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Effects of original orientation on compressive creep behaviors of hot-extruded Mg–3Al–1Zn alloy rod
Journal of Alloys and Compounds 806 (2019) 1105e1108
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Correspondence
Effects of original orientation on compressive creep behaviors of hot-extruded Mge3Ale1Zn alloy rod a b s t r a c t Keywords: Magnesium Creep Dislocation Twin
Compressive creep anisotropic behaviors were observed for a hot-extruded Mge3Ale1Zn alloy rod at 423 K. Heavy basal slip accelerated the creep rate along transverse and 45 directions. Inversely, strong interactions between high densities of prismatic dislocations and {10e12} twins enhanced the creep resistance along extrusion direction. Although twinning was reported to induce yield softening during uniaxial loading, it could be beneficial for creep resistance even applied stress over yield stress. © 2019 Elsevier B.V. All rights reserved.
1. Introduction Due to hexagonal close-packed structure and easy activation of {10e12} twinning, commercial magnesium (Mg) alloys always have strong anisotropy at low temperature [1e5]. Hou et al. [6] found that twinning dominates the uniaxial compressive process of AZ31 alloy at room temperature while prismatic slip dominates the tensile process. Yin et al. [7] indicated that twinning induces the tension-compression yield asymmetry in strong-textured Mg alloys since twinning can easily accelerate yield softening. Although the role of twinning is well-known under uniaxial loading, it is still unclear for the role of twinning in creep at low temperature. Previous reports only focused on the dynamic precipitation during creep process [8e11]. For example, Celikin et al. [9] indicated that Mn atoms and Mg12Ce phases could enhance the creep resistance of MgeMneCe alloy via dislocation pinning. Li et al. [10] found that metastable phases were formed more rapidly during creep compared to only artificial aging. Koundinya et al. [11] designed Mg-based alloys without rare-earth addition and claimed that tiny Mg2Ca phases could increase the load-bearing capacity and creep resistance. However, it is regrettable that very few reports involved the role of twinning in creep process and rare studies researched the creep anisotropy to date. Thus, it is of much importance to understand the effects of original orientation on the creep properties of strong-textured Mg alloys at low temperature. 2. Experimental procedures The material was provided by a commercial hot-extruded AZ31 alloy (Al 2.68, Zn 0.75, Mn 0.68, Si 0.003, Fe 0.003 and Cu 0.001 mass fraction %, the remainder being Mg) with a diameter of 20 mm. The conventional description is used for the two orthogonal directions of extruded rod: ED for extrusion direction and TD for transverse direction. The compressive axis (CA) was varied in ED-TD plane with 0 , 45 and 90 to ED (Fig. S1). For briefness, the samples with three original orientations were named as ED, 45 and TD samples, https://doi.org/10.1016/j.jallcom.2019.07.193 0925-8388/© 2019 Elsevier B.V. All rights reserved.
respectively. Rectangular samples with dimensions of 11 8 8 mm3 were machined parallel to three different original orientations. These samples were homogenized at 733 K for 8 h and water quenched, resulting in equiaxed grains with an average size of ~50 mm. Uniaxial compressive tests in triplicate were performed at 423 K with a strain rate of 3 103 s1 and the resultant average values are presented in Table 1 and Fig. S2. ED sample exhibited the lowest yield stress while TD sample showed the highest. Compressive creep tests were performed at 423 K under 70e110 MPa, with pre-heating for 15 min before loading and immediate water quenching after testing. The microstructures were observed using electron backscatter diffraction (EBSD) apparatus and transmission electron microscopy (TEM). All the observations were performed parallel to CA after electro-polishing or ion milling. To elucidate the activities of slip systems caused by uniaxial compressive loading, the commercial software ABAQUS and microscopic hardening law [1] were employed in the crystal plasticity finite element model (CPFEM). Initial EBSD data employed in CPFEM simulation are shown in Fig. S3, and varied hardening parameters are listed in Table S1. 3. Results and discussion Fig. 1(a) shows the anisotropic creep results under three typical applied stresses. All samples have two creep stages, including primary and steady stages. According to the creep strain shown in Fig. 1(a) and the steady creep rate presented in Table 2, it is evident that ED sample has the highest creep resistant while 45 sample has the lowest. Fig. 1(b) shows the stress exponents of ED, 45 and TD samples, which can be calculated by the classical equation [12]:
n¼
vln_ε vlns T
(1)
Where n is stress exponent, ε_ is steady creep rate, s is applied stress and T is absolute temperature. The stress exponent has been widely
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Correspondence / Journal of Alloys and Compounds 806 (2019) 1105e1108
Table 1 Results of uniaxial compressive tests at 423 K.
Table 2 Steady creep rate of ED, 45 and TD samples creep tested at 423 K.
Sample
Yield stress/MPa
Ultimate compressive stress/MPa
Ductility/%
s/MPa
ε_ ED /s1
ε_ 45 /s1
ε_ TD /s1
ED 45 TD
66 158 182
240 195 209
26.6 42.6 35.1
70 80 90 100 110
5.00 108 7.30 108 1.06 107 1.43 107 1.75 107
1.14 107 1.63 107 2.52 107 3.44 107 4.28 107
9.25 108 1.44 107 1.92 107 2.51 107 3.21 107
accepted as the representation of creep mechanism. Grain boundary slide is the dominant creep mechanism for n < 3 while dislocation slip dominates the creep process for n > 3 [13]. Here, the stress exponents of ED, 45 and TD samples are 2.71, 3.02 and 2.82, respectively. Considering the relatively low creep temperature at 423 K, the creep mechanisms of three orientated samples are possible of dislocation slip with slight boundary migration. Fig. 2 shows the inverse pole figures, no-colored grain maps and corresponding {0001} pole figures of ED, 45 and TD samples crept for 50 h under 90 MPa. The black lines represent high-angle boundaries (HABs) above 15 and the white lines represent low-angle boundaries (LABs) from 2 to 15 . Clearly, ED sample has high densities of HABs in grain interiors while 45 and TD samples have plenty of LABs. Since low-temperature creep tests have minor effects on the grain size and texture intensity, the newly formed pole in the center is possibly attributed to {10e12} twinning. To identify {10e12} twins more precisely, white background is used where black lines still represent HABs but LABs are outlined by blue lines. Meanwhile, red lines represent twinned structures with ~86 misorientations. As can be seen, large amounts of {10e12} twins appear in ED sample whereas both TD and 45 samples have fewer twins. Inversely, the proportions of LABs in ED, 45 and TD samples are 10%, 39% and 25%, respectively. The large amounts of LABs in 45 and TD samples are probably caused by basal slip, since basal slip can successively induce the accumulation of low strain [13]. Therefore, one of the reasons for creep anisotropy is the different activities of twinning and basal slip. In addition, the well evolved HABs and low fraction of LABs in ED sample imply the frequent occurrence of non-basal slip, otherwise only twinning cannot accommodate creep strain increment. Fig. 3 shows the CPFEM simulation results, which correspond to the relative activities of deformation modes for ED, 45 and TD samples under uniaxial compressive testing at 423 K. In ED sample, the activation of basal slip drops sharply while twining is easily activated. When the relative activities of basal slip and twinning approach, prismatic slip becomes important especially for the deformation after yielding. Unlike ED sample, 45 and TD samples are mainly dominated by basal slip while twinning acts a secondary role and prismatic slip has a low activity. Pyramidal 〈cþa〉 slip is hardly activated in all samples, suggesting that it is a minor factor
in the creep anisotropy at 423 K and just acts a role of accompanying the strain induced by other deformation modes. Hereinbefore, twinning has been confirmed as one of the reasons for creep anisotropy whereas pyramidal slip has negligible effect. TEM bright fields are thus taken to analyze the effects of prismatic slip on creep anisotropy. Since both 45 and TD samples have fewer twins and more basal dislocations, the characterization for prismatic slip can be omitted for 45 sample. Using two-beam mode, Fig. 4 shows the bright fields of ED and TD samples crept for 50 h under 90 MPa. The incident beam directions are both B ¼ [2-1-10] and the diffraction vectors are both g ¼ [01e10]. Under this condition, only dislocations can be observed. The straight lines parallel to the basal plane trace are basal dislocations, while other short segments approximately perpendicular to the basal plane trace are prismatic dislocations (indicated by yellow arrows). In Fig. 4(a), ED sample almost has similar densities of prismatic and basal dislocations, indicating the easy occurrence of cross-slip. Moreover, no obvious dislocation can be observed inside the twins while evident pile-ups of prismatic dislocations exist along the twin boundaries. It is suggested that the cross-slip containing prismatic dislocations has strong interactions with {10e12} twins (a corresponding schematic diagram is shown in Fig. S4). Conversely, in Fig. 4(b), most dislocations in TD sample are lying on basal planes, indicating the lower density of prismatic dislocations in TD sample. Therefore, basal slip is the dominant creep mechanisms of both 45 and TD samples while twinning and cross-slip dominates the creep of ED sample. In conclusion, different original orientations induce different deformation modes, which directly trigger the obvious creep anisotropy. Easy activation of basal slip in 45 and TD samples accelerates creep strain increment, resulting in their weak creep resistance. In contrast, both the prismatic slip itself and the strong interactions between prismatic slip and twinning lead to higher creep resistance in ED sample. Although twinning usually induces an early yield softening during uniaxial compression, it is beneficial for creep resistance. This new finding is extremely important, which proposes the availability of pre-deformation introducing {10e12} twins to enhance creep resistance even when applied stress is higher than yield stress.
Fig. 1. (a) Creep strain versus creep time curves and (b) steady creep rate versus applied stress plots of ED, 45 and TD samples tested at 423 K.
Fig. 2. Inverse pole figures and corresponding no-colored grain maps of (a), (b) ED, (c), (d) 45 and (e), (f) TD samples. Observation direction is along compressive direction.
Fig. 3. Relative activities of different deformation modes for (a) ED, (b) 45 and (c) TD samples.
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Correspondence / Journal of Alloys and Compounds 806 (2019) 1105e1108
Fig. 4. TEM bright fields taken by two-beam mode: (a) ED and (b) TD samples. Incident beam directions are both B ¼ [2-1-10] and diffraction vectors are both g ¼ [01e10].
4. Summary Obvious compressive creep anisotropic behavior was observed for the hot-extruded AZ31 alloy rod at 423 K. Although ED sample has the lowest yield stress, it has the highest creep resistance compared to 45 and TD samples. The creep anisotropy is attributed to different original orientations promoting different dominant creep mechanisms. Heavy basal slip and few prismatic dislocations in 45 and TD samples lead to rapid increment in creep strain. Inversely, plenty of {10e12} twins and prismatic dislocations dominate the creep process of ED sample and their strong interactions lead to high creep resistance. Thus, a new perspective can be proposed that twinning conduces to creep resistance of strongtextured Mg alloys, regardless of yield softening. Data availability statement The raw and processed data required to reproduce these findings cannot be shared at this moment due to technical and time limitations. Acknowledgements The authors gratefully acknowledge the financial supports received from National Natural Science Foundation of China (Grants No. 51771230 and U1864209), Natural Science Foundation of Hunan Province (Grant No. 2019JJ40376) and Distinguished Professor Project of Central South University (Grant No. 202045009). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.jallcom.2019.07.193. References [1] W.Y. Huang, Q.H. Huo, Z.W. Fang, Z.Y. Xiao, Y. Yin, Z. Tan, X.Y. Yang, Damage analysis of hot-rolled AZ31 Mg alloy sheet during uniaxial tensile testing
under different loading directions, Mater. Sci. Eng. A 710 (2018) 289e299. [2] W.Y. Huang, X.Y. Yang, Y. Yang, T. Mukai, T. Sakai, Effect of yttrium addition on the hot deformation behaviors and microstructure development of magnesium alloy, J. Alloy. Comp. 786 (2019) 118e125. [3] D. Nugmanov, M. Knezevic, M. Zecevic, O. Sitdikov, M. Markushev, I.J. Beyerlein, Origin of plastic anisotropy in (ultra)-fine-grained MgeZneZr alloy processed by isothermal multi-step forging and rolling: experiments and modeling, Mater. Sci. Eng. A 713 (2018) 81e93. [4] J. Majhi, A.K. Mondal, Microstructure and impression creep characteristics of squeeze-cast AZ91 magnesium alloy containing Ca and/or Bi, Mater. Sci. Eng. A 744 (2019) 691e703. [5] R.A. Michi, G. Kim, B.W. Kim, W. Lee, D.C. Dunand, Compressive creep behavior of hot-pressed Mg 1.96 Al 0.04 Si 0.97 Bi 0.03, Scr. Mater. 148 (2018) 10e14. [6] D.W. Hou, Y.Z. Zhu, Q.Z. Li, T.M. Liu, H.M. Wen, Effect of {10-12} twinning on the deformation behavior of AZ31 magnesium alloy, Mater. Sci. Eng. A 746 (2019) 314e321. [7] D.L. Yin, J.T. Wang, J.Q. Liu, X. Zhao, On tension-compression yield asymmetry in an extruded Mg-3Al-1Zn alloy, J. Alloy. Comp. 478 (2009) 789e795. [8] J. Wang, L. Luo, Q.H. Huo, Y.F. Shi, Z.Y. Xiao, Y.X. Ye, X.Y. Yang, Creep behaviors of a highly concentrated Mg-18 wt%Gd binary alloy with and without artificial aging, J. Alloy. Comp. 774 (2019) 1036e1045. [9] M. Celikin, R. Gauvin, M. Pekguleryuz, Dynamic co-precipitation of a-Mn/ Mg12Ce in creep resistant Mg-Sr-Mn-Ce alloys, Mater. Sci. Eng. A 719 (2018) 199e205. [10] R. Li, J. Zhang, G. Fu, L. Zong, B. Guo, Y. Yu, Y. Su, Y. Hao, Different precipitation hardening behaviors of extruded Mge6Gde1Ca alloy during artificial aging and creep processes, Mater. Sci. Eng. A 715 (2018) 186e193. [11] N.T.B.N. Koundinya, R.S. Kottada, Achieving exceptional creep resistance in rare-earth-free Mg-base alloys by engineering the shape, size and fraction of eutectic, particles and precipitates, Scr. Mater. 162 (2019) 121e126. [12] Y.F. Shi, L. Luo, Q.H. Huo, J. Wang, Z.Y. Xiao, J.C. Guo, X.Y. Yang, Enhancing creep properties of a hot-rolled Mg-4Y binary alloy via a new thought of inhibiting cross-slip, Mater. Char. 147 (2019) 64e71. [13] Z.W. Fang, Q.H. Huo, J. Wang, Z.Y. Xiao, D.X. Zhang, W.Y. Huang, M.C. Zhao, X.Y. Yang, Creep behaviors of hot compressed Mg-4Y-2Nd-0.2Zn-0.5Zr alloy with and without aging, Mater. Sci. Eng. A 708 (2017) 460e468.
Weiying Huang, Qinghuan Huo**, Zhirou Zhang, Jiao Tang Educational Key Laboratory of Nonferrous Metal Materials Science and Engineering, School of Materials Science and Engineering, Central South University, Changsha, 410083, China Aki Hashimoto Technology Div. Nippon Paint Surf Chemicals Co. LTD., 4-1-15 Minamishinagawa, Shinagawa-ku, Tokyo, 140-8675, Japan Xuyue Yang* Educational Key Laboratory of Nonferrous Metal Materials Science and Engineering, School of Materials Science and Engineering, Central South University, Changsha, 410083, China **
Corresponding author.
*
Corresponding author. E-mail address: [email protected] (Q. Huo). E-mail address: [email protected] (X. Yang). 14 May 15 July 17 July Available online 25 July
2019 2019 2019 2019
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Correspondence
Effects of original orientation on compressive creep behaviors of hot-extruded Mge3Ale1Zn alloy rod a b s t r a c t Keywords: Magnesium Creep Dislocation Twin
Compressive creep anisotropic behaviors were observed for a hot-extruded Mge3Ale1Zn alloy rod at 423 K. Heavy basal slip accelerated the creep rate along transverse and 45 directions. Inversely, strong interactions between high densities of prismatic dislocations and {10e12} twins enhanced the creep resistance along extrusion direction. Although twinning was reported to induce yield softening during uniaxial loading, it could be beneficial for creep resistance even applied stress over yield stress. © 2019 Elsevier B.V. All rights reserved.
1. Introduction Due to hexagonal close-packed structure and easy activation of {10e12} twinning, commercial magnesium (Mg) alloys always have strong anisotropy at low temperature [1e5]. Hou et al. [6] found that twinning dominates the uniaxial compressive process of AZ31 alloy at room temperature while prismatic slip dominates the tensile process. Yin et al. [7] indicated that twinning induces the tension-compression yield asymmetry in strong-textured Mg alloys since twinning can easily accelerate yield softening. Although the role of twinning is well-known under uniaxial loading, it is still unclear for the role of twinning in creep at low temperature. Previous reports only focused on the dynamic precipitation during creep process [8e11]. For example, Celikin et al. [9] indicated that Mn atoms and Mg12Ce phases could enhance the creep resistance of MgeMneCe alloy via dislocation pinning. Li et al. [10] found that metastable phases were formed more rapidly during creep compared to only artificial aging. Koundinya et al. [11] designed Mg-based alloys without rare-earth addition and claimed that tiny Mg2Ca phases could increase the load-bearing capacity and creep resistance. However, it is regrettable that very few reports involved the role of twinning in creep process and rare studies researched the creep anisotropy to date. Thus, it is of much importance to understand the effects of original orientation on the creep properties of strong-textured Mg alloys at low temperature. 2. Experimental procedures The material was provided by a commercial hot-extruded AZ31 alloy (Al 2.68, Zn 0.75, Mn 0.68, Si 0.003, Fe 0.003 and Cu 0.001 mass fraction %, the remainder being Mg) with a diameter of 20 mm. The conventional description is used for the two orthogonal directions of extruded rod: ED for extrusion direction and TD for transverse direction. The compressive axis (CA) was varied in ED-TD plane with 0 , 45 and 90 to ED (Fig. S1). For briefness, the samples with three original orientations were named as ED, 45 and TD samples, https://doi.org/10.1016/j.jallcom.2019.07.193 0925-8388/© 2019 Elsevier B.V. All rights reserved.
respectively. Rectangular samples with dimensions of 11 8 8 mm3 were machined parallel to three different original orientations. These samples were homogenized at 733 K for 8 h and water quenched, resulting in equiaxed grains with an average size of ~50 mm. Uniaxial compressive tests in triplicate were performed at 423 K with a strain rate of 3 103 s1 and the resultant average values are presented in Table 1 and Fig. S2. ED sample exhibited the lowest yield stress while TD sample showed the highest. Compressive creep tests were performed at 423 K under 70e110 MPa, with pre-heating for 15 min before loading and immediate water quenching after testing. The microstructures were observed using electron backscatter diffraction (EBSD) apparatus and transmission electron microscopy (TEM). All the observations were performed parallel to CA after electro-polishing or ion milling. To elucidate the activities of slip systems caused by uniaxial compressive loading, the commercial software ABAQUS and microscopic hardening law [1] were employed in the crystal plasticity finite element model (CPFEM). Initial EBSD data employed in CPFEM simulation are shown in Fig. S3, and varied hardening parameters are listed in Table S1. 3. Results and discussion Fig. 1(a) shows the anisotropic creep results under three typical applied stresses. All samples have two creep stages, including primary and steady stages. According to the creep strain shown in Fig. 1(a) and the steady creep rate presented in Table 2, it is evident that ED sample has the highest creep resistant while 45 sample has the lowest. Fig. 1(b) shows the stress exponents of ED, 45 and TD samples, which can be calculated by the classical equation [12]:
n¼
vln_ε vlns T
(1)
Where n is stress exponent, ε_ is steady creep rate, s is applied stress and T is absolute temperature. The stress exponent has been widely
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Correspondence / Journal of Alloys and Compounds 806 (2019) 1105e1108
Table 1 Results of uniaxial compressive tests at 423 K.
Table 2 Steady creep rate of ED, 45 and TD samples creep tested at 423 K.
Sample
Yield stress/MPa
Ultimate compressive stress/MPa
Ductility/%
s/MPa
ε_ ED /s1
ε_ 45 /s1
ε_ TD /s1
ED 45 TD
66 158 182
240 195 209
26.6 42.6 35.1
70 80 90 100 110
5.00 108 7.30 108 1.06 107 1.43 107 1.75 107
1.14 107 1.63 107 2.52 107 3.44 107 4.28 107
9.25 108 1.44 107 1.92 107 2.51 107 3.21 107
accepted as the representation of creep mechanism. Grain boundary slide is the dominant creep mechanism for n < 3 while dislocation slip dominates the creep process for n > 3 [13]. Here, the stress exponents of ED, 45 and TD samples are 2.71, 3.02 and 2.82, respectively. Considering the relatively low creep temperature at 423 K, the creep mechanisms of three orientated samples are possible of dislocation slip with slight boundary migration. Fig. 2 shows the inverse pole figures, no-colored grain maps and corresponding {0001} pole figures of ED, 45 and TD samples crept for 50 h under 90 MPa. The black lines represent high-angle boundaries (HABs) above 15 and the white lines represent low-angle boundaries (LABs) from 2 to 15 . Clearly, ED sample has high densities of HABs in grain interiors while 45 and TD samples have plenty of LABs. Since low-temperature creep tests have minor effects on the grain size and texture intensity, the newly formed pole in the center is possibly attributed to {10e12} twinning. To identify {10e12} twins more precisely, white background is used where black lines still represent HABs but LABs are outlined by blue lines. Meanwhile, red lines represent twinned structures with ~86 misorientations. As can be seen, large amounts of {10e12} twins appear in ED sample whereas both TD and 45 samples have fewer twins. Inversely, the proportions of LABs in ED, 45 and TD samples are 10%, 39% and 25%, respectively. The large amounts of LABs in 45 and TD samples are probably caused by basal slip, since basal slip can successively induce the accumulation of low strain [13]. Therefore, one of the reasons for creep anisotropy is the different activities of twinning and basal slip. In addition, the well evolved HABs and low fraction of LABs in ED sample imply the frequent occurrence of non-basal slip, otherwise only twinning cannot accommodate creep strain increment. Fig. 3 shows the CPFEM simulation results, which correspond to the relative activities of deformation modes for ED, 45 and TD samples under uniaxial compressive testing at 423 K. In ED sample, the activation of basal slip drops sharply while twining is easily activated. When the relative activities of basal slip and twinning approach, prismatic slip becomes important especially for the deformation after yielding. Unlike ED sample, 45 and TD samples are mainly dominated by basal slip while twinning acts a secondary role and prismatic slip has a low activity. Pyramidal 〈cþa〉 slip is hardly activated in all samples, suggesting that it is a minor factor
in the creep anisotropy at 423 K and just acts a role of accompanying the strain induced by other deformation modes. Hereinbefore, twinning has been confirmed as one of the reasons for creep anisotropy whereas pyramidal slip has negligible effect. TEM bright fields are thus taken to analyze the effects of prismatic slip on creep anisotropy. Since both 45 and TD samples have fewer twins and more basal dislocations, the characterization for prismatic slip can be omitted for 45 sample. Using two-beam mode, Fig. 4 shows the bright fields of ED and TD samples crept for 50 h under 90 MPa. The incident beam directions are both B ¼ [2-1-10] and the diffraction vectors are both g ¼ [01e10]. Under this condition, only dislocations can be observed. The straight lines parallel to the basal plane trace are basal dislocations, while other short segments approximately perpendicular to the basal plane trace are prismatic dislocations (indicated by yellow arrows). In Fig. 4(a), ED sample almost has similar densities of prismatic and basal dislocations, indicating the easy occurrence of cross-slip. Moreover, no obvious dislocation can be observed inside the twins while evident pile-ups of prismatic dislocations exist along the twin boundaries. It is suggested that the cross-slip containing prismatic dislocations has strong interactions with {10e12} twins (a corresponding schematic diagram is shown in Fig. S4). Conversely, in Fig. 4(b), most dislocations in TD sample are lying on basal planes, indicating the lower density of prismatic dislocations in TD sample. Therefore, basal slip is the dominant creep mechanisms of both 45 and TD samples while twinning and cross-slip dominates the creep of ED sample. In conclusion, different original orientations induce different deformation modes, which directly trigger the obvious creep anisotropy. Easy activation of basal slip in 45 and TD samples accelerates creep strain increment, resulting in their weak creep resistance. In contrast, both the prismatic slip itself and the strong interactions between prismatic slip and twinning lead to higher creep resistance in ED sample. Although twinning usually induces an early yield softening during uniaxial compression, it is beneficial for creep resistance. This new finding is extremely important, which proposes the availability of pre-deformation introducing {10e12} twins to enhance creep resistance even when applied stress is higher than yield stress.
Fig. 1. (a) Creep strain versus creep time curves and (b) steady creep rate versus applied stress plots of ED, 45 and TD samples tested at 423 K.
Fig. 2. Inverse pole figures and corresponding no-colored grain maps of (a), (b) ED, (c), (d) 45 and (e), (f) TD samples. Observation direction is along compressive direction.
Fig. 3. Relative activities of different deformation modes for (a) ED, (b) 45 and (c) TD samples.
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Correspondence / Journal of Alloys and Compounds 806 (2019) 1105e1108
Fig. 4. TEM bright fields taken by two-beam mode: (a) ED and (b) TD samples. Incident beam directions are both B ¼ [2-1-10] and diffraction vectors are both g ¼ [01e10].
4. Summary Obvious compressive creep anisotropic behavior was observed for the hot-extruded AZ31 alloy rod at 423 K. Although ED sample has the lowest yield stress, it has the highest creep resistance compared to 45 and TD samples. The creep anisotropy is attributed to different original orientations promoting different dominant creep mechanisms. Heavy basal slip and few prismatic dislocations in 45 and TD samples lead to rapid increment in creep strain. Inversely, plenty of {10e12} twins and prismatic dislocations dominate the creep process of ED sample and their strong interactions lead to high creep resistance. Thus, a new perspective can be proposed that twinning conduces to creep resistance of strongtextured Mg alloys, regardless of yield softening. Data availability statement The raw and processed data required to reproduce these findings cannot be shared at this moment due to technical and time limitations. Acknowledgements The authors gratefully acknowledge the financial supports received from National Natural Science Foundation of China (Grants No. 51771230 and U1864209), Natural Science Foundation of Hunan Province (Grant No. 2019JJ40376) and Distinguished Professor Project of Central South University (Grant No. 202045009). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.jallcom.2019.07.193. References [1] W.Y. Huang, Q.H. Huo, Z.W. Fang, Z.Y. Xiao, Y. Yin, Z. Tan, X.Y. Yang, Damage analysis of hot-rolled AZ31 Mg alloy sheet during uniaxial tensile testing
under different loading directions, Mater. Sci. Eng. A 710 (2018) 289e299. [2] W.Y. Huang, X.Y. Yang, Y. Yang, T. Mukai, T. Sakai, Effect of yttrium addition on the hot deformation behaviors and microstructure development of magnesium alloy, J. Alloy. Comp. 786 (2019) 118e125. [3] D. Nugmanov, M. Knezevic, M. Zecevic, O. Sitdikov, M. Markushev, I.J. Beyerlein, Origin of plastic anisotropy in (ultra)-fine-grained MgeZneZr alloy processed by isothermal multi-step forging and rolling: experiments and modeling, Mater. Sci. Eng. A 713 (2018) 81e93. [4] J. Majhi, A.K. Mondal, Microstructure and impression creep characteristics of squeeze-cast AZ91 magnesium alloy containing Ca and/or Bi, Mater. Sci. Eng. A 744 (2019) 691e703. [5] R.A. Michi, G. Kim, B.W. Kim, W. Lee, D.C. Dunand, Compressive creep behavior of hot-pressed Mg 1.96 Al 0.04 Si 0.97 Bi 0.03, Scr. Mater. 148 (2018) 10e14. [6] D.W. Hou, Y.Z. Zhu, Q.Z. Li, T.M. Liu, H.M. Wen, Effect of {10-12} twinning on the deformation behavior of AZ31 magnesium alloy, Mater. Sci. Eng. A 746 (2019) 314e321. [7] D.L. Yin, J.T. Wang, J.Q. Liu, X. Zhao, On tension-compression yield asymmetry in an extruded Mg-3Al-1Zn alloy, J. Alloy. Comp. 478 (2009) 789e795. [8] J. Wang, L. Luo, Q.H. Huo, Y.F. Shi, Z.Y. Xiao, Y.X. Ye, X.Y. Yang, Creep behaviors of a highly concentrated Mg-18 wt%Gd binary alloy with and without artificial aging, J. Alloy. Comp. 774 (2019) 1036e1045. [9] M. Celikin, R. Gauvin, M. Pekguleryuz, Dynamic co-precipitation of a-Mn/ Mg12Ce in creep resistant Mg-Sr-Mn-Ce alloys, Mater. Sci. Eng. A 719 (2018) 199e205. [10] R. Li, J. Zhang, G. Fu, L. Zong, B. Guo, Y. Yu, Y. Su, Y. Hao, Different precipitation hardening behaviors of extruded Mge6Gde1Ca alloy during artificial aging and creep processes, Mater. Sci. Eng. A 715 (2018) 186e193. [11] N.T.B.N. Koundinya, R.S. Kottada, Achieving exceptional creep resistance in rare-earth-free Mg-base alloys by engineering the shape, size and fraction of eutectic, particles and precipitates, Scr. Mater. 162 (2019) 121e126. [12] Y.F. Shi, L. Luo, Q.H. Huo, J. Wang, Z.Y. Xiao, J.C. Guo, X.Y. Yang, Enhancing creep properties of a hot-rolled Mg-4Y binary alloy via a new thought of inhibiting cross-slip, Mater. Char. 147 (2019) 64e71. [13] Z.W. Fang, Q.H. Huo, J. Wang, Z.Y. Xiao, D.X. Zhang, W.Y. Huang, M.C. Zhao, X.Y. Yang, Creep behaviors of hot compressed Mg-4Y-2Nd-0.2Zn-0.5Zr alloy with and without aging, Mater. Sci. Eng. A 708 (2017) 460e468.
Weiying Huang, Qinghuan Huo**, Zhirou Zhang, Jiao Tang Educational Key Laboratory of Nonferrous Metal Materials Science and Engineering, School of Materials Science and Engineering, Central South University, Changsha, 410083, China Aki Hashimoto Technology Div. Nippon Paint Surf Chemicals Co. LTD., 4-1-15 Minamishinagawa, Shinagawa-ku, Tokyo, 140-8675, Japan Xuyue Yang* Educational Key Laboratory of Nonferrous Metal Materials Science and Engineering, School of Materials Science and Engineering, Central South University, Changsha, 410083, China **
Corresponding author.
*
Corresponding author. E-mail address: [email protected] (Q. Huo). E-mail address: [email protected] (X. Yang). 14 May 15 July 17 July Available online 25 July
2019 2019 2019 2019