HAL Id: jpa-00226555
https://hal.archives-ouvertes.fr/jpa-00226555
Submitted on 1 Jan 1987
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
VARIATION IN STRUCTURE AND PROPERTIES IN AN Al-Li-Cu-Mg-Zr ALLOY PRODUCED BY
EXTRUSION PROCESSING
A. Mukhopadhyay, H. Flower, T. Sheppard
To cite this version:
A. Mukhopadhyay, H. Flower, T. Sheppard. VARIATION IN STRUCTURE AND PROPERTIES IN AN Al-Li-Cu-Mg-Zr ALLOY PRODUCED BY EXTRUSION PROCESSING. Journal de Physique Colloques, 1987, 48 (C3), pp.C3-219-C3-228. �10.1051/jphyscol:1987325�. �jpa-00226555�
JOURNAL DE PHYSIQUE
Colloque C3, suppl6ment au n09, Tome 48, septembre 1 9 8 7
VARIATION I N STRUCTURE AND PROPERTIES IN AN Al-Li-Cu-Mg-Zr ALLOY PRODUCED BY EXTRUSION PROCESSING
A.K. MUKHOPADHYAY, H.M. FLOWER and T. SHEPPARD
I m p e r i a l C o l l e g e , D e p a r t m e n t of M a t e r i a l s , GB-London SW7 2 B P ,
G r e a t -Bri t a i n
Synopsis
The e f f e c t s o f e x t r u s i o n processing v a r i a b l e s on t h e s t r u c t u r e and p r o p e r t i e s o f an A1 -Li-Cu-Mg-Zr a1 l o y (8090 t y p e ) have been i n v e s t i g a t e d . A combination o f l i g h t and transmission e l e c t r o n microscopy have been used t o c h a r a c t e r i s e t h e as extruded m i c r o s t r u c t u r e s and t h e p r e c i p i t a t i o n r e a c t i o n s which take p l a c e on subsequent h e a t treatment. The corresponding mechanical p r o p e r t i e s have been determined by hardness, t e n s i l e and f r a c t u r e toughness t e s t methods. As extruded t e n s i l e p r o p e r t i e s are a f f e c t e d by t h e processing v a r i a b l e s w h i l s t w i t h i n heat t r e a t e d m a t e r i a l the p r e c i p i t a t i o n processes c o n t r o l t h e mechanical p r o p e r t i e s o f t h e a l l o y . The e f f e c t s o f v a r i a t i o n i n heat treatment i n v o l v i n g n a t u r a l ageing and s t r e t c h i n g on t h e f r a c t u r e toughness are discussed i n r e l a t i o n t o the m i c r o s t r u c t u r a l changes produced. By s u i t a b l e process and heat treatment c o n t r o l , good combinations o f s t r e n g t h , toughness and d u c t i l i t y can be obtained.
I n t r o d u c t i o n
The widespread use o f aluminium a l l o y s c o n t a i n i n g l i t h i u m has, u n t i l q u i t e r e c e n t l y , been hindered because o f t h e inadequate f r a c t u r e p r o p e r t i e s which are t y p i c a l o f s u p e r l a t t i c e a l l o y s i n which co-planar s l i p and subsequent s t r a i n l o c a l i s a t i o n leads t o premature g r a i n boundary f a i l u r e . The r e c e n t widespread development o f q u a r t e r n a r y Al-Li-Cu-Mg a l l o y s appears t o have, a t l e a s t p a r t i a l l y , overcome t h i s problem by i n t r o d u c i n g p r e c i p i t a t i o n r e a c t i o n s i n v o l v i n g t h e S (A12CuMg) and lj (A12CuLi) phases i n a d d i t i o n t o t h e 5 ' (A13Li) s t r e n g t h e n i n g p r e c i p i t a t e . The f o r m a t i o n o f t h e S phase concurrent w i t h 6' p r e c i p i t a t i o n has been shown1 t o promote d u c t i l i t y and toughness by d i s p e r s i n g co-planar s l i p and hence producing a commercialty acceptable balance o f p r o p e r t i e s . I n the U n i t e d Kingdom LITAL A and LITAL B were developed w h i l s t i n t h e U n i t e d States t h e q u a r t e r n a r y a l l o y s 8090, 8091, 2090 and 2091 w i t h m o d i f i e d compositions have reached production.
These a l l o y s are l i k e l y t o f i n d a p p l i c a t i o n i n extruded product form because o f t h e complex shapes which can r e a d i l y be produced by t h e process.
Moreover, i n conventional aluminium a1 l o y s 2 o p t i m i s a t i o n o f t h e process leads t o t h e p r o p e r t i e s being s i g n i f i c a n t l y modified, u s u a l l y r e s u l t i n g i n improved s t r e n g t h and toughness. A r e c e n t study by Parson and sheppard3 i n d i c a t e d t h e e x t e n t t o which processing would s i g n i f i c a n t l y vary t h e p r o p e r t i e s i n an A1-Mg-Li-Cu a l l o y . However, t h e a l l o y had a composition q u i t e d i f f e r e n t t o those c u r r e n t l y being pursued commercially. The work r e p o r t e d i n t h i s communication concerns t h e e f f e c t o f e x t r u s i o n processing on t h e s t r u c t u r e and p r o p e r t i e s o f an a l l o y encompassed by t h e AA 8090 s p e c i f i c a t i o n .
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987325
JOURNAL DE PHYSIQUE
Experimental Procedure
Material was supplied by the Aluminum Company of America in the form of 75mm diameter billets machined out of DC cast i n g o t s . The c o m p o s i t i o n
of the alloy is given in Table I.
TABLE I. Alloy Composition in wt%
2.50 1.04 1.11 0.12 0.04 0.04 0.01 bal
Billets were homogenised in an air circulating furnace, the lithium depleted layer being machined off before extrusion. Extrusion was psrformed in the direct mode in a 5MN press with a 75mm diameter container. Ram speeds utilised were in the range of 3-15 mm s-I and the round bar extrusion ratio varied from 20:i t o 80:l. Initial billet temperatures were varied from 400°C to 500°C. The material could not be extruded below 350°C using a 20:l reduction ratio and the lowest ram speed whilst the highest orocessing temperature was restricted to 500°C to avoid the risk of incipient melting. Heating for extrusion was by induction giving a heat-up rate of 125OC/min and the electrically heated press container was maintained at 30°C below the initial billet temperature. Unless otherwise stated, all extrusions were press quenched.
All high temperature solution treatments and low temperature ageing treatments were carried out in the air circulating furnaces. A standard solution treatment temperature of 530°C was used throughout. Extrudes made a t 500°C were solutionised for 2 0 minutes while 4 0 minutes was employed for the products of lower temperature extrusion. Ageing was performed at 190°C. Heat treatments were established from age-hardening curves to give three tempers, underaged (UA), peak aged (PA) and overaged (OA). The hardness data were obtained using a Vickers diamond indenter with a lOkg load. A combination of light microscopy, using anodised surfaces and polarised liqht, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used t o characterise the microstructures and the precipitation reactions which took place on subsequent heat treatment. TEM foils were electropolished by standard methods using a 30% nitric acid/70% methanol solution.
Tensile testing was performed on standard Hounsfield-13 and Hounsfield-12 tes pieces using a cross head speed of 0.2mm/minute. A
8
modified Terratek short rod fracture toughness test was used t o assess fracture properties. This method produces excellent correlation with K I C values determined in accordance with ASTM method E399.
Results and Discussion
As-Cast Material and Homogenisation
In the as-cast material the phases observed within the matrix and at the grain boundaries were copper-r.i ch. The precipitates within the matrix were found to have an average composition o f 15-19%Cu, 2.5%Mg (balance A1 ) and some contained a fine periodic stacking fault structure indexed as cubic with a = 2.09nm resembling the Li bearing C phase recently reported5. Analysis for Li could not be made and hence these precipitates remained unspecified. Grain boundaries were decorated with an Al-Cu-Mg eutectic of average composition 22%Cu, 5.5%Mg (balance Al) and an unidentified iron rich phase (9%Fe, 5%Cu, 4'2349, <1%Si [bal A l l ) was also present in small volumes. Differential scanning calorimetry revealed a eutectic melting temperature of 547OC and almost complete dissolution of these phases was achieved by homogenising at 537OC for 2 4 hours.
Effect of Processing Variables on the Product Structure
For all the extrusion conditions investigated the surface region was fully recrystallised, the core essentially unrecrystallised and the mid-radius location parria I l y recrystal 1 ised (except for material extruded be1 ow 450°C). An increase in extrusion temperature increased the volume fraction recrystallised, the grains becoming finer and more uniformly distributed. At the lower temperatures the recrystallised grains were observed to be coarser. Increasing the ram speed or the reauctlon ratio increased the depth of the recrystallised annulus and the core increasingly exhibited partial recrystallisation. Thus as the temperature compensated strain rate is increased so is the volume fraction recrystallised. Figure 1 indicates the structural variations observed under varying process conditions. The structures illustrated in Figure 1 were extremely resistant to further static recrystallisation remaining essentially unchanged after the solution treatment at 530°C. The only modification observed in morphology was the growth of the existing small recrystallised grains. Even when the extrudates were allowed to air cool the structures remained unchanged. This inhibition of static recrystallisation in Z r containing A1-Li alloys has previously been observed. by Makin and stobbs6 who attributed the phenomenon to the solute drag effect of Li on grain boundaries together with boundary pinning by AlgZr precipitates.
The present observations were a clear indication that the recrystallisation was occurring dynamically under the influence of strain during the deformation process. A consistent feature of the structures shown in Figure 1 is the banded nature of the recrystallised grains and the proximity of the nucleation points to original grain boundaries.
Inspection by TEM revealed that under all extrusion conditions, notably at lower reduction ratios and ram speeds, recrystallisation was nucleated by local migration of original grain boundaries. Figure 2 is one illustration of this mecnanism in which the portions o f the high angle boundary limiting the bulge are pinned by the second phase particles, p.
Selected area diffraction patterns covering the periphery of the bulge region (from A,B,C) confirm the high misorientation of its interface with the surrounding matrix. Recrystallisation by this mechanism could occur either during or immediately after deformation without any incubation period. This mechanism is responsible for most of the recrystallised grains observed within the press quenched structures. Since increasing ram speed, reduction ratio and temperature all increase the volume fraction of new grains, it seems likely that the process is dynamic; this is further supported by the fact that extrusions performed at lower temperatures do not subsequently recrystallise during the solution soak. TEM also revealed that this bulging mechanism was supplemented by a second process at higher- deformation rates. TEM indicated the presence of highly misoriented subgrains adjacent to original high angle grain boundaries indicating that rotation recrystallisation may also be taking place. In this mechanism these subgrains must rotate to accommodate the inhomogeneous strain at the originai boundary thus formtng a new high angle boundary with both original grains. These new grains were frequently observed to contain substructures indicating the process to be dynamic and similar to that recently shown to be responsible for recrystallisation in A1-Mg a1 1 oys7.
Extrudates produced at 500°C remained single phase during extrusion.
However, at lower temperatures coarse (<lkm) intragranular Cu,Mg rich particles were produced as a result of the thermal exposure (Figure 3).
C3-222 JOURNAL l3E PHYSIQUE
The E f f e c t o f Process and Heat Treatment Parameters on T e n s i l e P r o p e r t i e s
As-Extruded P r o p e r t i e s
T e n s i l e t e s t i n g was performed on extrudates processed a t v a r y i n g temperatures and r e d u c t i o n r a t i o s and a ram speed o f 3mm/sec. The r e s u l t s are presented i n F i g u r e 4 which i n d i c a t e s t h a t t h e t e n s i l e s t r e n g t h i s increased bv both i n c r e a s i n g temperature and r e d u c t i o n r a t i o b u t d u c t i l i t y i s r e l a t i v e l y i n s e n s i t i v e t o t h e processing parameters b u t i s l e a s t where t h e volume f r a c t i o n o f Cu,Mg r i c h p a r t i c l e s i s g r e a t e s t and t h e degree o f r e c r y s t a l l i s a t i o n i s l e a s t a f t e r e x t r u s i o n a t 400°C. The v a r i a b l e s had a s i m i l a r e f f e c t on p r o o f s t r e s s except a t t h e h i g h e s t e x t r u s i o n temperature where t h e p r o p e r t i e s were observed t o decrease w i t h i n c r e a s i n g e x t r u s i o n r a t i o . This i s c o n s i s t e n t w i t h t h e increased volume f r a c t i o n r e c r y s t a l l i s e d observed i n t h e m i c r o s t r u c t u r e s . The general increase i n s t r e n g t h w i t h temperature and e x t r u s i o n r a t i o i s most probably due t o t h e s o l u t i o n i s i n g e f f e c t as t h e temperature of t h e emergent extrude i s increased due t o e i t h e r increased i n i t i a l thermal energy o r conversion o f work t o heat d u r i n g t h e process.
Heat Treated P r o p e r t i e s
The age hardening curves f o r t h e a l l o y s o l u t i o n i s e d f o r 20 minutes a t 530°C i n d i c a t e d t h a t e x t r u s i o n a t e i t h e r 500°C o r 400°C r e s u l t e d i n t h e same peak hardness b u t t h e 400°C e x t r u d a t e had i n f e r i o r p r o p e r t i e s p r i o r t o peak. TEM i n v e s t i g a t i o n revealed incomplete s o l u t i o n i s i n g of t h e Cu,Mg r i c h p a r t i c l e s produced by 400°C e x t r u s i o n . I n c r e a s i n g t h e s o l u t i o n time t o 40 minutes r e s u l t e d i n i d e n t i c a l behaviour i n b o t h t h e 400°C and 500°C extrudates; i t was, t h e r e f o r e , adopted as t h e standard s o l u t i o n treatment f o r extrudes produced beTow 500°C.
The v a r i a t i o n i n t e n s i l e p r o p e r t i e s i n t h e f u l l y s o l u t i o n i s e d and aged c o n d i t i o n (T6) i s shown i n Figures 5 and 6. The p r o p e r t i e s i n t h e underaged, peak aged and overaged c o n d i t i o n s a r e presented as f u n c t i o n s o f t h e r e d u c t i o n r a t i o and two e x t r u s i o n temperatures. The p r o p e r t i e s do n o t appear t o be extremely s e n s i t i v e t o t h e processing v a r i a b l e s although d i f f e r e n c e s can be detected; both i n c r e a s i n g e x t r u s i o n r a t i o and i n c r e a s i n g temperature l e a d t o improved elongations and small d i f f e r e n c e s i n t e n s i l e s t r e n g t h . The p r o p e r t y d i f f e r e n c e s a t l e a s t f o r round r o d e x t r u s i o n , are e l i m i n a t e d by t h e ageing sequence.
I n t h e peak aged c o n d i t i o n , TEM i n d i c a t e d t h a t both homogeneously nucleated 6' and S phases were present t o g e t h e r w i t h sparse heterogeneously nucleated S and TI phase p a r t i c l e s on sub-boundaries ( F i g u r e 7 ) . The homogeneously d i s t r i b u t e d 6'and S gave r i s e t o h i g h s t r e n g t h (UTS = 580MPa) and reasonable d u c t i l i t y ( = 7% e l . ) i n t h e peak aged m a t e r i a l . The observation o f homogeneously nucleated S phase i s c o n s i s t e n t w i t h p r e v i o u s work which i n d i c a t e s t h a t as t h e upper end o f t h e L i t a l A s p e c i f i c a t i o n i a n g e t h e Cu + Mg c o n c e n t r a t i o n a r e s u f f i c i e n t t o cause such p r e c i p i t a t i o n . Natural ageing f u r t h e r promoted homogeneous S p r e c i p i t a t i o n and delayed t h e onset o f overaging i n t h e a r t i f i c i a l l y aged c o n d i t i o n ; on t h e other hand, s t r e t c h i n g p r i o r t o ageing promoted heterogeneous f o r m a t i o n o f S a t t h e expense o f homogeneous p r e c i p i t a t i o n ( F i g u r e 8 ) .
E f f e c t o f Heat Treatment on t h e F r a c t u r e Toughness
The e f f e c t o f v a r y i n g h e a t treatment c y c l e on t h e f r a c t u r e toughness o f t h e a l l o y has so f a r o n l y been i n v e s t i g a t e d f o r an e x t r u s i o n performed a t 500°C, 20:l and ram speed o f 3mm/sec. I n a l l cases l o a d was a p p l i e d a t 90° t o t h e e x t r u s i o n d i r e c t i o n . The v a r i a t i o n s i n heat treatment i n v o l v e d
n a t u r a l ageing and s t r e t c h i n g and combinations o f these f a c t o r s summarised i n t h e legend t o F i g u r e 9. F i g u r e 9 a l s o i n d i c a t e s t h e SR4 values obtained f o r a l l o y s AA 2014 and AA 2024 which were t e s t e d as c o n t r o l s . The a1 l o y was t e s t e d i n t h e UA, PA and OA c o n d i t i o n s as i n d i c a t e d i n t h e f i g u r e . For a l l c o n d i t i o n s t h e f r a c t u r e toughness decreased w i t h ageing t i m e and was improved by t h e i n s e r t i o n o f n a t u r a l ageing before t h e 190°C treatment; t h e exception being t h e combination o f n a t u r a l ageing and s t r e t c h i n g . Poor toughness values were i n f a c t associated w i t h any c y c l e which i n c l u d e d t h e 2% s t r e t c h .
These r e s u l t s i n d i c a t e t h e c r i t i c a l r o l e o f S phase p r e c i p i t a t i o n l n determining t h e mechanical p r o p e r t i e s . Property improvements i n t h i s a l l o y are associated w i t h t h e p r o d u c t i o n and refinement o f a homogeneous d i s t r i b u t i o n o f t h i s phase. Thus n a t u r a l ageing i s b e n e f i c i a l w h i l e s t r e t c h i n g i s d e t r i m e n t a l . T h i s may appear t o c o n f l i c t w i t h t h e conclusion o f Gregson and ~ l o w e r l t h a t s t r e t c h i n g i s b e n e f i c i a l i n a d i l u t e L i t a l A composition. However, i n t h a t work, the o n l y mode o f S n u c l e a t i o n achievable i n p r a c t i c a l heat treatment times, and i n t h e absence o f n a t u r a l ageing, was heterogeneous. Hence, s t r e t c h i n g r e f i n e d t h e d i s t r i b u t i o n o f S and improved t h e p r o p e r t i e s . I n the present case, s t r e t c h i n g encourages heterogeneous S formation a t t h e expense o f homogeneous p r e c i p i t a t i o n and thus coarsens t h e p a r t i c l e d i s p e r s i o n . The conclusion i n b o t h cases i s t h e same : refinement o f t h e S d i s p e r s i o n r e s u l t s i n improved s t r e n g t h and toughness.
Conclusions
1. An optimum homogenisation schedule was e s t a b l i s h e d f o r DC c a s t A1-2.5Li-1.OCu-l.lMg-0.12 wt%Zr a l l o y . Annealing f o r 24 hours a t 537OC r e s u l t s i n complete d i s s o l u t i o n o f t h e as c a s t phases w i t h no s i g n o f i n c i p i e n t m e l t i n g .
2. E x t r u s i o n produces m i c r o s t r u c t u r e s which v a r y through t h e extrude s e c t i o n : t h e surface was f u l l y r e c r y s t a l l i s e d w h i l s t t h e c o r e was e s s e n t i a l l y u n r e c r y s t a l l i s e d . The volume f r a c t i o n r e c r y s t a l l i s e d increases w i t h i n c r e a s i n g temperature, e x t r u s i o n r a t i o and ram speed.
It i s proposed t h a t r e c r y s t a l l i s a t i o n i s dynamic and occurs by g r a i n boundary b u l g i n g and by r o t a t i o n r e c r y s t a l l i s a t i o n .
3. The extruded s t r u c t u r e i s extremely r e s i s t a n t t o s t a t i c r e c r y s t a l 1 is a t i o n d u r i n g subsequent heat treatment.
4. The as extruded t e n s i l e p r o p e r t i e s a r e a f f e c t e d by t h e processing v a r i a b l e s ; w h i l s t , w i t h i n the heat t r e a t e d m a t e r i a l , t h e mechanical p r o p e r t i e s a r e dominated by t h e p r e c i p i t a t i o n processes which occur.
The p r o d u c t i o n o f homogeneous1 y d i s t r i b u t e d 6' and S p r e c i p i t a t e phases r e s u l t s i n h i g h s t r e n g t h ( = 580 MPa) and reasonable d u c t i l i t y
( 2 7% e l .) i n peak aged m a t e r i a l .
5. The f r a c t u r e toughness of t h e m a t e r i a l i s improved when i t i s subjected t o n a t u r a l ageing p r i o r t o a r t i f i c i a l ageing. The improvement i n p r o p e r t i e s r e s u l t s from t h e refinement o f t h e homogeneous d i s t r i b u t i o n o f S phase w i t h i n t h e m i c r o s t r u c t u r e .
Acknowledgements
The p r o v i s i o n o f a research g r a n t by t h e Aluminum Company o f America (ALCOA) i s g r a t e f u l l y acknowledged.
References
1. P. J. Gregson and H.M. Flower, Acta M e t a l l , 33, 1985, p.527.
2. T. Sheppard, "Aluminium E x t r u s i o n Technology Seminar - III", 107,
Aluminium Association, Washington, D.C., 1986.
3. N.C. Parson and T. Sheppard, "Aluminium-Lithium A l l o y s III", 2 2 2 , ed. D. Baker, P.J. Gregson, S.J. H a r r i s and C.J. Peel, I n s t . Metals, London, 1986.
C3-224 J O U R N A L D E PHYSIQUE
4. "A Simp1 i f i e d Method f o r Measuring Plane S t r a i n F r a c t u r e Toughness", Engineering F r a c t u r e Mechanics, 2, No.2, 1977, p.361.
5. A. Loiseau and G. Lapasset, J. de Physique, 47, 1986, C3-331.
6. P.L. Makin and W.M. Stobbs i n Ref.3, p.392.
7. F.J. Humphreys and M.R. Drury, "Aluminium Technology '86", ed.
T. Sheppard, I n s t . M e t a l s . London, 1986, p.191.
8. H.M. Flower and P.J. b r e a s o n . Mat.Sci.Tech., 3, 1987, p.81.
FIGURE 1. Extrudate Grain S t r u c t u r e
(a) 500°C, 20: 1 , extrudate surface; (b) 400°C, 20: 1, extrudate surface (c) 500°C, 20:1, extrudate core, (d) 500°C, 80:1, extrudate core (e) 450°C, 20:1, extrudate core when annealed for 5 hours a t 530°C
under argon atmosphere.
FIGURE 2. TEM micrograph showing recrystallisation by grain boundary bulging mechanism.
FIGURE 3 . Precipiiation of second phase particles formed due to an i n i t i a l b i l l e t temperature of 400°C;
TEM micrograph of longitudinal section.
C3-226 JOURNAL DE PHYSIQUE
AS EXTRUDED
520
I
TENSILE PROPERTIES
360 1
5 0 0 ~ ~ INITIAL
7 4 5 0 0 ~ BILLET 4 0 0 ~ ~ TEMPERATURES W 10
Fig.4
20:l 50:l 80:l REDUCTION RATIO
T 6 TENSILE PROPERTIES
BILLET TEMPERATURE - 4 0 0 ~ ~ ~ ~ ~
4 5 0 I 350
U.A. P.A. O.A. U.A. P.A. O.A.
20:l REDUCTION RATIO U.A. P.A. O.A.
630 t T6 TENSILE PROPERTIES 550 f
610 INITIAL BILLET TEMPERATURE -
450 I
_
U.A. P.A. O.A.
350
U.A. P.A. O.A.
"'1
S/+
0 80:l 50:lW 6 A 20:1
* 4 REDUCTION RATIO
Fig.6 2
U.A. P.A. 0.A.
FIGURE 7. Homogeneous S p r e c i p i t a t i o n within t h e material when s o l u t i o n - t r e a t e d , water quenched and aged f o r 24 hours a t 190°C; <loo> A1 o r i e n t a t i o n .
C3-228 JOURNAL DE PHYSIQUE
FIGURE 8. S p r e c i p i t a t i o n within t h e material when s o l u t i o n t r e a t e d , water quenched and ( a ) 2% s t r e t c h e d , ( b ) NA 1 month and 2% s t r e t c h e d , ( c ) NA 1 month and a r t i f i c i a l l y aged f o r 24 hours a t 190°C.
( a ) and (c) (<110> A1 o r i e n t a t i o n ) , ( b ) (<112> A1 o r i e n t a t i o n ) .
6 -
U.A P.A. O.A.
SHORT ROD FRACTURE TOUGHNESS
1 INDICATOR TEST
26 24
-
- .k AA 2024
22 -
20 - NATURALLY AGED ( NA 1 1 MONTH
jt AA 2014
18 - ( U O . Z = 4 1 0 MPa 1
o NA 1 MONTH , 2 % STRETCHED
16 -
14 - 2% STRETCHED
10 NO PREAGEING TREATMENT
8
