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THE DEVELOPMENT OF 8090 AND 8091 ALLOY EXTRUSIONS
M. Reynolds, E. Creed
To cite this version:
M. Reynolds, E. Creed. THE DEVELOPMENT OF 8090 AND 8091 ALLOY EXTRUSIONS. Journal de Physique Colloques, 1987, 48 (C3), pp.C3-195-C3-207. �10.1051/jphyscol:1987323�. �jpa-00226553�
JOURNAL D E PHYSIQUE
C o l l o q u e C 3 , supplbment au n o 9 , Tome 48, septembre 1987
THE DEVELOPMENT OF 8090 AND 8091 ALLOY EXTRUSIONS
M.A. REYNOLDS and E. CREED
Alcan I n t e r n a t i o n a l L t d . , Southam road. B a n b u r y , GB-Oxon OX16 7SP. G r e a t - B r i t a i n
ABSTRACT
T h i s paper f o c u s e s a t t e n t i o n on t h e m a n u f a c t u r i n g , mechanical p r o p e r t i e s , and m i c r o s t r u c t u r a l a s p e c t s of 8090 and 8091 a l l o y s i n t h e e x t r u d e d form. The paper draws upon t h e e x p e r i e n c e of commercially e x t r u d i n g t h e a l l o y s a t Alcan High Duty E x t r u s i o n s and upon t h e r e s u l t s of e x t r u s i o n t r i a l s c a r r i e d o u t by Alcan
I n t e r n a t i o n a l . These t r i a l s d e a l t w i t h s p e c i f i c a s p e c t s of e x t r u s i o n s , i n
p a r t i c u l a r t o show t h e i n t e r p l a y between t h e v a r i o u s p r o c e s s p a r a m e t e r s i n v o l v e d i n f a b r i c a t i n g e x t r u d e d p r o d u c t s u i t a b l e f o r a e r o s p a c e a p p l i c a t i o n . The paper w i l l show how s u c h f a c t o r s a s e x t r u s i o n c o n d i t i o n s ( p r e h e a t t e m p e r a t u r e and e x t r u s i o n s p e e d , e x t r u s i o n r a t i o , a s p e c t r a t i o ) and f i n a l thermomechanical t r e a t m e n t s ( s t r e t c h i n g and a g e i n g ) i n f l u e n c e t h e a l l o y ' s m i c r o s t r u c t u r e . The v a r i a t i o n i n mechanical p r o p e r t i e s , i n p a r t i c u l a r s t r e n g t h and f r a c t u r e t o u g h n e s s , w i l l be d i s c u s s e d i n terms of t h e m i c r o s t r u c t u r e s observed. Emphasis is placed on examining t h e s i m i l a r i t i e s and d i f f e r e n c e s between t h e b e h a v i o u r of t h i n (2 mm) and t h i c k (25 mm) e x t r u s i o n s .
INTRODUCTION
The background t o t h e development f he Al-Li-Cu-Mg-Zr a l l o y s , d e s i g n a t e d 8090 and 8091 h a s been r e p o r t e d and i n i t i a l d a t a h a s been p r e s e n t e d t o show t h e p r o p e r t i e s which can be ~ b t a i n e d ( l , ~ ' ~ ) . T h i s paper d e a l s w i t h t h e p r o p e r t i e s of e x t r u s i o n s . The e x t r u s i o n of 8090 and 8091 a l l o y s h a s been found t o b e r e a d i l y a c h i e v e d i n commercial p r a c t i c e , e x c e p t f o r r e c t i f i c a t i o n , where t h e h i g h modulus c a n l e a d t o d i f f i c u l t i e s i n m a i n t a i n i n g t h e h i g h t o l e r a n c e s r e q u i r e d f o r a e r o s p a c e a p p l i c a t i o n s . The work r e p o r t e d h e r e i n c o n c e r n s b o t h t h e e f f e c t of e x t r u s i o n c o n d i t i o n s and p o s t e x t r u s i o n h e a t t r e a t m e n t on m i c r o s t r u c t u r e and mechanical p r o p e r t i e s .
P a r s o n e t a 1 ( 4 * 5 ) have shown t h a t e x t r u s i o n c o n d i t i o n s a f f e c t t h e m i c r o s t r u c t u r e and p r o p e r t i e s of A1-Li-Cu-Mg a l l o y s b u t have n o t s t u d i e d t h e c o m p o s i t i o n s developed by Alcan. M i c r o s t r u c t u r a l f e a t u r e s of importance t o b o t h t h e s t r e n g t h and f r a c t u r e toughness of t h e s e a l l o y s which a r e determined by changes i n t h e e x t r u s i o n c o n d i t i o n s a r e sub-grain s t r u c t u r e and t h e d e g r e e of r e c r y s t a l l i s a t i o n .
E x t r u s i o n t r i a l s were c a r r i e d o u t under a wide r a n g e of p r o c e s s i n g c o n d i t i o n s t o produce m a t e r i a l w i t h v a r i a t i o n s i n m i c r o s t r u c t u r e . The e x t r u s i o n c o n d i t i o n s were chosen t o c o v e r t h e r a n g e of v a r i a b l e s e n c o u n t e r e d i n commercial p r a c t i c e . The e f f e c t of t h e s e v a r i a b l e s on m i c r o s ~ r u c t u r e and mechanical p r o p e r t i e s is d e t a i l e d i n t h i s paper.
Data i s a l s o p r e s e n t e d from commercially produced e x t r u s i o n s . M a t e r i a l from t h i s s o u r c e h a s been used t o show how a s p e c t r a t i o , s e c t i o n t h i c k n e s s , and p o s t e x t r u s i o n h e a t t r e a t m e n t i n f l u e n c e mechanical properties. P a r t i c u l a r a t t e n t i o n is given t o
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987323
C3-196 JOURNAL DE PHYSIQUE
t h e F i n a l Thermo Mechanical T r e a t m e n t (FTMT) and i t w i l l be shown how t h e s e f a c t o r s ( s t r e t c h i n g and a g e i n g c o n d i t i o n s ) can d r a m a t i c a l l y a l t e r t h e b a l a n c e of s t r e n g t h and t o u g h n e s s .
The b i l l e t employed was a l l machined from r e c t a n g u l a r s e c t i o n s l a b c a s t i n t h e A1-Li c a s t i n g c e n t r e a t Alcan P l a t e , Birmingham.
EXPERIMENTAL PROCEDURE
E x t r u s i o n t r i a l s were c a r r i e d o u t o n commercial e x t r u s i o n p r e s s e s . Two s e c t i o n s i z e s were used, namely 100 mm x 25 mm and 20 nrm x 2 mm. F o r t h e l a r g e r s e c t i o n 8090 b i l l e t s of 210 mm d i a m e t e r were used ( s e e T a b l e 1 f o r c o m p o s i t i o n ) . These b i l l e t s were homogenised 24 h a t 5 5 5 ' ~ b e f o r e b e i n g p r e h e a t e d t o t h e r e q u i r e d e x t r u s i o n t e m p e r a t u r e u s i n g a g a s - f i r e d oven. The c o n t a i n e r t e m p e r a t u r e was s e t a t 380°C and a 90 mm l o n g d i s c a r d was used. E x t r u s i o n p r e h e a t t e m p e r a t u r e was v a r i e d from 355OC t o 485OC and e x t r u s i o n speed ranged from 1.6 m/min t o 8.0 m/min. The e x t r u d e d s e c t i o n s were s o l u t i o n t r e a t e d f o r 1 h r a t 52S°C, c o l d w a t e r quenched, and s t r e t c h e d 2.5%. E x t r u d i n g 100 m x 25 nrm f l a t b a r from 210 nrm d i a m e t e r b i l l e t g i v e a n e x t r u s i o n r a t i o of 14: 1.
The s m a l l e r s e c t i o n , 20 mn x 2 mm, was e x t r u d e d from 66 mm d i a m e t e r b i l l e t s ( e x t r u s i o n r a t i o 8 5 : l ) . Both 8090 and 8091 b i l l e t s were e x t r u d e d ( s e e Table 1 f o r c o m p o s i t i o n s ) . The b i l l e t s were i n d u c t i o n p r e h e a t e d t o t h e r e q u i r e d t e m p e r a t u r e . The c o n t a i n e r t e m p e r a t u r e was s e t a t 440°C and a 10 arm d i s c a r d used. E x t r u s i o n p r e h e a t t e m p e r a t u r e was v a r i e d from 400°C t o 500°C and e x t r u s i o n speed ranged from 2 mlmin t o 20 m/min. The e x t r u d a t e was s o l u t i o n t r e a t e d f o r 15 d n s a t 54OoC, c o l d w a t e r quenched and s t r e t c h e d 2%.
S e l e c t e d e x t r u s i o n s were a l s o examined which had been produced under commercial e x t r u s i o n c o n d i t i o n s i n B r i t i s h Alcan. T h i s p a r t i c u l a r l y a p p l i e s t o t h e d a t a on t h i c k 8091.
T e n s i l e and f r a c t u r e t o u g h n e s s t e s t i n g was c a r r i e d o u t on t h e e x t r u d e d s e c t i o n s . I n t h e c a s e of t h e 100 mm x 25 mm s e c t i o n f r a c t u r e t o u g h n e s s was determined u s i n g compact t e n s i o n s p e c i m e n s i n a c c o r d a n c e w i t h ASTM E399 whereas f o r t h e 20 mm x 2 mm s e c t i o n Navy Tear t e s t s were used. The e x t r u d a t e m i c r o s t r u c t u r e was a s s e s s e d u s i n g s t a n d a r d m e t a l l o g r a p h i c t e c h n i q u e s .
RESULTS
E x t r u s i o n C o n d i t i o n s
F i g u r e 1 shows t h e i n f l u e n c e of e x t r u s i o n c o n d i t i o n s on t h e 0.2% proof s t r e s s o f t h e 100 mm x 25 mm s e c t i o n a f t e r a g e i n g 16 h r s a t 1 9 0 ' ~ . The e x t r u s i o n c o n d i t i o n s a r e e x p r e s s e d a s l n ( Z ) where Z i s t h e t e m p e r a t u r e compensated s t r a i n r a t e d e f i n e d a s ;
where e* = mean e q u i v a l e n t s t r a i n r a t e OH = a c t i v a t i o n e n e r g y o f d e f o r m a t i o n
R = U n i v e r s a l Gas Content
T = T e m p e r a t u r e of e x t r u d a t e (OK)
The r e s u l t s i n F i g u r e L a r e from t h e $ w i d t h , # t h i c k n e s s t e s t p o s i t i o n . The 0.2%
P.S. i n c r e a s e s l i n e a r l y w i t h l n ( Z ) e x h i b i t i n g a r a n g e of a b o u t 30-40 XPa depending o n ( l 5 s t d i r e c t i o n . T h i s o b s e r v a t i o n i s i n agreement w i t h t h e work of P a r s o n e t a 1 and i s a t t r i b u t e d t o i n c r e a s e s i n t h e m a t e r i a l s u b s t r u c t u r a l s t r e n g t h e n i n g component w i t h i n c r e a s i n g l n ( Z ) . The e x t r u s i o n s a l l showed an 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 g r a i n s t r u c t u r e , t y p i c a l of t h a t shown i n F i g u r e 5 ( a ) .
For t h e h i g h ( 8 5 : l ) e x t r u s i o n r a t i o 8090 20 arm x 2 mm s e c t i o n t h e r e i s a s m a l l e r change i n s t r e n g t h w i t h e x t r u s i o n c o n d i t i o n s , a s shown i n F i g u r e 2. T h i s i s b e c a u s e t h e e x t r u s i o n is e s s e n t i a l l y r e c r y s t a l l i s e d , a s shown i n F i g u r e 3 and hence sub
s t r u c t u r e c a n n o t p l a y a r o l e i n d e v e l o p i n g t h e m a t e r i a l ' s s t r e n g t h . The 8091 a l l o y showed t h e same p a t t e r n of r e s u l t s b u t t h e range of s t r e n g t h with l n ( Z ) was n e a r l y d o u b l e ( i . e . 20 MPa).
F i g u r e 4 shows t h e e f f e c t of e x t r u s i o n c o n d i t i o n s on t h e f r a c t u r e toughness of t h e 8090 100 mm x 25 mm s e c t i o n . For a wide r a n g e of p r e h e a t t e m p e r a t u r e and e x t r u s i o n s p e e d s t h e f r a c t u r e t o u g h n e s s does n o t v a r y s i g n i f i c a n t l y w i t h p r o c e s s i n g
c o n d i t i o n s . Only t h e sample e x t r u d e d a t h i g h speed (5 m/min) from a h i g h p r e h e a t t e m p e r a t u r e (485OC) showed a s i g n i f i c a n t l o s s I n toughness. T h i s l o s s o n l y o c c u r r e d a t t h e e x t r u s i o n backend which would have e x p e r i e n c e d t h e h i g h e s t t e m p e r a t u r e due t o f r i c t i o n a l h e a t i n g e f f e c t s . ( I t i s of i n t e r e s t t o n o t e t h a t t h i s sample was a t t h e l i m i t of v i a b l e e x t r u s i o n c o n d i t i o n s s i n c e h o t t e a r i n g o c c u r r e d i f t h e speed was f u r t h e r i n c r e a s e d ) . F i g u r e 5 shows t h e s t r u c t u r e of t h i s e x t r u s i o n a t t h e f r o n t and back ends. A s i g n i f i c a n t d e g r e e of r e c r y s t a l l i s a t i o n h a s o c c u r r e d a t t h e back end which p r o b a b l y e x p l a i n s t h e lower f r a c t u r e toughness measured i n t h i s p o s i t i o n . F i g u r e 6 shows t h e r e s u l t s of Navy Tear t e s t s on t h e 20 arm x 2 nrm s e c t i o n . L i t t l e o r no change i n f r a c t u r e toughness i s found w i t h change i n e x t r u s i o n c o n d i t i o n s . T h i s i s a t t r i b u t e d t o t h e f a c t t h a t t h e s e c t i o n was f u l l y r e c r y s t a l l i s e d . The 8090 a l l o y e x h i b i t e d h i g h e r toughness and l e s s s c a t t e r t h a n t h e 8091 m a t e r i a l .
Commercial E x t r u s i o n s
The t y p i c a l l o n g i t u d i n a l t e n s i l e p r o p e r t i e s of commercially e x t r u d e d 8090 1'00 m x 25 nrm f l a t b a r aged 16 h a t 190°C a r e shown i n F i g u r e 7. The d a t a i s based on e i g h t l o t s and 28 i n d i v i d u a l r e s u l t s f o r each p o s i t i o n . The i n c r e a s e i n s t r e n g t h from t h e f r o n t t o t h e back i s due t o t h e change i n l n ( Z ) d u r i n g e x t r u s i o n which r e s u l t s i n an i n c r e a s e i n s u b s t r u c t u r e s t r e n g t h e n i n g . T h e v a r i a t i o n ixa p r o p e r t i e s a c r o s s t h e w i d t h of t h e s e c t i o n i s due t o i n c r e a s e d d e f o r m a t i o n i n t h e o u t e r r e g i o n s of t h e e x t r u d a t e which r e s u l t s i n a h i g h l y t e x t u r e d more f i b r o u s g r a i n s t r u c t u r e i n t h e o u t e r r e g i o n s , a s i l l u s t r a t e d i n F i g u r e 8. The v e r y f i n e s u b s t r u c t u r e a s s o c i a t e d w i t h t h e edge of t h e m a t e r i a l can produce a l a r g e i n c r e a s e i n t e n s i l e p r o p e r t i e s , sometimes a s much a s LOO MPa over a d j a c e n t r e g i o n s . T h i s i s i n c o n t r a s t t o a l l o y s such a s 2014 which e x h i b i t a c o a r s e r e c r y s t a l l i s e d o u t e r band of lower s t r e n g t h . A s i m i l a r p a t t e r n of r e s u l t s i s shown i n F i g u r e 9 f o r commercially e x t r u d e d 8091.
E f f e c t of Ageing
F r a c t u r e t o u g h n e s s i n t h e T-L d i r e c t i o n , a s shown i n F i g u r e s 7 and 9 i s low i n m a t e r i a l aged 16 h a t . Ageing a t lower t e m p e r a t u r e s r e s u l t s i n l e s s g r a i n boundary p r e ~ i p i t a t i o n ~ ' ~ : ~ a n d t h i s a p p e a r s t o o f f e r t h e o p p o r t u n i t y t o use lower a g e i n g t e m p e r a t u r e s (150°C o r 170°C) t o o b t a i n an improved b a l a n c e of t e n s i l e s t r e n g t h and f r a c t u r e toughness i n both 8090 and 8091 e x t r u d e d s e c t i o n s . F i g u r e 10 shows t h e e f f e c t o f v a r y i n g a g e i n g t e m p e r a t u r e on t h e s t r e n g t h f t o u g h n e s s
r e l a t i o n s h i p f o r b o t h 8090 and 8091 100 arm x 25 arm s e c t i o n b a r . The use of such lower a g e i n g t e m p e r a t u r e s n o t o n l y g i v e s t h e o p p o r t u n i t y f o r h i g h toughness and a c c e p t a b l e s t r e n g t h i n h i g h s t r e n g t h tempers b u t a l s o t o o b t a i n a damage-tolerant temper. F i g u r e 11 shows 8090 i n a l i g h t l y aged temper i n comparison t o 2024 T3511 d a t a from MIL.HANDBOOK V. In-plane toughness e x c e e d s t h a t o b t a i n e d i n 2024 a t h i g h e r s t r e n g t h l e v e l s w h i l e t h r o u g h i c k n e s s t o u g h n e s s i s s i m i l a r . F a t i g u e c r a c k growth r a t e d a t a on p l a t e indicates?'! t h a t t h e s e l i g h t l y aged tempers do have a complete b a l a n c e of damage t o l e r a n t c h a r a c t e r i s t i c s .
E f f e c t of S t r e t c h i n g
An a l t e r n a t i v e way t o improve t h e o v e r a l l b a l a n c e of mechanical p r o p e r t i e s i s t o modify t h e d e g r e e of c o l d work p r i o r t o . T h i s a s p e c t i s covered i n d e t a i l
i n o t h e r Alcan p a p e r s i n t h i s c o n f e r e n c e fg:fyf F i g u r e 12 shows t h e e f f e c t on t e n s i l e s t r e n g t h of v a r i o u s l e v e l s of s t r e t c h . As found f o r p l a t e , high l e v e l s of s t r e t c h i n c r e a s e t e n s i l e s t r e n g t h . By c o r o l l a r y w i t h t h e d a t a on p l a t e i t would be expected t h a t f r a c t u r e toughness was e s s e n t i a l l y c o n s t a n t f o r a l l t h e l e v e l s of s t r e t c h ( a t t h e same a g e i n g c o n d i t i o n s ) . However, i t must be r e c o g n i s e d t h a t high
C3-198 JOURNAL DE PHYSIQUE
l e v e l s of s t r e t c h c a n n o t be a p p l i e d t o a l l e x t r u s i o n s b e c a u s e i t may l e a d t o problems of t o l e r a n c e c o n t r o l on complex s e c t i o n s .
Aspect R a t i o
F i g u r e 1 3 shows how a s p e c t r a t i o a f f e c t s t h e t e n s i l e p r o p e r t i e s o f ' 8090. T h i s p r o p e r t y v a r i a t i i s a t t r i b u t e d t o the e f f e c t of t e x t u r e and has been d i s c u s s e d i n d e t a i l elsewhere?').
S e c t i o n T h i c k n e s s E f f e c t s
F i g u r e 14 shows t h e e f f e c t o f s e c t i o n t h i c k n e s s on t h e t e n s i l e p r o p e r t i e s of 8090 e x t r u d e d s e c t i o n s o v e r t h e t h i c k n e s s range 1.5 nan t o 52 mm. Lower p r o p e r t i e s a r e found a s s e c t i o n t h i c k n e s s d e c r e a s e s , which i s a t t r i b u t e d t o an i n c r e a s e i n
r e c r y s t a l l i s a t i o n ( s e e s e c t i o n 1 of t h i s p a p e r ) . S t a t i c r e c r y s t a l l i s a t i o n o c c u r s i n t h i n e x t r u d e d s e c t i o n s and a c o a r s e r e c r y s t a l l i s e d o u t e r band may form i f
i n a p p r o p r i a t e e x t r u s i o n c o n d i t i o n s a r e used. The d e g r e e of r d c r y s t a l l i s a t i o n can be changed by a l t e r i n g b o t h t h e h e a t i n g r a t e t o t h e s o l u t i o n h e a t t r e a t m e n t t r a t u r e and t h e t i m e of t h e s o l u t i o n h e a t t r e a t m e n t , a s found p r e v i o u s l y f o r s h e e t ?yU.
DISCUSSION
The d e g r e e t o which e x t r u s i o n c o n d i t i o n s a f f e c t t h e t e n s i l e p r o p e r t i e s of b o t h 8090 and 8091 depends on whether o r n o t r e c r y s t a l l i s a t i o n o c c u r s . I n t h i c k e r s e c t i o n s ( t y p i c a l l y > 5 mm) r e c r y s t a l l i s a t i o n i s d i f f i c u l t t o a c h i e v e e i t h e r d u r i n g e x t r u s i o n o r i n p o s t - e x t r u s i o n h e a t t r e a t m e n t . E x t r u s i o n c o n d i t i o n s c a n be changed t o
maximise t e n s i l e p r o p e r t i e s and f r a c t u r e toughness by c o n t r o l l i n g s u b s t r u c t u r e development, a s i s w e l l r e c o g n i s e d f o r o t h e r aluminium a l l o y s . However, e x t r u s i o n c o n d i t i o n s must b e c a r e f u l l y c o n t r o l l e d t o avoid r e c r y s t a l l i s a t i o n which a d v e r s e l y a f f e c t s f r a c t u r e t o u g h n e s s . Thin s e c t i o n s , which by t h e i r v e r y n a t u r e a r e e x t r u d e d w i t h h i g h e x t r u s i o n r a t i o s , tend t o r e c r y s t a l l i s e and t h i s produces s l i g h t l y l o w e r t e n s i l e p r o p e r t i e s . T h i s e f e t i s w e l l r e c o g n i s e d and c u r r e n t l y i s s u e d m a t e r i a l s p e c i f i c a t i o n s r e f l e c t thisf1'$.
Commercial aluminium-lithium b a s e a l l o y s c o n t a i n zirconium which r e s u l t s i n t h e development of s t r o n g t e x t u r e s and t h i s g i v e s r i s e t o a 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 w i t h i n a s i n g l e e x t r u s i o n . It i s perhaps f o r t u n a t e t h a t l o w e s t
8 s 1
s t r e n g t h p o s i t i o n c o i n c i d e s w i t h t h e u s u a l l y s p e c i f i e d t e s t p o s i t i o n .
F r a c t u r e t o u g h n e s s i n t h e T-L o r i e n t a t i o n has been shown t o be low i n 8090 and 8091 e x t r u s i o n s when aged f o r 16 h a t 190°C. T h i s can be d r a m a t i c a l l y improved by u s i n g lower a g e i n g t e m p e r a t u r e s . T h i s b o t h t a k e s a d v a n t a g e of t h e reduced g r a i n boundary p r e c i p i t a t i o n t o improve toughness and g i v e s more c o n t r o l o v e r t h e d e g r e e of a g e i n g a l l o w i n g m a t e r i a l t o b e aged t o j u s t below peak p r o p e r t i e s . The e f f e c t of such a g e i n g tr e n t s on t h e s t r e s s - c o r r o s i o n r e s i s t a n c e of t h e s e a l l o y s i s documented
7"f. The u s e of i n c r e a s e d s t r e t c h i n g , which i s c o n s i d e r e d b e n e f i c i a l f o r
p l a t e
e'sew2er~, m y o n l y b e a p p l i c a b l e t o simple e x t r u s i o n s e c t i o n s .
The range over which 8090 and 8091 can be e x t r u d e d t o g i v e a c c e p t a b l e t e n s i l e p r o p e r t i e s and t h e scope f o r p o s t e x t r u s i o n h e a t t r e a t m e n t , which can be used t o maximise t h e f r a c t u r e c h a r a c t e r i s t i c s , i s now w e l l u n d e r s t o o d . Both a l l o y s can b e produced t o compete w i t h c o n v e n t i o n a l a l l o y s b o t h i n h i g h s t r e n g t h and damage t o l e r a n t tempers.
CONCLUSIONS
1. Changes i n e x t r u s i o n c o n d i t i o n s have more e f f e c t on t e n s i l e p r o p e r t i e s i f t h e s u b s t r u c t u r e i s r e t a i n e d .
2. F r a c t u r e t o u g h n e s s c a n be improved by r e d u c i n g t h e time and t e m p e r a t u r e of a g e i n g w h i l e s t i l l o b t a i n i n g a s a t i s f a c t o r y l e v e l of t e n s i l e s t r e n g t h . Compensating f o r reduced t e n s i l e p r o p e r t i e s by i n c r e a s e d l e v e l s of s t r e t c h i s u n l i k e l y t o b e b e n e f i c i a l f o r a l l s e c t i o n s .
3. F r a c t u r e toughness i s reduced i f r e c r y s t a l l i s a t i o n i s allowed t o occur.
4. 8090 h a s g r e a t p o t e n t i a l i n t h e l i g h t l y aged c o n d i t i o n as a damage t o l e r a n t m a t e r i a l comparable w i t h 2024 T3511.
5. Thick s e c t i o n s e x h i b i t h i g h e r t e n s i l e p r o p e r t i e s t h a n t h i n s e c t i o n s due t o s u b s t r u c t u r e s t r e n g t h e n i n g and the e f f e c t of r e c r y s t a l l i s a t i o n .
ACKNOWLEDGEMENTS
The a u t h o r s a r e g r a t e f u l t o Alcan I n t e r n a t i o n a l f o r p e r m i s s i o n t o p u b l i s h t h i s work.
REFERENCES
1. W.S. M i l l e r , A.J. C o r n i s h , A.P. T i t c h e n e r and D.A. B e n n e t t , Proc. 2nd I n t . Aluminium-Lithium Conf. (Monteray C.A.), Eds. T.H. S a n d e r s Jr., and E.A. S t a r k e Jr., TMS-AIME 1984, p.335.
2. C.J. P e e l , B. Evans, C.A. Baker, D.A. B e n n e t t , P.J. Gregson, H.M. Flower. In Ref.1 p.363.
3. M.A. Reynolds, A. Gray, E. Creed, R.M. Jordan, A.P. T i t c h e n e r . Proc. 3rd I n t .
Aluminium-Lithium Conf. (Oxford U.K.), Eds. C. Baker, P.J. Gregson,
S.J. H a r r i s , C.J. P e e l . Pub. I n s t . of M e t a l s 1986, p.57.
4. N.C. Parson, T. Sheppard. I n Ref.1, p.53.
5. N.C. Parson, T. Sheppard. I n Ref.3, p.222.
6. J. White, W.S. M i l l e r . T h i s c o n f e r e n c e ( p a p e r 95).
7. R. Grimes. T h i s c o n f e r e n c e ( p a p e r 1 0 ) .
8. W.S. M i l l e r , J. White, M.A. Reynolds. T h i s c o n f e r e n c e ( p a p e r 5 8 ) .
9. I . G . Palmer, R.E. Lewis, D.D. Crocks. Proc. 1st I n t . Aluminium-Lithium Conf.
( S t o n e Mountain GA.), Eds. T,H. Sanders Jr., and E.A. S t a r k e J r . TMS-AL'IE 1981, p.241.
10. I.G. Palmer, W.S. M i l l e r , D.J. Lloyd and M . J . B u l l . I n Ref .3, p.565.
11. B r i t i s h Aerospace M a t e r i a l s p e ; i f i c a t i o n . BAEM 4150.
12. B r i t i s h S t a n d a r d 3L100.
13. A. Gray. T h i s c o n f e r e n c e ( p a p e r 32).
14. R.F. Ashton, D.S. Thompson, E.A. S t a r k e Jr. and F.S. L i n . I n Ref.3, p.66.
JOURNAL DE PHYSIQUE
TABLE 1
Chemical composition ef the billets used in the Alcan International trials
Section Size Alloy Composition
%Li
*
%Mg %Zr-
LONG.
TRANS.
/
Figure 1 Influence of extrusion conditions on the back-end longitudinal 0.2% proof stress of 8090 100 mm x 25 mm flat bar, aged 16 h/190°C.
Figure 2 I n f l u e n c e of e x t r u s i o n c o n d i t i o n s on t h e l o n g i t u d i n a l 0.2% proof s t r e s s of 8090 20 mu x 2 mu f l a t bar, aged 16 h/19O0C.
Figure 3 Grain s t r u c t u r e o f the 8090 20 nun x 2 mm f l a t bar.
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F r a c t u r e Toughness
L-T M P a f i
( a ) FRONT END
3 9
36
3 3
3 0
2 7
2 4
(b) BACK E N D
r
A F
t
-
1:
7m/min '1.6mL!n. l.6mm/min, A 8 F1'
1l.6m/min.
-8m/min. 1,6m/min
-
- A %
5m/min.
I I I I I I
350 375 400 425 4 5 0 475 500
Figure 5 Grain structure of the 100 mm x 25 mm 8090 f l a t bar extruded a t 5 m/min from a preheat temperature of 485°C.
B i l l e t Temperature ( O C
Figure 4 E f f e c t of extrusion c o n d i t i o n s on the fracture toughness of 8090 BOO mn x 25 mm f l a t bar aged 16 h/190°C.
N.T.S.
- PS.
1.0 l I I I I I
375 400 425 450 47 5 500
B i l l e t Temperature ( O C )
Figure 6 Navy tear t e s t r e s u l t s obtained on the 8090 and 8091 20 tmn x 2 tmn s e c t i o n a f t e r ageing for 16 h/190°C.
Figure 7 Typical longitudinal t e n s i l e properties of commercially produced 8090 100 m x 25 m f l a t bar aged 16 h/190°c.
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EDGE
f WIDTH
CORE
200 P"
Figure 8 Variation in grain structure across a commercially extruded 100 mm x 25 m m flat bar.
MPa 6 50 600 5 5 0 5 0 0 45 0 400 350 300 2 50 200
EDGE EDGE ' 1 4 ~ ' 1 4 ~ CORE CORE Kq L-T Kq T-L FRONT BACK FRONT BACK FRONT BACK BACK BACK
Figure 9 Longitudinal t e n s i l e properties of commercially extruded 8090 100 mm x 25 rmu f l a t bar aged 16 h/190°C.
,c Y P a G
58 0 A 6090
34 30 -
26 -
22 - 7 . \ \. * 1 5 0 0 (
- \
le - 15h/190°c . \ 150°C
I I 1 I 1 L I I I I I I I I I I I
340 360 380 400 420 440 460 480 500 TRANSVERSE 0.2% PROOF STRESS ( MPa)
Figure 10 E f f e c t of ageing a t 150'C and 170°C on t h e 0.2% proof stress/T-L fracture toughness r e l a t i o n s h i p f o r 8090 and 8091 100 mm x 25 m f l a t bar.
JOURNAL DE PHYSIQUE
Figure 11 Comparison of lightly aged 8090 tensile and fracture toughness properties with 2024 T3511 data from MIL.HANDBOOK V in the thickness range 19-37 mm.
MPa
3 4 5 6
% STRETCH
Figure 12 Shows the effect of stretching on the longitudinal tensile properties of 100 mm x 25 mm 8090 flat bar aged 16 h/190°C.
MPa EL. % 6 0 0
I
ASPECT RATIO
Figure 13 Effect of aspect r a t i o on 8090 peak aged t e n s i l e properties.
ELONG.
U.T.S.
0.2%PS.
SECTION THICKNESS (rnrn)
Figure 14 Effect of section thickness on t e n s i l e properties of 8090 T8511 extruded section.
