Accumulative channel-die compression bonding (ACCB): A new severe plastic deformation process to produce bulk nanostructured metals

This paper introduces a new severe plastic deformation process to produce bulk nanostructured metals: accumulative channel-die compression bonding (ACCB). In the ACCB process, which can be applied to thick billets, the procedure of cutting, stacking and compression bonding in a channel-die is repeated to provide an ultrahigh plastic strain. This process was trialed with high purity aluminum. A fully recrystallized aluminum sample was deformed by ACCB at room temperature for up to 10 cycles, corresponding to an equivalent strain of 8.0. The initially coarse grains were subdivided by deformation-induced high-angle boundaries, and the fraction of such high-angle boundaries increased with increasing strain. Several cycles of ACCB led to a quite uniform ultrafine structure dominated by high-angle grain boundaries. The average boundary spacing of the 10-cycles ACCB sample was as small as 690 nm. The maximum ultimate tensile strength of the ACCB samples was 130 MPa after 5 cycles. Further ACCB cycles, however, led to a slight decrease in strength due to enhanced recovery and boundary migration during the deformation process. It has been demonstrated that the ACCB process can be used to produce bulk nanostructured metals of relatively large dimensions. The results suggest that the ACCB process is equivalent to conventional rolling deformation at high strains.