Enhanced damping capacity of magnesium alloys by tensile twin boundaries Yujie Cui, a Yunping Li, b,⇑ Shihai Sun, a Huakang Bian, a Hua Huang, c Zhongchang Wang, d Yuichiro Koizumi e and Akihiko Chiba a,e a School of Engineering, Tohoku University, Sendai 980-8577, Japan b Department of Materials Science and Engineering, Central South University, Changsha 410083, China c National Engineering Research Center of Light Alloy Net Forming, Shanghai JiaoTong University, 200240 Shanghai, China d WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan e Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan Received 30 November 2014; revised 6 January 2015; accepted 7 January 2015 Available online 28 January 2015 We propose a novel method to fabricate Mg alloys with enhanced damping capacity without sacrificing mechanical properties by introducing {10 12} twin boundaries. We find that the twin boundaries and their reciprocating movements play a significant role in remarkably enhancing the damping capacity of Mg alloys at high vibration strain amplitude. Such enhancement is especially pronounced in a slightly hot-forged sample with a subsequent annealing at 250 °C for a short period, where incoherent twinning boundaries can be reorganized into coherent ones. Crown Copyright Ó 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Mg alloys; Twin boundary; Damping capacity; Plastic deformation Damping capacity of magnesium (Mg) is generally dominated by basal slip, which absorbs the external vibration energy through reciprocating motion of dislocations. The high damping capacity of pure Mg can usually be ascribed to the extremely low critical resolved shear stress (CRSS) of basal slip (0.6 MPa) as compared to that of non-basal slip systems (>38 MPa) [1,2]. However, damping capacity of Mg is signif- icantly reduced once it is alloyed in order to improve its mechanical properties [3]. The reduction in damping capacity has been ascribed to the inhibition of dislocation motion in basal planes and the lowered sweeping activity by solution atoms and precipitates [4, 5], leading to an increased CRSS for basal slip (e.g. to 2 MPa for AZ31 alloy) [6]. Several techniques have been applied to modify the damp- ing capacity of Mg alloys by adding Ni [4], Cu [7], or heat treatment [8]. However, these methods generally either dete- riorate the mechanical properties or lead to other problems, such as complications in manufacturing. In addition, the influence of cold or hot working on damping capacity of Mg alloys has also been studied by Fan et al. [9] via equal- channel angular pressing and Kamado et al. [10] by cold-roll- ing. The results indicated that plastic deformation to large strain level is unfavourable for enhancing the damping capac- ity of Mg alloys because it leads to an extremely high disloca- tion density that lowers the mobility of dislocations through their mutual interaction. This poses a further considerable challenge for the development of Mg alloys with a high damping capacity, the origin of which is twofold. On the one hand, it is difficult to improve the density of mobile dis- locations in basal planes on a large scale, because a high den- sity of dislocations generally leads to low mobility due to their mutual interactions. On the other hand, although the new interfaces formed via doping other elements or phases may play a role in increasing the damping capacity of Mg alloys, such effect is small because the intrinsic defects such as the non-coherent interface greatly inhibit the interface motion [11]. Novel methods to substantially enhance the damping capacity of Mg alloys, without compromising mechanical properties, would be highly valuable for engineer- ing applications as well as in fundamental scientific research. It is well known that {1 0 1 2} tensile twin boundaries in Mg are movable and can shrink and grow even at a stress much lower than the nucleation stress [11–14]. CRSS for the growth of {1 0 1 2} twin was found to be 2–3 MPa for AZ31 alloys [6], which is slightly higher but very close to that of the basal slip system (approximately 2 MPa) [15,16]. However, no clear evidence has been provided, and it remains unknown how twins can affect the damping capacity of Mg alloys, and also to what extent the damping capacity can be improved, although Tsai et al. [17] indicated that twins may be crucial for increasing the damping capacity of Mg1 wt.% Zr alloys. In this work, we introduce a large number of {1 0 1 2} twins in AZ31Mg alloy through hot compression, and demonstrate, for the http://dx.doi.org/10.1016/j.scriptamat.2015.01.002 1359-6462/Crown Copyright Ó 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +86 138 0739 9012.; e-mail: lyping@ csu.edu.cn Available online at www.sciencedirect.com ScienceDirect Scripta Materialia 101 (2015) 8–11 www.elsevier.com/locate/scriptamat