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A study on the micro-formability of Al 5083 superplastic alloy using micro-forging method
Materials Science and Engineering A 449–451 (2007) 338–342
A study on the micro-formability of Al 5083 superplastic alloy using micro-forging method S.G. Kang a , Y.S. Na b,∗ , K.Y. Park a , J.E. Jeon a , S.C. Son a , J.H. Lee b a
b
Mechanical and Automotive Engineering, University of Ulsan, Ulsan, South Korea Materials Research Station, Korea Institute of Machinery and Materials, Changwon, South Korea Received 23 August 2005; received in revised form 23 December 2005; accepted 9 January 2006
Abstract Micro-formability of superplastic Al 5083 alloy as a candidate material for micro-forming was investigated by varying the forming parameters such as time, load and temperature. Micro-forging machine and Si micro-dies with V-groove were employed for micro-forming test. Microformability was estimated by comparing Rf values (=Af /Ag ), where Ag is cross-sectional area of V-groove, and Af the filled area by micro-formed sample. The Rf values increased with increasing load and time when the forming temperatures were in the range where superplasticity of Al 5083 alloy is manifest. On the other hand, the Rf values decreased as the forming temperatures got away from the superplastic temperature of Al 5083 alloy. Maximum Rf value (0.9952) was reached at temperature 530 ◦ C, load 96 N and time 20 min. © 2006 Elsevier B.V. All rights reserved. Keywords: Micro-forming; Micro-forging; Al 5083; Superplasticity; Micro-parts
1. Introduction As the demand for miniaturization of various devices and parts is increasing, easier and cheaper fabrication process is ever required for manufacturing micro-parts such as pins for ICcarriers, fasteners, micro-screws, lead frames, sockets and any kind of connecting elements [1]. Even if most of micro-parts are currently manufactured by the advanced lithographic technologies, mass production of micro-parts with reasonable precision and low cost may be realized by employing micro-scale metal forming processes such as micro-forging and micro-extrusion, etc. [2]. In particular, superplastic deformation generally occurring in metals with very small grain size less than 10 m [3] can be considered as a promising micro-forming mode. It is also well known that Al 5083 alloy is a representative superplastic alloy showing the low temperature superplasticity [4]. However, the differences between the micro-scale metal forming and the conventional deformation of metals make it essential to improve the understanding for metal forming process in micro-scale in order to optimize the process condition. Therefore, in this work, V-groove micro-patterns of Si-based
∗
Corresponding author. E-mail address: [email protected] (Y.S. Na).
0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.01.166
micro-dies were superplastically transferred on Al 5083 superplastic alloy by applying micro-forging method. Micro-forming was conducted by varying the process conditions like materials temperature, applied load and loading time. Micro-formability of Al 5083 superplastic alloy was estimated by observing the transferred patterns with scanning electron microscope. Threedimentional pyramidal-type patterns were also transferred on Al 5083 plate by employing the optimized process condition. 2. Experimental Micro-forming tests of Al 5083 alloy were carried out using a specially developed apparatus for superplastic micro-forging (Fig. 1). Si-based micro-dies with V-groove and pyramidal shape pattern shown in Fig. 2 were fabricated by anisotropic etching method, and used for micro-forming test. The width (Wd ) of Vgroove and the length of basal square of pyramids (L) were 30, 50 and 100 m, respectively. A 5 mm × 5 mm of V-groove Si die was placed on 2.5 mm × 2.5 mm of Al 5083 plate with 1 mm thickness before conducting micro-forming. Specimen and die were heated to a temperature between 430 and 550 ◦ C by a small electric heater and subjected to compressive load by controlling dead weights. The applied load was selected in the range of 8–96 N, and the forming time was between 5 and 20 min. Grain size of Al 5083 superplastic alloy used in this study was
S.G. Kang et al. / Materials Science and Engineering A 449–451 (2007) 338–342
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conducted by employing the optimal process condition that had been obtained from V-groove micro-forming experiments. 3. Results and discussion
Fig. 1. Schematic illustration of apparatus for superplastic micro-forging.
6–15 m even if it is not shown in this article. Micro-formability of Al 5083 alloy was estimated by comparing Rf values (=Af /Ag ), where Ag is the cross-sectional area of V-groove, and Af the filled area by micro-formed sample, as suggested by Saotome et al. [5]. Additionally, radius of curvature (ρ) of micro-formed pattern tip was also used as an index for estimating micro-formability. Micro-forming of three-dimentional pyramidal-type pattern was
Fig. 3 shows micro-patterns formed using V-groove microdie with Wd = 100 m for various Al alloys. Micro-forming was conducted at 520 ◦ C under compressive load of 66 N for 20 min. Grain size of Al 5083 alloy used in this work was about 10 m that is generally required for superplastic deformation [6], while those of the conventional Al alloys (Al 1050 and Al 5020) were larger than 50 m. As shown in Fig. 3, V-groove pattern was transferred most correctly for Al 5083 superplastic alloy rather than for the conventional Al alloys. This observation can be explained by the deformation model suggested by Saotome et al. [7]. They have suggested that micro-patterns can be more correctly transferred to the materials having smaller grains than that having relatively larger grains. In order to investigate the effect of the forming condition on micro-formability of Al 5083 superplastic alloy, micro-forming tests were conducted by varying forming time, temperature and load. Fig. 4 shows the representative cross-sectional views of the micro-formed patterns with V-groove dies. As shown in Fig. 4, V-groove micro-patterns were better transferred as forming time, temperature and load increased. Rf value, a parameter indexing micro-formability, was calculated by measuring the cross-sectional area of the microformed patterns from the scanning electron micrographs. Fig. 5 shows the variation of Rf and ρ with forming time for the
Fig. 2. SEM images of Si-based micro-dies with V-groove (a and b) and pyramidal shape pattern (c and d). (a) Wd = 30 m; (b) Wd = 50 m; (c) L = 30 m; (d) L = 100 m.
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Fig. 3. SEM images of micro-patterns formed using V-groove micro-die with Wd = 100 m for Al 1050 (a), Al 5020 (b), and Al 5083 (c).
samples micro-formed at 490 ◦ C and 96 N. Rf value continuously increases with increasing the forming time up to 20 min. Superplastic deformation of Al 5083 alloy by grain boundary sliding and grain rotation during micro-forming leads a con-
tinuous metal flow into the micro V-groove, and results in the increase of Rf with forming time. However the increasing rate of Rf with forming time is reduced as Rf reaches 1 due to the tip size of V-groove comparable to the grain size of Al 5083 alloy.
Fig. 4. Typical cross-sectional views of micro-formed patterns with V-groove die (Wd = 100 m). (a) 490 ◦ C, 96 N for 5 min; (b) 490 ◦ C, 96 N for 20 min; (c) 530 ◦ C, 37 N for 20 min; (d) 530 ◦ C, 96 N for 20 min.
S.G. Kang et al. / Materials Science and Engineering A 449–451 (2007) 338–342
Fig. 5. Variation of Rf and ρ with forming time for Al 5083 samples microformed at 490 ◦ C and 96 N (Wd = 100 m).
The variation of Rf value with temperature, when microforming was conducted at 96 N for 20 min, is shown in Fig. 6. As expected, higher Rf value could be realized when micro-forming was conducted at superplastic temperature range (490–550 ◦ C) of Al 5083 alloy. It should be noted that maximum Rf value was obtained at 530 ◦ C due to the competitive operation between grain boundary sliding and grain growth with increasing temperature. Rf value also increases with increasing the forming load as shown in Fig. 7. However it should be noted that the increasing rate of Rf value is reduced with the forming load because the superplastic deformation is achieved only in a specific strain rate range. It is well known that superplastic deformation of a polycrystalline metal occurs by grain boundary sliding and grain rotation [6]. Therefore, grain size may affect the micro-formability because increase of grain size requires the deformation of grain itself for the continuous metal flow into the corner tip of micro Vgroove. Fig. 6 implies that micro-forming should be conducted at the temperature where rapid grain growth is not observed. An optimal forming condition has been selected from the micro-forming experiments for Al 5083 superplastic alloy with
Fig. 6. Variation of Rf and ρ with temperature for Al 5083 samples micro-formed at 96 N for 20 min (Wd = 100 m).
341
Fig. 7. Variation of Rf and ρ with forming load for Al 5083 samples microformed at 530 ◦ C for 20 min (Wd = 100 m).
V-groove dies. By applying the selected optimal condition (530 ◦ C, 96 N and 20 min), three-dimentional pyramidal-type micro-patterns were transferred on Al 5083 plates. The scanning electron micrographs of micro-formed patterns are shown
Fig. 8. Scanning electron micrographs of pyramidal patterns micro-formed at 530 ◦ C and 96 N for 20 min. The edge length L of the impression is (a) L = 100 m; (b) L = 50 m; (c) L = 30 m.
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in Fig. 8. Transfer of pyramidal pattern was improved as the edge length of basal square of pyramid (L) increases. This result implies that micro-formability is closely related to the number of grains involved in micro-forming. It can also be inferred that the grain size of micro-formed materials should be controlled along the pattern size to be formed for obtaining better microformability. 4. Conclusions Micro-formability of Al 5083 superplastic alloy has been investigated using micro-forging method. The results can be summarized as follows: (i) It has been observed from the micro-forming tests of Al 5083 alloy with V-groove dies that micro-formability indexed by Rf value is improved as the forming time and load increase. Meanwhile, optimal transfer of micro-pattern has been achieved when temperature of Al 5083 alloy was maintained to 530 ◦ C. (ii) Micro-forming of Al 5083 superplastic alloy with V-groove die (Wd = 100 m) has been optimized at the forming con-
dition given as follows: load = 96 N, temperature = 530 ◦ C, forming time = 20 min. (iii) Micro-formability is closely related to the number of grains involved in micro-forming. The grain size of micro-formed materials should be reduced as the pattern size to be formed decreases. (iv) It is clear from this study that not only Al 5083 superplastic alloy is a suitable material for micro-forming, but also micro-forging is one of promising processes for fabricating three-dimentional micro-parts. References [1] M. Geiger, M. Kleiner, R. Eckstein, N. Tiesler, U. Engel, Ann. CIRP 50 (2) (2001) 445. [2] F. Vollertsen, Z. Hu, H. Schulze Niehoff, C. Theiler, J. Mater. Proc. Technol. 151 (2004) 70. [3] L. Lin, Z. Liu, L. Chen, T. Liu, S. Wu, Met. Mater. Int. 10 (2004) 501. [4] K.T. Park, D.Y. Hwang, D.H. Shin, Met. Mater. Int. 8 (2002) 519. [5] Y. Saotome, T. Hatori, T. Zhang, A. Inoue, Mater. Sci. Eng. A 304–306 (2001) 716. [6] G. Pollard, J. Kor. Inst. Met. Mater. 9 (1971) 123. [7] Y. Saotome, T. Zhang, A. Inoue, Mater. Res. Soc. Proc. 554 (1999) 385.
A study on the micro-formability of Al 5083 superplastic alloy using micro-forging method S.G. Kang a , Y.S. Na b,∗ , K.Y. Park a , J.E. Jeon a , S.C. Son a , J.H. Lee b a
b
Mechanical and Automotive Engineering, University of Ulsan, Ulsan, South Korea Materials Research Station, Korea Institute of Machinery and Materials, Changwon, South Korea Received 23 August 2005; received in revised form 23 December 2005; accepted 9 January 2006
Abstract Micro-formability of superplastic Al 5083 alloy as a candidate material for micro-forming was investigated by varying the forming parameters such as time, load and temperature. Micro-forging machine and Si micro-dies with V-groove were employed for micro-forming test. Microformability was estimated by comparing Rf values (=Af /Ag ), where Ag is cross-sectional area of V-groove, and Af the filled area by micro-formed sample. The Rf values increased with increasing load and time when the forming temperatures were in the range where superplasticity of Al 5083 alloy is manifest. On the other hand, the Rf values decreased as the forming temperatures got away from the superplastic temperature of Al 5083 alloy. Maximum Rf value (0.9952) was reached at temperature 530 ◦ C, load 96 N and time 20 min. © 2006 Elsevier B.V. All rights reserved. Keywords: Micro-forming; Micro-forging; Al 5083; Superplasticity; Micro-parts
1. Introduction As the demand for miniaturization of various devices and parts is increasing, easier and cheaper fabrication process is ever required for manufacturing micro-parts such as pins for ICcarriers, fasteners, micro-screws, lead frames, sockets and any kind of connecting elements [1]. Even if most of micro-parts are currently manufactured by the advanced lithographic technologies, mass production of micro-parts with reasonable precision and low cost may be realized by employing micro-scale metal forming processes such as micro-forging and micro-extrusion, etc. [2]. In particular, superplastic deformation generally occurring in metals with very small grain size less than 10 m [3] can be considered as a promising micro-forming mode. It is also well known that Al 5083 alloy is a representative superplastic alloy showing the low temperature superplasticity [4]. However, the differences between the micro-scale metal forming and the conventional deformation of metals make it essential to improve the understanding for metal forming process in micro-scale in order to optimize the process condition. Therefore, in this work, V-groove micro-patterns of Si-based
∗
Corresponding author. E-mail address: [email protected] (Y.S. Na).
0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.01.166
micro-dies were superplastically transferred on Al 5083 superplastic alloy by applying micro-forging method. Micro-forming was conducted by varying the process conditions like materials temperature, applied load and loading time. Micro-formability of Al 5083 superplastic alloy was estimated by observing the transferred patterns with scanning electron microscope. Threedimentional pyramidal-type patterns were also transferred on Al 5083 plate by employing the optimized process condition. 2. Experimental Micro-forming tests of Al 5083 alloy were carried out using a specially developed apparatus for superplastic micro-forging (Fig. 1). Si-based micro-dies with V-groove and pyramidal shape pattern shown in Fig. 2 were fabricated by anisotropic etching method, and used for micro-forming test. The width (Wd ) of Vgroove and the length of basal square of pyramids (L) were 30, 50 and 100 m, respectively. A 5 mm × 5 mm of V-groove Si die was placed on 2.5 mm × 2.5 mm of Al 5083 plate with 1 mm thickness before conducting micro-forming. Specimen and die were heated to a temperature between 430 and 550 ◦ C by a small electric heater and subjected to compressive load by controlling dead weights. The applied load was selected in the range of 8–96 N, and the forming time was between 5 and 20 min. Grain size of Al 5083 superplastic alloy used in this study was
S.G. Kang et al. / Materials Science and Engineering A 449–451 (2007) 338–342
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conducted by employing the optimal process condition that had been obtained from V-groove micro-forming experiments. 3. Results and discussion
Fig. 1. Schematic illustration of apparatus for superplastic micro-forging.
6–15 m even if it is not shown in this article. Micro-formability of Al 5083 alloy was estimated by comparing Rf values (=Af /Ag ), where Ag is the cross-sectional area of V-groove, and Af the filled area by micro-formed sample, as suggested by Saotome et al. [5]. Additionally, radius of curvature (ρ) of micro-formed pattern tip was also used as an index for estimating micro-formability. Micro-forming of three-dimentional pyramidal-type pattern was
Fig. 3 shows micro-patterns formed using V-groove microdie with Wd = 100 m for various Al alloys. Micro-forming was conducted at 520 ◦ C under compressive load of 66 N for 20 min. Grain size of Al 5083 alloy used in this work was about 10 m that is generally required for superplastic deformation [6], while those of the conventional Al alloys (Al 1050 and Al 5020) were larger than 50 m. As shown in Fig. 3, V-groove pattern was transferred most correctly for Al 5083 superplastic alloy rather than for the conventional Al alloys. This observation can be explained by the deformation model suggested by Saotome et al. [7]. They have suggested that micro-patterns can be more correctly transferred to the materials having smaller grains than that having relatively larger grains. In order to investigate the effect of the forming condition on micro-formability of Al 5083 superplastic alloy, micro-forming tests were conducted by varying forming time, temperature and load. Fig. 4 shows the representative cross-sectional views of the micro-formed patterns with V-groove dies. As shown in Fig. 4, V-groove micro-patterns were better transferred as forming time, temperature and load increased. Rf value, a parameter indexing micro-formability, was calculated by measuring the cross-sectional area of the microformed patterns from the scanning electron micrographs. Fig. 5 shows the variation of Rf and ρ with forming time for the
Fig. 2. SEM images of Si-based micro-dies with V-groove (a and b) and pyramidal shape pattern (c and d). (a) Wd = 30 m; (b) Wd = 50 m; (c) L = 30 m; (d) L = 100 m.
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Fig. 3. SEM images of micro-patterns formed using V-groove micro-die with Wd = 100 m for Al 1050 (a), Al 5020 (b), and Al 5083 (c).
samples micro-formed at 490 ◦ C and 96 N. Rf value continuously increases with increasing the forming time up to 20 min. Superplastic deformation of Al 5083 alloy by grain boundary sliding and grain rotation during micro-forming leads a con-
tinuous metal flow into the micro V-groove, and results in the increase of Rf with forming time. However the increasing rate of Rf with forming time is reduced as Rf reaches 1 due to the tip size of V-groove comparable to the grain size of Al 5083 alloy.
Fig. 4. Typical cross-sectional views of micro-formed patterns with V-groove die (Wd = 100 m). (a) 490 ◦ C, 96 N for 5 min; (b) 490 ◦ C, 96 N for 20 min; (c) 530 ◦ C, 37 N for 20 min; (d) 530 ◦ C, 96 N for 20 min.
S.G. Kang et al. / Materials Science and Engineering A 449–451 (2007) 338–342
Fig. 5. Variation of Rf and ρ with forming time for Al 5083 samples microformed at 490 ◦ C and 96 N (Wd = 100 m).
The variation of Rf value with temperature, when microforming was conducted at 96 N for 20 min, is shown in Fig. 6. As expected, higher Rf value could be realized when micro-forming was conducted at superplastic temperature range (490–550 ◦ C) of Al 5083 alloy. It should be noted that maximum Rf value was obtained at 530 ◦ C due to the competitive operation between grain boundary sliding and grain growth with increasing temperature. Rf value also increases with increasing the forming load as shown in Fig. 7. However it should be noted that the increasing rate of Rf value is reduced with the forming load because the superplastic deformation is achieved only in a specific strain rate range. It is well known that superplastic deformation of a polycrystalline metal occurs by grain boundary sliding and grain rotation [6]. Therefore, grain size may affect the micro-formability because increase of grain size requires the deformation of grain itself for the continuous metal flow into the corner tip of micro Vgroove. Fig. 6 implies that micro-forming should be conducted at the temperature where rapid grain growth is not observed. An optimal forming condition has been selected from the micro-forming experiments for Al 5083 superplastic alloy with
Fig. 6. Variation of Rf and ρ with temperature for Al 5083 samples micro-formed at 96 N for 20 min (Wd = 100 m).
341
Fig. 7. Variation of Rf and ρ with forming load for Al 5083 samples microformed at 530 ◦ C for 20 min (Wd = 100 m).
V-groove dies. By applying the selected optimal condition (530 ◦ C, 96 N and 20 min), three-dimentional pyramidal-type micro-patterns were transferred on Al 5083 plates. The scanning electron micrographs of micro-formed patterns are shown
Fig. 8. Scanning electron micrographs of pyramidal patterns micro-formed at 530 ◦ C and 96 N for 20 min. The edge length L of the impression is (a) L = 100 m; (b) L = 50 m; (c) L = 30 m.
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in Fig. 8. Transfer of pyramidal pattern was improved as the edge length of basal square of pyramid (L) increases. This result implies that micro-formability is closely related to the number of grains involved in micro-forming. It can also be inferred that the grain size of micro-formed materials should be controlled along the pattern size to be formed for obtaining better microformability. 4. Conclusions Micro-formability of Al 5083 superplastic alloy has been investigated using micro-forging method. The results can be summarized as follows: (i) It has been observed from the micro-forming tests of Al 5083 alloy with V-groove dies that micro-formability indexed by Rf value is improved as the forming time and load increase. Meanwhile, optimal transfer of micro-pattern has been achieved when temperature of Al 5083 alloy was maintained to 530 ◦ C. (ii) Micro-forming of Al 5083 superplastic alloy with V-groove die (Wd = 100 m) has been optimized at the forming con-
dition given as follows: load = 96 N, temperature = 530 ◦ C, forming time = 20 min. (iii) Micro-formability is closely related to the number of grains involved in micro-forming. The grain size of micro-formed materials should be reduced as the pattern size to be formed decreases. (iv) It is clear from this study that not only Al 5083 superplastic alloy is a suitable material for micro-forming, but also micro-forging is one of promising processes for fabricating three-dimentional micro-parts. References [1] M. Geiger, M. Kleiner, R. Eckstein, N. Tiesler, U. Engel, Ann. CIRP 50 (2) (2001) 445. [2] F. Vollertsen, Z. Hu, H. Schulze Niehoff, C. Theiler, J. Mater. Proc. Technol. 151 (2004) 70. [3] L. Lin, Z. Liu, L. Chen, T. Liu, S. Wu, Met. Mater. Int. 10 (2004) 501. [4] K.T. Park, D.Y. Hwang, D.H. Shin, Met. Mater. Int. 8 (2002) 519. [5] Y. Saotome, T. Hatori, T. Zhang, A. Inoue, Mater. Sci. Eng. A 304–306 (2001) 716. [6] G. Pollard, J. Kor. Inst. Met. Mater. 9 (1971) 123. [7] Y. Saotome, T. Zhang, A. Inoue, Mater. Res. Soc. Proc. 554 (1999) 385.