Strengthening Mechanisms and Electrochemical Behavior of Ultrafine-Grained Commercial Pure Copper Fabricated by Accumulative Roll Bonding

In this study, the four-cycle accumulative roll bonding (ARB) process at room temperature was successfully used for grain refining in commercial pure copper. Atomic force microscopy (AFM) images revealed that the average grain size reduced from about 26 µm in the unprocessed material to about 180 nm after four cycles of ARB. Also, transmission electron microscopy image indicated that the average grain size reached to 200 nm after four cycles. The yield strength of the ultrafine-grained pure copper after fourth cycle (360 MPa) was about 400 pct higher than that of the annealed unprocessed sample (70 MPa). The contribution of dislocations in strengthening of the pure copper decreased from ~30 to ~3 pct whit increasing the number of ARB cycles from 1 to 4. Scanning electron microscopy micrographs of fractured surfaces of the tensile test specimens revealed that ductile fracture of annealed sample with deep equiaxed dimples replaced by shear ductile rupture with shallow and small elongated dimples in ARB-processed samples. Moreover, electrochemical impedance spectroscopy and Mott–Schottky analysis showed that the electrochemical behavior improved by increasing the number of ARB cycle.