Developing Processing Routes for the Equal-Channel Angular Pressing of Age-Hardenable Aluminum Alloys
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INTRODUCTION
EQUAL-CHANNEL angular pressing (ECAP) has now become an attractive processing procedure for producing grain refinement in bulk materials. Typically, ultrafine grains are produced by ECAP with average sizes in the submicrometer or even the nanometer level.[1] Processing by ECAP is an example of the application of severe plastic deformation (SPD) in which high strains are imposed on the sample and the dislocations introduced in the straining process rearrange to form arrays of high-angle boundaries.[2] This type of processing generally leads to a significant increase in the strength of the material at ambient temperature by comparison with their coarse-grained counterparts,[3] and, in addition, there is a potential for achieving excellent superplastic forming properties at elevated temperatures.[4] ZHI CHAO DUAN, formerly Research Assistant, is Postdoctoral Fellow, the Departments of Aerospace & Mechanical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089-1453. NGUYEN Q. CHINH, Associate Professor, is with the Department of Materials Physics, Eo¨tvo¨s Lora´nd University, H-1117 Budapest, Hungary. CHENG XU, formerly Research Assistant Professor, with the Departments of Aerospace & Mechanical Engineering and Materials Science, University of Southern California, is Professor, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, Zhejiang 315201, People’s Republic of China. TERENCE G. LANGDON, is Professor, Departments of Aerospace & Mechanical Engineering, University of Southern California, and Research Professor, Materials Research Group, School of Engineering Sciences, University of Southampton, Southampton SO17 1BJ, United Kingdom. Contact e-mail: [email protected] This article is based on a presentation given in the symposium entitled ‘‘Mechanical Behavior of Nanostructured Materials,’’ which occurred during the TMS Spring Meeting in San Francisco, CA, February 15–19, 2009, under the auspices of TMS, the TMS Electronic, Magnetic, and Photonic Materials Division, the TMS Materials Processing and Manufacturing Division, the TMS Structural Materials Division, the TMS Nanomechanical Materials Behavior Committee, the TMS Chemistry and Physics of Materials Committee, and the TMS/ASM Mechanical Behavior of Materials Committee. Article published online November 6, 2009 802—VOLUME 41A, APRIL 2010
To date, much of the research on ECAP has concentrated on relatively soft materials such as pure fcc metals or solid solution alloys. For example, there have been extensive evaluations of the application of ECAP to high-purity aluminum[5–8] and Al-Mg solid solution alloys.[9–14] By contrast, there has been only a limited number of reports on the pressing of more complex alloys, such as Al-Zn-Mg-(Cu) alloys and the 7000 series of Al alloys, where aging treatments and precipitation kinetics become important features of the processing method. To date, there are reports of the processing by ECAP of the Al-7034 alloy,[15–22] the Al-7050 alloy,[
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