Abstract
It has been reported that metals with ultrafine grains(UFG) show outstanding properties such as high strength and toughness at ambient temperature and high corrosion resistance. Intense plastic deformation is considered to be the most appropriate process for grain refinement. We have proposed a novel rolling process, i.e. accumulative roll-bonding (ARB) process, which is capable of producing intensive plastic deformation in a sheet material without any dimensional changes. Ultrafine grained ferrous and aluminum alloy sheets, of which mean grain size is less than 1μm and with very high strength have been successfully fabricated by this process. In this study, the ARB process has been applied to oxigen free copper, whose stacking fault energy is lower than ferrous alloys and aluminum alloys. At lower strain (less than 4), dislocation cell structure develops in the specimens. At higher strain (lager than 4), ultra-fine recrystallized grains appear, whose grain size is about 1 μm. After 7 cycles, lager recrystallized grains with grain size of about 5 μm appear. Tensile strength increased from 215MPa to 425MPa by 11 cycles of ARB. Total elongation decreased from 55% to 10% after 1 cycle, but it tended to increase slightly with increasing equivalent strain.
