DOI: 10.1002/adem.201100139 Low Temperature Plasticity of an Ultrafine-Grained Al–3Mg Alloy Prepared by Accumulative Roll Bonding** By Sergii Eduardovich Shumilin, Milos Janec ˇek, * Nikolai Vasilievich Isaev, Petr Homola and Robert Kral The basic principle of all severe plastic deformation (SPD) processes consists in inducing an extremely high plastic strain into the material, whereas no shape and dimension changes occur during the straining. The high strain causes deformation and fragmentation of intermetallic particles and significant increase of the volume fraction of grain/subgrain boundaries that results in substantial grain refinement and improved strength of the metals and their alloys. [1–3] Various kinds of special SPD processes have been proposed, and some of them have actually succeeded in producing bulk ultrafine grained (UFG) materials. Besides two most popular and wide-spread SPD methods—equal-channel angular pressing (ECAP) and high-pressure torsion (HPT), an accumulative roll bonding (ARB) method is also well-known. This method, that uses only conventional rolling equipment and for this reason is promising for commercial application in industry, allows to produce the UFG material in the form of sheets and has been successfully applied to various metallic materials. Using the ARB method, it is possible to obtain metals and alloys with grain size ranging from 1 to 0.1 mm. [4,5] The influence of the ARB process on the strength and ductility at room temperature (RT) and higher temperatures has been studied on different UFG materials, including Al–Mg alloys. [6] Nevertheless, there is only limited quantity of work related to the behavior at lower temperatures. Several authors only reported enhanced strength and strain hardening rate of UFG Al as the deformation temperature decreases from RT to 4.2 K. [7–10] These and other mechanical features of such materials stimulate a great interest to study physical mechan- isms of plastic deformation in the wide temperature range. In this work, the mechanical properties of ARB processed Al–3Mg were investigated by uniaxial tension in temperature range from 0.5 to 295 K. 1. Results and Discussion Stress–strain diagrams s–e for Al–3Mg after three ARB-cycles for different temperatures are presented in the Figure 1. At RT the Potrevin–Le Chatelier effect (repeated stress drops) is observed. With decreasing temperature from 77 to 20 K, the deformation curves begin to be smooth. Nevertheless, at 4.2 and 0.5 K the low-temperature serrated (stress drops) deformation (LTSD) was found. For small strains at 4.2 K the separate drops divided by smooth areas were found. As the strain increases the smooth areas gradually reduce and the stress drops succeed immediately one after another. The average amplitude of stress drops increases with deformation reaching the value of 70 MPa near the ultimate stress s m . At the temperature of 0.5 K the plastic deformation exhibits serrations already near the yield stress, but the amplitude of stress drop decreases as compared to the one at 4.2 K and the same level of flow stress. It should be noted that the temperature 0.5 K is below the critical temperature of superconducting transition in aluminum. COMMUNICATION [*] Prof. M. Janec ˇek Department of Physics of Materials, Charles University, CZ-161 16 Prague, (Czech Republic) E-mail: janecek@met.mff.cuni.cz Dr. S. E. Shumilin, Dr. N. V. Isaev National Academy of Sciences of Ukraine, Institute of Low Temperature Physics and Engineering, 61103 Kharkov, (Ukraine) Dr. P. Homola Aeronautical Research and Test Institute, CZ-199 05 Prague, (Czech Republic) Dr. R. Kral Department of Physics of Materials, Charles University, CZ-121 16 Prague, (Czech Republic) [**] This study was financially supported by GACR under the project 106/09/0482. Partial financial support by the Ministry of Education, Youth and Sports under the research program MSM 0021620834 is also gratefully acknowledged. Many efforts have been made recently to produce ultrafine grained (UFG) structural metallic materials having submicrometer grain sizes, since UFG materials are expected to perform superior mechanical properties, i.e., a high strength, good elongation and, mainly superplastic formability at lower temperatures and higher strain rates. One of the promising ways to produce bulk UFG materials is the severe plastic deformation (SPD). ADVANCED ENGINEERING MATERIALS 2012, 14, No. 1-2 ß 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 35