Fatigue-Property Enhancement of Magnesium Alloy, AZ31B, through Equal-Channel-Angular Pressing
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INTRODUCTION
EQUAL-channel-angular pressing (ECAP) is a deformation-processing technique, which induces a large strain into the billet as it is pressed through the two intersecting channels (usually at 90 deg) with the same cross section. Different microstructures can be developed when using different strain paths (or routes A through C) by rotating the billet between consecutive pressings through modifying the shear planes and shear directions. The ECAP has been successfully used to refine grains down to the submicrometer or even nanometer range in order to increase the strength in many metallic alloys and composites.[1] However, due to the reduced ductility in most ECAP-processed metals, usually, a deterioration of the fatigue life in the low-cycle-fatigue regime, with intermediate to high plastic-strain amplitudes, is reported, for example, in pure Cu[2] and Al alloys.[3] LIANG WU, GRIGORETA M. STOICA, HAO-HSIANG LIAO, and GONGYAO WANG, Graduate Students, DOUGLAS E. FIELDEN, Instrument Maker Supervisor, and PETER K. LIAW, Professor, are with the Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996-2200, USA. Contact e-mail: [email protected] SEAN R. AGNEW, Assistant Professor, is with the Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22904-4745, USA. E. ANDREW PAYZANT, Senior R&D Staff Member Supervisor, is with the Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. LIJIA CHEN, Professor, is with the Department of Materials Science and Engineering, The University of Tennessee, is with the School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110023, People’s Republic of China. This article is based on a presentation given in the symposium entitled ‘‘Deformation and Fracture from Nano to Macro: A Symposium Honoring W.W. Gerberich’s 70th Birthday,’’ which occurred during the TMS Annual Meeting, March 12–16, 2006 in San Antonio, Texas and was sponsored by the Mechanical Behavior of Materials and Nanomechanical Behavior Committees of TMS. Article published online June 13, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS A
On the other hand, in the high-cycle-fatigue regime with intermediate to low plastic-strain amplitudes, the fatigue life is strongly enhanced, due to the increased strength.[4,5] In contrast, Mg alloys deformed through ECAP exhibit a ductility enhancement and a significant yield-strength reduction, probably due to the crystallographic texture transformation.[6,7,8] The Mg-based alloys, as potential lightweight structural materials with applications in the automobile, aircraft, and electronics industries, have attracted extensive research efforts, which are usually focused on such monotonic mechanical behavior as tensile and compressive properties, but there is only limited research work on the fatigue behavior of Mg-based alloys, particularly processed by ECAP.[9,10] Hence, the objectives of this study are to further understand the fa
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