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Texture of Al-Cu alloys deformed by ECAP

J. Kusnierz1,a, M-H Mathon2,b , T. Baudin3c, Z. Jasienski1d, R. Penelle3e 1Institute of Metallurgy and Materials Science (IMMS), Polish Academy of Sciences,

30-059 Kraków, 25 Reymonta Str., Poland 2Laboratoire Leon Brillouin, CEA – CNRS, CEA Saclay, France

3Laboratoire de Physico-Chimie de l’Etat Solide, UMR–CNRS 8648, France

aemail:nmkusnie@imim-pan.krakow.pl, bemail:mhmathon@cea.fr, cemail:Thierry.Baudin@lpces.u-psud.fr, demail:nmjasien@imim-pan.krakow.pl,

eemail:richard.penelle@lpces.u-psud.fr

Keywords: equal-channel angular pressing (ECAP), severe plastic deformation, texture, aluminium alloys.

Abstract. Materials of ultra-fine grained microstructure (sub-micrometer grain size) exhibit large strength, hardness and ductility and also the increased toughness in comparison with conventional coarse-grained ones. In these materials also the super-plastic flow at lower temperatures is observed. This behaviour may be interesting when aluminium alloys like AlCuZr, used in superplastic forming, are considered. In the paper, the methods of preparing such materials by equal-channel angular pressing (ECAP) is proposed and the texture analysis, based on neutron diffraction pole figure measurements and calculated orientation distribution function of two alloys AlCu4SiMn and AlCu5AgMgZr is discussed. The influence of short time recrystallization is discussed in relation with TEM and SEM observations.

Introduction Superplastic forming (SPF) has been still interesting for automotive, aerospace and aircraft industries, particularly in the case of AlCuZr alloys (trade name SUPRAL), in which the grain growth is inhibited by Al3Zr particles [1-4]. Superplastic deformation is observed when the deformation process involves the grain boundary sliding. It occurs at the strain rate inversely proportional to the square of grain size [5]. The direct consequence of that is the tendency to decrease the grain size of such a deformed material. Recently, the increased interest in materials of the ultra-fine grained (UFG) structure, with the grain size of sub-micrometers order, known as nanocrystalline materials when the grain diameter is below 100 nm, is due to the evident advantages resulting from the development of such a structure and manifested by increased strength properties and greater hardness at higher ductility. The low temperature superplastic flow occurring in these materials permits to reduce the drawing temperature of complicated products [6] and thus may be interesting when aluminium alloys like AlCuZr, used in superplastic forming, are considered; moreover the increase of application of these alloys is reported [7].

Equal-channel angular pressing Equal-channel angular pressing (ECAP) method [6,8] consists in successive extrusion steps of a sample through an angular die, which introduces cumulative severe plastic deformation

Materials Science Forum Vols. 495-497 (2005) pp 851-856Online available since 2005/Sep/15 at www.scientific.net© (2005) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/MSF.495-497.851

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 132.166.23.204, CEA Saclay (I894) DSM/SAC/UST/SVI, Gif Sur Yvette Cedex, France-17/10/14,11:49:26)

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without changing its shape. The extrusion is performed in several passes according to the scheme of equal-channel angular pressing presented in Fig. 1. The equivalent deformation ε per pass is close to 1 [6]. In route C the sample is rotated 180o around its longitudinal axis between each pass.

Fig. 1. Scheme of equal-channel angular pressing (ECAP).

Material and experimental technique Experiments were performed on two Al alloys: 1) AlCu5AgMgZr alloy [4] - marked D, with chemical composition in weight %: Cu 5.0, Mn 0.2, Ag 0.7, Mg 0.8, Zr 0.4 and grain size d = 10÷20 µm, initially solution treated for 0.5 h at 530 oC and then aged 2 h at 250 oC and 2) AlCu4SiMn - marked P, consisted of: Cu 4.0, Mn 1.0, Si 0.8, Mg 0.6 and Fe 0.4 [9]. ECAP process was executed by means of INSTRON 6025 testing machine with a specially constructed equipment attached [8]. Final deformations and experimental conditions are presented in Table 1.

Material ECAP equivalent

deformation ε

Sample Temperature of pressing

[oC]

Recrystallization

AlCu5AgMgZr 2.7 D23* 20 - AlCu5AgMgZr 4.0 D254 250÷300 - AlCu5AgMgZr 4.0 D254w - 450oC/10 min

AlCu4SiMn 4.0 P14 250÷300 - AlCu4SiMn 4.0 P14w - 450oC/10 min

Table 1. Conditions of ECAP processing; D23* - aging during 2 h in 250oC between each

pass and ε = 0.9 per pass [8] The changes of crystallographic orientations were studied by the method of pole figures. The measurements of pole figures, with the normal ND parallel to the emerging direction ED and RD along the direction of the acting piston (PP in Fig. 2), were performed using scanning electron microscopy (SEM) equipped with orientation imaging microscopy (OIM™) software with electron back scattering diffraction (EBSD) technique for local texture or using neutron diffraction method at Leon Brillouin Laboratory of CEA/Saclay, France for the global texture.

C

180

ED

PP 90o

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Fig. 2. Orientation of measured samples; texture and

structure observation were effected on the surface 2,

PP – pressing direction, ED – extrusion direction (see

Fig. 1), in pole figures RD ║ PP, ND ║ ED.

Results and discussion

Multiple procedure of pressing up to ε ~ 4 (four passes) was effected on samples of 10x10 mm2 cross section, according to route C, i.e. with 180o rotation about the sample axis which followed each pass. In the case of D23 samples, the aging procedure during 2 h at 250 oC was applied between each pass; for samples D254 and P14 the ECAP procedure was performed at temperature 250÷300 oC, D254w and P14w were annealed 10 min in 450 oC (see Table 1). Texture measurements. The inspection of pole figures measured by neutron diffraction technique (global texture) of deformed alloys up to ε ~ 4, i.e. D254, P14 in Fig. 3, demonstrates similarities in distribution of orientation; short time recrystallization (10 min in 450 oC) results in lowering dispersion of orientations only (compare P14 and P14w in Fig. 3). Smaller rotations are observed in sample deformed up ε ~ 2.7 (Fig. 3, sample D23) because generally when the deformation is smaller then the rotation is smaller [8]. The electron back scattering diffraction (EBSD) technique for local texture reveals more clearly the differences which appear in the texture of annealed samples (Fig. 4, compare D254 as deformed and D254w as annealed). In short time recrystallized sample i.e. D254w (Fig. 4), a lower dispersion of orientation and lack of certain components have been observed and apart from it the distribution of orientation of P14 sample in Fig. 4 resembles the recrystallized one i.e. D254w.

Main components Sample ECAP ε

Temperature of pressing [oC]

Neutrons EBSD D23 2.7 20 (001)[110]

(322)[43 3 ] -

D254 4.0 250÷300 (210)[1 2 3 ] ( 2 10)[1 2 3 ]

(210)[1 2 3 ] ( 2 10)[1 2 3 ]

D254w 4.0 D254 + recr. 450oC/10m - (123)[5 4 1] (1 2 3 )[5 4 1]

P14 4.0 250÷300 (001)[110] (221)[ 2 12]

(221)[2 7 ,10]

(320)[23 ,12] (123)[63 4 ]

P14w 4.0 P14 + recr. 450oC/10m (221)[ 2 12] (134)[ 7 5 2 ] (135)[310]

-

Table 2. Main components of texture

PP

ED 1

23

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The structure observed by means of transmission electron microscopy of ECAP deformed up to ε ~ 4 AlCu5AgMgZr alloy (bright field BF and dark field DF photographs of D254 in Fig. 5 [10]) present the grains of diameter d ~1 µm, embedded in layers of elongated inclusions. In the AlCu6Zr alloy (Supral 100) it was observed that processing by ECAP refines the grain size to d ≤ 2 µm [11]. Similar results of grain refinement (d ~ 2 µm) had been obtained for 7475 aluminium alloy (AlZn6Mg2Cu2CrZr) by ECAP processing in 400 oC up to ε above 6 by Goloborodko, Sitdikov, Sakai, Kaibyshev and Miura [12]. The grains with width dw = 1÷5 µm, elongated in the transverse direction are presented in the background of randomly distributed inclusions in AlCu4SiMn alloy (bright field BF and dark field DF photographs of P14 in Fig. 6). One can note a significant selective grain growth in transverse direction. OIM™ observations of recrystallized D254w sample show grain growth in comparison with grains registered by OIM™ of the deformed D254 sample (Fig. 7a and 7b). This grain growth seems to be very selective and results in appearance of certain components in the orientation distribution of the recrystallized D254w contrary to the deformed D254 in which grain orientations are spread and dispersed (Fig. 4). The orientation distribution of P14 sample is similar to the recrystallized D254w one (compare P14 with D254w pole figures in Fig. 4) and proves relatively large and recrystallized grains observed in P14 sample (Fig. 7c).

Conclusions The changes of orientation during the ECAP processing deduced from the global texture measurement (neutron diffraction) are strongly dependent on deformation; the both studied alloys behave similarly. Main components of local texture obtained by EBSD are in accordance with neutron measured global texture ones; larger dispersion is observed in local texture measurements. The short time recrystallization induces selective grain growth and lowers the orientation dispersion which was observed in EBSD measurements.

References [1] T.G. Nieh, J. Wadsworth and O.D. Sherby, Superplasticity in Metals and Ceramics, Cambridge University Press, Cambridge, (1997) pp. 58-68 [2] D.J. Lloyd and D.M. Moore, The Metallurgical Society of AIME, (1982) pp.147-172 [3] B.M. Watts, M.J. Stowell, B.L. Baikie and D. Owen, Metal Science 10 (1976) 189-206 [4] J. Dutkiewicz, P. Malczewski, J. Kuśnierz, T. G. Nieh, Proc. 2nd Int. Conf. on Light Materials for Transportation Systems (LiMAT-2001), ed. N.J .Kim, C.S. Lee, D. Eylon, Pohang 2001, Korea, Vol. I, pp. 387-392 [5] T.G. Langdon, Acta Metall. Mater. 42(1994), 2437 – 2443 [6] J. C. Williams, E. A. Starke, Jr., Acta Materialia 51 (2003), 5775 – 5799 [7] R.Z. Valiev, R.K. Ismagaliev, I.V. Alexandrov, Progr. Mater. Scie. 45(2000), 103-189 [8] J. Kuśnierz, Archives of Metallurgy, 45/4 (2001), 375 [9] J. Kuśnierz, Archives of Metallurgy, 38(1993),221 [10] J. Kuśnierz, M-H Mathon, J. Dutkiewicz, T. Baudin, Arch. of Metallurgy – in press [11] S. Lee, M. and all, Proc. 2nd Int. Conf. on Light Materials for Transportation Systems (LiMAT-2001), ed. N.J .Kim, C.S. Lee, D. Eylon, Pohang 2001, Korea, Vol. I, pp. 399-404 [12] A. Goloborodko, O. Sitdikov, T. Sakai, R. Kaibyshev, H. Miura, Materials Transactions 44(2003), 766-774

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D23n ▲ (322)[4 3 3 ]

(001)[110]

▲ (210)[1 2 3 ]

( 2 10)[ 1 2 3 ]n

wn

▲ (221)[ 2 12] ● (135)[310]

(134)[75 2]

n ▲ (221)[ 2 12] ● (001)[110]

(221)[2 7 10]

{111}

D254e

RD

▲ (210)[1 2 3 ]

( 2 10)[1 2 3 ]

D254we

{111RD

▲ (123)[5 4 1] ●(1 2 3 )[5 4 1]

{111}

P14e

RD

▲ (123)[63 4 ] ● (320)[23 12]

Fig. 3. {111} pole figures of ECAP processed samples: a) D23n, b) D254n, c) P14wn, d) P14n, e) D254e, f) D254we and P14e; n -neutrons, e – EBSD.

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EBSD TEM

D254 a

D254wb

P14c

1 µm

D254 DF

d

1µm

DFP14

e

Fig. 4. Photographs of ECAP processed alloys: D254 - a and d, D254w – b, P14 – c and e; a, b and c – EBSD, d and e – TEM.

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DOI References

[1] T.G. Nieh, J. Wadsworth and O.D. Sherby, Superplasticity in Metals and Ceramics, ambridge University

Press, Cambridge, (1997) pp. 58-68

doi:10.1017/CBO9780511525230.006 [6] J. C. Williams, E. A. Starke, Jr., Acta Materialia 51 (2003), 5775 – 5799

doi:10.1016/j.actamat.2003.08.023 [1] T.G. Nieh, J. Wadsworth and O.D. Sherby, Superplasticity in Metals and Ceramics, Cambridge University

Press, Cambridge, (1997) pp. 58-68

doi:10.1017/CBO9780511525230.006 [6] J. C. Williams, E. A. Starke, Jr., Acta Materialia 51 (2003), 5775 5799

doi:10.1016/j.actamat.2003.08.023