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Macro-, micro- and mesotexture evolutions of continuous cast and direct chill cast AA 3105 aluminum alloy during cold rolling
Materials and Engineering A357 (2003) 277 /296 www.elsevier.com/locate/msea
Macro-, micro- and mesotexture evolutions of continuous cast and direct chill cast AA 3105 aluminum alloy during cold rolling Jiantao Liu, James G. Morris * Department of Chemical and Materials Engineering, University of Kentucky, 177 Anderson Hall, Lexington, KY 40506-0046, USA Received 6 December 2002; received in revised form 4 March 2003
Abstract Industrially produced hot bands of continuous cast (CC) and direct chill (DC) cast AA 3105 aluminum alloy were cold rolled to different reductions from 10 to 90%. Macrotexture evolution of the deformation texture in the CC and DC materials was investigated by using three-dimensional orientation distribution functions (ODFs) that were determined by X-ray diffraction. The electron backscatter diffraction (EBSD) technique was adopted to investigate micro- and mesotexture during the early stages of cold rolling (5/40%). Results showed that the macrotexture evolution for CC and DC materials during cold rolling follows the same path. a and b fibers become developed beyond 50% cold rolling in both CC and DC materials. The highest intensity along the b fiber (skeleton line) is located between the Copper and the S orientations in both materials. There exists a path by which Cube orientation (0 0 1)[1 0 0] transforms to the Brass orientation (0 1 1)[2 1¯ 1] through the CubeND orientation (0 0 1)[1 1¯ 0] after certain cold rolling reductions. In both CC and DC materials, a cell structure develops with the indication of increasing coincidence site lattice (CSL) a1 boundaries during the early stages of cold rolling while high-angle boundaries (HABs) are randomized over the misorientation angle. There is no evidence for the development of twin boundaries in both CC and DC materials when the cold rolling reduction is less than 40%. Cold rolling texture itself is not responsible for the different recrystallization behaviors that cause different earing behaviors between CC and DC aluminum alloys. # 2003 Published by Elsevier B.V. Keywords: Aluminum alloy; Continuous cast; Texture
1. Introduction AA 3XXX aluminum alloys find wide applications in the transportation, food and beverage, and packaging industries. In these applications, control of the plastic anisotropy of the sheet is of great importance in order to ensure the formability of the final product and to reduce the waste of the material resulting from earing behavior. Conventionally, aluminum sheet is mainly produced by the direct chill (DC) cast technology. Continuous cast (CC) technology, a new technology, however provides both energy and economic savings while reducing environmental emissions that become more and more urgent issues in today’s environment. Compared with
* Corresponding author. Tel.: /1-859-257-8090; fax: /1-859-3231929. E-mail addresses: [email protected] (J. Liu), [email protected] (J.G. Morris). 0921-5093/03/$ - see front matter # 2003 Published by Elsevier B.V. doi:10.1016/S0921-5093(03)00210-7
DC cast technology, CC technology also takes advantage of high productivity. However, controlling plastic anisotropy of CC material sheet is more difficult than that of DC material sheet during thermomechanical processing. It is well known that the deformation texture components Copper, Brass and S contribute to 458 earing while the recrystallization texture component Cube yields 0/908 earing. Previous works [1 /4] have found that the Cube texture component can easily be obtained by annealing the cold rolled DC material and consequently leads to 0/908 earing which balances very well the 458 earing caused by cold rolling. However, it is very difficult to obtain the Cube texture component after annealing cold rolled CC material. Consequently, aluminum sheet made by the CC process displays 458 earing behavior even after complete recrystallization. As a result, somewhat different earing behavior is usually observed in the final sheet product made from CC material.
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A critical question is whether there exist differences in the cold rolling texture evolution between CC and DC materials and what role does the cold rolling texture evolution play in affecting the recrystallization texture and hence the earing behaviors. In order to answer the above questions, it is essential to trace the texture evolution of CC and DC material sheets during cold rolling. This work is part of a project where the ultimate goal is to improve the formability of CC material sheet to the same level as DC material sheet. The principal aim of the present work is to monitor the macro-, micro- and mesotexture evolutions of AA 3105 CC and DC materials during cold rolling.
2. Experimental 2.1. Materials and procedures Materials were industrially produced hot bands of CC and DC AA 3105 materials. The chemical compositions are given in Table 1. Plates of 6.2 /88.9 /114.3 mm3 (thickness /width /length) were cut from the DC hot band and plates with dimensions of 3.5 /88.9 /114.3 mm3 (thickness /width /length) were cut from the CC hot band. The cut plates were then processed according to procedures shown in Fig. 1. The purpose of the hightemperature homogenization for a long time is to generate a completely recrystallized microstructure and to eliminate the difference of solid solution supersaturation status between CC and DC materials. The homogenized plates were homogeneously cold rolled to different reductions from 10 to 90% on a two high laboratory rolling mill with rolls 100 mm in diameter. 2.2. Microstructure examination Samples for microstructure examination were cut from the plates in a normal direction (ND) and rolling direction (RD) cross-section, cold mounted and mechanically polished per standard metallographic practices. Subsequently, the samples were electropolished using 1.5 vol.% pct HNO3 /5.0 vol.% pct HClO4 acids in methanol at 27 V for 3 s at room temperature to remove the deformation layer. Finally, the samples were anodized using Barker’s reagent (5 vol.% pct HBF4 in
water) at 15 V for 1 min at room temperature to reveal the microstructure under polarized light optical microscopy. 2.3. Texture measurement 2.3.1. Macrotexture Samples for macrotexture measurements were sectioned in the rolling plane (RD and the transverse direction (TD) cross-section) at the mid-thickness position of the plate. The surface for measurement was carefully polished to minimize surface stress. Texture measurements were carried out on a Rigaku D/MAX X-ray goniometer using Cu Ka radiation by means of the Schulz reflection method [5]. Three incomplete pole figures {1 1 1}, {2 0 0}, {2 2 0} up to a tilting angle of 758 (amax /758) were measured. All incomplete pole figure data were corrected for defocusing error and background intensity. Three-dimensional orientation distribution functions (ODFs) f(g) were calculated by using the arbitrarily defined cell (ADC) method [6]. ODFs are expressed by using Bunge’s notation system [7]. The orientations g are described by three Euler angles 81, F, 82, which transform the crystallographic orientation into the sample coordinate system specified by RD, TD, and ND. The ODFs are represented in the three-dimensional Euler space in the range 085/81, F , 82 5/908 by way of iso-intensity contour lines in different sections with 82 constant. Each texture component is fitted by using a number of Gauss-type scattering functions for quantitative analysis [8]. Therefore, the volume fraction Mi of each texture component i is calculated by determining the central orientations gi , the orientation intensity fi , and the scattering width ci . 2.3.2. Microtexture The electron backscatter diffraction (EBSD) technique is based on the discovery [9] and application [10] of Kikuchi patterns. Remarkable progress [11 /13] in this technique has been made in the past 20 years. The stationary beam is focused to a fine point on the highly tilted sample and the diffracted back scattering electrons form Kikuchi patterns on a phosphor screen. The orientation of the local lattice can be obtained by digitizing two appropriate zones in the Kikuchi pattern. In FCC material, two zones on the band passing
Table 1 Compositions of experimental materials, wt.% Alloy
Si
Fe
Cu
Mn
Mg
Cr
Ni
Zn
Ti
Al
AA 3105 CC AA 3105 DC
0.30 0.38
0.64 0.65
0.19 0.14
0.61 0.52
0.55 0.43
/ 0.05
/ 0.01
/ 0.06
/ 0.02
Balance Balance
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Fig. 1. Thermomechanical procedures of AA 3105 aluminum alloy.
through 1 1 1, 1 1 2, 1 1 4 and 3 3 2 are usually selected for digitizing. Furthermore, the orientation information of an interested area can be collected by an electron beam movement controlled by a computer with selected step size. Samples for microtexture measurements were also sectioned in the rolling plane at the mid-thickness position of the plate. The surface for measurement was mechanically polished followed by electropolishing using the same solution used for microstructure examination to remove the deformation layer. In this study, EBSD work was carried out using a Hitachi 3200N SEM interfaced to a Unix workstation with orientation image microscopy (OIM) software from TexSEM Laboratories, Inc. (Draper, UT) installed. The sample was mounted on a pre-tilted sample holder with a tilt angle of 728 for better pattern quality. The geometry of the sample setup is shown in Fig. 2. Note that TD points out of the paper. An example of
Fig. 2. Geometry of the sample setup for EBSD measurement.
the EBSD pattern and its indexing solution using OIM are shown in Fig. 3(a) and (b), respectively. The acceleration voltage and working distance were maintained at 20 kV and 20 mm, respectively. Image scan was adopted and each image contains at least 10,000 pixels (orientations). In order to ensure the reliability of the data, each data set was subject to a cleanup step using an algorithm that checks to determine if the orientation is different from its immediate neighbors. All nearest neighbor pixels must differ in orientation by more than a tolerance angle that is set to 58. Less than 5% of the data was changed in this cleanup operation.
2.3.3. Mesotexture Mesotexture is depicted by grain boundary misorientation plots in this work. The (sub)grain boundary, especially coincidence site lattice (CSL) types, can be characterized and quantified from misorientation information obtained by running a EBSD scan. The misorientation is correlated because the calculation of misorientation is based on the neighbor grains. The (sub)grain boundary can be classified by different neighbor misorientations: low-angle boundaries (LABs, u B/58), moderately misoriented boundaries (MMBs, 585/u B/158) and high-angle boundaries (HABs, 158 5/u ). Owing to the spatial resolution of the EBSD system, misorientations of less than 1.58 were not identified. CSL boundaries are defined following Brandon’s criterion [14]. All misorientation and CSL distributions are presented in the manner of a histogram plot.
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Fig. 3. An example of EBSD pattern from AA 3105 aluminum alloy at 20 kV with working distance of 20 mm (a) and its indexing solution using OIM (b).
3. Results
dimension of grains in the RD direction is at least five times than in the ND direction.
3.1. Microstructures of hot bands
3.2. Textures of hot bands
The as-received hot bands of both CC (Fig. 4(a)) and DC (Fig. 4(b)) materials show typical pancake grain structures that occur at conditions of high hot rolling reductions. After homogenization, CC and DC hot bands were completely recrystallized with elongated grain structures (Fig. 4(c)) and equiaxed grain structures (Fig. 4(d)), respectively. As shown in Fig. 4(c), the
3.2.1. Macrotextures Fig. 5(a) and (b) show ODFs of the as-received hot bands of CC and DC materials, respectively. The intensities of typical orientations have been indexed. The texture of the CC hot band shows a typical rolling texture with a well developed b fiber starting from the Copper orientation {1 1 2}1 1 1 through the S orien-
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Fig. 4. Microstructures of as-received AA 3105 (a) CC hot band, (b) DC hot band, (c) CC hot band after homogenization per procedures shown in Fig. 1 and (d) DC hot band after homogenization per procedures shown in Fig. 1.
tation {1 2 3}6 3 4 and ending at the Brass orientation {0 1 1}2 1 1. The maximum orientation intensity along the b fiber is found between the Copper orientation and the S orientation with a value of 8.3. The texture of the DC hot band displays a combination of a rolling texture and a recrystallization texture (Fig. 5(b)) with a CubeRD orientation {0 1 3}1 0 0. As can be seen from Fig. 5(b), the maximum orientation intensity on the b fiber is also located between the Copper orientation and the S orientation. After homogenization, the recrystallization texture in the CC hot band (Fig. 6(a)) is characterized by a strong CubeND orientation accompanied by CubeND fiber. However, the recrystallization texture of the DC hot band (Fig. 6(b)) contains a strong Cube orientation {0 0 1}1 0 0 with an intensity up to 8.5. 3.2.2. Microtextures Fig. 7 presents the inverse pole figure (IPF) maps of homogenized hot bands with respect to the ND direction. Each grain is painted with a color based on its crystal orientation. The grain size of the recrystallized CC hot band (Fig. 7(a)) is larger than that of the DC hot
band (Fig. 7(b)). It can be verified that the recrystallized grains are mostly elongated along the RD in the CC hot band. As shown in Fig. 7(a), the elongated grains are usually oriented with a P orientation {0 1 1}1 2 2. In Fig. 7(b), a grain with the Cube orientation is highlighted. Cube clusters, neighbor grains with their 0 0 1 crystal direction parallel to the ND direction, are dominant in the DC hot band. 3.2.3. Mesotextures Fig. 8(a) and (b) show misorientation distributions of homogenized CC and DC hot bands, respectively. The corresponding CSL grain boundary distributions is given in Fig. 9(a) and (b). Obviously, HABs are dominant in both CC (Fig. 8(a)) and DC materials (Fig. 8(b)). Grain boundary populations is not uniformly distributed with respect to misorientation angle. It can be seen that there exist peaks in the ranges 30/ 36.58, 40/458, and 55 /62.88. The peak located in the range 40/458 can be ascribed to randomly oriented Cubes [15], which were also reported in AA 2004 [16] and AA 5083 aluminum alloys [17 /19]. The population of a1 boundaries (LABs/MMBs) in DC material (Fig.
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Fig. 5. Complete ODFs of as-received AA 3105 (a) CC and (b) DC hot bands.
Fig. 6. Complete ODFs of AA 3105 (a) CC and (b) DC hot bands after homogenization per procedures shown in Fig. 1.
9(b)) is found to be higher than that in CC material (Fig. 9(a)). In general, the number of CSL boundaries is low in both materials except for a well developed a29
boundary in the DC hot band. This suggests that the misorientation peaks in the ranges 30 /36.58 and 55/
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Fig. 7. IPF maps of homogenized AA 3105 (a) CC and (b) DC hot bands. {1 1 1} pole figures are given for pointed grains.
62.88 (shown in Fig. 8) are mostly contributed by disordered grain boundaries.
3.3. Macrotexture evolution during cold rolling ODFs of CC and DC materials with increasing cold rolling reduction are shown in Figs. 10 and 11, respectively. Three sections of 82 /08, 82 /458 and 82 /658 are selected to show the formation of typical deformation orientations Brass, Copper and S along the b fiber. By watching the section of 82 /08, the evolution of the a fiber can be tracked. Volume fractions of
Gauss-type texture components are calculated and plotted as a function of the cold rolling reduction in Fig. 12. The orientation intensities vs. cold rolling reductions along the a fiber are displayed in Fig. 13. The orientation intensities along the b fiber (skeleton line) and their positions in Euler space 81, F as function of 82 are given in Figs. 14 and 15 for CC and DC materials, respectively.
3.3.1. CC material As shown in Fig. 10(a), the intensity of the CubeND orientation decreases rapidly after 10% cold rolling. The
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Fig. 8. Grain boundary misorientation distributions of homogenized AA 3105 (a) CC and (b) DC hot bands.
CubeND fiber then develops without much intensity change until at 60% cold rolling reduction when the orientations flow to the Brass position. After 70% cold rolling, the Brass orientation is well formed and becomes sharper and more intense during further cold rolling. Fig. 10(b) displays the formation process of the Copper orientation. Orientations spread out from the
CubeND position and form a peak away from the Copper orientation with an intensity of 3.2 after 50% cold rolling. This peak moves toward the position of the Copper orientation and becomes stronger with increasing cold rolling reduction. Finally, the intensity of Copper orientation increases to 7.4. The S orientation develops in the same way (Fig. 10(c)). After 50% cold
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Fig. 9. CSL grain boundary distributions of homogenized AA 3105 (a) CC and (b) DC hot bands.
rolling, a peak near the CubeND orientation forms and then moves toward the S orientation and becomes more intense beyond 60% cold rolling. Volume fractions of typical orientations are plotted versus cold rolling reduction in Fig. 12(a). It can be seen that the volume fraction of the CubeND orientation decreases from about 12% before cold rolling to 0 after 60% cold rolling. A similar trend can be observed for the {1 0 0} fibers that are mostly contributed to by the
CubeND fiber. After 50% cold rolling, the volume fraction of deformation orientations such as Copper, Copper/S, S, S/Brass and Brass start to increase. The volume fraction of the Copper orientation reaches about 30% and becomes the largest of all deformation orientations after 90% cold rolling. The volume fraction of random orientations remains constant until 50% cold rolling and then drops rapidly while deformation textures start to evolve.
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Fig. 10. Complete ODFs of completely recrystallized (RX) AA 3105 CC hot band under various cold rolling reductions at sections of (a) 82 /08, (b) 82 /458 and (c) 82 /658.
The development of the a fiber is illustrated in Fig. 13(a). The a fiber becomes well formed beyond 70% cold rolling. The intensity along the a fiber is uniformly distributed before the cold rolling reduction reaches 70% beyond which the Brass orientation becomes stronger and sharper. It is interesting to note that a small peak is observed around {0 1 1}1 2 2 during the early stages of cold rolling, which indicates the existence of the P orientation. Fig. 14(a) and (b) give the intensity distributions and positions of the b fiber (skeleton line) during cold
rolling, respectively. At low cold rolling reductions ( B/50%), no apparent b fiber is formed (Fig. 14(a)). An apparent increase of orientation intensity is observed along the b fiber after 50% cold rolling. However, the rate of increase of the orientation intensity is not uniform along the b fiber. The intensity of Copper/S is higher than all other orientations along the b fiber. This trend becomes more pronounced beyond 80% cold rolling. The position of the b fiber (skeleton line) is revealed in Fig. 14(b). After 50% cold rolling, the position of the b fiber (skeleton line) is far away from
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Fig. 11. Complete ODFs of completely recrystallized (RX) AA 3105 DC hot band under various cold rolling reductions at sections of (a) 82 /08, (b) 82 /458 and (c) 82 /658.
the sharp position and becomes sharp at high cold rolling reductions (/50%). 3.3.2. DC material Fig. 11 shows the ODFs of DC material during cold rolling. Starting from a strong Cube orientation, the orientation intensity around the Cube position becomes weak when the cold rolling reduction is increased (Fig. 11(a)). The intensity of the Brass orientation reaches 2.0 after 80% cold rolling and increases by 1.5 after 90%
cold rolling. It is worth noting that the Cube orientation transforms to the CubeND orientation and then flows to the Brass position after 80% cold rolling in the same way as it occurs in CC material after 80% cold rolling. The evolutions of the Copper (Fig. 11(b)) and the S (Fig. 11(c)) orientations in DC material during cold rolling are similar to those previously described for CC material. The intensities of the Copper and S orientations in DC material are lower than those in the CC material.
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Fig. 12. Dependence of the volume fraction of various texture components in AA 3105 (a) CC and (b) DC materials on the cold rolling reduction.
The volume fraction of the Cube orientation reaches 11% after homogenization of the hot band (Fig. 12(b)). The volume fraction of the Cube orientation decreases to 0 after 90% cold rolling. The volume fraction of the CubeND fiber, reflected through {1 0 0} fibers, remains above 10% until 80% cold rolling and then decreases during further cold rolling. Orientations start to flow to the b fiber at Copper, Copper/S, S, Brass/S and Brass positions after 80% cold rolling and then increase during further cold rolling. It is worth noting that the volume fractions of the Copper/S, S, Brass/S and Brass orienta-
tions converge to about 12% while the volume fraction of the Copper orientation, increases by about 15% after 80% cold rolling, and reaches 29% after 90% cold rolling. The volume fraction of random orientations drops rapidly after 80% cold rolling when the b fiber develops. As shown in Fig. 13(b), no apparent a fiber is developed in DC material until 80% cold rolling. The a fiber in DC material is less intense than that in CC material during the cold rolling. Again, there exists a small peak around {0 1 1}1 1 1 during the early stages
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Fig. 13. Orientation intensity of orientations of AA 3105 (a) CC and (b) DC materials along the a fiber under different cold rolling reductions.
of cold rolling, which is believed to be related to the P orientation though the position of the peak is shifted from 70 to 608 in 81. Fig. 15 presents the evolution of the intensity and position (skeleton line) of the b fiber. The Copper/S orientation becomes more intense than other deformation orientations along the b fiber (Fig. 15(a)). Compared with the position of the b fiber in CC material
(Fig. 14(b)), the position of the b fiber in DC material appears sharper during the whole cold rolling process (Fig. 15(b)). 3.4. Microtexture evolution during cold rolling IPFs for the ND, TD and RD directions of CC and DC materials after 40% cold rolling are plotted in Fig.
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Fig. 14. Orientation intensity of orientations of AA 3105 CC material along the b fiber (skeleton line) (a) and their exact positions in Euler space 81, F as function of 82 (b).
16(a) and (b), respectively. In CC material (Fig. 16(a)), the orientations concentrate around 1 0 0 in the ND direction while most grains are oriented close to 1 0 5 in the TD direction. It can also be observed that orientations scatter towards 1 1 0 other than 1 1 1 in the ND direction. Weak textures around 1 1 5 and 3 1 3 are observed in the RD direction. In DC material (Fig. 16(b)), orientations concentrate close to 1 0 0 in the ND, TD and RD directions. The
concentration around 2 2 3 with respect to the RD direction is worth noting. 3.5. Mesotexture evolution during cold rolling Fig. 17 (a) and (b) present grain boundary misorientation distributions of CC and DC materials after 40% cold rolling, respectively. The two distributions look similar. Two points are noteworthy: first, HABs,
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Fig. 15. Orientation intensity of orientations of AA 3105 DC material along the b fiber (skeleton line) (a) and their exact positions in Euler space 81, F as function of 82 (b).
which are still dominant, are randomized over the misorientation angle; second, compared with the distributions before deformation (Fig. 8), the fraction of grain boundaries with misorientation angles between 58 and 158 is increased, which indicates the development of MMBs. Fig. 18 displays CSL grain boundary distributions in CC (Fig. 18(a)) and DC (Fig. 18(b)) materials after 40%
cold rolling. Obviously, a1 boundaries are well developed in both materials compared with the homogenized states (Fig. 9), especially in DC material where the population of a1 boundaries is almost double that in the homogenized states (Fig. 9(b)). There is no evidence of the development of twin boundaries (a3, a9, a27a and 27b) in both CC and DC materials when the cold rolling reduction is less than 40%.
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Fig. 16. IPFs of AA 3105 (a) CC and (b) DC hot bands after 40% cold rolling.
4. Discussion 4.1. Macrotexture evolution during cold rolling The evolution of rolling textures of various f.c.c. metals have been intensively investigated and discussed in the literatures [8] [20 /23] by using ODFs. It is well accepted [8,20,21,24,25] that at low degrees of rolling, the orientations along the a and b fibers are homogeneously developed. This homogeneity, however, is destroyed with increasing degree of rolling. With increasing degree of rolling the orientations flow along the a fiber to the Brass position and therefore make the Brass orientation more intense. The a fiber disappears
and only leaves a peak around the Brass orientation at very high degrees of rolling. Simultaneously, orientations flow into the b fiber as the rolling reduction increases. The development of orientations along the b fiber, however is not uniform, and mainly concentrates at the Copper, Brass and S positions. The evolution of textures of both AA 3105 CC and DC materials follow the above rules during cold rolling. At low cold rolling reductions (B/60%), the a and b fibers, though weak, are uniformly developed in both CC and DC materials (Figs. 13, 14(a) and 15(a)). At intermediate and high cold rolling reductions (/60%), the intensities around the Brass, Copper and S orientations increase rapidly and form peaks in the CC material. However, the b fiber is not well formed until high cold rolling reductions (]/ 80%) are attained. Finally, the S orientation becomes the strongest orientation along the b fiber in both materials, which also has been observed in Al [20], Copper [21], and Al /Cu alloy [26] at high rolling reductions. Zhou et al. [27,28] investigated the formation of rolling textures for f.c.c. polycrystals by using a ratedependent crystal plasticity model. They show that during deformation, orientations move either directly into the b fiber or first into the a fiber and then along the a fiber to the b fiber and finally towards the corresponding stable orientations. The former path is supported by the results in this work. It is known that the Cube orientation transforms to the S orientation during rolling deformation [29]. However, the results in this work indicate another way by which the CubeND orientation transforms into the S orientation during cold rolling of CC (Fig. 10(c)) and DC (Fig. 11(c)) materials. Another interesting finding of this work is a path starting from the Cube orientation (0 0 1)[1 0 0] through the CubeND orientation (0 0 1)[1 1¯ 0] to the Brass orientation (0 1 1)[2 1¯ 1]; which can be observed at 82 /08 section in both CC (60% cold rolling, Fig. 10(a)) and DC (80% cold rolling, Fig. 11(a)) materials. In CC material (Fig. 10(a)), the CubeND fiber develops at low and cold rolling reductions (B/50%). Then, orientations flow from the CubeND fiber to the Brass position directly. A similar situation is also observed in DC material. In DC material, the Cube orientation transforms into the CubeND orientation and forms a CubeND fiber from which orientations flow to the Brass orientation during cold rolling. This suggests that the Cube orientation rotates towards the CubeND orientation and then to the Brass orientation during cold rolling. A schematic map of the rotation is drawn in Fig. 19. It can be seen that starting from point a of the Cube orientation, the orientation passes through points b, c, d, e, and finally reaches point f of the Brass orientation. This transformation is finished after 90% cold rolling for both CC and DC materials. In general, the development
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Fig. 17. Grain boundary misorientation distributions AA 3105 (a) CC and (b) DC hot bands after 40% cold rolling.
of cold rolling textures in AA 3105 CC and DC materials follows the same path. 4.2. Microtexture evolution during cold rolling The IPF of CC material in the ND direction is characterized by scattering of orientations from 1 0 0 towards 1 1 0, which indicates the develop-
ment of the CubeND fiber in CC material. In DC material, however, the 1 0 0 texture in all three directions ND, TD and RD suggests the existence of the Cube {0 0 1}1 0 0 component. Therefore, the microtexture results shown in Fig. 16 are in agreement with macrotexture results shown in Figs. 10 and 11 that present a weak CubeND fiber in CC material and the Cube orientation in DC material after 40% cold rolling,
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Fig. 18. CSL grain boundary distributions of AA 3105 (a) CC and (b) DC hot bands after 40% cold rolling.
respectively. F.c.c. metals usually develop strong 1 1 0 fiber textures during compression. The IPF corresponding to the ND direction of CC material (Fig. 16(a)) indicates that orientations flow toward the 1 1 0 orientation after 40% cold rolling. In DC material (Fig. 16(b)), the 1 1 0 fiber also develops accompanied by a fiber between the 1 1 0 and 1 1 3 components,
which is usually observed in high stacking fault energy materials. 4.3. Mesotexture evolution during cold rolling The evolution of grain boundaries has been traced in both CC and DC materials during the early stages of
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Fig. 19. Schematic map for transformation from the Cube orientation to the Brass orientation during cold rolling of AA 3105 aluminum alloy. {1 1 1} pole figures show the transformation steps (small crosses indicate the positions of corresponding Euler angles in pole figures).
cold rolling (5/40%). In both CC and DC materials, a1 boundaries are well developed during the early stages of cold rolling. There is not a remarkable change in twin boundaries (a3, a9, a27a and 27b) during the early stages of cold rolling. Therefore, mechanical twins are not an acting mechanism in these stages. Instead, grains are subdivided by way of forming cell walls (a1 boundaries). These cell walls transform to HABs during further cold rolling by misorientation increase.
5. Conclusions In this work, macro-, micro- and meso-texture evolutions in industrially produced hot bands of CC and DC
AA 3105 aluminum alloy during cold rolling have been studied. The following conclusions can be drawn. (1) After complete recrystallization, a stronger Cube orientation is observed in DC hot band than in CC hot band. a and b fibers become well developed beyond 50% cold rolling in both CC and DC materials. The highest intensity along the b fiber (skeleton line) is located between the Copper and the S orientations in both materials. (2) There exists a path by which Cube orientation (0 0 1)[1 0 0] transforms to the Brass orientation (0 1 1)/ ¯ 1] through the CubeND orientation (0 0 1)[1 1¯ 0] /[2 1 after certain cold rolling reductions. (3) In both CC and DC materials, a cell structure develops with the indication of increasing CSL a1 boundaries during the early stages of cold rolling
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while HABs are randomized over the misorientation angle. (4) There is no evidence of the development of twin boundaries (a3, a9, a27a and 27b) in either CC or DC materials when the cold rolling reduction is less than 40%. (5) Macro-, micro- and mesotexture evolutions follow the same path for both CC and DC materials. This implies that the cold rolling texture itself is not responsible for the different recrystallization behaviors that cause different earing behaviors between CC and DC aluminum alloys.
Acknowledgements Financial support from U.S. Department of Energy (under Contract No. DE-FC07-01ID14193) is gratefully acknowledged.
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[7] H.J. Bunge:, Texture Analysis in Material Science, 1st ed., Butterworths, London, 1982, p. 1. [8] J. Pospiech, K. Lu¨cke, Acta Metall. 23 (1975) 997. [9] S. Kikuchi, Jpn. J. Phys. 5 (1928) 83. [10] J.A. Venables, C.J. Harland, Philos. Mag. 27 (1973) 1193. [11] D.J. Dingley, Scanning Electron Microsc. 2 (1984) 569. [12] B.L. Adams, S.I. Wright, K. Kunze, Metall. Trans. A 24 (1993) 819. [13] N.C. Krieger-Lassen, D. Juul Jensen, K. Conradsen, Scanning Microsc. 6 (1992) 115. [14] D.G. Brandon, Acta Metall. 14 (1966) 1479. [15] J.K. MacKenzie, Biometrica 45 (1958) 229. [16] T.R. McNelley, D.L. Swisher, M.T. Pe´rez-Prado, Metall. Mater. Trans. A 33 (2002) 279. [17] T.R. McNelley, M.E. McMahon, S.J. Hales, Scripta Mater. 36 (1997) 369. [18] M. Eddahbi, T.R. McNelley, O.A. Ruano, Metall. Mater. Trans. A 32 (2001) 1093. [19] M.T. Pe´rez-Prado, G. Gonza´lez-Doncel, O.A. Ruano, T.R. McNelley, Acta Mater. 49 (2001) 2259. [20] J. Hirsch, E. Nes, K. Lu¨cke, Acta Metall. 35 (1987) 427. [21] J. Hirsch, K. Lu¨cke, Acta Metall. 36 (1988) 2863. [22] S. Panchanadeeswaran, D.P. Field, Acta Metall. Mater. 43 (1995) 1683. [23] O. Engler, Acta Mater. 48 (2000) 4827. [24] S. Panchanadeeswaran, D.P. Field, Acta Metall. Mater. 43 (1995) 1683. [25] O. Engler, Acta Mater. 48 (2000) 4827. [26] O. Engler, Acta Metall. 37 (1989) 2743. [27] Y. Zhou, K.W. Neale, L.S. To´th, Textures Microstruct. 14-18 (1991) 1055. [28] Y. Zhou, L.S. To´th, K.W. Neale, Acta Metall. Mater. 40 (1992) 3179. [29] G.D. Ko¨hlhoff, B. Krentscher, K. Lu¨cke:, in: C.M. Brakman, P. Jongenburger, E.J. Mittemeijer (Eds.), Proceedings of the 7th International Conference on Textures, The Netherlands Society of Materials Science, Noordwijkerhout, The Netherlands, 1984, p. 95.
Macro-, micro- and mesotexture evolutions of continuous cast and direct chill cast AA 3105 aluminum alloy during cold rolling Jiantao Liu, James G. Morris * Department of Chemical and Materials Engineering, University of Kentucky, 177 Anderson Hall, Lexington, KY 40506-0046, USA Received 6 December 2002; received in revised form 4 March 2003
Abstract Industrially produced hot bands of continuous cast (CC) and direct chill (DC) cast AA 3105 aluminum alloy were cold rolled to different reductions from 10 to 90%. Macrotexture evolution of the deformation texture in the CC and DC materials was investigated by using three-dimensional orientation distribution functions (ODFs) that were determined by X-ray diffraction. The electron backscatter diffraction (EBSD) technique was adopted to investigate micro- and mesotexture during the early stages of cold rolling (5/40%). Results showed that the macrotexture evolution for CC and DC materials during cold rolling follows the same path. a and b fibers become developed beyond 50% cold rolling in both CC and DC materials. The highest intensity along the b fiber (skeleton line) is located between the Copper and the S orientations in both materials. There exists a path by which Cube orientation (0 0 1)[1 0 0] transforms to the Brass orientation (0 1 1)[2 1¯ 1] through the CubeND orientation (0 0 1)[1 1¯ 0] after certain cold rolling reductions. In both CC and DC materials, a cell structure develops with the indication of increasing coincidence site lattice (CSL) a1 boundaries during the early stages of cold rolling while high-angle boundaries (HABs) are randomized over the misorientation angle. There is no evidence for the development of twin boundaries in both CC and DC materials when the cold rolling reduction is less than 40%. Cold rolling texture itself is not responsible for the different recrystallization behaviors that cause different earing behaviors between CC and DC aluminum alloys. # 2003 Published by Elsevier B.V. Keywords: Aluminum alloy; Continuous cast; Texture
1. Introduction AA 3XXX aluminum alloys find wide applications in the transportation, food and beverage, and packaging industries. In these applications, control of the plastic anisotropy of the sheet is of great importance in order to ensure the formability of the final product and to reduce the waste of the material resulting from earing behavior. Conventionally, aluminum sheet is mainly produced by the direct chill (DC) cast technology. Continuous cast (CC) technology, a new technology, however provides both energy and economic savings while reducing environmental emissions that become more and more urgent issues in today’s environment. Compared with
* Corresponding author. Tel.: /1-859-257-8090; fax: /1-859-3231929. E-mail addresses: [email protected] (J. Liu), [email protected] (J.G. Morris). 0921-5093/03/$ - see front matter # 2003 Published by Elsevier B.V. doi:10.1016/S0921-5093(03)00210-7
DC cast technology, CC technology also takes advantage of high productivity. However, controlling plastic anisotropy of CC material sheet is more difficult than that of DC material sheet during thermomechanical processing. It is well known that the deformation texture components Copper, Brass and S contribute to 458 earing while the recrystallization texture component Cube yields 0/908 earing. Previous works [1 /4] have found that the Cube texture component can easily be obtained by annealing the cold rolled DC material and consequently leads to 0/908 earing which balances very well the 458 earing caused by cold rolling. However, it is very difficult to obtain the Cube texture component after annealing cold rolled CC material. Consequently, aluminum sheet made by the CC process displays 458 earing behavior even after complete recrystallization. As a result, somewhat different earing behavior is usually observed in the final sheet product made from CC material.
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A critical question is whether there exist differences in the cold rolling texture evolution between CC and DC materials and what role does the cold rolling texture evolution play in affecting the recrystallization texture and hence the earing behaviors. In order to answer the above questions, it is essential to trace the texture evolution of CC and DC material sheets during cold rolling. This work is part of a project where the ultimate goal is to improve the formability of CC material sheet to the same level as DC material sheet. The principal aim of the present work is to monitor the macro-, micro- and mesotexture evolutions of AA 3105 CC and DC materials during cold rolling.
2. Experimental 2.1. Materials and procedures Materials were industrially produced hot bands of CC and DC AA 3105 materials. The chemical compositions are given in Table 1. Plates of 6.2 /88.9 /114.3 mm3 (thickness /width /length) were cut from the DC hot band and plates with dimensions of 3.5 /88.9 /114.3 mm3 (thickness /width /length) were cut from the CC hot band. The cut plates were then processed according to procedures shown in Fig. 1. The purpose of the hightemperature homogenization for a long time is to generate a completely recrystallized microstructure and to eliminate the difference of solid solution supersaturation status between CC and DC materials. The homogenized plates were homogeneously cold rolled to different reductions from 10 to 90% on a two high laboratory rolling mill with rolls 100 mm in diameter. 2.2. Microstructure examination Samples for microstructure examination were cut from the plates in a normal direction (ND) and rolling direction (RD) cross-section, cold mounted and mechanically polished per standard metallographic practices. Subsequently, the samples were electropolished using 1.5 vol.% pct HNO3 /5.0 vol.% pct HClO4 acids in methanol at 27 V for 3 s at room temperature to remove the deformation layer. Finally, the samples were anodized using Barker’s reagent (5 vol.% pct HBF4 in
water) at 15 V for 1 min at room temperature to reveal the microstructure under polarized light optical microscopy. 2.3. Texture measurement 2.3.1. Macrotexture Samples for macrotexture measurements were sectioned in the rolling plane (RD and the transverse direction (TD) cross-section) at the mid-thickness position of the plate. The surface for measurement was carefully polished to minimize surface stress. Texture measurements were carried out on a Rigaku D/MAX X-ray goniometer using Cu Ka radiation by means of the Schulz reflection method [5]. Three incomplete pole figures {1 1 1}, {2 0 0}, {2 2 0} up to a tilting angle of 758 (amax /758) were measured. All incomplete pole figure data were corrected for defocusing error and background intensity. Three-dimensional orientation distribution functions (ODFs) f(g) were calculated by using the arbitrarily defined cell (ADC) method [6]. ODFs are expressed by using Bunge’s notation system [7]. The orientations g are described by three Euler angles 81, F, 82, which transform the crystallographic orientation into the sample coordinate system specified by RD, TD, and ND. The ODFs are represented in the three-dimensional Euler space in the range 085/81, F , 82 5/908 by way of iso-intensity contour lines in different sections with 82 constant. Each texture component is fitted by using a number of Gauss-type scattering functions for quantitative analysis [8]. Therefore, the volume fraction Mi of each texture component i is calculated by determining the central orientations gi , the orientation intensity fi , and the scattering width ci . 2.3.2. Microtexture The electron backscatter diffraction (EBSD) technique is based on the discovery [9] and application [10] of Kikuchi patterns. Remarkable progress [11 /13] in this technique has been made in the past 20 years. The stationary beam is focused to a fine point on the highly tilted sample and the diffracted back scattering electrons form Kikuchi patterns on a phosphor screen. The orientation of the local lattice can be obtained by digitizing two appropriate zones in the Kikuchi pattern. In FCC material, two zones on the band passing
Table 1 Compositions of experimental materials, wt.% Alloy
Si
Fe
Cu
Mn
Mg
Cr
Ni
Zn
Ti
Al
AA 3105 CC AA 3105 DC
0.30 0.38
0.64 0.65
0.19 0.14
0.61 0.52
0.55 0.43
/ 0.05
/ 0.01
/ 0.06
/ 0.02
Balance Balance
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Fig. 1. Thermomechanical procedures of AA 3105 aluminum alloy.
through 1 1 1, 1 1 2, 1 1 4 and 3 3 2 are usually selected for digitizing. Furthermore, the orientation information of an interested area can be collected by an electron beam movement controlled by a computer with selected step size. Samples for microtexture measurements were also sectioned in the rolling plane at the mid-thickness position of the plate. The surface for measurement was mechanically polished followed by electropolishing using the same solution used for microstructure examination to remove the deformation layer. In this study, EBSD work was carried out using a Hitachi 3200N SEM interfaced to a Unix workstation with orientation image microscopy (OIM) software from TexSEM Laboratories, Inc. (Draper, UT) installed. The sample was mounted on a pre-tilted sample holder with a tilt angle of 728 for better pattern quality. The geometry of the sample setup is shown in Fig. 2. Note that TD points out of the paper. An example of
Fig. 2. Geometry of the sample setup for EBSD measurement.
the EBSD pattern and its indexing solution using OIM are shown in Fig. 3(a) and (b), respectively. The acceleration voltage and working distance were maintained at 20 kV and 20 mm, respectively. Image scan was adopted and each image contains at least 10,000 pixels (orientations). In order to ensure the reliability of the data, each data set was subject to a cleanup step using an algorithm that checks to determine if the orientation is different from its immediate neighbors. All nearest neighbor pixels must differ in orientation by more than a tolerance angle that is set to 58. Less than 5% of the data was changed in this cleanup operation.
2.3.3. Mesotexture Mesotexture is depicted by grain boundary misorientation plots in this work. The (sub)grain boundary, especially coincidence site lattice (CSL) types, can be characterized and quantified from misorientation information obtained by running a EBSD scan. The misorientation is correlated because the calculation of misorientation is based on the neighbor grains. The (sub)grain boundary can be classified by different neighbor misorientations: low-angle boundaries (LABs, u B/58), moderately misoriented boundaries (MMBs, 585/u B/158) and high-angle boundaries (HABs, 158 5/u ). Owing to the spatial resolution of the EBSD system, misorientations of less than 1.58 were not identified. CSL boundaries are defined following Brandon’s criterion [14]. All misorientation and CSL distributions are presented in the manner of a histogram plot.
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Fig. 3. An example of EBSD pattern from AA 3105 aluminum alloy at 20 kV with working distance of 20 mm (a) and its indexing solution using OIM (b).
3. Results
dimension of grains in the RD direction is at least five times than in the ND direction.
3.1. Microstructures of hot bands
3.2. Textures of hot bands
The as-received hot bands of both CC (Fig. 4(a)) and DC (Fig. 4(b)) materials show typical pancake grain structures that occur at conditions of high hot rolling reductions. After homogenization, CC and DC hot bands were completely recrystallized with elongated grain structures (Fig. 4(c)) and equiaxed grain structures (Fig. 4(d)), respectively. As shown in Fig. 4(c), the
3.2.1. Macrotextures Fig. 5(a) and (b) show ODFs of the as-received hot bands of CC and DC materials, respectively. The intensities of typical orientations have been indexed. The texture of the CC hot band shows a typical rolling texture with a well developed b fiber starting from the Copper orientation {1 1 2}1 1 1 through the S orien-
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Fig. 4. Microstructures of as-received AA 3105 (a) CC hot band, (b) DC hot band, (c) CC hot band after homogenization per procedures shown in Fig. 1 and (d) DC hot band after homogenization per procedures shown in Fig. 1.
tation {1 2 3}6 3 4 and ending at the Brass orientation {0 1 1}2 1 1. The maximum orientation intensity along the b fiber is found between the Copper orientation and the S orientation with a value of 8.3. The texture of the DC hot band displays a combination of a rolling texture and a recrystallization texture (Fig. 5(b)) with a CubeRD orientation {0 1 3}1 0 0. As can be seen from Fig. 5(b), the maximum orientation intensity on the b fiber is also located between the Copper orientation and the S orientation. After homogenization, the recrystallization texture in the CC hot band (Fig. 6(a)) is characterized by a strong CubeND orientation accompanied by CubeND fiber. However, the recrystallization texture of the DC hot band (Fig. 6(b)) contains a strong Cube orientation {0 0 1}1 0 0 with an intensity up to 8.5. 3.2.2. Microtextures Fig. 7 presents the inverse pole figure (IPF) maps of homogenized hot bands with respect to the ND direction. Each grain is painted with a color based on its crystal orientation. The grain size of the recrystallized CC hot band (Fig. 7(a)) is larger than that of the DC hot
band (Fig. 7(b)). It can be verified that the recrystallized grains are mostly elongated along the RD in the CC hot band. As shown in Fig. 7(a), the elongated grains are usually oriented with a P orientation {0 1 1}1 2 2. In Fig. 7(b), a grain with the Cube orientation is highlighted. Cube clusters, neighbor grains with their 0 0 1 crystal direction parallel to the ND direction, are dominant in the DC hot band. 3.2.3. Mesotextures Fig. 8(a) and (b) show misorientation distributions of homogenized CC and DC hot bands, respectively. The corresponding CSL grain boundary distributions is given in Fig. 9(a) and (b). Obviously, HABs are dominant in both CC (Fig. 8(a)) and DC materials (Fig. 8(b)). Grain boundary populations is not uniformly distributed with respect to misorientation angle. It can be seen that there exist peaks in the ranges 30/ 36.58, 40/458, and 55 /62.88. The peak located in the range 40/458 can be ascribed to randomly oriented Cubes [15], which were also reported in AA 2004 [16] and AA 5083 aluminum alloys [17 /19]. The population of a1 boundaries (LABs/MMBs) in DC material (Fig.
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Fig. 5. Complete ODFs of as-received AA 3105 (a) CC and (b) DC hot bands.
Fig. 6. Complete ODFs of AA 3105 (a) CC and (b) DC hot bands after homogenization per procedures shown in Fig. 1.
9(b)) is found to be higher than that in CC material (Fig. 9(a)). In general, the number of CSL boundaries is low in both materials except for a well developed a29
boundary in the DC hot band. This suggests that the misorientation peaks in the ranges 30 /36.58 and 55/
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Fig. 7. IPF maps of homogenized AA 3105 (a) CC and (b) DC hot bands. {1 1 1} pole figures are given for pointed grains.
62.88 (shown in Fig. 8) are mostly contributed by disordered grain boundaries.
3.3. Macrotexture evolution during cold rolling ODFs of CC and DC materials with increasing cold rolling reduction are shown in Figs. 10 and 11, respectively. Three sections of 82 /08, 82 /458 and 82 /658 are selected to show the formation of typical deformation orientations Brass, Copper and S along the b fiber. By watching the section of 82 /08, the evolution of the a fiber can be tracked. Volume fractions of
Gauss-type texture components are calculated and plotted as a function of the cold rolling reduction in Fig. 12. The orientation intensities vs. cold rolling reductions along the a fiber are displayed in Fig. 13. The orientation intensities along the b fiber (skeleton line) and their positions in Euler space 81, F as function of 82 are given in Figs. 14 and 15 for CC and DC materials, respectively.
3.3.1. CC material As shown in Fig. 10(a), the intensity of the CubeND orientation decreases rapidly after 10% cold rolling. The
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Fig. 8. Grain boundary misorientation distributions of homogenized AA 3105 (a) CC and (b) DC hot bands.
CubeND fiber then develops without much intensity change until at 60% cold rolling reduction when the orientations flow to the Brass position. After 70% cold rolling, the Brass orientation is well formed and becomes sharper and more intense during further cold rolling. Fig. 10(b) displays the formation process of the Copper orientation. Orientations spread out from the
CubeND position and form a peak away from the Copper orientation with an intensity of 3.2 after 50% cold rolling. This peak moves toward the position of the Copper orientation and becomes stronger with increasing cold rolling reduction. Finally, the intensity of Copper orientation increases to 7.4. The S orientation develops in the same way (Fig. 10(c)). After 50% cold
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Fig. 9. CSL grain boundary distributions of homogenized AA 3105 (a) CC and (b) DC hot bands.
rolling, a peak near the CubeND orientation forms and then moves toward the S orientation and becomes more intense beyond 60% cold rolling. Volume fractions of typical orientations are plotted versus cold rolling reduction in Fig. 12(a). It can be seen that the volume fraction of the CubeND orientation decreases from about 12% before cold rolling to 0 after 60% cold rolling. A similar trend can be observed for the {1 0 0} fibers that are mostly contributed to by the
CubeND fiber. After 50% cold rolling, the volume fraction of deformation orientations such as Copper, Copper/S, S, S/Brass and Brass start to increase. The volume fraction of the Copper orientation reaches about 30% and becomes the largest of all deformation orientations after 90% cold rolling. The volume fraction of random orientations remains constant until 50% cold rolling and then drops rapidly while deformation textures start to evolve.
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Fig. 10. Complete ODFs of completely recrystallized (RX) AA 3105 CC hot band under various cold rolling reductions at sections of (a) 82 /08, (b) 82 /458 and (c) 82 /658.
The development of the a fiber is illustrated in Fig. 13(a). The a fiber becomes well formed beyond 70% cold rolling. The intensity along the a fiber is uniformly distributed before the cold rolling reduction reaches 70% beyond which the Brass orientation becomes stronger and sharper. It is interesting to note that a small peak is observed around {0 1 1}1 2 2 during the early stages of cold rolling, which indicates the existence of the P orientation. Fig. 14(a) and (b) give the intensity distributions and positions of the b fiber (skeleton line) during cold
rolling, respectively. At low cold rolling reductions ( B/50%), no apparent b fiber is formed (Fig. 14(a)). An apparent increase of orientation intensity is observed along the b fiber after 50% cold rolling. However, the rate of increase of the orientation intensity is not uniform along the b fiber. The intensity of Copper/S is higher than all other orientations along the b fiber. This trend becomes more pronounced beyond 80% cold rolling. The position of the b fiber (skeleton line) is revealed in Fig. 14(b). After 50% cold rolling, the position of the b fiber (skeleton line) is far away from
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Fig. 11. Complete ODFs of completely recrystallized (RX) AA 3105 DC hot band under various cold rolling reductions at sections of (a) 82 /08, (b) 82 /458 and (c) 82 /658.
the sharp position and becomes sharp at high cold rolling reductions (/50%). 3.3.2. DC material Fig. 11 shows the ODFs of DC material during cold rolling. Starting from a strong Cube orientation, the orientation intensity around the Cube position becomes weak when the cold rolling reduction is increased (Fig. 11(a)). The intensity of the Brass orientation reaches 2.0 after 80% cold rolling and increases by 1.5 after 90%
cold rolling. It is worth noting that the Cube orientation transforms to the CubeND orientation and then flows to the Brass position after 80% cold rolling in the same way as it occurs in CC material after 80% cold rolling. The evolutions of the Copper (Fig. 11(b)) and the S (Fig. 11(c)) orientations in DC material during cold rolling are similar to those previously described for CC material. The intensities of the Copper and S orientations in DC material are lower than those in the CC material.
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Fig. 12. Dependence of the volume fraction of various texture components in AA 3105 (a) CC and (b) DC materials on the cold rolling reduction.
The volume fraction of the Cube orientation reaches 11% after homogenization of the hot band (Fig. 12(b)). The volume fraction of the Cube orientation decreases to 0 after 90% cold rolling. The volume fraction of the CubeND fiber, reflected through {1 0 0} fibers, remains above 10% until 80% cold rolling and then decreases during further cold rolling. Orientations start to flow to the b fiber at Copper, Copper/S, S, Brass/S and Brass positions after 80% cold rolling and then increase during further cold rolling. It is worth noting that the volume fractions of the Copper/S, S, Brass/S and Brass orienta-
tions converge to about 12% while the volume fraction of the Copper orientation, increases by about 15% after 80% cold rolling, and reaches 29% after 90% cold rolling. The volume fraction of random orientations drops rapidly after 80% cold rolling when the b fiber develops. As shown in Fig. 13(b), no apparent a fiber is developed in DC material until 80% cold rolling. The a fiber in DC material is less intense than that in CC material during the cold rolling. Again, there exists a small peak around {0 1 1}1 1 1 during the early stages
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Fig. 13. Orientation intensity of orientations of AA 3105 (a) CC and (b) DC materials along the a fiber under different cold rolling reductions.
of cold rolling, which is believed to be related to the P orientation though the position of the peak is shifted from 70 to 608 in 81. Fig. 15 presents the evolution of the intensity and position (skeleton line) of the b fiber. The Copper/S orientation becomes more intense than other deformation orientations along the b fiber (Fig. 15(a)). Compared with the position of the b fiber in CC material
(Fig. 14(b)), the position of the b fiber in DC material appears sharper during the whole cold rolling process (Fig. 15(b)). 3.4. Microtexture evolution during cold rolling IPFs for the ND, TD and RD directions of CC and DC materials after 40% cold rolling are plotted in Fig.
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Fig. 14. Orientation intensity of orientations of AA 3105 CC material along the b fiber (skeleton line) (a) and their exact positions in Euler space 81, F as function of 82 (b).
16(a) and (b), respectively. In CC material (Fig. 16(a)), the orientations concentrate around 1 0 0 in the ND direction while most grains are oriented close to 1 0 5 in the TD direction. It can also be observed that orientations scatter towards 1 1 0 other than 1 1 1 in the ND direction. Weak textures around 1 1 5 and 3 1 3 are observed in the RD direction. In DC material (Fig. 16(b)), orientations concentrate close to 1 0 0 in the ND, TD and RD directions. The
concentration around 2 2 3 with respect to the RD direction is worth noting. 3.5. Mesotexture evolution during cold rolling Fig. 17 (a) and (b) present grain boundary misorientation distributions of CC and DC materials after 40% cold rolling, respectively. The two distributions look similar. Two points are noteworthy: first, HABs,
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Fig. 15. Orientation intensity of orientations of AA 3105 DC material along the b fiber (skeleton line) (a) and their exact positions in Euler space 81, F as function of 82 (b).
which are still dominant, are randomized over the misorientation angle; second, compared with the distributions before deformation (Fig. 8), the fraction of grain boundaries with misorientation angles between 58 and 158 is increased, which indicates the development of MMBs. Fig. 18 displays CSL grain boundary distributions in CC (Fig. 18(a)) and DC (Fig. 18(b)) materials after 40%
cold rolling. Obviously, a1 boundaries are well developed in both materials compared with the homogenized states (Fig. 9), especially in DC material where the population of a1 boundaries is almost double that in the homogenized states (Fig. 9(b)). There is no evidence of the development of twin boundaries (a3, a9, a27a and 27b) in both CC and DC materials when the cold rolling reduction is less than 40%.
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Fig. 16. IPFs of AA 3105 (a) CC and (b) DC hot bands after 40% cold rolling.
4. Discussion 4.1. Macrotexture evolution during cold rolling The evolution of rolling textures of various f.c.c. metals have been intensively investigated and discussed in the literatures [8] [20 /23] by using ODFs. It is well accepted [8,20,21,24,25] that at low degrees of rolling, the orientations along the a and b fibers are homogeneously developed. This homogeneity, however, is destroyed with increasing degree of rolling. With increasing degree of rolling the orientations flow along the a fiber to the Brass position and therefore make the Brass orientation more intense. The a fiber disappears
and only leaves a peak around the Brass orientation at very high degrees of rolling. Simultaneously, orientations flow into the b fiber as the rolling reduction increases. The development of orientations along the b fiber, however is not uniform, and mainly concentrates at the Copper, Brass and S positions. The evolution of textures of both AA 3105 CC and DC materials follow the above rules during cold rolling. At low cold rolling reductions (B/60%), the a and b fibers, though weak, are uniformly developed in both CC and DC materials (Figs. 13, 14(a) and 15(a)). At intermediate and high cold rolling reductions (/60%), the intensities around the Brass, Copper and S orientations increase rapidly and form peaks in the CC material. However, the b fiber is not well formed until high cold rolling reductions (]/ 80%) are attained. Finally, the S orientation becomes the strongest orientation along the b fiber in both materials, which also has been observed in Al [20], Copper [21], and Al /Cu alloy [26] at high rolling reductions. Zhou et al. [27,28] investigated the formation of rolling textures for f.c.c. polycrystals by using a ratedependent crystal plasticity model. They show that during deformation, orientations move either directly into the b fiber or first into the a fiber and then along the a fiber to the b fiber and finally towards the corresponding stable orientations. The former path is supported by the results in this work. It is known that the Cube orientation transforms to the S orientation during rolling deformation [29]. However, the results in this work indicate another way by which the CubeND orientation transforms into the S orientation during cold rolling of CC (Fig. 10(c)) and DC (Fig. 11(c)) materials. Another interesting finding of this work is a path starting from the Cube orientation (0 0 1)[1 0 0] through the CubeND orientation (0 0 1)[1 1¯ 0] to the Brass orientation (0 1 1)[2 1¯ 1]; which can be observed at 82 /08 section in both CC (60% cold rolling, Fig. 10(a)) and DC (80% cold rolling, Fig. 11(a)) materials. In CC material (Fig. 10(a)), the CubeND fiber develops at low and cold rolling reductions (B/50%). Then, orientations flow from the CubeND fiber to the Brass position directly. A similar situation is also observed in DC material. In DC material, the Cube orientation transforms into the CubeND orientation and forms a CubeND fiber from which orientations flow to the Brass orientation during cold rolling. This suggests that the Cube orientation rotates towards the CubeND orientation and then to the Brass orientation during cold rolling. A schematic map of the rotation is drawn in Fig. 19. It can be seen that starting from point a of the Cube orientation, the orientation passes through points b, c, d, e, and finally reaches point f of the Brass orientation. This transformation is finished after 90% cold rolling for both CC and DC materials. In general, the development
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Fig. 17. Grain boundary misorientation distributions AA 3105 (a) CC and (b) DC hot bands after 40% cold rolling.
of cold rolling textures in AA 3105 CC and DC materials follows the same path. 4.2. Microtexture evolution during cold rolling The IPF of CC material in the ND direction is characterized by scattering of orientations from 1 0 0 towards 1 1 0, which indicates the develop-
ment of the CubeND fiber in CC material. In DC material, however, the 1 0 0 texture in all three directions ND, TD and RD suggests the existence of the Cube {0 0 1}1 0 0 component. Therefore, the microtexture results shown in Fig. 16 are in agreement with macrotexture results shown in Figs. 10 and 11 that present a weak CubeND fiber in CC material and the Cube orientation in DC material after 40% cold rolling,
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Fig. 18. CSL grain boundary distributions of AA 3105 (a) CC and (b) DC hot bands after 40% cold rolling.
respectively. F.c.c. metals usually develop strong 1 1 0 fiber textures during compression. The IPF corresponding to the ND direction of CC material (Fig. 16(a)) indicates that orientations flow toward the 1 1 0 orientation after 40% cold rolling. In DC material (Fig. 16(b)), the 1 1 0 fiber also develops accompanied by a fiber between the 1 1 0 and 1 1 3 components,
which is usually observed in high stacking fault energy materials. 4.3. Mesotexture evolution during cold rolling The evolution of grain boundaries has been traced in both CC and DC materials during the early stages of
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Fig. 19. Schematic map for transformation from the Cube orientation to the Brass orientation during cold rolling of AA 3105 aluminum alloy. {1 1 1} pole figures show the transformation steps (small crosses indicate the positions of corresponding Euler angles in pole figures).
cold rolling (5/40%). In both CC and DC materials, a1 boundaries are well developed during the early stages of cold rolling. There is not a remarkable change in twin boundaries (a3, a9, a27a and 27b) during the early stages of cold rolling. Therefore, mechanical twins are not an acting mechanism in these stages. Instead, grains are subdivided by way of forming cell walls (a1 boundaries). These cell walls transform to HABs during further cold rolling by misorientation increase.
5. Conclusions In this work, macro-, micro- and meso-texture evolutions in industrially produced hot bands of CC and DC
AA 3105 aluminum alloy during cold rolling have been studied. The following conclusions can be drawn. (1) After complete recrystallization, a stronger Cube orientation is observed in DC hot band than in CC hot band. a and b fibers become well developed beyond 50% cold rolling in both CC and DC materials. The highest intensity along the b fiber (skeleton line) is located between the Copper and the S orientations in both materials. (2) There exists a path by which Cube orientation (0 0 1)[1 0 0] transforms to the Brass orientation (0 1 1)/ ¯ 1] through the CubeND orientation (0 0 1)[1 1¯ 0] /[2 1 after certain cold rolling reductions. (3) In both CC and DC materials, a cell structure develops with the indication of increasing CSL a1 boundaries during the early stages of cold rolling
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while HABs are randomized over the misorientation angle. (4) There is no evidence of the development of twin boundaries (a3, a9, a27a and 27b) in either CC or DC materials when the cold rolling reduction is less than 40%. (5) Macro-, micro- and mesotexture evolutions follow the same path for both CC and DC materials. This implies that the cold rolling texture itself is not responsible for the different recrystallization behaviors that cause different earing behaviors between CC and DC aluminum alloys.
Acknowledgements Financial support from U.S. Department of Energy (under Contract No. DE-FC07-01ID14193) is gratefully acknowledged.
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