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Texture evolution of rolled AA5052 alloy sheets after annealing
Journal of Materials Processing Technology 187–188 (2007) 578–581
Texture evolution of rolled AA5052 alloy sheets after annealing K.J. Kim a,∗ , H.-T. Jeong b , K.S. Shin c , C.-W. Kim d a
CAE Team, Ssang Yong Motor Co., 150-3 Chilgoi-dong, Pyungtaek-si, Gyeonggi-do 459-711, Republic of Korea b Department of Metallurgical Engineering, Kangnung National University, 120 Gangneung Daehangno, Gangneung City, Gangwon-do 210-702, Republic of Korea c School of Materials Science and Engineering, Seoul National University, San 56-1 Shinrim-dong, Kwanak-ku, Seoul 151-742, Republic of Korea d Mechanical Engineering, U&I Corporation Research Center in Korea University, 635, Bio-technology B/D, 5ga, Anam-dong, Sungbuk-gu, Seoul 136-701, Republic of Korea
Abstract To fabricate the aluminum alloys with good drawability, the textures evolution of the AA5052 sheets after rolling and subsequent annealing was studied. The measurement of the deformation textures was carried out for the sheets in which were cold rolled with high reduction ratio by using the symmetric roll. In addition, the change of the recrystallization texture was investigated after heat treatments of the rolled sheets with various heat treatment conditions. Rolling without lubrication and subsequent annealing led to the formation of favorable rot-CND {0 0 1}1 1 0 and ␥-fiber ND//1 1 1 textures in AA5052 sheets. From the results, the ␥-fiber ND//1 1 1 component well evolved during rolling at high reduction ratio (reduction over 92%, l/d parameter over 6.3). Among shear deformation textures, the ␥-fiber ND//1 1 1 was not rotated during recrystallization (350 ◦ C). The 5052 aluminum alloy sheet after rolling at high reduction ratio and subsequent annealing had the higher plastic strain ratio, however, the planar anisotropy of this sheet was higher than before. © 2006 Elsevier B.V. All rights reserved. Keywords: AA5052 sheet; Shear texture; Rolling; Anisotropy; ND//1 1 1
1. Introduction In order to apply the 5052 aluminum alloy sheets to the automotive body panels, the roll formed metal sheets having good drawability and the lower planar anisotropy are needed and these characteristics are closely related with textures evolution [1–4]. For increasing the drawability, it is needed to improve the plastic strain ratio (R-value) of the aluminum alloys. For increasing the plastic strain ratio in the aluminum alloy sheets, which are FCC metals, the sheets should be roll formed that they have well evolved shear texture components. When the sheets were loaded higher by shear deformation, the friction coefficient, μ was increased [5]. Among shear deformation textures, if, especially, the ␥-fiber ND//1 1 1 was well evolved, the planar anisotropy decreased and the sheet drawability increased, on the other hand, if the rot-CND {1 0 0}1 1 0 component was well evolved, the planar anisotropy increased [1,2,4,5]. The main purpose was to fabricate the sheets having higher drawability for applying the aluminum sheets for automotive body panels in the present study.
Since the anisotropy and the drawability were highly dependent on the R-value, the R-value test was carried out. 2. Experimental procedures 2.1. Roll forming and annealing of AA5052 alloy sheets The initial state of the 4.5 mm in thickness 5052 aluminum alloys are fabricated by hot rolling and the homogenization treatment at 500 ◦ C was carried out before cold rolling in the present study. The cold rolling conditions of the 5052 aluminum alloys designed in the present study were made up of roll diameter (127 mm), rolling temperature (room temperature), rolling speed (400 rpm), total four pass cold rolled, total reduction ratio (92.8%; over 50% reduction per one pass) and the l/d parameters (6.28) [3–5], thus the various sheets were obtained having the shear textures. For applying the high friction between the roll bite and the specimen, the lubrication was not applied to the roll bite in order to achieve more evolved shear deformation textures. The formation of recrystallization texture was investigated from the heat treatment of the specimens, which were well evolved on the shear texture from rolling. In order to examine the recrystallization texture of the 5052 aluminum sheets, the annealing was conducted on a salt bath with various holding time (0, 180 and 1200 s, respectively) at 350 ◦ C.
2.2. Characterization of AA5052 alloy sheets ∗
Corresponding author. E-mail address: [email protected] (K.J. Kim).
0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.11.214
Specimens for the measurement of the pole figure in order to analyze the textures of the rolled aluminum sheet were prepared after mechanical polishing
K.J. Kim et al. / Journal of Materials Processing Technology 187–188 (2007) 578–581
579
and those of surface deformation layer of 10 mm in thickness were removed from chemical polishing with 10% NaOH solution in the present study. Then {1 1 1}, {2 0 0} and {2 2 0} pole figures were measured from Schultz reflection method. The measuring equipment was a Seifert 3003 and the voltage and the current were applied for 30 kV and 15 mA, respectively. Using target was the Co target, which had been well recommended in FCC metals. The plastic strain ratio is the important barometer to evaluate deep drawing capability and the anisotropy of the sheet. In general, since the roll formed sheets have the planar anisotropy following tensile orientation, the specimens were prepared with different specimen angles, 0◦ , 45◦ and 90◦ to the sheet rolling direction. The plastic strain ratio (R) was measured with 2-extensometers that were installed in the tensile and transverse directions, respectively, during tensile tests in order to evaluate the planar anisotropy. The plastic strain ratio is defined as shown in Eq. (1). Here, ε22 and ε33 is transverse and thickness true strain, respectively. R=
ε22 ε33
(1)
In addition, the plastic strain ratio was obtained from the average value of 0.05–0.10 tensile strain and average plastic strain ratio (Rm ) and the planar anisotropy of the R-value (R) were calculated from the following Eqs. (2) and (3), where the R0 , R45 and R90 were the plastic strain ratio when the angles between the rolling direction and the tensile axis were 0◦ , 45◦ and 90◦ , respectively. Rm =
R0 + R90 + 2R45 4
(2)
R =
R0 + R90 − 2R45 2
(3)
3. Experimental results and discussion 3.1. Rolling and recrystallization texture Fig. 1 shows the change in texture developed in the 5052 aluminum alloy sheet during heat treatment at 350 ◦ C with various annealing time compared to the texture before heat treatment. In case of the 5052 aluminum alloy sheet with l/d parameter of 6.28 before heat treatment, the pole intensity of ␥-fiber ND//1 1 1 was very high. However, the pole intensity of rot-CND {0 0 1}1 1 0 decreased but the pole intensity of ␥fiber ND//1 1 1 increased with annealing time. For example, in case of annealing time for 180 s, the pole intensity of rot-CND {0 0 1}1 1 0 orientation decreased but the pole intensity of ␥fiber ND//1 1 1 orientation increased. As shown in Fig. 1(a–c), the ␥-fiber ND//1 1 1 did not rotate to other orientations until after heat treatments for 1200 s.
Fig. 1. Measured (1 1 1) pole figures of AA5052 sheets after annealing at 350 ◦ C for (a) 0 s, (b) 180 s and (c) 1200 s.
3.2. Plastic strain ratio and anisotropy Fig. 2 shows the plastic strain ratio, the average plastic strain ratio and the anisotropy of the plastic strain ratio of the 5052 aluminum alloy sheets annealed with holding time for 180 and 1200 s at 350 ◦ C. The plastic strain ratio was the highest with heat-treated holding time for 1200 s at 350 ◦ C and the average plastic strain ratio was 1.53, which was higher than those of the Al alloys reported in the literature. It resulted from that the ␥fiber ND//1 1 1 components were developed as the preferred orientation in the sheet fabricated by the rolling process proposed in this study and did not rotate to other orientations, and the pole intensity of ␥-fiber ND//1 1 1 components increased after
Fig. 2. Measured R-values of symmetrically rolled AA5052 sheets for different annealing times.
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K.J. Kim et al. / Journal of Materials Processing Technology 187–188 (2007) 578–581
Table 1 Lankford values for some ideal orientations by Lequeu et al. [2] Ideal orientation
R0
R45
R90
Rm
|R|
{0 0 1}1 1 0 {1 1 1}1 1 0 {1 1 1}1 1 2 {1 1 2}1 1 0 {0 0 1}1 0 0 {1 1 0}1 1 2 {1 1 2}1 1 1 {1 2 3}6 3 4
0.00 1.84 1.84 0.53 1.00 0.50 1.00 0.72
1.00 1.89 1.89 1.89 0.00 2.09 1.89 1.81
0.00 1.95 1.95 1.00 1.00 1.00 0.50 0.83
0.53 1.91 1.91 1.29 0.53 1.35 1.29 1.27
0.30 0.04 0.04 0.34 0.30 0.46 0.34 0.35
recrystallization. However, the anisotropy of the plastic strain ratio was from −1.17 to −1.22, which was still high. Table 1 shows the plastic strain ratio of ideal orientations (about single crystals) calculated by Lequeu et al. [2]. The average plastic strain ratio of ␥-fiber {1 1 1}1 1 0 and {1 1 1}1 1 2 orientations was the highest value of 1.91 and the lowest planar anisotropy and they should generate an excellent drawability. In addition, rot-CND {0 0 1}1 1 0 orientation, which is rotated by 45◦ to the ND axis of cube {0 0 1}1 0 0 orientation, and cube {0 0 1}1 0 0 orientation have the lowest plastic strain ratio and the highest anisotropy. It was well known fact that the polycrystal sheets having strong ␥-fiber {1 1 1}u v w orientation show both the highest average plastic strain ratio and the lowest planar anisotropy can be found from the empirical and calculated papers by utilizing the similar calculation method about the single crystals [1,2]. 3.3. Effect of annealing on plastic strain ratio and texture The analysis of pole intensity of ␥-fiber ND//1 1 1 at (1 1 1) pole figure measured after annealing of the 5052 aluminum alloy sheets with holding time for 0, 180 and 1200 s at 350 ◦ C was compared to the result of measured plastic strain ratio as shown in Fig. 3. After annealing with holding time for 180 s at 350 ◦ C, the pole intensity of ␥-fiber ND//1 1 1 increased rapidly and showed the maximum value at 350 ◦ C for 1200 s. In addition, the measured average plastic strain ratio increased
Fig. 3. Measured pole intensity of ND//1 1 1 ␥-fiber and R-values of AA5052 sheets following as annealing time at 350 ◦ C.
Fig. 4. Schematic presentation of simplified array of dislocations by shear deformation.
proportionally with increasing the pole intensity of ␥-fiber ND//1 1 1. Since the preferred orientations might rotate and change to the random orientation increasingly during annealing, the measured (1 1 1) pole figure of the 5052 aluminum alloy sheet annealed at 350 ◦ C shows that the pole intensities of rot-CND {0 0 1}1 1 0 component have tendency to decreases with increasing annealing time as shown in Fig. 1. Therefore, the planar anisotropy of the plastic strain ratio increases proportionally with the pole intensity of rot-CND {0 0 1}1 1 0 as shown in Figs. 1 and 2. In case of the shear deformation, because most of slips occur to the rolling direction or rolling plane, dislocation structures of the shear-deformed materials have more planar than those of the plane strain compressive materials. Fig. 4 shows more simplified model containing dislocations array about these explanations. Dislocation arrays are placed in planar shape due to the shear stress following dislocation sources SA and SB as shown in Fig. 5. In addition, in case of the shear-deformed (0 0 1)[1 1 0] orientation, the shear strain of (1 1 1)[1 1 0] slip systems is much higher than other slip systems and that makes duplex slip occur. In addition, the dislocations of the duplex slip have the same slip direction as shown in Fig. 5 [7]. Accordingly, dislocation dipoles are formed by dislocation sources, and these accelerate the annihilation and rearrangement of dislocations. By these reasons, it can be explained that the driving force of recrystallization was lost, even though the thermal activation occurred on it. Therefore, as shown in Fig. 1(a–c), the ␥-fiber ND//1 1 1
Fig. 5. Dislocation sources SA and SB operate under resolved shear stress τ, and dislocations A1 , A2 , A3 , . . . interact with B1 , B2 , B3 , . . . of opposite sign to form an array of dipoles.
K.J. Kim et al. / Journal of Materials Processing Technology 187–188 (2007) 578–581
did not rotate to other orientations until after heat treatments for 1200 s. 4. Conclusion (1) From the symmetric rolling with the high shape parameters (l/d parameter) in room temperature, the shear deformation could be obtained and then the typical shear texture components were proved by ␥-fiber ND//1 1 1 and rot-CND {0 0 1}1 1 0. (2) The 5052 aluminum sheets with ␥-fiber ND//1 1 1 component were fabricated by applying the shear deformation with l/d parameter of 6.28. After these sheets were heattreated with various holding time at 350 ◦ C, the change and rotation of the textures were investigated. The initial shear deformation texture, especially, ␥-fiber ND//1 1 1 was not rotated during heat treatment in holding time of 180– 1200 s. (3) The rolling process and heat treatment conditions that shear deformation texture, ␥-fiber ND//1 1 1 did not rotate other orientation (e.g. Cu {1 1 2}1 1 1, etc.) during recrystallization were confirmed.
581
Acknowledgements This research was in part financially supported by a grant from the Center for Advanced Materials Processing (CAMP) of the 21st Century Frontier R&D Program funded by the Ministry of Commerce, Industry and Energy (MOCIE), Republic of Korea. References [1] D.N. Lee, K.H. Oh, Calculation of plastic strain ratio from the texture of cubic metal sheet, J. Mater. Sci. 20 (1985) 3111–3118. [2] P. Lequeu, J.J. Jonas, Modeling of the plastic anisotropy of textured sheet, Metall. Trans. 19A (1988) 105–120. [3] T. Kamijo, H. Adachihara, H. Fukutomi, Formation for a (0 0 1)[1 0 0] deformation structure in aluminum single crystals of an S-orientation, Acta Mater. 41 (3) (1993) 975–985. [4] Y. Saito, H. Utsunomiya, H. Suzuki, T. Sakai, Improvement in the R-value of aluminum strip by a continuous shear deformation process, Scripta Mater. 42 (2000) 1139–1144. [5] K.J. Kim, Plastic strain ratios and planar anisotropy of AA5182/ polypropylene/AA5182 sandwich sheets, Int. J. Auto. Technol. 6 (3) (2005) 259–268. [7] D. Hall, D.J. Bacon, Introduction to Dislocations, 3rd ed., Oxford Press, 1984.
Texture evolution of rolled AA5052 alloy sheets after annealing K.J. Kim a,∗ , H.-T. Jeong b , K.S. Shin c , C.-W. Kim d a
CAE Team, Ssang Yong Motor Co., 150-3 Chilgoi-dong, Pyungtaek-si, Gyeonggi-do 459-711, Republic of Korea b Department of Metallurgical Engineering, Kangnung National University, 120 Gangneung Daehangno, Gangneung City, Gangwon-do 210-702, Republic of Korea c School of Materials Science and Engineering, Seoul National University, San 56-1 Shinrim-dong, Kwanak-ku, Seoul 151-742, Republic of Korea d Mechanical Engineering, U&I Corporation Research Center in Korea University, 635, Bio-technology B/D, 5ga, Anam-dong, Sungbuk-gu, Seoul 136-701, Republic of Korea
Abstract To fabricate the aluminum alloys with good drawability, the textures evolution of the AA5052 sheets after rolling and subsequent annealing was studied. The measurement of the deformation textures was carried out for the sheets in which were cold rolled with high reduction ratio by using the symmetric roll. In addition, the change of the recrystallization texture was investigated after heat treatments of the rolled sheets with various heat treatment conditions. Rolling without lubrication and subsequent annealing led to the formation of favorable rot-CND {0 0 1}1 1 0 and ␥-fiber ND//1 1 1 textures in AA5052 sheets. From the results, the ␥-fiber ND//1 1 1 component well evolved during rolling at high reduction ratio (reduction over 92%, l/d parameter over 6.3). Among shear deformation textures, the ␥-fiber ND//1 1 1 was not rotated during recrystallization (350 ◦ C). The 5052 aluminum alloy sheet after rolling at high reduction ratio and subsequent annealing had the higher plastic strain ratio, however, the planar anisotropy of this sheet was higher than before. © 2006 Elsevier B.V. All rights reserved. Keywords: AA5052 sheet; Shear texture; Rolling; Anisotropy; ND//1 1 1
1. Introduction In order to apply the 5052 aluminum alloy sheets to the automotive body panels, the roll formed metal sheets having good drawability and the lower planar anisotropy are needed and these characteristics are closely related with textures evolution [1–4]. For increasing the drawability, it is needed to improve the plastic strain ratio (R-value) of the aluminum alloys. For increasing the plastic strain ratio in the aluminum alloy sheets, which are FCC metals, the sheets should be roll formed that they have well evolved shear texture components. When the sheets were loaded higher by shear deformation, the friction coefficient, μ was increased [5]. Among shear deformation textures, if, especially, the ␥-fiber ND//1 1 1 was well evolved, the planar anisotropy decreased and the sheet drawability increased, on the other hand, if the rot-CND {1 0 0}1 1 0 component was well evolved, the planar anisotropy increased [1,2,4,5]. The main purpose was to fabricate the sheets having higher drawability for applying the aluminum sheets for automotive body panels in the present study.
Since the anisotropy and the drawability were highly dependent on the R-value, the R-value test was carried out. 2. Experimental procedures 2.1. Roll forming and annealing of AA5052 alloy sheets The initial state of the 4.5 mm in thickness 5052 aluminum alloys are fabricated by hot rolling and the homogenization treatment at 500 ◦ C was carried out before cold rolling in the present study. The cold rolling conditions of the 5052 aluminum alloys designed in the present study were made up of roll diameter (127 mm), rolling temperature (room temperature), rolling speed (400 rpm), total four pass cold rolled, total reduction ratio (92.8%; over 50% reduction per one pass) and the l/d parameters (6.28) [3–5], thus the various sheets were obtained having the shear textures. For applying the high friction between the roll bite and the specimen, the lubrication was not applied to the roll bite in order to achieve more evolved shear deformation textures. The formation of recrystallization texture was investigated from the heat treatment of the specimens, which were well evolved on the shear texture from rolling. In order to examine the recrystallization texture of the 5052 aluminum sheets, the annealing was conducted on a salt bath with various holding time (0, 180 and 1200 s, respectively) at 350 ◦ C.
2.2. Characterization of AA5052 alloy sheets ∗
Corresponding author. E-mail address: [email protected] (K.J. Kim).
0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.11.214
Specimens for the measurement of the pole figure in order to analyze the textures of the rolled aluminum sheet were prepared after mechanical polishing
K.J. Kim et al. / Journal of Materials Processing Technology 187–188 (2007) 578–581
579
and those of surface deformation layer of 10 mm in thickness were removed from chemical polishing with 10% NaOH solution in the present study. Then {1 1 1}, {2 0 0} and {2 2 0} pole figures were measured from Schultz reflection method. The measuring equipment was a Seifert 3003 and the voltage and the current were applied for 30 kV and 15 mA, respectively. Using target was the Co target, which had been well recommended in FCC metals. The plastic strain ratio is the important barometer to evaluate deep drawing capability and the anisotropy of the sheet. In general, since the roll formed sheets have the planar anisotropy following tensile orientation, the specimens were prepared with different specimen angles, 0◦ , 45◦ and 90◦ to the sheet rolling direction. The plastic strain ratio (R) was measured with 2-extensometers that were installed in the tensile and transverse directions, respectively, during tensile tests in order to evaluate the planar anisotropy. The plastic strain ratio is defined as shown in Eq. (1). Here, ε22 and ε33 is transverse and thickness true strain, respectively. R=
ε22 ε33
(1)
In addition, the plastic strain ratio was obtained from the average value of 0.05–0.10 tensile strain and average plastic strain ratio (Rm ) and the planar anisotropy of the R-value (R) were calculated from the following Eqs. (2) and (3), where the R0 , R45 and R90 were the plastic strain ratio when the angles between the rolling direction and the tensile axis were 0◦ , 45◦ and 90◦ , respectively. Rm =
R0 + R90 + 2R45 4
(2)
R =
R0 + R90 − 2R45 2
(3)
3. Experimental results and discussion 3.1. Rolling and recrystallization texture Fig. 1 shows the change in texture developed in the 5052 aluminum alloy sheet during heat treatment at 350 ◦ C with various annealing time compared to the texture before heat treatment. In case of the 5052 aluminum alloy sheet with l/d parameter of 6.28 before heat treatment, the pole intensity of ␥-fiber ND//1 1 1 was very high. However, the pole intensity of rot-CND {0 0 1}1 1 0 decreased but the pole intensity of ␥fiber ND//1 1 1 increased with annealing time. For example, in case of annealing time for 180 s, the pole intensity of rot-CND {0 0 1}1 1 0 orientation decreased but the pole intensity of ␥fiber ND//1 1 1 orientation increased. As shown in Fig. 1(a–c), the ␥-fiber ND//1 1 1 did not rotate to other orientations until after heat treatments for 1200 s.
Fig. 1. Measured (1 1 1) pole figures of AA5052 sheets after annealing at 350 ◦ C for (a) 0 s, (b) 180 s and (c) 1200 s.
3.2. Plastic strain ratio and anisotropy Fig. 2 shows the plastic strain ratio, the average plastic strain ratio and the anisotropy of the plastic strain ratio of the 5052 aluminum alloy sheets annealed with holding time for 180 and 1200 s at 350 ◦ C. The plastic strain ratio was the highest with heat-treated holding time for 1200 s at 350 ◦ C and the average plastic strain ratio was 1.53, which was higher than those of the Al alloys reported in the literature. It resulted from that the ␥fiber ND//1 1 1 components were developed as the preferred orientation in the sheet fabricated by the rolling process proposed in this study and did not rotate to other orientations, and the pole intensity of ␥-fiber ND//1 1 1 components increased after
Fig. 2. Measured R-values of symmetrically rolled AA5052 sheets for different annealing times.
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K.J. Kim et al. / Journal of Materials Processing Technology 187–188 (2007) 578–581
Table 1 Lankford values for some ideal orientations by Lequeu et al. [2] Ideal orientation
R0
R45
R90
Rm
|R|
{0 0 1}1 1 0 {1 1 1}1 1 0 {1 1 1}1 1 2 {1 1 2}1 1 0 {0 0 1}1 0 0 {1 1 0}1 1 2 {1 1 2}1 1 1 {1 2 3}6 3 4
0.00 1.84 1.84 0.53 1.00 0.50 1.00 0.72
1.00 1.89 1.89 1.89 0.00 2.09 1.89 1.81
0.00 1.95 1.95 1.00 1.00 1.00 0.50 0.83
0.53 1.91 1.91 1.29 0.53 1.35 1.29 1.27
0.30 0.04 0.04 0.34 0.30 0.46 0.34 0.35
recrystallization. However, the anisotropy of the plastic strain ratio was from −1.17 to −1.22, which was still high. Table 1 shows the plastic strain ratio of ideal orientations (about single crystals) calculated by Lequeu et al. [2]. The average plastic strain ratio of ␥-fiber {1 1 1}1 1 0 and {1 1 1}1 1 2 orientations was the highest value of 1.91 and the lowest planar anisotropy and they should generate an excellent drawability. In addition, rot-CND {0 0 1}1 1 0 orientation, which is rotated by 45◦ to the ND axis of cube {0 0 1}1 0 0 orientation, and cube {0 0 1}1 0 0 orientation have the lowest plastic strain ratio and the highest anisotropy. It was well known fact that the polycrystal sheets having strong ␥-fiber {1 1 1}u v w orientation show both the highest average plastic strain ratio and the lowest planar anisotropy can be found from the empirical and calculated papers by utilizing the similar calculation method about the single crystals [1,2]. 3.3. Effect of annealing on plastic strain ratio and texture The analysis of pole intensity of ␥-fiber ND//1 1 1 at (1 1 1) pole figure measured after annealing of the 5052 aluminum alloy sheets with holding time for 0, 180 and 1200 s at 350 ◦ C was compared to the result of measured plastic strain ratio as shown in Fig. 3. After annealing with holding time for 180 s at 350 ◦ C, the pole intensity of ␥-fiber ND//1 1 1 increased rapidly and showed the maximum value at 350 ◦ C for 1200 s. In addition, the measured average plastic strain ratio increased
Fig. 3. Measured pole intensity of ND//1 1 1 ␥-fiber and R-values of AA5052 sheets following as annealing time at 350 ◦ C.
Fig. 4. Schematic presentation of simplified array of dislocations by shear deformation.
proportionally with increasing the pole intensity of ␥-fiber ND//1 1 1. Since the preferred orientations might rotate and change to the random orientation increasingly during annealing, the measured (1 1 1) pole figure of the 5052 aluminum alloy sheet annealed at 350 ◦ C shows that the pole intensities of rot-CND {0 0 1}1 1 0 component have tendency to decreases with increasing annealing time as shown in Fig. 1. Therefore, the planar anisotropy of the plastic strain ratio increases proportionally with the pole intensity of rot-CND {0 0 1}1 1 0 as shown in Figs. 1 and 2. In case of the shear deformation, because most of slips occur to the rolling direction or rolling plane, dislocation structures of the shear-deformed materials have more planar than those of the plane strain compressive materials. Fig. 4 shows more simplified model containing dislocations array about these explanations. Dislocation arrays are placed in planar shape due to the shear stress following dislocation sources SA and SB as shown in Fig. 5. In addition, in case of the shear-deformed (0 0 1)[1 1 0] orientation, the shear strain of (1 1 1)[1 1 0] slip systems is much higher than other slip systems and that makes duplex slip occur. In addition, the dislocations of the duplex slip have the same slip direction as shown in Fig. 5 [7]. Accordingly, dislocation dipoles are formed by dislocation sources, and these accelerate the annihilation and rearrangement of dislocations. By these reasons, it can be explained that the driving force of recrystallization was lost, even though the thermal activation occurred on it. Therefore, as shown in Fig. 1(a–c), the ␥-fiber ND//1 1 1
Fig. 5. Dislocation sources SA and SB operate under resolved shear stress τ, and dislocations A1 , A2 , A3 , . . . interact with B1 , B2 , B3 , . . . of opposite sign to form an array of dipoles.
K.J. Kim et al. / Journal of Materials Processing Technology 187–188 (2007) 578–581
did not rotate to other orientations until after heat treatments for 1200 s. 4. Conclusion (1) From the symmetric rolling with the high shape parameters (l/d parameter) in room temperature, the shear deformation could be obtained and then the typical shear texture components were proved by ␥-fiber ND//1 1 1 and rot-CND {0 0 1}1 1 0. (2) The 5052 aluminum sheets with ␥-fiber ND//1 1 1 component were fabricated by applying the shear deformation with l/d parameter of 6.28. After these sheets were heattreated with various holding time at 350 ◦ C, the change and rotation of the textures were investigated. The initial shear deformation texture, especially, ␥-fiber ND//1 1 1 was not rotated during heat treatment in holding time of 180– 1200 s. (3) The rolling process and heat treatment conditions that shear deformation texture, ␥-fiber ND//1 1 1 did not rotate other orientation (e.g. Cu {1 1 2}1 1 1, etc.) during recrystallization were confirmed.
581
Acknowledgements This research was in part financially supported by a grant from the Center for Advanced Materials Processing (CAMP) of the 21st Century Frontier R&D Program funded by the Ministry of Commerce, Industry and Energy (MOCIE), Republic of Korea. References [1] D.N. Lee, K.H. Oh, Calculation of plastic strain ratio from the texture of cubic metal sheet, J. Mater. Sci. 20 (1985) 3111–3118. [2] P. Lequeu, J.J. Jonas, Modeling of the plastic anisotropy of textured sheet, Metall. Trans. 19A (1988) 105–120. [3] T. Kamijo, H. Adachihara, H. Fukutomi, Formation for a (0 0 1)[1 0 0] deformation structure in aluminum single crystals of an S-orientation, Acta Mater. 41 (3) (1993) 975–985. [4] Y. Saito, H. Utsunomiya, H. Suzuki, T. Sakai, Improvement in the R-value of aluminum strip by a continuous shear deformation process, Scripta Mater. 42 (2000) 1139–1144. [5] K.J. Kim, Plastic strain ratios and planar anisotropy of AA5182/ polypropylene/AA5182 sandwich sheets, Int. J. Auto. Technol. 6 (3) (2005) 259–268. [7] D. Hall, D.J. Bacon, Introduction to Dislocations, 3rd ed., Oxford Press, 1984.