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Effect of deformation path on texture and tension properties of submicrocrystalline Al-Mg-Si alloy fabricated by differential speed rolling
Accepted Manuscript Effect of deformation path on texture and tension properties of submicrocrystalline Al-Mg-Si alloy fabricated by differential speed rolling H.W. Yang, I.P. Widiantara, Y.H. Joo, Y.G. Ko PII: DOI: Reference:
S0167-577X(17)31628-2 https://doi.org/10.1016/j.matlet.2017.11.012 MLBLUE 23378
To appear in:
Materials Letters
Received Date: Accepted Date:
25 October 2017 2 November 2017
Please cite this article as: H.W. Yang, I.P. Widiantara, Y.H. Joo, Y.G. Ko, Effect of deformation path on texture and tension properties of submicrocrystalline Al-Mg-Si alloy fabricated by differential speed rolling, Materials Letters (2017), doi: https://doi.org/10.1016/j.matlet.2017.11.012
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of deformation path on texture and tension properties of submicrocrystalline AlMg-Si alloy fabricated by differential speed rolling H. W. Yang, I P. Widiantara, Y. H. Joo, Y. G. Ko* Plasticity Control and Mechanical Modeling Lab. School of Materials Science and Engineering, Yeungnam University, Gyeongsan 38541, Republic of Korea
Abstract The work investigated the effect of deformation path on texture and tension properties of submicrocrystalline Al-Mg-Si alloy sample processed by differential speed rolling (DSR). DSR was performed on the present samples rotated between passage utilizing three paths, such as no rotation, rotations along the transverse and rolling axes toward deformation direction in order to understand the roles of the different characteristics of macro-shear. When both no rotation and rotation along the transverse axis were applied, high strength but low ductility would be obtained due to the presence of fine grains together with lamellar bands. A good combination of strength (~312 MPa) and ductility (~7.4 %) was attained by means of rotation along the rolling axis, giving rise to the conjugation of macro-shear bands. This was explained in relation to the interpretation of recrystallization texture components. Keywords: Al-Mg-Si alloy; Differential speed rolling; Deformation path; Texture; Tension properties
1. Introduction Submicrocrystalline (SMC) metallic materials whose grain size was below ~1 µm have been known one of the promising candidates for a variety of industrial applications because of their superior mechanical properties to their microcrystalline counterparts [1]. As reported earlier [2,3], they could be fabricated through severe plastic deformation (SPD) imparting intense shear strain. Among these methods, differential speed rolling (DSR) where different speeds for the upper and lower rolls were controlled was reported to be desirable for achieving the formation of submicrocrystalline structure which was influenced by the deformation variables, such as roll speed ratio, deformation number, temperature, and route, etc. [4,5]. According to the current research reported by Polkowski et al. [4,5], two deformation variables, such as roll speed ratio and deformation path, played an important role in affecting the formation of SMC structure. It was well established that an increase in roll speed ratio imposed the appreciable amount of shear strain required for grain reduction unless the severe segment on the sample surface would take place. Recently, Kotiba and Ko [2]
demonstrated using deformation route where the sample was rotated 180˚ along the rolling direction between the adjacent passes that an increase in strength and ductility of AZ31 Mg alloy was achieved simultaneously since the first shear plane was crossed by the second shear plane, suppressing texture hardening. As aforementioned, deformation path would also modify the texture in a manner that the conventional rolling deformation resulted in plane-strain texture components while shear deformation produced shear texture components. This would lead to a significant change in mechanical properties. Up to the present investigation, the effect of deformation path on texture and mechanical properties remained undocumented for Al alloys. Therefore, the present study investigates the influence of deformation path on texture and mechanical response of SMC Al-Mg-Si alloy. The optimum deformation path is suggested based on the results of mechanical assessment as well as texture analysis through orientation distribution function (ODF).
2. Material and methods The as-received sample was an Al-Mg-Si alloy sheet with a chemical composition of 0.91Mg-0.72Si-0.52Fe0.21Cu-0.19Cr, and balance Al (wt.%). Prior to DSR, the present samples underwent homogenization treatment at 823 K for 3 h followed by air cooling, resulting in the average grain size of ~45 µm. DSRs were performed utilizing two same-sized rolls with a roll speed ratio of 1:4 for the lower and upper rolls where the speed of the lower was fixed at ~5 m/min. The samples were subjected to thickness reduction of 30 % per pass. Thus the total reduction of 75 % was achieved after 4-pass DSR. To investigate the role of deformation path, the samples were rotated between each pass by no rotation (NR), rotation along the transverse axis (RT), and rotation along the rolling axis (RR) as shown in Fig. 1. The macro-shear patterns were also implemented. The central regions of each sample were observed via electron back-scattered diffraction. Inverse pole figure (IPF) maps were used to analyze the misorientation of every single grain. Orientation distribution function (ODF) drawn from IPF map was used to analyze the various texture components present in the deformed samples. Mechanical properties were examined by tension test with an initial strain rate of 10-3/s per ASTM E8 where the gauge length and thickness of the specimens were 25.4 and 1 mm. At least five samples were tested under the same conditions to gain reliability of the present data.
3. Results and discussion Figure 1 presents the EBSD results showing IPF maps of the present samples deformed by NR, RT, and RR methods. It is apparent that microstructures of both the NR and RT samples comprised the well-developed
lamellar-like structures whose widths were estimated to be 3~10 µm as shown in Fig. 1a and 1b. Considering the macro-shear planes induced by DSR as shown in insets, the shear deformation was localized on the same plane although the thickness of the sample would tend to decrease with increasing DSR number. Thus, most lamellar bands formed by first DSR would be remained. In addition, some new grains begun to occur mainly in the vicinity of lamellar boundaries. The number of the new grains in the RT sample was higher than that in the NR sample since RT offered the reversed shear pattern at every even-numbered operation. It is worth noting, however, that the degree of grain refinement in the NR and RT samples would not be as pronounced as that in the RR sample. In case of RR, the first macro-shear band would be crossed with the macro-shear band generated by second DSR (Fig. 1c). This fact allowed the lamellar-like grains formed after the odd-numbered pass to restore their equiaxed shape after the even-number pass in order to accommodate the plastic strain by DSR. Accordingly, the RR sample exhibited higher fraction of SMC equiaxed grains than those in the NR and RT samples while the lamellar bands were sacrificed. We suggested based on the different morphologies of the grains with respect to deformation path that grain refinement mechanism in Al alloys during DSR would be associated with strain-induced grain subdivision. The ODF results of the samples via NR, RT, and RR methods were presented in the Euler angle range using the non-orthonormal sample symmetry. As shown in Fig. 2a at specific sections of ϕ2 = 0°, 45°, and 65°, the general textures observed in FCC metals were three-fold, such as (i) plane-strain texture components of Brass, Copper, and S, (ii) shear texture components of E, F, and H, and (iii) recrystallization texture components of Cube, Goss, and P [6]. Some grains with recrystallization components were detected more or less for all samples due to dynamic recrystallization (DRX). It is interesting to note that the number of the grains with recrystallization texture in the RR sample was higher than those in the NR and RT samples, which agreed with the present observations in Fig. 1. Generally, the driving force for nucleation and growth of the newly-formed grains during deformation was related to the strain gradient [7]. Since the intersections of the lamellar bands which formed by the macro-shear bands would result in large strain gradient, RR method was desirable for providing the sites preferential for nucleation. This would trigger relatively higher fraction of DRX grains via RR than those via NR and RT as confirmed by Fig. 2c and 2d. Figure 3 presents the tension properties of the samples deformed via NR, RT, and RR methods. The strength increased in the order of RT < NR < RR while the ductility increased in the order of NR < RT < RR. Several things could be drawn. First, the tensile strength of the NR sample was higher than that via RT while the ductility of the NR sample was lower than that via RT due to the narrow width of lamellar bands shown in Fig.
1. Second, the RR sample exhibited a good combination of strength and ductility, approaching to ~312 MPa and ~7.4 %. The moderate ductility observed in the RR sample was explained by strain hardening features as seen from Fig. 3b. The RR sample showed superior strain hardening rate to the others. This would be connected to the suitable ductility whose value was estimated to be true strain of ~3.1 % due to the presence of SMC equiaxed grains having recrystallization components. Thus, DSR using RR would be desirable for improving mechanical properties. Interestingly, the strength and ductility of the RR sample were comparably higher than Al alloys deformed by other SPDs. Jandaghi et al. [8] reported utilizing constrained groove pressing that the tensile strength and elongation of ~200 MPa and ~3 %. The tensile strength and elongation of ~240 MPa and ~6 % were achieved by equal channel angular pressing [9]. Although the optimum deformation path would be proposed in this study, further investigation utilizing static annealing treatment will be necessary to improve the ductility higher than ~10 % that was reliable value for industrial applications.
4. Conclusions The mechanical characteristics of SMC Al-Mg-Si alloy sample were studied based on texture affected by deformation path during DSR. Most of the grains were refined in the sample deformed by RR while both NR and RT would give rise to the coexistence of lamellar bands and fine grains that were initiated mainly at the lamellar boundaries. In addition, the occurrence of recrystallization texture in the RR sample was likely to be activated to greater extent than those by NR and RT because the conjugation of the macro-shear bands would trigger the formation of nucleation sites for DRX. Hence, a good combination of strength and ductility was achieved via RR where SMC equiaxed grains led to high strength whereas the formation of recrystallization texture was responsible for moderate ductility.
References [1] R. Valiev, Nanostructuring of metals by severe plastic deformation for advanced properties, Nat. Mater. 3 (2004) 511-516. [2] K. Hamad, Y.G. Ko, A cross-shear deformation for optimizing the strength and ductility of AZ31 magnesium alloys, Sci. Rep. 6 (2016) 29954. [3] C. Ma, L. Hou, J. Zhang, L. Zhuang, Influence of thickness reduction per pass on strain, microstructures and mechanical properties of 7050 Al alloy sheet processed by asymmetric rolling, Mater. Sci. Eng. A 650 (2016) 454468. [4] W. Polkowski, P. Jóźwik, Z. Bojar, Differential speed rolling of Ni3Al based intermetallic alloy-analysis of the deformation process, Mater. Lett. 139 (2015) 46-49.
[5] W. Polkowski, A. Polkowska, D. Zasada, Characterization of high strength nickel thin sheets fabricated by differential speed rolling method, Mater. Charact. 130 (2017) 173-180. [6] V. Randle, O. Engler, Introduction to Texture Analysis: Macrotexture, Microtexture and Orientation Mapping, Gordon and Breach Sci. Publ., Amsterdam (2000). [7] T. Sakai, A. Belyakov, R. Kaibyshev, H. Miura, J.J. Jonas, Dynamic and post-dynamic recrystallization under hot, cold and severe plastic deformation conditions, Prog. Mater. Sci. 60 (2014) 130-207. [8] M.R. Jandaghi, H. Pouraliakbar, G. Khalaj, M.-J. Khalaj, A. Heidarzadeh, Study on the post-rolling direction of severely plastic deformed aluminum-manganese-silicon alloy, Arch. Civil Mech. Eng. 16 (2016) 876-887. [9] H. Jia, R. Bjørge, K. Marthinsen, R.H. Mathiesen, Y. Li, Soft particles assisted grain refinement and strengthening of an Al-Bi-Zn alloy subjected to ECAP, Mater. Sci. Eng. A 703 (2017) 304-313.
Figure captions Fig. 1. IPF maps of the DSR-deformed samples via (a) NR, (b) RT, and (c) RR methods. Fig. 2. ODF images showing (a) the ideal texture components of FCC metals [6] and (b) the constituent texture components and their maximum values of the DSR-deformed samples via NR, RT, and RR methods. (c) Distributions of ODF intensity values and (d) relative fractions of texture components. Fig. 3. (a) Room-temperature engineering stress-strain curves of the DSR-deformed samples via NR, RT, and RR methods and (b) their strain hardening rates.
Acknowledgement This work was supported by the Basic Research Program supported by Yeungnam University (#217A380064).
Figure 1
Figure 2
Figure 3
Highlights 1. Effects of DSR paths were investigated 2. Rotation 180° (RR sample) resulted in equiaxed grains with recrystallization texture 3. RR sample exhibited superior strength and ductility
S0167-577X(17)31628-2 https://doi.org/10.1016/j.matlet.2017.11.012 MLBLUE 23378
To appear in:
Materials Letters
Received Date: Accepted Date:
25 October 2017 2 November 2017
Please cite this article as: H.W. Yang, I.P. Widiantara, Y.H. Joo, Y.G. Ko, Effect of deformation path on texture and tension properties of submicrocrystalline Al-Mg-Si alloy fabricated by differential speed rolling, Materials Letters (2017), doi: https://doi.org/10.1016/j.matlet.2017.11.012
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of deformation path on texture and tension properties of submicrocrystalline AlMg-Si alloy fabricated by differential speed rolling H. W. Yang, I P. Widiantara, Y. H. Joo, Y. G. Ko* Plasticity Control and Mechanical Modeling Lab. School of Materials Science and Engineering, Yeungnam University, Gyeongsan 38541, Republic of Korea
Abstract The work investigated the effect of deformation path on texture and tension properties of submicrocrystalline Al-Mg-Si alloy sample processed by differential speed rolling (DSR). DSR was performed on the present samples rotated between passage utilizing three paths, such as no rotation, rotations along the transverse and rolling axes toward deformation direction in order to understand the roles of the different characteristics of macro-shear. When both no rotation and rotation along the transverse axis were applied, high strength but low ductility would be obtained due to the presence of fine grains together with lamellar bands. A good combination of strength (~312 MPa) and ductility (~7.4 %) was attained by means of rotation along the rolling axis, giving rise to the conjugation of macro-shear bands. This was explained in relation to the interpretation of recrystallization texture components. Keywords: Al-Mg-Si alloy; Differential speed rolling; Deformation path; Texture; Tension properties
1. Introduction Submicrocrystalline (SMC) metallic materials whose grain size was below ~1 µm have been known one of the promising candidates for a variety of industrial applications because of their superior mechanical properties to their microcrystalline counterparts [1]. As reported earlier [2,3], they could be fabricated through severe plastic deformation (SPD) imparting intense shear strain. Among these methods, differential speed rolling (DSR) where different speeds for the upper and lower rolls were controlled was reported to be desirable for achieving the formation of submicrocrystalline structure which was influenced by the deformation variables, such as roll speed ratio, deformation number, temperature, and route, etc. [4,5]. According to the current research reported by Polkowski et al. [4,5], two deformation variables, such as roll speed ratio and deformation path, played an important role in affecting the formation of SMC structure. It was well established that an increase in roll speed ratio imposed the appreciable amount of shear strain required for grain reduction unless the severe segment on the sample surface would take place. Recently, Kotiba and Ko [2]
demonstrated using deformation route where the sample was rotated 180˚ along the rolling direction between the adjacent passes that an increase in strength and ductility of AZ31 Mg alloy was achieved simultaneously since the first shear plane was crossed by the second shear plane, suppressing texture hardening. As aforementioned, deformation path would also modify the texture in a manner that the conventional rolling deformation resulted in plane-strain texture components while shear deformation produced shear texture components. This would lead to a significant change in mechanical properties. Up to the present investigation, the effect of deformation path on texture and mechanical properties remained undocumented for Al alloys. Therefore, the present study investigates the influence of deformation path on texture and mechanical response of SMC Al-Mg-Si alloy. The optimum deformation path is suggested based on the results of mechanical assessment as well as texture analysis through orientation distribution function (ODF).
2. Material and methods The as-received sample was an Al-Mg-Si alloy sheet with a chemical composition of 0.91Mg-0.72Si-0.52Fe0.21Cu-0.19Cr, and balance Al (wt.%). Prior to DSR, the present samples underwent homogenization treatment at 823 K for 3 h followed by air cooling, resulting in the average grain size of ~45 µm. DSRs were performed utilizing two same-sized rolls with a roll speed ratio of 1:4 for the lower and upper rolls where the speed of the lower was fixed at ~5 m/min. The samples were subjected to thickness reduction of 30 % per pass. Thus the total reduction of 75 % was achieved after 4-pass DSR. To investigate the role of deformation path, the samples were rotated between each pass by no rotation (NR), rotation along the transverse axis (RT), and rotation along the rolling axis (RR) as shown in Fig. 1. The macro-shear patterns were also implemented. The central regions of each sample were observed via electron back-scattered diffraction. Inverse pole figure (IPF) maps were used to analyze the misorientation of every single grain. Orientation distribution function (ODF) drawn from IPF map was used to analyze the various texture components present in the deformed samples. Mechanical properties were examined by tension test with an initial strain rate of 10-3/s per ASTM E8 where the gauge length and thickness of the specimens were 25.4 and 1 mm. At least five samples were tested under the same conditions to gain reliability of the present data.
3. Results and discussion Figure 1 presents the EBSD results showing IPF maps of the present samples deformed by NR, RT, and RR methods. It is apparent that microstructures of both the NR and RT samples comprised the well-developed
lamellar-like structures whose widths were estimated to be 3~10 µm as shown in Fig. 1a and 1b. Considering the macro-shear planes induced by DSR as shown in insets, the shear deformation was localized on the same plane although the thickness of the sample would tend to decrease with increasing DSR number. Thus, most lamellar bands formed by first DSR would be remained. In addition, some new grains begun to occur mainly in the vicinity of lamellar boundaries. The number of the new grains in the RT sample was higher than that in the NR sample since RT offered the reversed shear pattern at every even-numbered operation. It is worth noting, however, that the degree of grain refinement in the NR and RT samples would not be as pronounced as that in the RR sample. In case of RR, the first macro-shear band would be crossed with the macro-shear band generated by second DSR (Fig. 1c). This fact allowed the lamellar-like grains formed after the odd-numbered pass to restore their equiaxed shape after the even-number pass in order to accommodate the plastic strain by DSR. Accordingly, the RR sample exhibited higher fraction of SMC equiaxed grains than those in the NR and RT samples while the lamellar bands were sacrificed. We suggested based on the different morphologies of the grains with respect to deformation path that grain refinement mechanism in Al alloys during DSR would be associated with strain-induced grain subdivision. The ODF results of the samples via NR, RT, and RR methods were presented in the Euler angle range using the non-orthonormal sample symmetry. As shown in Fig. 2a at specific sections of ϕ2 = 0°, 45°, and 65°, the general textures observed in FCC metals were three-fold, such as (i) plane-strain texture components of Brass, Copper, and S, (ii) shear texture components of E, F, and H, and (iii) recrystallization texture components of Cube, Goss, and P [6]. Some grains with recrystallization components were detected more or less for all samples due to dynamic recrystallization (DRX). It is interesting to note that the number of the grains with recrystallization texture in the RR sample was higher than those in the NR and RT samples, which agreed with the present observations in Fig. 1. Generally, the driving force for nucleation and growth of the newly-formed grains during deformation was related to the strain gradient [7]. Since the intersections of the lamellar bands which formed by the macro-shear bands would result in large strain gradient, RR method was desirable for providing the sites preferential for nucleation. This would trigger relatively higher fraction of DRX grains via RR than those via NR and RT as confirmed by Fig. 2c and 2d. Figure 3 presents the tension properties of the samples deformed via NR, RT, and RR methods. The strength increased in the order of RT < NR < RR while the ductility increased in the order of NR < RT < RR. Several things could be drawn. First, the tensile strength of the NR sample was higher than that via RT while the ductility of the NR sample was lower than that via RT due to the narrow width of lamellar bands shown in Fig.
1. Second, the RR sample exhibited a good combination of strength and ductility, approaching to ~312 MPa and ~7.4 %. The moderate ductility observed in the RR sample was explained by strain hardening features as seen from Fig. 3b. The RR sample showed superior strain hardening rate to the others. This would be connected to the suitable ductility whose value was estimated to be true strain of ~3.1 % due to the presence of SMC equiaxed grains having recrystallization components. Thus, DSR using RR would be desirable for improving mechanical properties. Interestingly, the strength and ductility of the RR sample were comparably higher than Al alloys deformed by other SPDs. Jandaghi et al. [8] reported utilizing constrained groove pressing that the tensile strength and elongation of ~200 MPa and ~3 %. The tensile strength and elongation of ~240 MPa and ~6 % were achieved by equal channel angular pressing [9]. Although the optimum deformation path would be proposed in this study, further investigation utilizing static annealing treatment will be necessary to improve the ductility higher than ~10 % that was reliable value for industrial applications.
4. Conclusions The mechanical characteristics of SMC Al-Mg-Si alloy sample were studied based on texture affected by deformation path during DSR. Most of the grains were refined in the sample deformed by RR while both NR and RT would give rise to the coexistence of lamellar bands and fine grains that were initiated mainly at the lamellar boundaries. In addition, the occurrence of recrystallization texture in the RR sample was likely to be activated to greater extent than those by NR and RT because the conjugation of the macro-shear bands would trigger the formation of nucleation sites for DRX. Hence, a good combination of strength and ductility was achieved via RR where SMC equiaxed grains led to high strength whereas the formation of recrystallization texture was responsible for moderate ductility.
References [1] R. Valiev, Nanostructuring of metals by severe plastic deformation for advanced properties, Nat. Mater. 3 (2004) 511-516. [2] K. Hamad, Y.G. Ko, A cross-shear deformation for optimizing the strength and ductility of AZ31 magnesium alloys, Sci. Rep. 6 (2016) 29954. [3] C. Ma, L. Hou, J. Zhang, L. Zhuang, Influence of thickness reduction per pass on strain, microstructures and mechanical properties of 7050 Al alloy sheet processed by asymmetric rolling, Mater. Sci. Eng. A 650 (2016) 454468. [4] W. Polkowski, P. Jóźwik, Z. Bojar, Differential speed rolling of Ni3Al based intermetallic alloy-analysis of the deformation process, Mater. Lett. 139 (2015) 46-49.
[5] W. Polkowski, A. Polkowska, D. Zasada, Characterization of high strength nickel thin sheets fabricated by differential speed rolling method, Mater. Charact. 130 (2017) 173-180. [6] V. Randle, O. Engler, Introduction to Texture Analysis: Macrotexture, Microtexture and Orientation Mapping, Gordon and Breach Sci. Publ., Amsterdam (2000). [7] T. Sakai, A. Belyakov, R. Kaibyshev, H. Miura, J.J. Jonas, Dynamic and post-dynamic recrystallization under hot, cold and severe plastic deformation conditions, Prog. Mater. Sci. 60 (2014) 130-207. [8] M.R. Jandaghi, H. Pouraliakbar, G. Khalaj, M.-J. Khalaj, A. Heidarzadeh, Study on the post-rolling direction of severely plastic deformed aluminum-manganese-silicon alloy, Arch. Civil Mech. Eng. 16 (2016) 876-887. [9] H. Jia, R. Bjørge, K. Marthinsen, R.H. Mathiesen, Y. Li, Soft particles assisted grain refinement and strengthening of an Al-Bi-Zn alloy subjected to ECAP, Mater. Sci. Eng. A 703 (2017) 304-313.
Figure captions Fig. 1. IPF maps of the DSR-deformed samples via (a) NR, (b) RT, and (c) RR methods. Fig. 2. ODF images showing (a) the ideal texture components of FCC metals [6] and (b) the constituent texture components and their maximum values of the DSR-deformed samples via NR, RT, and RR methods. (c) Distributions of ODF intensity values and (d) relative fractions of texture components. Fig. 3. (a) Room-temperature engineering stress-strain curves of the DSR-deformed samples via NR, RT, and RR methods and (b) their strain hardening rates.
Acknowledgement This work was supported by the Basic Research Program supported by Yeungnam University (#217A380064).
Figure 1
Figure 2
Figure 3
Highlights 1. Effects of DSR paths were investigated 2. Rotation 180° (RR sample) resulted in equiaxed grains with recrystallization texture 3. RR sample exhibited superior strength and ductility