Spatial and Temporal Characteristics of Propagating Deformation Bands in AA5182 Alloy at Room Temperature
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ALUMINUM alloys are important technological materials primarily due to their attractive strength-toweight ratio. They are used in diverse applications ranging from packaging to the aeronautical industry. Important candidates for such applications are the alloys from the 5000 series whose primary alloying element is Mg. They may be rolled into thin sheets and offer significant strength. However, their plastic deformation at room temperature is discontinuous, with the strain localizing in narrow bands that leave undesirable traces on the surface of the final product. This is the signature of the Portevin–Le Chatelier (PLC) phenomenon, which manifests itself in certain ranges of temperature and strain rate. The repeated strain localization is due to the negative strain rate sensitivity (SRS) of the material, which, in turn, is correlated with smaller scale phenomena associated with interactions between solute and dislocations, referred to as dynamic strain aging (DSA). The technological goal is to increase the SRS to R. NOGUEIRA DE CODES, Associate Professor, is with LMT-Cachan, ENS de Cachan/CNRS/UPMC, F-94235 Cachan, France. O.S. HOPPERSTAD and O.-G. LADEMO, Professors, are with the Structural Impact Laboratory-SIMLab, Centre for ResearchBased Innovation (CRI), and Department of Structural Engineering, NTNU, NO-7491 Trondheim, Norway. O. ENGLER, Professor, is with Hydro Aluminium Deutschland GmbH, R&D Center Bonn, D-53014 Bonn, Germany. J.D. EMBURY, Emeritus Professor, is with Material Sciences and Engineering, McMaster University, Hamilton, ON, Canada L8S 4L7. A. BENALLAL, Professor, is with LMT-Cachan, ENS de Cachan/CNRS/UPMC. Contact e-mail: [email protected] Manuscript submitted August 4, 2010. Article published online June 22, 2011 3358—VOLUME 42A, NOVEMBER 2011
positive values in the range of temperatures and strain rates relevant for industrial processes. This would ensure material stability during processing and would eliminate the PLC phenomenon. In particular, in Al-Mg alloys, it is desirable to increase the SRS and to eliminate the PLC effect at room temperature. As proposed by Cottrell,[1,2] the unstable plastic flow observed in Al-Mg alloys can be a result of solutedislocation interaction at the microscopic level. To date, a full understanding of the micromechanical mechanisms and the relevant factors affecting the macroscopic behavior of serrated plastic flow is still lacking. However, the cause of the PLC effect is negative steady-state SRS, which is attributed to DSA associated with conditions when point defects can diffuse toward mobile dislocations and temporarily arrest them.[3,4] The results of DSA are higher flow stress and greater work hardening at lower strain rates than for higher ones, and further serrated stress-strain curves, discontinuous plastic flow, and propagating deformation bands during plastic straining. An interesting historical presentation of the various studies of the PLC effect can be found in Reference 5. In this article, we provide experimental data on the mechanical behavior o
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