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JMEPEG (2013) 22:1666–1671 DOI: 10.1007/s11665-012-0436-4

Inhomogeneity Through Warm Equal Channel Angular Pressing Majid Vaseghi, Hyoung Seop Kim, Ali Karimi Taheri, and Amir Momeni (Submitted January 27, 2012; in revised form October 11, 2012; published online December 1, 2012) In this study, the hardness inhomogeneity of billets during multi-passes of equal channel angular pressing (ECAP) at elevated temperatures is investigated and the effect of large strain deformation during ECAP on the hardness inhomogeneity characteristics due to dynamic aging of aluminum 6061 under a variety of temperatures and ram speed was studied by TEM and hardness measurements. The hardness results showed that the hardness distribution is more homogenous after four passes using the pressing route Bc. However, when the deformation temperature was considered, performing ECAP at 100 °C may provide the most homogeneous microstructure after multi-pressing as long as the total number of pressing passes is four. This indicates that a lower temperature (in the range of warm working) is favorable for achieving an ultrafine-grained/nanomaterial with a more homogenous microstructure. In order to quantify the inhomogeneity in the cross section of the as-pressed sample, an inhomogeneity index has been defined. The results show an increase in the hardness in the first pass with significant inhomogeneous deformation and a transition toward a more homogeneous structure with subsequent passes.

Keywords

age hardening, aluminum, equal channel angular processing, hardness, inhomogeneity, nanostructured material

1. Introduction Aluminum alloys are increasingly used in buildings, vehicles, and aerospace, principally for weight savings. The production of homogeneous parts is as important as the mechanical and physical properties of such parts. Today, severe plastic deformation (SPD) techniques are used to produce bulk ultrafine-grained and nanostructured materials. It has been well documented that equal channel angular pressing (ECAP) leads to considerable grain refinement in metals and alloys for the production of materials having superior properties including high strength and ductility (Ref 1-3). SPD processing requires the generation of dislocations and dislocation movement, which initiate inhomogeneous plastic deformation, largely due to the formation of persistent slip bands. When plastic deformation is performed on alloys, there are extra

Majid Vaseghi, Department of Materials Science and Engineering, Hamedan University of Technology, 65155-579 Hamedan, Iran; and Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 790-784, Korea; Hyoung Seop Kim, Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 790-784, Korea; Ali Karimi Taheri, Department of Materials Science and Engineering, Sharif University of Technology, 11155-9466 Tehran, Iran; and Amir Momeni, Department of Materials Science and Engineering, Hamedan University of Technology, 65155-579 Hamedan, Ir