Elevated Temperature Effects on the Plastic Anisotropy of an Extruded Mg-4 Wt Pct Li Alloy: Experiments and Polycrystal
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MAGNESIUM (Mg) alloys are being increasingly researched and evaluated for several structural applications within the automotive, aerospace, and consumer electronic industries due to their high strength-to-weight ratio. The automobile industry, for instance, is already using cast Mg alloys.[1,2] However, there are many other alloys, such as wrought Mg alloys, that possess much MARCEL RISSE, Scientific Assistant, and WALTER REIMERS, Professor, are with the Metallische Werkstoffe, Technische Universita¨t Berlin, Ernst-Reuter-Platz 1, 10587, Berlin, Germany. Contact e-mail: [email protected] MARTIN LENTZ, Postdoctoral Researcher, formerly with the Metallische Werkstoffe, Technische Universita¨t Berlin, is now with the Hydro Aluminium Rolled Products GmbH, Research and Development Bonn, P.O. Box 2468, 53014, Bonn, Germany. CHRISTOPH FAHRENSON, Technical Staff Member, is with the Zentraleinrichtung Elektronenmikroskopie, Technische Universita¨t Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany. MARKO KNEZEVIC, Assistant Professor, is with the Department of Mechanical Engineering, University of New Hampshire, Durham, NH, 03824. IRENE J. BEYERLEIN, Professor, is with the Department of Mechanical Engineering, Materials Department, University of California at Santa Barbara, Santa Barbara, CA, 93106. Manuscript submitted June 6, 2016. Article published online November 3, 2016 446—VOLUME 48A, JANUARY 2017
higher strengths. To use wrought Mg alloys, the main hurdle to overcome is their limited room-temperature ductility. Enhancing the ductility of Mg alloys requires a better understanding of the plastic deformation mechanisms involved in their mechanical behavior. In Mg and its alloys, most often, hai basal slip is the easiest slip mode to activate, and the other available modes, such as hai prismatic slip or hc þ ai pyramidal slip, are relatively harder.[3–7] For a polycrystalline Mg material to accommodate a general applied deformation, activation of different sets of slip systems within the differently oriented crystals in the polycrystal is needed.[7–12] Accordingly, in the event that nonbasal slip is much more difficult to activate than basal slip, pronounced macroscopic plastic anisotropy (PA) and potential strain localizations and macroscale instabilities can occur, thereby lowering overall ductility and formability.[13–15] As one solution, Mg-Li alloys are being considered as attractive structural material candidates, not only for their intrinsic lightweightness, but also for long elongations in tension and compression tests and ease in room-temperature rolling compared to pure Mg.[13,16] It was further shown in Reference 17 that the Mg-4 wt pct Li alloy exhibits less room-temperature PA compared to METALLURGICAL AND MATERIALS TRANSACTIONS A
pure Mg. These more desirable deformation responses have been attributed to higher contributions of prismatic and pyramidal slip. Some evidence has been provided in Reference 18, where transmission electron microscopy (TEM) analysis revealed that deformed Mg-15 at. pct L
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