A {001} 100 oriented aluminum single crystal was deformed by nine cycles of accumulative roll bonding which corresponded to a total equivalent strain of ε=7.2. The formation of {4 4 11} 11 11 8 component in deformation texture was examined by using electron back-scatter diffraction method. The specimen processed by five cycles ARB (ε=4) developed four variants of {123} 634 orientation in the deformation texture. Between the five and nine cycles, the four variants of {123} 634 rotated toward {4 4 11} 11 11 8 and {112} 111 orientations. The specimen after the ninth cycle had a weak texture which was mainly composed of {4 4 11} 11 11 8 , {112} 111 and {123} 634 components. The results obtained in the present study indicate that {4 4 11} 11 11 8 and {112} 111 become the primary and secondary stable orientations in the specimens deformed by accumulative roll bonding to the extremely high strain. The occurrence of the cyclic ratcheting which was reported by Heason et al. was also investigated. The cyclic ratcheting, which causes the formation of {4 4 11} 11 11 8 in the center layer, did not have much effect on the {001} 100 oriented single crystal.
The enhancement of strength of a Cu 1.4 massNi 0.25 massP 0.1 massZr alloy, in which the Ni and P contents are about twice larger than those in commercial Cu Ni P alloys, has been tried by means of combining accumulative roll bonding (ARB) process by 7 cycles and aging treatment at 350 to 450°C. For the sake of comparison, the mechanical properties of the alloy conventionally cold rolled to a reduction of 50 and 90 and aged at 350 to 450°C have also been examined. The grain sizes of the Cu Ni P Zr specimens deformed by 7 cycle ARB process and 90 cold rolling were refined down to about 0.4 mm and 4 mm, respectively, and the fractions of high angle grain boundaries in the specimens were nearly the same, about 45. Initial aging, subsequent ARB process or 90 cold rolling and re aging at 400°C produced the Cu Ni P Zr alloy highly strengthened. The alloy, initially aged, then ARB processed and re aged, had a tensile strength of 780 MPa, an elongation of 6 up to failure and an electrical conductivity of 56 IACS. The differences in yield strength among the re aged specimens after 50 and 90 cold rolling and ARB process are explained by the differences among the dislocation density, grain size and inter precipitate spacing. (Received December 20, 2010; Accepted June 3, 2011) Keywords: copper nickel phosphorus alloy, accumulative roll bonding process, tensile property, grain refinement strengthening, precipitation strengthening, dislocation strengthening
Using Vickers hardness measurements and TEM observation, this study investigated the aging behavior of ultrafine-grained UFG Al-0.5%Si-0.5%Ge alloy fabricated using six-cycle ARB processing. The hardness of the starting specimen of ultrafine-grained Al-0.5%Si-0.5%Ge alloy is about 2.3 times higher than that of the coarsegrained specimen. The starting UFG specimen showed ultrafine grains with mean size of 156 nm. The hardness of a UFG specimen aged at 473 K decreased monotonously with increasing aging time. From TEM observations of the microstructure of UFG specimen aged after long-term aging at 473 K, results show that the mean size of ultrafine grains increased significantly with increasing aging time. Furthermore, few precipitates exist inside gains, although many coarse precipitates exist at grain boundaries. The hardness of UFG specimen aged at 373 K showed the maximum value. From TEM observations, results showed many elongated ultrafine grains, with many precipitates formed on the grain boundaries and inside grains of the specimens aged at 373 K. These results suggest that precipitation hardening strongly affected the hardness in this alloy because it has many elongated ultrafine grains. Many fine Si-Ge precipitates formed inside grains of the UFG specimen aged at 373 K in long-term aging.
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