THE ROLLING TEXTURE DEVELOPMENT IN AN 8090 Al-Li ALLOY

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THE ROLLING TEXTURE DEVELOPMENT IN AN 8090 Al-Li ALLOY

J. Hirsch, O. Engler, K. Lücke, M. Peters, K. Welpmann

To cite this version:

J. Hirsch, O. Engler, K. Lücke, M. Peters, K. Welpmann. THE ROLLING TEXTURE DEVELOP- MENT IN AN 8090 Al-Li ALLOY. Journal de Physique Colloques, 1987, 48 (C3), pp.C3-605-C3-611.

�10.1051/jphyscol:1987370�. �jpa-00226601�

JOURNAL DE PHYSIQUE

Colloque C3, supplbment au n09, Tome 48, septembre 1987

THE ROLLING TEXTURE DEVELOPMENT IN AN 8090 A1-Li ALLOY

J. HIRSCH, 0. ENGLER, K. LUCKE, M. PETERS* and K. WELPMANN*

Institut fur Allgemeine Metallkunde und Metallphysik RWTH Aachen, Kopernikusstr. 14, 0-5100 Aachen, F.R.G.

* 0 ~ ~ ~ ~ , 1 n s t i t u t fur Werkstoff-Forschung, 0-5000 Koln 90, F.R.G.

Abstract

The texture development in cold rolled 8090 A1-Li alloy is investi- gated with the help of quantitative ODF analysis. By variation of the starting conditions (initial texture, grain shape, age harden- ing) the systematic dependence of the rolling texture on these para- meters is analysed. The results are given in form of volume frac- tions of characteristic texture components and density and orienta- tion of the characteristic fcc rolling texture fibre. They are com- pared to results of texture simulations, based on Taylor type theo- ries. The influence of particles on texture formation is discussed.

Introduction

Mechanical anisotropy in metallic materials is often caused by the preferred orientation distribution of the crystallites, i.e. by its texture. Especially in sheet material of ~ l - i i alloys as a new-pro- mising generation of A1 alloys the observed textures are often very pronounced and of special importance for the mechanical behaviour

(e.g. / 1 - 3 / ) . However, so far only a few more qualitative texture observations exist and a systematic investigation of rolling texture formation is still missing. .The rolling texture development in fcc materials has been investigated by means of modern ODF analysis in great detail and compared to theoretical predictions / 4 / . It has been shown how the starting conditions /5/ and the aging conditions can strongly influence the final rolling texture / 6 / . In the present work by systematic variation of these parameters their effect on the rolling texture devel3qnent in an 8090 A1-Li alloy have been analyned quantitatively.

Fig. 1 Starting texture Fig. 2 Rolling plate sections

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987370

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Experimental procedure and results

From a hot rolled 8090 A1-Li plate (25 mm thick) with a strong 1011) (211) texture (Fig. 1) three s a m ~ l e s were cut in different ways (pig. 2 ) in order-to obtain diffkrent starting textures for further cold rolling. According to the direction of the new sheet plane nor- mal with respect to the original sample coordinates (=normal plane No, rolling Ro and transverse direction To) they shall be denoted as N, R, T , respectively (Fig. 2). The corresponding different start- ing textures can be descriebed by the dominant texture components (011) (211) "B", 1112) (111) "C" and t1111 (112) "Y". I ^*

Before the final cold rolling the samples were solution heat treated for 20 min. at 5 0 0 ' ~ in order to improve formability. One set (I) of samples was cold rolled immediately after quenching. A second set (11) was rolled after being kept for 30 days at room tem- perature. A third set (111) was artificially aged for 1 h at 190-c

(i.e. to an underaged condition ) . For sample set I specimens were taken at 50%, 7 5 % , 90%, 95% and 98% rolling reductions. For sets I1 and I11 (except for samples N) only 50% cold rolling reduction could be achieved due to embrittlement of the material.

Fig. 3=50%red. (Contour Levels: 1-2-4-7-12)

Fig. 4=95%red. (Contour Levels: 1-2-4-7-12) Fig. 3 and 4 1111) Pole figures of A1-Li rolling textures

I * ^B and C correspond to the well known "brass"- and "copperu-orien-

tation but single letters are chosen as abreviations as proposed

in / 4 / for convenience and in order to avoid misinterpretation.

7 ' 4 ' . \P, = const.

1 . ^{I h l} 1 ^{A h} 1 1

a ) N 95% red

7 '+“ v,= const.

Fig. 5 ODFs of two typical rolling textures of samples N and R plot- ted in sections o f y =const. of the Euler space 2

Texture measurements were carried out on a fully automatic X-ray texture goniometer /7/. In reflection mode four incomplete pole figures ( flll), {2003, 12201, 11133) were measured and correct- ed with respect to defocussing error and background intensity. In Figs. 3 and 4 some examples of {I113 pole figures (normalized to random intensity) are given for the rolling textures after 50% and 95% reduction of samples I. The 3-dimensional orientation distribu- tion functions (ODFs) were calculated by the series expansion method

/ 8 / . In Fig. 5 two of them are presented in the 3-dim. Euler angle

space (yl, # , y2) in sections of y2=const. They are ghost corrected according to the method of Lticke et a1 /lo/. Further evaluation of the abstract ODF data by Gauss model calculation and sceleton line analysis /9/ was carried out. So a more comprehensive texture repre- sentation could be achieved either by giving the volume fractions of the Gauss model components which fit best to the experimental textures (Fig. 6) or by plotting the lines of maximum orientation density (Figs. 7).

After high reduction the rolling textures of the sample N shows the typical pure metal (copper) type rolling texture with a preferred [123]<634) S orientation (Fig.3,sa) It consists of a ra- ther homogeneously occugied 9rien;ation tube in$erse$ting the 1.

Euler-spac? from C (90 , 30 , ⁴⁵ ) over S (59 , 34 , 63') towards B (34 , 45 , 90').The Stexture is developed quite fast up to 50%

volume fraction (Fig. 6a) out of the initial C011)(211) B texture (Fig. I). For sample R the initially present /112)<111) C texture dominates in the final rolling texture (Fig.4,sb)with a density maxi- mum of f(g)= 57 and 80% volume fraction at 90% red. (Fig. 6b, com- bined with its TD scatterings). Also sample T develops a strong 11121

(111) C texture but slower and less sharps than sample R (Fig. 6c).

JOURNAL DE PHYSIQUE

In the final textures sytematic scatterings of the main tex- ture components occur and besides the stable orientations soFe micor c9mponents can be observed in Fig. 5 , n a ~ e l y ~ i01&) (100) G (0 , 45 ,

0 ) and near i001j (110) ND rot. Cube (45 , 0 , 0 ) . The latter is part of a TD scattering of the strong 11121 (111) C component in sam- ple R (Fig. 5b) and T, and it is slightly shifted around ND for sam- ple N (Fig. 5a).For series I1 and I11 only results of sample N could be obtained since samples R and T fractured at 50% reduction.These results of series 111 textures are comparable to that of series I except for a somewhat stronger B orientation. A typical 11111 pole figure of series I1 (aged at room temperature) is shown in Fig. 8.

It shows an even stronger B component(than samples I11 ) , also pre- sent in the initial hot rolling texture (Fig. 1).

Discussion

80Cj% 50% 75% 9p% 95%-%red. ,,Y/O ^{5O0/0 75% 9 '10 95%--3~d.}

i----i- ^- -1-

The rolling textures in cold rolled 8090 A1-Li show the typical fea- tures of the pure metal (copper) type rolling texture with its nain texture components: -{111) (112) C,

11233 <634> S and*foll] 011) B.

As could be shown in the present work by a detailed and quantitative ODF analysis the volume of these three components as well as their exact orientation strongly depend on the pretreatment, i.e. on the starting texture and on the aging conditions.

M I % . N MI '10-

I

40 -

Ph

20

,,'*

'o':, T-

-\ ^{X X r} Ph ^{I X}

O 6 I 2 3 i ' 6 1 2 3

- F

a ) b l 4

- E

,,Ox 50Y0 75% 9p/, 95%-%red.

MI %.

obtained from Gauss model analy- sis/9/.(The Mi of similar compo- nents are added and combined in one symbol in Fig. 6b).

symbol {hkl) (uvw) yp,. ^{0, y12} 11.1 0: 0 = (011) (211) 359LSV, 0' 5: 0 -- (123) (634) 59', 374 63"

C : A = {112) (111, 90",3s0. 45' Ph x = phon [random background) 4

T

Fig. 6 Volume fractions M of the

main rolling texture components,

The main features of the observed rolling texture development in series I are comparable to texture effects observed in pure A1

/ 4 , 5/. By comparison with theoretical predictions calculated on

the base of Taylor type theories under full constraints (PC) and relaxed constraints (RC) conditions they can be interpreted as (111) [110] multiple slip /4/. In Fig. 7 the resuLts of all 90% samples of series I and of sample N I1 (where the strongest textures were observed) are plotted in form of the maximum orientation densities along thefj-fibre (Fig. 7a) and their exact orientations in the Euler space, i.e. yl and p , as function of (Fig. 7b). Depending on the starting cond~tions a dominant ill21 (1f1) C texture component is found in samples R and T (9 =45 ) the latter being less sharp and expanding to the B componen$ ( y =90°) due to a certain part of grains, which were less favoura$ly oriented. Here only one part of the initial {ill) (112) Y texture component directly rotates into the stable El121 (111) C component while the rest first rotates to- wards {Oll] (100) G and 1011) (211) B and from these along the/3-fib- re towards C. This behaviour agrees very good with the predictions of the FC Taylor model (filled triangles i? Fig. 7). The exact orien- tation of the experimental peak is about 3 off the theoretical posi- tion. It shifts towards the prediction of the RC model, (calculated for relaxed shears parallel to the sheet plane, i.e. CNR and ENT),

p-fibre (orientation)

70°- Ip1

6 oO-

5 o0-

4 o0-

4 so 6 0 " 7S0

b 1 - ^{P H I 2}

Fig. 7 Sceleton line analysis of some rolling textures and comparison with theoretical predictions (normalized by changing the Gaussian half scatter width ( * ) of the 936 grains used for rolling texture simulation /4/).

a) Orientation density f(g)max b) Exact orientation in Euler space

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indicating a certain amount o f € shear to 'cake place.' The curves of sample N, however, are much cY8ser to the RC lines (filled circles in Fig. 7). This effect can be explained by the flat grains in sample N due to the preserved initial pre rolling structure, so that here the best conditions for relaxed shears exist which results in the observed stability of the S-orientation /4,11/.

The loll) ( 2 1 1 ) B orientation, however, is never preferred in one of the series I samples. This orientation is stable under conditions with no constraints (NC) by activation of only two slip systems. But it requires the relaxation of ETR shear which is most improbable for flat grains. Obviously the strong initial B component cannot maintain its stability (sample N).The B component and thus a certain preference for single slip i dominant in the age hardened series I1 samples. The fine coherent 8 particles being precipitated at room temperature can be cut by dislocations which causes a local softening effect on a slip system, once it has been activated. So only few slip systems remain active (regardless of local strain in- compatibilities), thus avoiding the S and C orientation which are stable under multiple slip conditions / 4 / . A similar mechanism might be active at high temperature rolling where also the B component predominates (Fig. 1). This texture component has the advantage to be much less sensitive to embrittlement under rolling in an aged condition where no cracking of the N samples was observed. In con- trast for samples R and T only limited reductions could be achieved.

Fig. 8 {lll] pole figure of 90% cold rolled RT aged sample NII

Fig. 9 Cracks on longitudinal surface of sample N I11 after 75% cold rolling reduction

In contrast to pure A1 the main rolling texture components show characteristic scatterings in the ODF, mainly in $ direction (Fig. 5). Parallel to the occurance of these scatterings a certain decrease of the main texture peaks can be observed (Fig. 6). For the samples R and T the C peak scatters around the transverse direc- tion, which can already be observed in the {111] pole figures (Fig.

4b, c). The wide scattering to sma4l g*values results in a density

peak of f(g)= 5 at {0011 <110) (45 , 0 , o~,). For sample N also a

new peak is found there, but somewhat rotated around ND, according

to the,dominant S peak which is also ND rotated with respect to the

C orientation. This type of scatterings have been interpreted as

rotated matrix areas adjacent to particles. The preferred scattering

towards {oo~] (110) then would indicate a stronger hindering effect of particles on dislocations of the coplanar pair of slip systems of the {I121 (111) C orientation possibly due to enhanced cross slip on the second active slip system pair with a common slip direction.

However, the observed very large scattering of the peaks would re- quire enormous dislocation pile ups which cannot be expected for these very fine dispersed and coherent particles. Therefore also another interpretation of orientation changes by TD rotation caused by a mechanism of intensive shear band formation must be considered which causes preferred cracking in the C oriented aged material.

Shear band formation also causes cracking observed on the longitudi- nal surfaces of the rolled sheets of aged material (e.g. Fig.9) and failiure of the C oriented samples I1 and 111.

Summary

The textures in cold rolled A1-Li alloys consist of the three main rolling texture components in fcc metals: ill21 (111) C , f123j (634) S and {011] (211) B-orientation. It has been shown that the amount of volume of each of these components and their exact orientation strongly depends on the three structural parameters: initial texture, grain shape and aging. Thus by variation of these three parameters a control of the final rolling texture within the given limits of stable textures can be achieved. Minor texture components and syste- matic scatterings are due to inhomogeneous deformation mechanisms.

References

/ 1/ M. Peters, J. Eschweiler, K. Welpmann, Scripta Met. 20(1986)259 / 2/ S. Fox, D.S. McDarmaid, H.M. Flowers, "Aluminium Technologyr86"

The Institute of Metals, London 3/B(1986)72

/ 3/ M.J. Bull, D.J. Lloyd, Proc. 3. Int. AlLi Conference The Institute of Metals, London (1986)402

/ 4/ J. Hirsch, K. Lucke, Acta Met. (1987) accepted

/ 5/ J. Hirsch, W. Mao, K. Liicke, "Aluminium Technology '86"

The Institute of Metals, London 3/B (1986) 66

/ 6/ K. Lucke, J. Hirsch, 0. Engler, T. Rickert, Proc. Int. Conf.

on A1 alloys, Charlottesville-Virginia (1986) Vol.111

/ 7/ J. Hirsch, G. Burmeister, L. Hoenen, K. Lucke, in "Experimental Techniques of Texture Analysis" ed. H.J. Bunge, DGM-Verlag

(1986)63

/ 8/ H. j. Bunge, "Mathematische Methoden der Texturanalyse" , Akademie Verlag Berlin (1969)

/ 9/ J. Hirsch, M. Loeck, L. Loof, K. Lucke, Proc. ICOTOM7, Noord- wijkerhoud (1984)765

/lo/ K. Lucke, J. Pospiech, K.H. Virnich, J. Jura, Acta Met. 29 (1981) 167

/11/ J. Hirsch, K. Lucke, H. Mecking, Proc. ICOTOM 7, Noordwijkerhoud

(1984) 83