Effect of texture types on microstructure evolution and mechanical properties of AZ31 magnesium alloy undergoing uniaxial tension deformation at room temperature

Materials Science & Engineering A 769 (2020) 138497

Contents lists available at ScienceDirect

Materials Science & Engineering A journal homepage: http://www.elsevier.com/locate/msea

Effect of texture types on microstructure evolution and mechanical properties of AZ31 magnesium alloy undergoing uniaxial tension deformation at room temperature Yu Chen a, Li Hu a, *, Laixin Shi a, **, Tao Zhou a, Jian Tu a, Qiang Chen b, Mingbo Yang a a b

College of Material Science and Engineering, Chongqing University of Technology, Chongqing, 400054, PR China Southwest Technology and Engineering Research Institute, Chongqing, 400039, PR China

A R T I C L E I N F O

A B S T R A C T

Keywords: AZ31 Mg alloy Non-basal texture Plastic deformation Twinning

Influence of texture type on mechanical properties and the evolution of microstructure and texture is thoroughly investigated via uniaxial tension experiment along rolling direction (RD) at room temperature on two different AZ31 alloy sheets. Electron backscattered diffraction (EBSD) measurements on deformed samples confirm that dislocation slip is the main deformation mechanism in as-received sheet with a typical basal texture, while dislocation slip and extension twinning (ET) both contribute to sustaining plastic strain in the sheet with a rare RD-split bimodal texture, which is fabricated by equal channel angular rolling and continuous bending process with subsequent annealing (ECAR-CB-A). Therefore, these two sheets demonstrate obviously different texture evolution during plastic deformation. As-received sheet maintains basal texture and further experience the concentration of basal poles towards normal direction (ND). However, ECAR-CB-A sheet not only undergoes the gradual diffusion and rotation of tilted basal poles to ND but also the development of a new TD-component texture. The activation of ET variants in ECAR-CB-A sheet is confirmed to play an important role in texture evolution, and the number of activated ET variants is increasing with the increase of angle between ND and caxis. In addition, acquired mechanics data demonstrate that ECAR-CB-A sheet possesses higher fracture elon­ gation (24%) and lower yield stress (73 MPa) as compared to as-received sample. This issue can be ascribed to the participation of ET to coordinate plastic deformation along c-axis and the easier activation of basal slip in ECAR-CB-A sheet.

1. Introduction Magnesium (Mg) alloys have been termed as desirable candidates in weight-critical structural materials in automobile and aerospace in­ dustries as they possess remarkable attractiveness including low density, high specific stiffness and strength and good damping property [1–4]. However, due to their hexagonal close-packed (HCP) structure, Mg alloy sheets fabricated by rolling and subsequent annealing treatment usually possess strong basal texture, which leads to the poor formability and ductility at room temperature, and further restricts the broad applica­ tion of Mg alloys [2,5,6]. It has been generally accepted that texture type has a great influence on the deformation behavior and the activities of slip/twinning modes during plastic deformation of Mg alloys [7–9]. Thus, many researches have been conducted for tailoring the texture of

Mg alloys in order to enhance their plasticity and ductility at room temperature. Recently, intelligent processing schemes utilizing severe plastic deformation (SPD) technologies including equal channel angular extrusion (ECAE) [10], high pressure torsion (HPT) [11] and large strain rolling (LSR) [12] have been proven to be effective ways to weaken basal texture by introducing strong shear deformation during the processing, and the corresponding tensile ductility of Mg alloy sheets at room temperature has been enhanced. However, no significant modification in the texture type of conventional Mg alloys has been realized and re­ ported. In our previous work, a novel technology, viz. equal channel angular rolling and continuous bending process with subsequent annealing (ECAR-CB-A), has been developed to manufacture AZ31 alloy sheet with a rare RD-split bimodal texture. The corresponding Erichsen

* Corresponding author. ** Corresponding author. E-mail address: [email protected] (L. Hu). https://doi.org/10.1016/j.msea.2019.138497 Received 4 August 2019; Received in revised form 30 September 2019; Accepted 2 October 2019 Available online 3 October 2019 0921-5093/© 2019 Elsevier B.V. All rights reserved.

Y. Chen et al.

Materials Science & Engineering A 769 (2020) 138497

Fig. 1. (a) Schematic illustration of tension specimen within the AZ31 alloy sheet; (b) The corresponding dimensions of manufactured tension specimen.

value of AZ31 alloy sheet produced by ECAR-CB-A process is determined to be 7.4 mm, which is much higher than that of 4.2 mm in the common hot-rolled sheet [13,14]. Obviously, it is of great significance to inves­ tigate the detailed deformation behavior and deformation mechanisms of this AZ31 alloy sheet fabricated by ECAR-CB-A process in order to further broaden the engineering application of Mg alloy. However, to date extensive experimental and simulation studies have been conducted on the plastic deformation behaviors and defor­ mation mechanisms of AZ31 alloy sheet with typical basal texture [9, 15–18]. Moreover, many researches have elucidated the effect of initial textures and loading directions on the flow curves and the strain hard­ ening behavior, although the as-received sheets also possess typical basal texture [8,19,20]. There still a lack of comprehensive under­ standing on the internal reasons of the superior formability and plas­ ticity on the AZ31 alloy sheet processed by ECAR-CB-A process with a special RD-split bimodal texture. Therefore, in the present study, two AZ31 alloy sheets with a typical basal texture and a RD-split bimodal texture are experimentally investigated via uniaxial tension tests at room temperature. The evolution of microstructure and texture is thoroughly analyzed with the help of electron backscattered diffraction (EBSD) measurement in order to elucidate the inherent deformation mechanisms underneath these experimental observations.

2. Material and methods Two kinds of AZ31 alloy (Mg–3Al–1Zn, in wt.%) sheets with distinctively various textures are adopted in the present study, as well as a conventional description for three orthogonal directions in AZ31 alloy sheets: RD for the rolling direction, TD for the transverse direction, and ND for the normal direction. As one kind of applied sheets with a typical basal texture, as-received AZ31 alloy sheet is a commercially hot-rolled sheet and subsequently annealed 1 h at 400 � C to assure a fully recrystallized microstructure with as few dislocations as possible. As for the other kind of applied sheets, ECAR-CB-A AZ31 alloy sheet is the one with a rare RD-split bimodal texture. The processing procedure of ECAR-CB-A AZ31 alloy sheet has been well documented in the literature [13], thus it would not be specified in the present study. Mechanical properties are conducted and measured by virtue of uniaxial tension experiments of these AZ31 alloy sheets along RD. Dog-bone shaped specimens with 22.5 mm in gauge length and 6 mm � 1.2 mm in cross-section were cut from these AZ31 alloy sheets by means of electro-discharge machining (EDM), as shown in Fig. 1. Then some samples were deformed by 6% and 12% at a constant strain rate of 10 3s 1 on a SANS testing machine at room temperature. Evolution of microstructure and texture during uniaxial tension was

Fig. 2. (a), (d) Inverse pole figure (IPF) maps; (b), (e) Statistic analysis of grain size; (c), (f) (0002), (10-10) pole figures of as-received AZ31 alloy sample and ECARCB-A AZ31 alloy sample before uniaxial tension. 2

Y. Chen et al.

Materials Science & Engineering A 769 (2020) 138497

Fig. 3. EBSD analysis of these two samples at the deformation degree of 6%: (a), (d) Inverse pole figure (IPF) maps; (b), (e) Grain boundaries (GB) maps; (c), (f) Kernel average misorientation (KAM) maps.

Fig. 4. EBSD analysis of these two samples at the deformation degree of 12%: (a), (c) Inverse pole figure (IPF) maps; (b), (e) Grain boundaries (GB) maps; (c), (f) Kernel average misorientation (KAM) maps.

characterized by EBSD on the RD-TD plane. The samples for EBSD measurement were firstly made by mechanical ground with 1200-grit SiC paper, then followed by electrochemical polishing in ACII electro­ lyte for 180 s at 0.03 A/20 V. EBSD observation was conducted on a FEI NOVA 400 Zeiss Sigma field emission scanning electron microscope equipped an HKL-Nordlys MAX detector. The applied step sizes for un­ deformed samples and deformed samples were chosen to be 2 μm and 1.5 μm respectively in order to confirm a good indexing rate of EBSD measurement.

3. Results and discussion 3.1. Evolution of microstructure during uniaxial tension Fig. 2 shows the initial microstructure and texture of as-received AZ31 alloy sheet and ECAR-CB-A AZ31 alloy sheet before tensile tests. The inverse pole figure (IPF) maps in Fig. 2 (a) and (d) clearly demon­ strate that these two sheets possess uniform and equiaxed microstruc­ ture. Moreover, the corresponding statistical analysis of grain size shown in Fig. 2 (b) and (e) indicates that there only exists a minor dif­ ference with regard to the average grain size in as-received AZ31 alloy sheet (11.05 μm) and ECAR-CB-A AZ31 alloy sheet (14.91 μm). 3

Y. Chen et al.

Materials Science & Engineering A 769 (2020) 138497

Fig. 5. Misorientation angle distribution of these two samples before and after tensile tests (a) As-received sample, (b) ECAR-CB-A sample.

Therefore, effect of grain size on the mechanical response of these two sheets can be excluded in the present study. Moreover, initial textures shown in Fig. 2 (c) and (f) demonstrate a huge difference in these two sheets. As-received AZ31 alloy sheet exhibits a strong basal texture with the c-axis of most grains parallel to ND. This texture component agrees well with the previous work in the hot-rolled and annealed condition [21]. Whereas, ECAR-CB-A AZ31 alloy sheet possesses a bimodal texture with the basal poles tilting about �40� away from ND to RD. This abnormal texture component is a rare and interesting finding for texture engineering of AZ31 alloy [13]. In addition, the maximum pole intensity in ECAR-CB-A sample (3.20) is much lower than the corresponding value (8.04) in as-received sample, further showing the huge gap be­ tween these two textures. Fig. 3 and Fig. 4 present the EBSD analysis of these two samples at the deformation degrees of 6% and 12% respectively, and collates the IPF maps, grain boundaries (GB) maps, and kernel average misorienta­ tion (KAM) maps. In IPF maps, two kinds of boundaries are included, namely the low angle boundary (LAB) whose misorientation ranges from 2� to 15� and the high angle boundary (HAB) whose misorientation is greater than 15� . It can be seen that as the deformation degree is rela­ tively small during uniaxial tension, there is no obvious change with respect to the morphology of individual grains. However, with the

progression of plastic deformation, the LAB occurs more frequently within each grain. This phenomenon is in good accordance with the distribution of misorientation angle in these two samples during uni­ axial tension, as displayed in Fig. 5. Before deformation, these two samples both possess a relatively uniform distribution in a range of misorientation angles above 15� . With the increase of plastic strain, a remarkable low-angle peak occurs at ~15� and it belongs to the LAB, which is usually related to the dislocation boundaries [22]. The afore­ mentioned observations demonstrate that dislocation slip is an impor­ tant way to sustain plastic strain in these two AZ31 alloy sheets. This issue can be further enhanced by the KAM maps during uniaxial tension, as shown in Fig. 3(c), (f) and Fig. 4(c), (f). In general, KAM refers to the average misorientation between a given point and its nearest neighbors within the same grain, and it has been widely accepted and adopted as an indicator of dislocation density during plastic deformation of metallic materials [23,24]. In the present study, the average KAM value increases from 1.05� to 1.46� in as-received sample during uniaxial tension and the corresponding value increases from 1.18� to 1.56� in ECAR-CB-A sample. Fig. 3 (b), (e) and Fig. 4 (b), (e) show the GB maps at the deformation degree of 6% and 12% respectively, as well as the twin boundaries of {10–12} extension twin (ET) (86� 〈1 210〉 � 5� ) and {10–11}

Fig. 6. (0002) pole figures of as-received sample and ECAR-CB-A sample at different deformation degrees. 4

Y. Chen et al.

Materials Science & Engineering A 769 (2020) 138497

Fig. 7. EBSD maps and (0002) pole figures of the selected ETs in these two samples at the deformation degree of 6%: (a), (c) As-received sample, (b), (d) ECAR-CBA sample.

compression twin (CT) (56� 〈1 210〉 � 5� ). As for as-received sample with typical basal texture, there exists a tiny ETs during plastic defor­ mation, while CTs are nearly absent. However, a considerable amount of

deformation twins occurs in ECAR-CB-A sample during uniaxial tension and they are identified to be almost ETs. This observation is also sup­ ported by the misorientation angle distribution in these two samples, as

Fig. 8. IPF map, KAM map, (0002) pole figure and ET variants map within selected grains of ECAR-CB-A sample at the deformation degree of 6%. 5

Y. Chen et al.

Materials Science & Engineering A 769 (2020) 138497

shown in Fig. 5, where the deformed ECAR-CB-A sample possesses a prominent peek at ~86� corresponding to misorientations across the boundaries of ETs, while no obvious peak emerges at ~86� in the deformed as-received sample. It is generally accepted that the activation of twin in Mg alloy during plastic deformation strongly depends on the relationship between the initial orientation and the loading direction. As for ET, it would be able to take shear strain of ~0.13 under stress states which give rise to the elongation along the c-axis [25]. Therefore, ETs can hardly be activated in as-received sample with typical basal texture during uniaxial tension along RD as the c-axis of most grains are nearly perpendicular to the loading axis. However, in ECAR-CB-A sample with a bimodal texture where basal poles tilt about �40� away from ND to RD, plastic deformation can begin with ETs as there is an angle between c-axis and loading direction, and therefore a stress component can be imposed along the c-axis.

Table 1 SF of six theoretical twin variants of selected grains in Fig. 7(b). V1

V2

V3

V4

V5

V6

1 2 3 4 5 6 7

0.21 0.09 0.19 0.21 0.23 0.25 0.33

0.17 0.09 0.15 0.22 0.23 0.24 0.36

0.09 0.21 0.09 0.08 0.06 0.11 0.36

0.09 0.25 0.09 0.03 0 0.16 0.33

0.22 0.18 0.22 0.01 0.05 0 0.28

0 0.07 0.24

8 9

0.40 0.45

0.40 0.46

0.31 0.46

0.35 0.44

0.28 0.45

0.33 0.41

0.27 0.22 0.27 0.05

Activated variants V4 V1, V3, V1, V1, V1, V1, V5 V1, V1, V5,

V2 V4 V2 V2 V2 V2, V4, V2, V6 V2, V4, V6

shear direction. Actually, SF analysis for six different variants of ET has been proven to be valid in the determination of variant selection during plastic deformation of Mg alloy [29–31]. The corresponding computed SF of each theoretical ET variants in selected grains are listed in Table 1. In the present study, the selected nine grains are further divided into three groups: (i) three grains with their c-axis inclined less than 25� toward ND; (ii) three grains with their c-axis tilted about 45� to ND; and (iii) three grains with their c-axis tilted more than 45� to ND. When the inclination angle between the c-axis and ND is relatively small (about 25� ), IPF maps demonstrate that there are at most two ET variants in the selected grain 1, 2 and 3. Moreover, all these ET variants rotates the initial orientation to TD. The corresponding SF analysis in Table 1 further enhances this observation and shows that the SF of each ET variants possesses a very small and positive value or even a negative one, demonstrating that these selected grains are not suitably oriented for ET. These experimentally observed ET variants with low SF could be mainly ascribed to the local strain accommodation during plastic deformation [32]. When the tilted angle between c-axis and ND con­ tinues to increase (about 45� to ND), the selected grain 4, 5 and 6 possess a relatively large SF (mainly in the range of 0–0.2) and two ET variants are activated in each grain, also rotating the initial orientation to TD. As reported previously, if the c-axis of individual grains are close to RD during uniaxial tension, almost six twin variants could be easily acti­ vated [33]. Hence, when the tilted angle grows to be larger than 45� , the smallest SF in all ET variants of grain 7, 8 and 9 increase obviously and at least three ET variants are activated in these parent grains. These ET variants on the one hand result in a new TD-component texture, on the other hand rotate the c-axis from RD toward ND, causing the concen­ tration of basal poles toward ND.

3.2. Evolution of texture during uniaxial tension Fig. 6 demonstrates the texture evolution of these two samples dur­ ing uniaxial tension. With regards to as-received sample, there only exists a tendency of reducing the spread of basal pole and concentrating basal pole to ND along with the increasing plastic strain. This observa­ tion is in good accordance with the previously reported results in Ref. [25]. However, as for ECAR-CB-A sample, texture evolution is totally different. On the one hand, the tilted basal poles gradually diffuse and rotate towards ND with the progression of plastic strain. On the other hand, a new TD-component texture occurs as the deformation degree increases from 6% to 12%. This obvious texture change during uniaxial tension of ECAR-CB-A sample can not be ascribed to the motion of widely reported dislocation slip modes including basal slip {0001}〈11–20〉, prismatic slip {10-10}〈11–20〉 and pyramidal slip {11–22}〈11–23〉, as they can only result in the gradual change of texture during plastic deformation of Mg alloys [26,27]. Therefore, texture evolution of ECAR-CB-A sample should mainly attribute to the activated ETs during plastic deformation. To further validate this conclusion, all the ETs within these two samples at the deformation degree of 6% are selected and shown in the EBSD maps, as well as the corresponding (0002) pole figures, as depicted in Fig. 7. It can be seen that although nearly all of the activated ETs within as-received sample rotate the c-axis from ND to TD and create a TD-texture component, there is a relatively small portion of ETs in the EBSD map, and therefore ETs has a minor influence on the texture evolution of as-received sample during uniaxial tension. However, as to ECAR-CB-A sample, the activated ETs possess a relatively large portion in the EBSD map and they not only result in the appearance of TD-texture component but also benefit in the concentration of basal poles towards ND. In fact, previous investigations have reported that there are six var­ iants of ET in Mg alloys during plastic deformation and they are often termed as V1 to V6. The activation of various ET variants has significant influence on the microstructure evolution of Mg alloys as well as the texture evolution during plastic loading [28]. To understand more precisely the twinning behavior and elucidate the relationship between grain orientations and the activated ET variants in ECAR-CB-A deformed sample, nine representative grains selected from Fig. 7(b) are thor­ oughly analyzed from different perspectives, as shown in Fig. 8, which contains the IPF maps, KAM maps, (0002) pole figures and twin variants selection in grains with different orientations by means of trace method and Schmid factor (SF) analysis. By analogy with dislocation glide, SF analysis can be also used in the case of twinning with a specific twinning plane normal and shear direction. The SF is defined as: m ¼ cosλcosφ

Grains

3.3. Mechanical properties during uniaxial tension The flow curves and work hardening behavior obtained from the tensile tests are displayed in Fig. 9. The corresponding detailed me­ chanical properties, including the 0.2% proof yield stress (YS), the ul­ timate tensile strength (UTS), the fracture elongation (FE) and the ratio of YS to UTS (YS/UTS) are listed in Table 2. It is clear that as-received sample exists an obvious two-stage strain hardening curve, while ECAR-CB-A sample experiences three distinctly different stages of work hardening, indicating that the former curve is mainly associated with dislocation slip and the latter curve is ascribed to the corporation of dislocation slip and deformation twinning [34,35]. In addition, it is interesting to find that ECAR-CB-A sample possesses a higher FE (24%) than as-received sample (14%). This observation can be ascribed to the fact that ETs has been enrolled into the plastic deformation of ECAR-CB-A sample, by comparison, there exists little ETs in as-received sample. As we know, ET has been termed as the main deformation mechanisms at room temperature to accommodate plastic strain along the c-axis of Mg alloys [33]. Moreover, it can be noted that although both samples have similar UTS, the YS and YS/UTS of as-received sample are about twice the

(1)

where λ represents the angle between the loading axis and the normal of twinning plane, φ stands for the angle between the loading axis and 6

Y. Chen et al.

Materials Science & Engineering A 769 (2020) 138497

Fig. 9. Measured true stress-strain curves (a) and the corresponding strain hardening curves (b) of as-received sample and ECAR-CB-A sample during uniax­ ial tension.

values of ECAR-CB-A sample. It is generally accepted that the initial texture can strongly influence the flow stress of Mg alloys during plastic deformation. Thus, the much lower YS and YS/UTS of ECAR-CB-A sample should be due to the special bimodal texture with the basal poles tilting about �40� away from ND to RD. To elucidate this texture effect, analysis of SF with regards to basal slip, prismatic slip and pyramidal slip is conducted in the present study. The

Table 2 Mechanical properties of various samples during uniaxial tension. Sample

YS (MPa)

UTS (MPa)

FE (%)

YS/UTS

As-received ECAR-CB-A

162 73

300 270

14 24

0.54 0.27

Fig. 10. Analysis of SF on different dislocation slip modes within as-received sample and ECAR-CB-A sample before uniaxial tension: (a) Basal slip, (b) Prismatic slip, (c) Pyramidal slip. 7

Y. Chen et al.

Materials Science & Engineering A 769 (2020) 138497

be shared at this time as the data also forms part of an ongoing study.

Table 3 The Statistical analysis of SF on different dislocation slip modes within asreceived sample and ECAR-CB-A sample. Sample

Basal slip

Prismatic slip

Pyramidal slip

As-received ECAR-CB-A

0.195 0.354

0.435 0.294

0.397 0.318

Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant Nos. 51805064, 51701034), the Scientific and Tech­ nological Research Program of Chongqing Municipal Education Com­ mission (Grant Nos. KJQN201801137, KJ1600922), the Basic and Advanced Research Project of CQ CSTC (Grant Nos. cstc2017jcy­ jAX0062, cstc2018jcyjAX0035, cstc2017jcyjAX0381) and Postgraduate innovation project of Chongqing University of Technology (Grant Nos. ycx20192041).

distributions of SF in these two samples before deformation are shown in Fig. 10. The corresponding statistical analysis on SF is displayed in Table 3. It should be noted that there only exists a relatively small dif­ ference with respect to the average SF value on pyramidal slip in these two samples. However, the average SF of basal slip (0.354) in ECAR-CB-A sample is much larger than the corresponding value (0.195) in as-received sample, while the average SF value for prismatic slip is much lower in ECAR-CB-A sample. This observation demonstrates that basal slip is easier to be activated in ECAR-CB-A sample by com­ parison with as-received sample. In fact, basal slip possesses the lowest critical resolved shear stress (CRSS) by comparison with other deformation mechanisms [36,37], and it has been proven to be the main deformation mechanism at the onset of plastic strain during uniaxial tension of AZ31 alloy sheet with a typical basal texture [26]. Therefore, the YS of Mg alloys mainly depends on the activation of basal slip and would be gradually reduced with the increase of SF for basal slip [35]. Consequently, the lower YS in ECAR-CB-A sample during uniaxial tension along RD could be explained and this phenomenon can be termed as the effect of texture softening, which has been depicted in Refs. [38,39].

References [1] J. Hirsch, T. Al-Samman, Superior light metals by texture engineering: optimized aluminum and magnesium alloys for automotive applications, Acta Mater. 61 (2013) 818–843, https://doi.org/10.1016/j.actamat.2012.10.044. [2] S.R. Agnew, J.F. Nie, Preface to the viewpoint set on: the current state of magnesium alloy science and technology, Scr. Mater. 63 (2010) 671–673, https:// doi.org/10.1016/j.scriptamat.2010.06.029. [3] J. Zhang, S. Yan, H. Qu, Recent progress in magnesium hydride modified through catalysis and nanoconfinement, Int. J. Hydrogen Energy 43 (2018) 1545–1565, https://doi.org/10.1016/j.ijhydene.2017.11.135. [4] M. Lentz, M. Risse, N. Schaefer, W. Reimers, I.J. Beyerlein, Strength and ductility with {10-11}-{10-12} double twinning in a magnesium alloy, Nat. Commun. 7 (2016) 11068. [5] S.B. Yi, C.H.J. Davies, H.G. Brokmeier, R.E. Bolmaro, K.U. Kainer, J. Homeyer, Deformation and texture evolution in AZ31 magnesium alloy during uniaxial loading, Acta Mater. 54 (2006) 549–562, https://doi.org/10.1016/j. actamat.2005.09.024. [6] H. Zhang, W.L. Cheng, J.F. Fan, B.S. Xu, H.B. Dong, Improved mechanical properties of AZ31 magnesium alloy sheets by repeated cold rolling and annealing using a small pass reduction, Mater. Sci. Eng. A 637 (2015) 243–250, https://doi. org/10.1016/j.msea.2015.04.057. [7] N.L. Li, G.J. Huang, R.L. Xin, Q. Liu, Effect of initial texture on dynamic recrystallization and deformation mechanisms in AZ31 Mg alloy extruded at 573K, Mater. Sci. Eng. A 569 (2013) 18–26, https://doi.org/10.1016/j. msea.2013.01.027. [8] B.S. Wang, R.L. Xin, G.J. Huang, Q. Liu, Effect of crystal orientation on the mechanical properties and strain hardening behavior of magnesium alloy AZ31 during uniaxial compression, Mater. Sci. Eng. A 534 (2012) 588–593, https://doi. org/10.1016/j.msea.2011.12.013. [9] A. Chapuis, P. Liu, Q. Liu, An experimental and numerical study of texture change and twinning-induced hardening during tensile deformation of an AZ31 magnesium alloy rolled plate, Mater. Sci. Eng. A 561 (2013) 167–173, https://doi. org/10.1016/j.msea.2012.11.018. [10] J. Suh, J. Victoria-Hernandez, D. Letzig, R. Golle, S. Yi, J. Bohlen, W. Volk, Improvement in cold formability of AZ31 magnesium alloy sheets processed by equal channel angular pressing, J. Mater. Process. Technol. 217 (2015) 286–293, https://doi.org/10.1016/j.jmatprotec.2014.11.029. [11] R.B. Figueiredo, S. Sabbaghianrad, A. Giwa, J.R. Greer, T.G. Langdon, Evidence for exceptional low temperature ductility in polycrystalline magnesium processed by severe plastic deformation, Acta Mater. 122 (2017) 322–331, https://doi.org/ 10.1016/j.actamat.2016.09.054. [12] F. Guo, D.F. Zhang, X.W. Fan, J.X. Li, L.Y. Jiang, F.S. Pan, Microstructure, texture and mechanical properties evolution of pre-twinning Mg alloys sheets during large strain hot rolling, Mater. Sci. Eng. A 655 (2016) 92–99, https://doi.org/10.1016/j. msea.2015.12.059. [13] J. Tu, T. Zhou, L. Liu, L.X. Shi, L. Hu, D.H. Song, B. Song, M.B. Yang, Q. Chen, F. S. Pan, Effect of rolling speeds on texture modification and mechanical properties of the AZ31 sheet by a combination of equal channel angular rolling and continuous bending at high temperature, J. Alloy. Comp. 768 (2018) 598–607, https://doi.org/10.1016/j.jallcom.2018.07.242. [14] D.H. Song, T. Zhou, J. Tu, L.X. Shi, B. Song, L. Hu, M.B. Yang, Q. Chen, L.W. Lu, Improved stretch formability of AZ31 sheet via texture control by introducing a continuous bending channel into equal channel angular rolling, J. Mater. Process. Technol. 259 (2018) 380–386, https://doi.org/10.1016/j.jmatprotec.2018.05.012. [15] S.G. Hong, S.H. Park, C.S. Lee, Role of {10-12} twinning characteristics in the deformation behavior of a polycrystalline magnesium alloy, Acta Mater. 58 (2010) 5873–5885, https://doi.org/10.1016/j.actamat.2010.07.002. [16] M.W. Vaughan, W. Nasim, E. Dogan, J.S. Herrington, G. Proust, A.A. Benzerga, I. Karaman, Interplay between the effects of deformation mechanisms and dynamic recrystallization on the failure of Mg-3Al-1Zn, Acta Mater. 168 (2019) 448–472, https://doi.org/10.1016/j.actamat.2019.02.010. [17] P.A. Lynch, M. Kunz, N. Tamura, M.R. Barnett, Time and spatial resolution of slip and twinning in a grain embedded within a magnesium polycrystal, Acta Mater. 78 (2014) 203–212, https://doi.org/10.1016/j. actamat. 2014.06.030. [18] P. Chen, B. Li, D. Culbertson, Y. Jiang, Contribution of extension twinning to plastic strain at low stress stage deformation of a Mg-1Al-1Zn alloy, Mater. Sci. Eng. A 709 (2018) 40–45, https://doi.org/10.1016/j. mesa.2017.10.038.

4. Conclusions Uniaxial tension experiments along RD were conducted at room temperature on AZ31 alloy sheets with different initial textures, including a typical basal texture fabricated by hot rolling and subse­ quent annealing and a rare RD-split bimodal texture produced by ECARCB-A process. Furthermore, the influence of texture type on micro­ structure and texture evolution as well as mechanical properties has been experimentally investigated. Therefore, the following conclusions can be drawn. (1) As for microstructural evolution, dislocation slip is the main carrier for plastic deformation of as-received sample with typical basal texture, while in ECAR-CB-A sample with a rare bimodal texture where the basal poles tilting about �40� away from ND to RD, both dislocation slip and ETs contribute to sustaining plastic stain during uniaxial tension. (2) In terms of texture evolution, as-received sample does not un­ dergo the change of texture type and only experience the reduction of the spread of basal pole. However, in ECAR-CB-A sample, the number of activated ET variants is increasing with the increase of angle between ND and c-axis, which contributes to the gradual diffusion and rotation of tilted basal poles to ND, so as to the development of a new TD-component texture during uni­ axial tension. (3) With regard to mechanical properties, the FE of ECAR-CB-A sample is 10% bigger the corresponding value in as-received sample, and this can be ascribed to the participation of ETs to accommodate plastic strain along the c-axis of individual grains. In addition, the special RD-split bimodal texture induces an effect of texture softening and results in larger SF in basal slip, and further leads to the smaller YS and YS/UTS (about 50%) in ECARCB-A sample as compared to as-received sample. Data availability The raw/processed data required to reproduce these findings cannot 8

Y. Chen et al.

Materials Science & Engineering A 769 (2020) 138497 [29] S.G. Hong, S.H. Park, C.S. Lee, Strain path dependence of {10-12} twinning activity in a polycrystalline magnesium alloy, Scr. Mater. 64 (2011) 145–148, https://doi. org/10.1016/j.scriptmat.2010.09.030. [30] P. Chen, F.X. Wang, J. Ombogo, B. Li, Formation of 60� <01-10> boundaries between {10-12} twin variants in deformation of a magnesium alloy, Mater. Sci. Eng. A 739 (2019) 173–185, https://doi.org/10.1016/j.msea.2018.10.029. [31] Q. Yu, J. Wang, Y.Y. Jiang, R.J. McCabe, N. Li, C.N. Tome’, Twin-twin interactions in magnesium, Acta Mater. 77 (2014) 28–42, https://doi.org/10.1016/j. actamat.2014.05.030. [32] A. Fern� andez, A. J� erusalem, I. Guti�errez-Urrutia, M.T. P�erez-Prado, Threedimensional investigation of grain boundary–twin interactions in a Mg AZ31 alloy by electron backscatter diffraction and continuum modeling, Acta Mater. 61 (2013) 7679–7692, https://doi.org/10.1016/j.actamat.2013.09.005. [33] S.H. Park, S.G. Hong, C.S. Lee, Activation mode dependent {10-12} twinning characteristics in a polycrystalline magnesium alloy, Scr. Mater. 62 (2010) 202–205, https://doi.org/10.1016/j.scriptamat.2009.10.027. [34] L. Jiang, J.J. Jonas, R.K. Mishra, A.A. Luo, A.K. Sachdev, S. Godet, Twinning and texture development in two Mg alloys subjected to loading along three different strain paths, Acta Mater. 55 (2007) 3899–3910, https://doi.org/10.1016/j. actamat.2007.03.006. [35] B. Song, R.L. Xin, N. Guo, C.Q. Chen, X.F. Yang, Q. Liu, Influence of basal slip activity in twin lamellae on mechanical behavior of Mg alloys, Mater. Lett. 176 (2016) 147–150, https://doi.org/10.1016/j.matlet.2016.04.113. [36] A. Pandey, F. Kabirian, J.H. Hwang, S.H. Choi, A.S. Khan, Mechanical responses and deformation mechanisms of an AZ31 Mg alloy sheet under dynamic and simple shear deformations, Int. J. Plast. 68 (2015) 111–131, https://doi.org/10.1016/j. ijplas.2014.12.001. [37] S.R. Agnew, M.H. Yoo, C.N. Tome, Application of texture simulation to understanding mechanical behavior of Mg and solid solution alloys containing Li or Y, Acta Mater. 49 (2001) 4277–4289, https://doi.org/10.1016/S1359-6454(01) 00297-X. [38] Y. Chino, K. Sassa, M. Mabuchi, Enhancement of tensile ductility of magnesium alloy produced by torsion extrusion, Scr. Mater. 59 (2008) 339–402, https://doi. org/10.1016/j.scriptamat.2008.04.013. [39] S.R. Agnew, J.A. Horton, T.M. Lillo, D.W. Brown, Enhanced ductility in strongly textured magnesium produced by equal channel angular processing, Scr. Mater. 50 (2004) 377–381, https://doi.org/10.1016/j.scriptamat.2003.10.006.

[19] M. Jahedi, B.A. McWilliams, P. Moy, M. Knezevic, Deformation twinning in rolled WE43-T5 rare earth magnesium alloy: influence on strain hardening and texture evolution, Acta Mater. 131 (2017) 221–232, https://doi.org/10.1016/j. actamat.2017.03.075. [20] M. Knezevic, A. Levinson, R. Harris, R.K. Mishra, R.D. Doherty, S.R. Kalidindi, Deformation twinning in AZ31: influence on strain hardening and texture evolution, Acta Mater. 58 (2010) 6230–6242, https://doi.org/10.1016/j. actamat.2010.07.041. [21] B. Hutchinson, J. Jain, M.R. Barnett, A minimum parameter approach to crystal plasticity modelling, Acta Mater. 60 (2012) 5391–5398, https://doi.org/10.1016/ j.actamat.2012.06.057. [22] T.Z. Han, G.S. Huang, Y.G. Wang, G.G. Wang, Y.C. Zhao, F.S. Pan, Enhanced mechanical properties of AZ31 magnesium alloy sheets by continuous bending process after V-bending, Prog. Nat. Sci. Mater. 26 (2016) 97–102, https://doi.org/ 10.1016/j.pnsc.2016.01.005. [23] Y.S. Wu, Z. Liu, X.Z. Qin, C.S. Wang, L.Z. Zhou, Effect of initial state on hot deformation and dynamic recrystallization of Ni-Fe based alloy GH984G for steam boiler applications, J. Alloy. Comp. 795 (2019) 370–384, https://doi.org/10.1016/ j.jallcom.2019.05.022. [24] R. Badji, T. Chauveau, B. Bacroix, Texture, misorientation and mechanical anisotropy in a deformed dual phase stainless steel weld joint, Mater. Sci. Eng. A 575 (2013) 94–103, https://doi.org/10.1016/j.msea.2013.03.018. [25] F. Kabirian, A.S. Khan, T.G. Herlod, Visco-plastic modeling of mechanical responses and texture evolution in extruded AZ31 magnesium alloy for various loading conditions, Int. J. Plast. 68 (2015) 1–20, https://doi.org/10.1016/j. ijplas.2014.10.012. [26] A. Chapuis, Z.Q. Wang, Q. Liu, Influence of material parameters on modeling plastic deformation of Mg alloys, Mater. Sci. Eng. A 655 (2016) 244–250, https:// doi.org/10.1016/j.msea.2015.12.067. [27] X.Q. Guo, A. Chapuis, P.D. Wu, Q. Liu, X.B. Mao, Experimental and numerical investigation of anisotropic and twinning behavior in Mg alloy under uniaxial tension, Mater. Des. 98 (2016) 333–343, https://doi.org/10.1016/j. matdes.2016.03.045. [28] G.D. Liu, R.L. Xin, X.G. Shu, C.P. Wang, Q. Liu, The mechanism of twinning activation and variant selection in magnesium alloys dominated by slip deformation, J. Alloy. Comp. 687 (2016) 352–359, https://doi.org/10.1016/j. jallcom.2016.06.136.

9