogeneity of the induced strain and, within this context, on the homogeneity of the resulting mechanical properties after one pass of ECAP at room temperature. We find that large scale ECAP without the application of a backpressure clearly leads to heterogeneous shear strains, causing heterogeneous mechanical properties. A pronounced maximum of hardness next to a local minimum at the billet's bottom occurs; in the absence of backpressure during processing, its expansion covers almost one half of the cross-section. The application of a backpressure close to the material's proof stress after processing (in this case 200 MPa) results in an excellent homogeneity with a negligible local heterogeneity at the bottom of the billet.