Contents lists available at ScienceDirect Materials Characterization journal homepage: www.elsevier.com/locate/matchar Orientation dependent recrystallization mechanism during static annealing of pure magnesium R.K. Sabat a , S.K. Sahoo b,⁎ , D. Panda b , U.K. Mohanty c , S. Suwas a a Department of Materials Engineering, IISc Bangalore, 560012, India b Department of Metallurgical & Materials Engineering, NIT Rourkela, 769008, India c Department of Mechanical Engineering, ITER, SOA University, Bhubaneswar 751030, India ARTICLE INFO Keywords: Commercially pure magnesium Annealing Texture Microstructure Low angle grain boundaries ABSTRACT In the present study, orientation dependent recrystallization mechanism in pure magnesium is discussed in light of the experimental results. Commercially pure magnesium was subjected to cold rolling of 90% reduction in thickness followed by annealing at 200 °C for different soaking times. Nucleation of no newly oriented grains could be observed during annealing. However, the rate of very low angle grain boundary (VLAGB) movement was found to be the rate controlling step for the formation of recrystallized grains. The formation of sub-grains from the parent grain was observed during annealing of the samples irrespective of the orientation of the grains. However, the rate of sub-grain formation was found to be fastest in the grains of orientations > 40° from the normal direction (ND) of the sample. It was further observed that the growth rate of orientations/grains was decreased with increasing their deviation from ND of the sample. A dominant basal texture was observed in the samples and the maximum weakening of basal texture was observed during 300 s of annealing time. 1. Introduction Poor formability at room temperature deformation of magnesium (Mg) and its alloys restricts their use in different structural applications such as automobiles and aerospace [1–3]. This is attributed to an in- adequate number of slip systems in Mg and its alloys [4,5]. Attempts have been made in the past to improve the formability of Mg through different thermo-mechanical processing, such as extrusion, asymmetric rolling, equal channel angular processing, etc. [6–16]. At room tem- perature the critical resolved shear stress (CRSS) for basal slip is lower than that of non-basal slip, such as the prismatic and pyramidal slip systems [17–19]. The basal slip system alone does not provide the re- quired independent slip systems to satisfy the Von Mises criterion of five independent slip systems for homogeneous deformation. This means that extension twinning is required to accommodate deformation at room temperature. With increasing temperature, the CRSS value quickly decreases for non-basal slip systems and activation of higher order slip systems is observed [17–19]. Variation of the processing conditions and addition of alloying elements are also expected to reg- ulate the texture of Mg for improving its formability. For example, addition of rare earth elements and Ca (calcium) to Mg weakens the basal texture after recrystallization and increase the ductility as well as formability of the Mg alloys [15,16,17,20–26]. The weakening of the recrystallization texture is related to the factors like particle simulated nucleation (PSN), shear band induced nucleation (SBIN) and deformation twin induced nucleation (DTIN) [26–38]. Further, it has been reported that the recrystallization texture does not dependent on the orientation of the nuclei only but on the growth of the specific orientation also. The preferential growth of the recrystallized grains with their c-axis parallel to ND has been reported in pure Mg [39] and AZ31 sheet [40,41]. Most of the above workers have attributed the weakening of texture to its nucleation phenomenon during recrystallization in Mg alloys. Recently, nucleation of no new orientations/grains was reported by R. K. Sabat and S.K. Sahoo [42] during static recrystallization of pure Mg. Nucleation of no new or- ientations at the twin-twin intersection was also reported by Sabat et al. [43] through ‘ex situ’ EBSD (electron backscattered diffraction) in- vestigation. The authors [42] have also been reported that the rotation of sub-grains through 10–30° with respect to the c-axis of the parent grain during annealing. However, the number of grains studied by the authors was statistically low and there was no clear information about the rate of formation of sub-grains in the parent grains of different orientations and their effect on the bulk texture during annealing [42]. Hence, an experiment was designed to study the effect of initial or- ientation on the rate of formation of sub-grains during annealing of the cold rolled pure Mg at 200 °C for varying annealing times. The detailed http://dx.doi.org/10.1016/j.matchar.2017.09.003 Received 5 May 2017; Received in revised form 3 September 2017; Accepted 5 September 2017 ⁎ Corresponding author. E-mail address: santoshsahoo@nitrkl.ac.in (S.K. Sahoo). Materials Characterization 132 (2017) 388–396 Available online 06 September 2017 1044-5803/ © 2017 Elsevier Inc. All rights reserved. MARK