Evolution of microstructure and strength during accumulative extrusion bonding of multilayered copper tubes

Accumulative extrusion bonding (AEB) was recently conceived as a novel severe plastic deformation (SPD) process to steady-state bond metals in the pursuit of manufacturing ultrafine-laminated bimetallic tubes. In a recent publication, we have reported details pertaining to the AEB process as uniquely suited to produce geometrical shapes such as tubes. The process has been successfully applied to extrusion bond a Cu-Cu bime-tallic tube at room temperature. The bonding was facilitated under about 68% radial strain, which is more than required for accumulative roll bonding (ARB) of the same material. In this paper, we present the main results from an experimental investigation into the evolution of interface crystallography and integrity, grain structure, crystallographic texture, and tensile strength of the Cu-Cu tube. While the interface maintains overall integrity, it exhibits wavy character locally due to grain-scale plasticity. These observations suggest that laminated structures could be achieved with the continuation of the process. Characterization of grain orientations on each side of the bond line reveals that bonding using AEB at room temperature produces a steady-state bond inde-pendent on preferential grain orientations. Grains become severely elongated along the extrusion direction, while texture forms a moderately strong {111} fiber during the process. A crystal plasticity simulation of texture evolution during the process reveals minor gradients in the texture over the through-thickness direction. Pre-dicted fields of strain during the process show that texture evolution is a consequence of not only large axial strain along the extrusion direction but also severe radial reduction and some shear strain. As a result of large microstructural changes, yield strength of the Cu-Cu tube remarkably increases over 5x in the axial direction relative to the annealed material.

Automated summary

Accumulative extrusion bonding (AEB) is a novel process for manufacturing ultrafine-laminated bimetallic tubes. This study presents the main results of using AEB to bond Cu-Cu bimetallic tubes, including the evolution of interface crystallography and integrity, grain structure, crystallographic texture, and tensile strength. The results show that AEB can achieve stable bonding at room temperature, with significantly increased yield strength in the axial direction.