Influence of the Processing Temperature on the Microstructure, Texture, and Hardness of the 7075 Aluminum Alloy Fabricat
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SEVERE plastic deformation (SPD) is one of the most effective ways to produce ultrafine-grained (UFG) materials, with a mean grain size smaller than 1 lm, in bulk macroscopic materials.[1,2] Ultrafine-grained materials are expected to perform prominent mechanical properties. Accumulative roll bonding (ARB), originally developed by Saito et al.,[3] is one of the most popular SPD techniques.[4–6] Accumulative roll bonding does not require any special equipment and enables the production of UFG structures in bulk sheet materials. Moreover, continuous rolling mills can be readily used in industry for ARB. For these reasons, ARB is perhaps the most promising SPD process for industrial practice. The ARB process consists of cutting sheets into stacks and roll bonding. By repeating this procedure, very high strains can be introduced into the material. As a result, significant structural refinement can be achieved.[7] It has been verified that the redundant shear strain that may be introduced to the material significantly contributes to grain refinement.[8,9] To date, the ARB process has been performed mostly by two layers stacking and rolling by 50 pct reduction in thickness. If the number of stacking layers and the reduction per pass increase, some advantages will be expected:[10,11] (1) the productivity P. HIDALGO, Ph.D. Student, C.M. CEPEDA-JIME´NEZ, Postdoctoral Researcher, O.A. RUANO, Professor, and F. CARREN˜O, Staff Researcher, are with the Department of Physical Metallurgy, CENIM, CSIC, 28040 Madrid, Spain. Contact e-mail: hidalgo@cenim. csic.es Manuscript submitted August 21, 2009. Article published online January 22, 2010 758—VOLUME 41A, MARCH 2010
would increase, (2) the bonding strength between the stacked layers would improve, and (3) more severe compressive and shear deformation could be introduced into the materials. The UFG metals produced by high strain deformation are generally characterized by a mixture of highangle boundaries (HABs) and low-angle boundaries (LABs). Furthermore, the presence of a density of interior dislocations within the volumes between the boundaries is also a common feature.[12] These characteristics strongly depend on the metal and some of the processing conditions applied, such as temperature. Additionally, similar textures to those obtained by conventional rolling are generated by ARB.[13,14] In the present investigation, a 3:1 reduction per pass ARB process was applied to the commercial 7075 aluminum alloy at three different temperatures for which a good bonding is achieved (300 C, 350 C, and 400 C). This alloy is one of the strongest wrought aluminum alloys, and as such, it is widely used for the construction of plane structures such as wings and fuselages because of its excellent strength/weight rate.[15] Application of the ARB process to the 7075 aluminum alloy would result in an improvement of the superplastic properties and thereby in important savings in the aeronautical industry. However, since this alloy is age hardenable, it contains thermally unstable precipitates that ma
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