Effect of Deformation Temperature on Microstructure and Mechanical Properties of AZ31 Mg Alloy Processed by Differential-Speed Rolling Mosab Kaseem, Bong Kwon Chung, Hae Woong Yang, Kotiba Hamad, Young Gun Ko * School of Materials Science and Engineering, Yeungnam University, Gyeongsan 712-749, South Korea article info Article history: Received 5 June 2014 Received in revised form 19 August 2014 Accepted 28 August 2014 Available online xxx Key words: Differential-speed rolling Magnesium alloy Mechanical properties Strain hardening A differential-speed rolling (DSR) was applied to AZ31 magnesium alloy sample at different rolling temperatures of 473, 523, 573, and 623 K with 1-pass and 2-pass operations. The microstructural evo- lution and mechanical properties of the deformed samples were investigated. The rolling temperature was found to be an important parameter affecting the microstructural development. After DSR at 473 K, the microstructure was more homogeneous than that obtained after deformation by equal-speed rolling (ESR). The fully recrystallized microstructures were generated after DSR at 573 and 623 K. As to me- chanical properties, the yield strength (YS) and ultimate tensile strength (UTS) decreased monotonously with increasing rolling temperature. In contrast, the elongation of the DSR-deformed samples was improved as the rolling temperature increased. The strain hardening exponent (n) calculated by Hollo- mon equation increased with increasing the rolling temperature, which would explain an increase in the uniform elongation. Copyright © 2015, The editorial office of Journal of Materials Science & Technology. Published by Elsevier Limited. All rights reserved. 1. Introduction Magnesium (Mg) and its alloys have recently attracted much interest in structural applications owing to high specific strength, good cast-ability, and excellent damping capacity [1e3] . Wrought Mg alloys were of special interest for use as structural parts because of the possibility of controlling more homogenous microstructure and higher mechanical properties as compared to the cast components. In particular, wrought Mg alloys processed by plastic forming processes, such as rolling, extrusion, and sheet forming, would offer a good combination of mechanical properties as compared to cast Mg alloys after plastic forming [4,5] . Nevertheless, wrought Mg alloys suffered from poor ductility and formability at room temperature, which has been a major concern for the industrial applications of wrought Mg alloys. In addition, conventional plastic forming pro- cesses were known to induce a strong basal texture, resulting in very poor cold-formability and mechanical anisotropy in the sec- ondary processing [6e10] . Controls of grain and texture by thermo-mechanical processing would be two important ways to enhance the mechanical response of Mg alloys. Mabuchi et al. [11] and Lin et al. [12] utilized an equal channel angular pressing (ECAP) method to enhance the ductility of Mg alloys at room temperature, in which a shear strain inclined to ~45  along with deformation direction was imparted. The high strain and/or strain rate in this process led to severe grain refine- ment, and texture evolution appeared with a rotation of the basal pole by ~45  to the ECAP direction. In recent years, differential- speed rolling (DSR) has been employed as a promising technique to improve the strength and ductility together of Mg alloys in the form of sheet on a large scale [13e17] . In DSR, the upper and lower rolls were supposed to be rotated at different speeds in order to induce the shear strain. The high amount of shear strain induced during process would refine the grain size. This could also lead to an inclination of the basal pole, causing the basal texture with weaker intensity than what the conventional rolling, so-called equal-speed rolling (ESR), generated. Therefore, the earlier results showed clearly that DSR process was considered an effective method to improve the ductility by lowering the basal texture intensity, and to enhance the strength by reducing the matrix grain size due to the shear deformation [15e17] . As such, Gong et al. [18] reported superior combination of elongation and tensile strength in the DSR- processed ZK60 Mg alloy sheet to the case of the ESR-processed sheet under the same condition of thickness reduction per pass. The microstructure and mechanical properties of Mg alloys were influenced by DSR with various processing parameters, such as temperature, deformation route, roll speed ratio, and thickness * Corresponding author. Prof.; Tel.: þ82 53 8102537; Fax: þ82 53 8104628. E-mail address: younggun@ynu.ac.kr (Y.G. Ko). Contents lists available at ScienceDirect Journal of Materials Science & Technology journal homepage: www.jmst.org http://dx.doi.org/10.1016/j.jmst.2014.08.016 1005-0302/Copyright © 2015, The editorial office of Journal of Materials Science & Technology. Published by Elsevier Limited. All rights reserved. Journal of Materials Science & Technology xxx (2015) 1e6 Please cite this article in press as: M. Kaseem, et al., Journal of Materials Science & Technology (2015), http://dx.doi.org/10.1016/ j.jmst.2014.08.016