CLOSING ADDRESS

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CLOSING ADDRESS

B. Dubost

To cite this version:

B. Dubost. CLOSING ADDRESS. Journal de Physique Colloques, 1987, 48 (C3), pp.C3-913-C3-919.

�10.1051/jphyscol:19873106�. �jpa-00226540�

CLOSING ADDRESS

B . DUBOST

Cegedur-Pechiney, Centre de Recherche et Developpement, B.P. 27 F-38340 Voreppe, France

C l o s e on 290 p a r t i c i p a n t s , r e p r e s e n t i n g 1 6 c o u n t r i e s , c o n v e n e d i n P a r i s f o r t h i s F o u r t h I n t e r n a t i o n a l Aluminium-Lithiurnconference. Over t h e t h r e e days, a t o t a l of 120 p a p e r s ( h 2 p r e s e n t e d o r a l l y and 78 p r e s e n t e d i n p o s t e r s e s s i o n s ) from n e a r l y a l l t h e m a j o r aluminium p r o d u c e r s , a i r c r a f t m a n u f a c t u r e r s ,

u n i v e r s i t y r e s e a r c h l a b o r a t o r i e s o r l a b o r a t o r i e s f r o m t h e p u b l i c s e c t o r , p r o v i d e d a n o v e r v i e w of t h e p r e s e n t s t a t e of r e s e a r c h and d e v e l o p m e n t i n t h e f i e l d o f a l u m i n i u m - l i t h i u m a l l o y s .

T r u e t o t h e t r a d i t i o n o f t h e s e i n t e r n a t i o n a l c o n f e r e n c e s on aluminium- l i t h i u m a l l o y s , t h e p a p e r s r e v i e w s d t h e s i t u a t i o n f r o m t h e v i e w p o i n t of t h e i n d u s t r y ( m a r k e t i n g , t e c h n o l o g y , c h a r a c t e r i z a t i o n , i m p l e m e n t a t i o n ) a s well a s more f u n d a m e n t a l i s s u e s ( p h y s i c a l m e t a l l u r g y , m i c r o s t r u c t u r a l c o n s i d e r a - t i o n s , b a s i c i n v e s t i g a t i o n s ) . T h i s d u a l v i e w p o i n t is r e f l e c t e d i n P a r f s I and I1 o f t h e C o n f e r e n c e P r o c e e d i n g s , and i t is i n t h i s o r d e r t h a t an a t t e m p t w i l l b e made a t a n "on t h e s p o t " a p p r e c i a t i o n o f t h e main c o n t r i - b u t i o n of t h i s C o n f e r e n c e .

A , Viewpoint o f t h e A i r c r a f t M a n u f a c t u r e r

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Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19873106

C3-914 JOURNAL DE PHYSIQUE 8. P r o d u c t i o n S t a t u s of A 1 - L i a l l o y s

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The two c a n d i d a t e s a r e 2091 T8X51 and 8090 T8X51.

The p r o p e r t i e s announced match t h o s e o f t h e c o n v e n t i o n a l a l l o y 2024 T351 and minimum t e n s i l e and t o u g h n e s s c a n now be g u a r a n t e e d , i n p a r t i c u l a r i n t h e s h o r t t r a n s v e r s e d i r e c t i o n , showing t h a t aluminium-1it.hium a l l o y s a r e n o t i n h e r e n t l y b r i t t l e .

Medium s t r e n g t h p l a t e s and e x t r u s i o n s ( s u b s t i t u t e s f o r 2214 T651)

...

E s s e n t i a l l y , t h e a v a i l a b l e a l l o y s a r e 8090 T8Y51 ( w i t h improved t o u g h n e s s ) and 2091 T851.

Promising c a n d i d a t e s a r e : 2090 TBEXX, 8091 T851 and a l l o y CP 276 T851.

The answer h a s n o t y e t been found, i n p a r t i c u l a r w i t h r e s p e c t t o 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 i n t h e s h o r t t r a n s v e r s e d i r e c t i o n . However, mechani- c a l l y a l l o y e d IN905XL, o b t a i n e d by t h e powder m e t a l l u r g y r o u t e h a s performed w e l l i n t e r m s of c o r r o s i o n r e s i s t a n c e .

On-going r e s e a r c h c o n c e r n s 2091 CP 276, 8090 and 8092. Alloy 2090 is n o t c o n s i d e r e d s u i t a b l e f o r f o r g i n g .

C. Alloy P r o d u c t i o n

Semi-continuous c a s t i n g

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For t h e f i r s t t i m e a t an A 1 - L i Conference, a good number o f p a p e r s d e a l t with t h e technology of semi-continuous c a s t i n g .

- S a f e t y : e x p l o s i o n h a z a r d s ( e x p l o s i o n of l i q u i d A1-Li i n c o n t a c t w i t h w a t e r ) l i n k e d w i t h high Li-content a l l o y s have been i d e n t i f i e d

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and h a s been t h e s u b j e c t t o i n t e n s i v e s t u d i e s by many A 1 - L i a l l o y producers.

- I m p u r i t i e s (Sodium) --- : There i s a c o n s e n s u s of p r o d u c e r s on t h e f a c t t h a t sodium e m b r i t t l e m e n t is n o t a problem f o r i n d u s r i a l q u a l i t y a l l o y s (Na

<

A new master a l l o y (Al-19LLi) w i t h low sodium c o n t e n t i s proposed.

- G r a i n r e f i n i n g --- : g r a i n r e f i n i n g d i m i n i s h e s c r a c k s e n s i t i v i t y i n semi- c o n t i n u o u s c a s t i n g of p l a t e s o r b i l l e t s .

I t is confirmed t h a t r e f i n i n g i s more d i f f i c u l t on Al-Li-Cu-(Mg)-Zr a l l o y s t h a n on c o n v e n t i o n a l a l l o y s b u t t h e critical v a r i a b l e s have been i d e n t i f i e d ( T i , Z r , Mg).

Ti-C-A1 seems t o be a more r e l i a b l e r e f i n e r t h a n t h e c l a s - s i c a l Ti-R-A1,while s i g n i f i c a n t r e s u l t s have a l s o been o b t a i n e d w i t h e l e c t r o m a g n e t i c s t i r r i n g .

- ---- ---- S c r a p Recycling --- : ^{There i s} no problem f o r b u l k s c r a p b u t t h i s remains a s o r e p o i n t f o r o t h e r p r o c e s s i n g s c r a p .

Mixing r u l e s have been p u t forward and p o s s i b l e r e c y c l i n g r o u t e s ( f o r i n s t a n c e on A1-Si c a s t i n g s ) were p r e s e n t e d .

Aluminium-Lithium c a s t i n g s must e v i d e n c e very s i g n i f i c a n t r e d u c t i o n s i n d e n s i t y t o m e r i t c o n s i d e r a t i o n .

I n i t i a l r e s u l t s were p r e s e n t e d c o n c e r n i n g medium s t r e n g t h s a n d c a s t i n g s and i n v e s t m e n t c a s t i n g s .

The f o c u s was on a l l o y s w i t h a h i g h l i t h i u m and/or d i s p e r s o i d ( Z r , Nb, W, Mo) c o n t e n t g i v i n g h i g h s t r e n g t h and v e r y low d e n s i t y p r o d u c t s r a t h e r t h a n on t h e Al-Li-Cu-Mg-Zr a l l o y s . C h a r a c t e r i z a t i o n i s n o t y e t v e r y e x t e n s i v e d e s p i t e q u i t e a number o f s t r u c t u r a l i n v e s t i g a t i o n s .

D. P r o c e s s i n g

S h e e t s (8090 T851, 2091 T8X51)

...

R e c r y s t a l l i z e d s t r u c t u r e s improve i s o t r o p y and damage t o l e r a n c e of s h e e t s . A combination of t o u g h n e s s and mechanical s t r e n g t h e q u i v a l e n t t o t h a t of a l l o y 2024 T3 can be achieved by an a s s o c i a t i o n o f r e c r y s t a l l i z e d s t r u c t u r e p l u s c o l d working a f t e r quenching p l u s s l i g h t underageing.

P l a t e s

-,---,---,--L---L--- (8090 2091 Tempers T8XX1)

The o v e r a l l s t r e n g t h - t o u g h n e s s combination and t h e e l o n g a t i o n i n t h e s h o r t t r a n s v e r s e d i r e c t i o n a r e improved by i n t e n s i v e c o l d working a f t e r s o l u t i o n h e a t - t r e a t m e n t , f o l l o w e d by s l i g h t a g e i n g (damage t o l e r a n t a l l o y s ) .

C3-916 JOURNAL DE PHYSIQUE

High o v e r a l l s t r e n g t h i s a f e a t u r e of t h e u n c r y s t a l l i z e d s t r u c t u r e s b u t i s o f f s e t by marked a n i s o t r o p y and g r a d i e n t s of m e c h a n i c a l p r o p e r t i e s

t h r o u g h t h e t h i c k n e s s , which i s c l o s e l y d e p e n d e n t on t h e t e x t u r e and t y p e o f p r e c i p i t a t e s i n t h e m a t r i x .

Thermo-mechanical p r o c e s s i n g c a n p r o d u c e a f i n e r e c r y s t a l l i z e d g r a i n s i z e , f a v o u r a b l e t o t h e t o u g h n e s s / y i e l d s t r e n g t h t r a d e - o f f .

E x t r u s i o n s ( a l l a l l o y s )

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The m e t a l l u r g i c a l e f f e c t s o f e x t r u s i o n have been f i r m l y e s t a b l i s h e d : t h e i n f l u e n c e o f t h e 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 t e m p e r a t u r e o n t h e t e n s i l e b e h a v i o u r and m e c h a n i c a l p r o p e r t i e s o f e x t r u d e d p a r t s i s

c l e a r l y d e m o n s t r a t e d . E x t r u s i o n maps have been p l o t t e d .

T h e - h i g h l i g h t i s on n e a r n e t s h a p e o r p r e c i s i o n d i e - f o r g i n g s o b t a i n e d by c o n v e n t i o n a l o r i s o t h e r m a l f o r g i n g . While t h e p r o b l e m s o f a n i s o t r o p y have n o t y e t been s o l v e d , a n o t h e r problem o f quench s e n s i t i v i t y o f h e a v y s e c t i o n f o r g i n g s h a s a r i s e n . Optimum a g e i n g t r e a t m e n t must b e d e v i s e d t o e n s u r e s a t i s f a c t o r y r e s i s t a n c e t o e x f o l i a t i o n and stress c o r r o s i o n .

E. Forming - S u p e r p l a s t i c i t y - S u r f a c e c o n d i t o n s - J o i n i n g

Forming o f 8090 and 2091 T3 s h e e t by t h e a i r c r a f t m a n u f a c t u r e r without.

need f o r p r i o r s o l u t i o n h e a t - t r e a t m e n t i s c o n s i d e r e d f e a s i b l e .

The p o s s i b i l i t y o f s u p e r p l a s t i c f o r m i n g is more t h a n e v e r a p r i m e a s s e t f r o m t h e p o i n t o f view of s a v i n g s i n c o s t and w e i g h t .

I n d u s t r i a l a l l o y s 2090 ( h o t - r o l l e d ) , 8090 and 8091 a r e showing p r o m i s e a f t e r thermornechanical p r o c e s s i n g t o promote dynamic r e c r y s t a l l i z a t i o n .

However, work is s t i l l r e q u i r e d t o up-grade t h e m e c h a n i c a l p r o p e r t i e s o f s ~ l p e r p l a s t i c formed a l l o y s , o r e v e n t h e p r o p e n s i t y t o c a v i t . a t i o n .

S u r f a c e c o n d i t i o n s

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S u b s u r f a c e p o r o s i t y i s o f t e n o b s e r v e d i n h e a t - t r e a t e d s e m i s and may b e d u e t o e i t h e r K i r k e n d a l l e f f e c t o r t h e p r e s e n c e o f u n i d e n t i f i e d i n t e r - m e t a l l i c p h a s e s : t h i s h a s s t i l l t o b e c l a r i f i e d .

P r o g r e s s h a s been made i n s u r f a c e a n a l y s i s : d e t e r m i n a t i o n o f s u p e r f i c i a l hydrogen, v i s u a l d e t e c t i o n a n d q u a n t i t a t i v e i n v e s t i g a t i o n o f s u b s u r f a c e l i t h i u m d e p l e t i o n .

Welding

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A new w e l d a b l e h i g h - s t r e n g t h a l l o y i s announced. On t h e o t h e r h a n d , t h e j o i n t e f f i c i e n c y o f a l l o y 8090 a f t e r e l e c t r o n beam w e l d i n g i s s t i l l somewhat l i m i t e d .

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(Al-Li-CU-Mg) o r i n d u s t r i a l a l l o y s ( w i t h Z r ) u s i n g t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y , h i g h r e s o l u t i o n e l e c t r o n m i c r o s c o p y and d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y .

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c o p r e c i p i t a t i o n ( b' TI o r 8 T1, S f o r 5, T2, 6 ^{) :} t h e major c o n t r i b u t i o n s o f T1, S t and 6 ' t o s t r e n g t h e n i n g have been i d e n t i f i e d i n u n d e r a g e d o r peak aged t e m p e r s ( a l l o y s 2090, 2091, 8090).

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mechanisms : where d o we p l a c e t h e boundary between Orowan l o o p and s h e a r i n g of p r e c i p i t . a t e s ? Q u a n t i t a t i v e i n v e s t i g a t i o n s a r e needed o n c o p r e c i p i t a t i o n h a r d e n i n g i n t e r n a r y a l l o y s , and e v e n more s o i n q u a t e r n a r y a l l o y s , i n p a r t i c u l a r i n u n d e r a g e d t e m p e r s .

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5'-A1

G. M i c r o s t r u c t u r e s

The c o n s t i t u t i o n of t h e Al-Li(Cu,Mg,Zn,Si) a l l o y s is b e t t e r known t h a n k s t o :

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New q u a n t a t i v e m i c r o - a n a l y t i c a l t e c h n i q u e s

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u s e d s e p a r a t e l y o r i n c o n j u n c t i o n w i t h o t h e r s , h a v e proved s u i t a b l e f o r t h e i n v e s t i g a t i o n o f A1-Li a l l o y s .

H, M e c h a n i c a l b e h a v i o u r a n d f r a c t u r e m e c h a n i c s

T e n s i l e b e h a v i o u r i s g o v e r n e d by a s t r o n g i n t e r a c t i o n of s t r u c t u r e , t e x t u r e ( g r a i n o r i e n t a t i o n ) and p r e c i p i t a t i o n .

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complex s l i p m c h a n i s m s . A s e l f - c o n s i s t e n t model was u s e d ; f o r q u a n t i t a t i v e m o d e l l i n g a g r e a t e r number o f e x p e r i m e n t a l d a t a on b o t h s i m p l e and complex a l l o y s o r o n s i n g l e c r y s t a l s a r e r e q u i r e d .

0 - 9 1 8 J O U R N A L DE PHYSIQUE

The m i c r o s t r u c t u r e ( p r e c i p i t a t i o n ) h a s l i t t l e e f f e c t on e l a s t i c i t y (Young * s modulus).

A 1 - L i a l l o y s e x h i b i t good low t e m p e r a t u r e p r o p e r t i e s f o r c r y o g e n i c a p p l i c a t i o n s ( e .g. 2090).

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u n f a v o u r a b l e i n f l u e n c e of c o a r s e i n t e r g r a n u l a r y p r e c i p i t a t i o n of i c o s a h e d r a l T2 phase durzing slow quenching, peak-or overageing.

, The b e n e f i c i a l e f f e c t s of underageing and of cold-working o r s t r e t c h i n g b e f o r e a g e i n g ( e f f e c t on t h e d i s t r i b u t i o n of p r e c i p i t a t e s a t g r a i n b o u n d a r i e s ) a r e confirmed.

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( r e c r y s t a l l i z a t i o n , underageing) a r e p u t f a r w a r d f o r damage t o l e r a n t p r o d u c t s ,

I. F a t i g u e

Comprehensive s t u d i e s f u r t h e r i n g t h e knowledge o f damage mechanisms and t h e f a t i g u e behaviour of b i n a r y A 1 - L i a l l o y s and commercial a l l o y s were p r e s e n t e d , c o v e r i n g b o t h c r a c k i n i t i a t i o n and c r a c k growth :

-

- t h e mechanisms of f a t i g u e c r a c k i n i t i a t i o n and growth a r e i d e n t i f i e d on b i n a r y and commercial a l l o y s : i n f l u e n c e of a g e i n g on planar-type s l i p , c r a c k branching ( m i c r o s t r u c t u r e 1 and mechanical a s p e c t s ) .

Good f a t i g u e behaviour o f 8090 under o v e r l o a d was demonstrated. Crack r e s i s t a n c e is improved w i t h i n c r e a s i n g L i c o n t e n t i n t h e a l l o y s .

J. C o r r o s i o n

S i g n i f i c a n t r e s u l t s a r e now a v a i l a b l e on t h e behaviour of some a l l o y s

(8090, 2090) exposed t o marine atmosphere. Worldwide c o n c e r t of p r o d u c e r s and a i r c r a f t m a n u f a c t u r e r s l e a d i n g t o i n t e r n a t i o n a 1 . s t a n d a r d i z a t i o n i s now c a l l e d f o r t o d e f i n e r e p r e s e n t a t i v e t e s t p r a c t i c e on samples.

The behaviour of some a l l o y s Al-LiCu-(Mg)-Zr (2091, 2090) i n t h e form o f c o a t e d s h e e t h a s proved a t l e a s t e q u i v a l e n t t o t h a t o f t h e c o n v e n t i o n a l r e f e r e n c e a l l o y s under s i m u l a t e d i n - f l i g h t c o n d i t i o n s .

Cladding o f t h e l a t t e r a l l o y s w i t h c o n v e n t i o n a l a l l o y s (1230) seems q u i t e a c c e p t a b l e w i t h o u t any change i n o p e r a t i n g p r a c t i c e .

s h o r t t r a n s v e r s e d i r e c t i o n , ( < 5 0 MPa), b u t no worse t h a n t h a t of

2XXX-53 o r - T 6 5 1 c o n v e n t i o n a l a l l o y s . Recent r e s u l t s c l a i m b e n e f i c i a l e f f e c t s o f s t r e t c h i n g b e f o r e a g e i n g , of z i n c a d d i t i o n s (1% and 3 t e s t e d ) and o f d u p l e x a g e i n g t r e a t m e n t on t h e combination of t o u g h n e s s and c o r r o s i o n r e s i s t a n c e i n t h e s h o r t t r a n s v e r s e d i r e c t i o n .

A s mentioned p r e v i o u s l y , heavy s e c t i o n f o r g i n g s f a l l below s t a n d a r d w i t h r e s p e c t t o t h e i r c o r r o s i o n r e s i s t a n c e i n t h e s h o r t t r a n s v e r s e d i r e c t i o n and improvement is c a l l e d f o r .

P r o g r e s s h a s been made i n u n d e r s t a n d i n g t h e mechanisms of s t r u c t u r a l c o r r o s i o n :

- t h e c a u s e is probably a n o d i c d i s s o l u t i o n and hydrogen embrit,tlement

- t h e samemechanismis probably t-he c u l p r i t i n c o r r o s i o n f a t i g u e a t low c r a c k growth r a t e s

-

To conclude t h i s b r i e f and unavoidably incomplete review, it i s c l e a r t h a t t h e r e c e n t g r e a t t e c h n i c a l and s c i e n t i f i c p r o g r e s s a c h i e v e d i n improving t h e p r o p e r t i e s of commercialnluminium-lithium a l l o y s and i n u n d e r s t a n d i n g t h e m e t a l l u r g i c a l mechanisms i n v o l v e d , have paved t h e way t o t h e u s e of t h e s e a l l o y s i n t h e a i r c r a f t i n d u s t r y i n t h e n e a r f u t u r e , p r o v i d i n g t h e problems of c o s t , r a t i o n a l i z a t i o n and a v a i l a b i l i t y can be overcome.

I n f a c t , s e v e r a l examples of a p p l i c a t i o n s were a l r e a d y on view a t t h e Paris-Le Bourget I n t e r n a t i o n a l Air Show, t h a t was h e l d i n p a r a l l e l w i t h t h i s Conference. But. it i s a l s o e v i d e n t t h a t a number of m e t a l l u r g i c a l problems.remain, i n p a r t i c u l a r a s f a r a s t h e q u a n t i t a t i v e modelling o f t h e mechanical behaviour of t h e m a t e r i a l s i s concerned, o r a t h o r o u g h u n d e r s t a n d i n g o f c o r r o s i o n mechanisms i n r e l a t i o n w i t h t h e complex m i c r o s t r u c t u r e . o f

commercial a l l o y s . I t i s n o t unwise t o p r e d i c t t h a t t h e r e s e a r c h r o u t e s d e p i c t e d i n t h e c o u r s e of t h i s Conference w i l l f u l f i l t h e i r promise, and t h a t t h e n e x t I n t e r n a t i o n a l Aluminium-Lithium Conference i n 1989 w i l l g i v e new answers t o t h e remaining q u e s t i o n s .