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INTERNAL FRICTION PEAKS OF Al-Mg ALLOYS
J. Othmezouri-Decerf
To cite this version:
J. Othmezouri-Decerf. INTERNAL FRICTION PEAKS OF Al-Mg ALLOYS. Journal de Physique
Colloques, 1983, 44 (C9), pp.C9-265-C9-270. �10.1051/jphyscol:1983936�. �jpa-00223383�
J O U R N A L DE PHYSIQUE
Colloque C9, suppliment au n012, Tome 44, dicembre 1983 page C9-265
INTERNAL FRICTION PEAKS OF A 1 - M g ALLOYS
J . Othmezouri-Decerf
Physique des Matgriaux de Synthe'se, Universitg Libre de BruxeZZes, Belgium
Rksumk - Des p i c s de f r o t t e m e n t i n t k r i e u r ont ktk o b s e r v k s B d e s f r k q u e n - c e s d ' e n v i r o n 1 Hz e t 2 . 4 Hz dans p l u s i e u r s alliages d'aluminium-magnk- s i u m ( l % , 5 % e t 1 3 % ) , l e s kchantillons ayant kt6 p r k a l a b l e m e n t s o u m i s B un t r a i t e m e n t d e v i e i l l i s s e m e n t dont la t e m p e r a t u r e ktait c o m p r i s e e n t r e
273 K et 303 K. Dans l e s t r o i s alliages ktudiks, l e s pics sont c a r a c t k r i s k s p a r l e u r instabilitk et l e u r m a u v a i s e reproductibilitk d ' u n e s s a i 'a l ' a u t r e . Des e x a m e n s plus fouillks ont kt6 r k a l i s k s s u r l ' a l l i a g e A1-Mg 1 3 % , oh l a pr6- prkcipitation (zones d e G u i n i e r - P r e s t o n ) s e produit a u c o u r s de t r a i t e m e n t s de v i e i l l i s s e m e n t t e l s que ceux mentionnks c i - d e s s u s et conduit B une v a r i a - tion d e s m o d u l e s d ' k l a s t i c i t k . Nous avons examink 1' ktat s t r u c t u r a l d e s kchantillons d1Al-Mg 13% apr'es v i e i l l i s s e m e n t e t apr'es m e s u r e de f r o t t e - m e n t i n t k r i e u r B b a s s e t e m p k r a t u r e p a r l a v a r i a t i o n du module de c i s a i l l e - m e n t d a n s l e domaine de r k v e r s i o n d e s zones G u i n i e r - P r e s t o n d e 303 K 'a 373 K.
L e s p i c s d e f r o t t e m e n t i n t k r i e u r o b s e r v k s d a n s l e s a l l i a g e s d'Al-Mg peuvent e t r e a t t r i b u k s B d e s changements locaux d e l ' k t a t s t r u c t u r a l induits p a r l e dkplacement d e s d i s l o c a t i o n s .
A b s t r a c t - Low t e m p e r a t u r e i n t e r n a l f r i c t i o n p e a k s have been o b s e r v e d a t f r e q u e n c i e s of about 1 Hz a n d 2 . 4 Hz i n s e v e r a l a l u m i n i u m - m a g n e s i u m a l l o y s ( I % , 5 % a n d 1 3 % ) on s a m p l e s aged a t t e m p e r a t u r e s varying between 273 K a n d 303 K. The observed peaks a r e c h a r a c t e r i z e d f o r the t h r e e alloys by t h e i r instability a n d poor reproducibility f r o m one t e s t t o the o t h e r f o r p r e s u m e d i d e n t i c a l m i c r o s t r u c t u r a l s t a t e s of t h e s a m p l e s . M o r e d e t a i l e d s t u d i e s w e r e m a d e on A1-Mg 13% alloy, w h e r e t h e p r e p r e c i p i t a t i o n (Gui- n i e r - P r e s t o n z o n e s ) occuring during t h e ageing t r e a t m e n t mentioned above, l e a d s t o v a r i a t i o n s of the e l a s t i c moduli. In o u r e x p e r i m e n t s , t h e m i c r o - s t r u c t u r a l s t a t e of t h e A1-Mg 13% s p e c i m e n s a f t e r ageing o r a f t e r low t e m - p e r a t u r e i n t e r n a l f r i c t i o n t e s t , w a s i n v e s t i g a t e d by m e a s u r i n g t h e v a r i a t i o n of the s h e a r modulus in t h e r e v e r s i o n t e m p e r a t u r e domain of t h e G u i n i e r - P r e s t o n zones f r o m 303 K t o 373 K. The observed i n t e r n a l friction peaks a r e tentatively i n t e r p r e t e d t o be due t o l o c a l s t r u c t u r a l changes u n d e r t h e influence of d i s l o c a t i o n motion.
I. Introduction.
-
The p u r p o s e of t h i s work w a s t o i n v e s t i g a t e t h e i n t e r a c t i o n bet- ween dislocations and substitutional solute a t o m s i n c o r r e l a t i o n with the ageing effect due t o the s o l u t e s . I n t e r n a l f r i c t i o n m e a s u r e m e n t s w e r e a t f i r s t conducted on a n A1-Mg 5 % alloy, a s t h e dynamic and s t a t i c s t r a i n ageing behaviour of this alloy was previously studied in our l a b o r a t o r y by t e n s i l e t e s t i n g / I , 2, 3/ .
E x p e r i m e n t s w e r e a l s o p e r f o r m e d on a m o r e dilute alloy, 1 wt
%
Mg, f o r t h e s a k e of c o m p a r i s o n with l i t e r a t u r e data; i n t e r n a l f r i c t i o n p e a k s a s c r ~ b e d t o t h e i n - t e r a c t i o n of d i s l o c a t i o n s with solute-vacancy c o m p l e x e s w e r e indeed denoted f o r s e v e r a l cold worked dilute a l u m i n i u m a l l o y s / 4 , 5, 6/
a m o n g o t h e r s dilute Al-Mg a l l o y s /7/.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983936
JOURNAL DE PHYSIQUE
It a p p e a r e d in the c o u r s e of t h i s work that peaks w e r e only o b s e r v e d a f t e r ageing f o r t i m e i n t e r v a l s m u c h longer than t h o s e needed t o produce a m a x i m u m a n c h o r r i n g effect a t t r i b u t e d t o a d e n s e C o t t r e l l a t m o s p h e r e of solutes a r o u n d d i s l o c a - t i o n s ; t h i s c r i t i c a l t i m e couldbe e v a l u a t e d f r o m p r e v i o u s s t a t i c s t r a i n ageing t e s - ting. In o r d e r t o i n v e s t i g a t e a p o s s i b l e link between c l u s t e r s of m a g n e s i u m a t o m s and t h e o b s e r v e d p e a k s , m e a s u r e m e n t s w e r e a l s o m a d e on a n A1-Mg 13% alloy w h e r e t h e f o r m a t i o n of G u i n i e r - P r e s t o n z o n e s during low t e m p e r a t u r e ageing i s a well e s t a b l i s h e d phenomenon /8, 9, l o / .
2. E x p e r i m e n t a l p r o c e d u r e . - High purity a l u m i n i u m - m a g n e s i u m a l l o y s of n o m i - n a l c o n t e n t s 1. 0, 5 . 0 a n d 13. 0 wt% m a g n e s i u m w e r e kindly donated by Pechiney - Voreppe. P l a t e s of 120 mrn length with s e c t i o n of 0 . 8 5 x 5 m m 2 w e r e p r e p a r e d f r o m r o l l e d s h e e t s . The s a m p l e s w e r e s u b m i t t e d t o p r e l i m i n a r y annealing t r e a t - m e n t s l i s t e d in t a b l e I; they w e r e usually a i r cooled a f t e r high t e m p e r a t u r e t r e a t - m e n t ; m o s t Al-Mg 1 3 % s p e c i m e n s w e r e w a t e r quenched. A f t e r homogeneization, e a c h s p e c i m e n was p r e p a r e d following one of the conditions s u m m a r i z e d i n table 11;
m o s t s a m p l e s w e r e a g e d b e f o r e i n t e r n a l f r i c t i o n t e s t i n g i n c o r r e l a t i o n with p r e - vious s t a t i c o r dynamic s t r a i n ageing e x p e r i m e n t s ( s e e conditions B B 2 , C1 and C - of t a b l e 11).
L T a b l e I.
T a b l e 11. - S u m m a r y of s p e c i m e n conditions.
Mg contents
"I, wt
0. 95 4 . 7 13. 0
Homogeneization t r e a t m e n t T e m p e r a t u r e
623 K 623 K 723 K R e c r y s t a l l i z a t i o n
t r e a t m e n t i n s a l t bath
In s i t u d e f o r m a t i o n b e f o r e i n t e r n a l f r i c t i o n t e s t
T
.
t e m p e r a t u r eL ~ I
2 s t r a i n - - - t2 J 1% o r 5 % T 2 9 190 K- - - k2
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T2 & 190K
T i m e 15 m i n i n s a l t bath 1 hour i n s a l t bath 16 h o u r s i n f u r n a c e T e m p e r a t u r e
823 K 823 K -
-
Ageing t r e a t m e n t T : t e m p e r a t u r e
t z : t i m e - - - - - -
273K 3 T a 4 3 1 3 ~ 6 h o u r s ( t < 8 m o n t h s
a h i d e m
i d e m
i d e m A 1
A 2
1
B2
1
C 2
T i m e 5 s e c 5 s e c - -
P r e d e f o r m a t i o n by t r a c t i o n T : t e m p e r a t u r e
&::
s t r a i n- - - - -
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-T 1 5 190K o r a m b i e n t
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n 1 %i d e m
I n t e r n a l f r i c t i o n m e a s u r e m e n t s w e r e m a d e with a n i n v e r t e d t o r s i o n pendulum using the f r e e decay method a t f r e q u e n c i e s of about 1 Hz o r 2 . 4 Hz depending on i n e r - t i a u s e d . The m a x i m u m v i b r a t i o n a l s h e a r s t r a i n was about 5 x o r The s p e c i m e n could be d e f o r m e d by t r a c t i o n i n the i n t e r n a l f r i c t i o n a p p a r u t u s . The l o - g a r i t h m i c d e c r e m e n t was m e a s u r e d by r e c o r d i n g f r e e t o r s i o n a l vibrations with a Photodyne spot follower. The frequency w a s d e t e r m i n e d using a p h o t o t r a n s i s t o r a n d a counter c i r c u i t . M e a s u r e m e n t s w e r e m a d e during heating r u n a t a r a t e of about 1 ~ / m i n .
3. E x p e r i m e n t a l r e s u l t s . - S p e c i m e n s t e s t e d i m m e d i a t e l y a f t e r homogeneization t r e a t m e n t (conditions A a n d A ) did not p r e s e n t i n t e r n a l f r i c t i o n peaks in t h e r a n g e of t e m p e r a t u r e e x p l o r e d f r o m about 173 K t o 293 K. Such behaviour was no- t e d many t i m e s f o r the t h r e e a l l o y s investigated. B e s i d e s , ageing o r s t r a i n ageing f a v o u r e d t h e a p p e a r a n c e of well defined peaks i n t h e r a n g e of t e m p e r a t u r e m e n t i o - ned above, e i t h e r the ageing t r e a t m e n t was followed by low t e m p e r a t u r e d e f o r m a - tion o r not. It will be s e e n f r o m t h e e x a m p l e s given i n the c o u r s e of t h i s p a p e r t h a t m o r e than one peak may be p r e s e n t . Independently of the p e r c e n t a g e of m a g n e - s i u m and of the s p e c i m e n condition, t h e o b s e r v e d peaks w e r e c h a r a c t e r i z e d by the
following behaviour :
-
a poor reproduc$.bility with r e g a r d t o the peak s h a p e , t o the peak height a n d s o - m e t i m e s t o t h e peak t e m p e r a t u r e f o r s a m p l e s i n p r e s u m e d i d e n t i c a l m i c r o s t r u c t u - r a l s t a t e (fig. 1 ) o r f o r the s a m e s p e c i m e n s u b m i t t e d t o i d e n t i c a l ageing t r e a t m e n t s (fig. 2 ) . A s i l l u s t r a t e d in fig. 1, i t happens that n o peak a t a l l was r e g i s t r e d f o r s o m e s p e c i m e n s p r e p a r e d following conditions leading t o t h e a p p e a r a n c e of p e a k s f o r s e v e r a l o t h e r s a m p l e s . P o o r reproducibility i n the peak s h a p e h a s a l s o been noted in t h e l i t e r a t u r e f o r cold-worked dilute /11/ a n d c o n c e n t r a t e d Cu-A1 a l l o y s /12/.F i g . 1. T h r e e s p e c i m e n s of A1-Mg 5 % F i g . 2 . One s a m p l e of A1-Mg 13% t e s - t a k e n f r o m adjacent r e g i o n s of t h e s h e e t t e d twice following B1 p r o c e d u r e . The a n d p r e p a r e d following p r o c e d u r e C 2 : s p e c i m e n was both t i m e s s u b m i t t e d t o a t = 50 d a y s , T = a m b i e n t t e m p e r a t u r e s h o r t homogeneization t r e a t m e n t of
a T 2 190 K.
2 two h o u r s a t 7 2 3 K , t h e r e a f t e r w a t e r quenched and a g e d 7 h o u r s a t 303 K.
0
- a d e c r e a s e in the p e a k height a n d a change i n t h e peak t e m p e r a t u r e f o r s u c c e s s i - ve r u n s . S e e f o r example fig. 3 a n d fig. 4. In t h i s l a s t f i g u r e , i t c a n be s e e n that a f t e r running t o a m b i e n t t e m p e r a t u r e , t h e high peak h a s completely d i s a p p e a r e d and t h e f r e q u e n c y l e v e l a t low t e m p e r a t u r e h a s been notably d e c r e a s e d .
I a I
200 250' 3001 zad 250 300
Temperature I K I TempemturelKl
C9-268 JOURNAL DE PHYSIQUE
-
n o d i s p l a c e m e n t of t h e p e a k t e m p e r a t u r e f o r m e a s u r e m e n t s m a d e a l t e r n a t e l y a t 1 H z a n d 2 . 4 H z d u r i n g o n e h e a t i n g r u n ( s e e fig. 5).225 250 275 225 250 275
Twnperature I K 1
.
2 n d run2 35 Ymnx =,tiL
2 30
LL
F i g . 3. A1-Mg 1
%;
B 1 : T = a m b i e n t F i g . 4. S a m p l e of A1-Mg1370
w a t e r t e m p e r a t u r e , t 2-
= 5 m o n k s . q u e n c h e d a f t e r t r e a t m e n t a t 7 2 3 K.A1-Mg 5 % , B 2 : T = 3 0 3 K , t = 3 0 d a y s ; B 1 : T = 3 0 3 K , t = 7 h o u r s .
a a
& = I % , T 2 = 1 9 0 % . 2
5 I I
225' 25d 275
10
50 IOO I I 150T m ~ e r a t u r e [ K ] Time lrnlnl
F i g . 5. A l t e r n a t e m e a s u r e m e n t s a t 1 H z F i g . 6. I n t e r n a l f r i c t i o n v e r s u s t e m p e - a n d 2 . 4 H z . r a t u r e ( l e f t ) a n d t i m e ( r i g h t s h o w i n g -41-Mg 1 % . BZ : -I = a m b i e n t t e m p e r a - t h e g r o w t h a n d d e c a y of 0-l) i n t h e v i - t u r e , t = 8 m o n t h s , a E = I % , T = 1 9 0 K .
2 2 c i n i t y of t h e p e a k t e m p e r a t u r e .
a A1-Mg 5 % - C 2 : E = 1 . 2 % , T = 1 9 0 K
A1-Mg 1 3 % , w a t e r q u e n c h i n g a f t e r h o m o - 1 1
g e n e i z a t i o n , B 1 : T = 3 0 3 K, t =7 h o u r s . T = a m b i e n t t e m p e r a t u r e , t = 3 m o n t h s
a a a
A1-Mg 1 3 %
-
w a t e r q u e n c h e d , B 1 : T = 3 0 3 K , t = 7 h o u r s .a a
S o m e e x p e r i m e n t s w e r e p e r f o r m e d t o t e s t t h e t i m e d e p e n d e n c e a t c o n s t a n t t e m p e r a - t u r e i n t h e v i c i n i t y of p e a k t e m p e r a t u r e . T w o e x a m p l e s a r e g i v e n on f i g . 6. T h e
p e a k t e m p e r a t u r e s f o r s i m i l a r e x p e r i m e n t s , w h e r e Q - ~ w a s r e c o r d e d d u r i n g c o n - t i n u o u s h e a t i n g , w e r e r e s p e c t i v e l y 238 K f o r A1-Mg 5 % a n d 233 K f o r A1-Mg 1 3 % . T o i n v e s t i g a t e t h e link b e t w e e n t h e s t r u c t u r a l s t a t e a n d t h e e x i s t e n c e of low t e m p e - r a t u r e p e a k s , e l a s t i c m o d u l u s m e a s u r e m e n t s w e r e p e r f o r m e d f r o m 303 K t o 373 K on A l - M g 1 3 % B s p e c i m e n s t o f o l l o w t h e r e v e r s i o n of t h e G u i n i e r - P r e s t o n z o n e s . S e e f i g . 71, w h e r e t h e v a r i a t i o n of f r e q u e n c y i s g i v e n f o r a w a t e r q u e n c h e d s p e c i - m e n , t o a v o i d p r e c i p i t a t i o n d u r i n g cooling, a n d f o r t w o a g e d s a m p l e s . I t w a s a s - s u m e d t h a t t h e s a m e s t r u c t u r a l s t a t e w a s a t t a i n e d a f t e r t o t a l r e v e r s i o n , s o t h a t t h e f r e q u e n c y l e v e l of e a c h s p e c i m e n w a s r e f e r r e d t o t h e one o b t a i n e d a t 373 K.
300 325 350 375 300 325 350 375 Temperature [ K I
F i g . 7
1 ) C h a n g e i n f r e q u e n c y a s a f u n c t i o n of t e m p e r a t u r e i n t h e G u i n i e r - P r e s t o n r e v e r s i o n r a n - g e .
2 ) a n d 3 ) R e l a t i v e v a r i a t i o n i n s h e a r m o d u l u s d e r i v e d f r o m f r e q u e n c y m e a s u r e m e n t s f o r s a m - p l e s a g e d 7 h o u r s a t 303K a f t e r w a t e r q u e n c h i n g . T h e s a m p l e s of f i g . 7 3 w e r e s u b m i t t e d b e f o r e m e a s u r e m e n t s i n t h e r e v e r s i o n z o n e t o i n t e r n a l f r i c t i o n t e s t i n g b e t w e e n 173 K a n d 293 K. R e s - p e c t i v e Q - I v a l u e s a n d p e a k t e m p e r a t u r e s a r e a l s o g i v e n ,
A n e t s l o p e c h a n g e d u e t o z o n e r e v e r s i o n i s n o t e d for s a m p l e s "b" a n d "c" a t a b o u t 3 2 5 K (fig. 7 1 ) , i n good a g r e e m e n t with r e s u l t s d e r i v e d f r o m u l t r a s o n i c m e a s u r e - m e n t s /8/. We a t t r i b u t e t h e s m a l l s l o p e c h a n g e a t 315 K f o r s p e c i m e n "a" t o t h e r e v e r s i o n of z o n e s f o r m e d d u r i n g t h e t i m e d e l a y of a b o u t 30 m i n u t e s b e t w e e n q u e n - c h i n g a n d f i r s t m e a s u r e m e n t s . A n e x t r a p o l a t e d d o t t e d l i n e w a s d r a w n b e l o w 315 K t o r e p r e s e n t t h e f r e q u e n c y l e v e l of a q u e n c h e d s p e c i m e n a n d c h o s e n a s r e f e r e n c e v a l u e f o r e v a l u a t i n g t h e s h e a r m o d u l u s v a r i a t i o n s . I t a p p e a r s f r o m t h e v a r i a t i o n of
A G / G
v e r s u s t e m p e r a t u r e (fig. 72 a n d 7 3 ) , t h a t a n i m p o r t a n t d e c r e a s e of m o d u l u s i s a l w a y s o b s e r v e d i n t h e r e v e r s i o n r a n g e , t h e only way by w h i c h t h e s t r u c t u r a l s t a t e s e e m s t o b e a f f e c t e d by t h e e x i s t e n c e of a low t e m p e r a t u r e i n t e r n a l f r i c t i o n p e a k i s t h r o u g h t h e high v a l u e s of s h e a r m o d u l u s a t 3 0 3 K c o m p a r e d with t h o s e d e r i v e d f o r s a m p l e s not p r e v i o u s l y s u b m i t t e d t o a low t e m p e r a t u r e i n t e r n a l f r i c - t i o n t e s t .T h e i n s t a b i l i t y of t h e s t r u c t u r a l s t a t e o b t a i n e d a f t e r s h o r t a g e i n g t i m e s i s d e n o t e d f o r s a m p l e "f" o n fig. 7 2 .
4 . D i s c u s s i o n .
- I n t e r n a l f r i c t i o n p e a k s w e r e o b s e r v e d a t low t e m p e r a t u r e only i n t h e a g e d s p e c i - m e n s of t h e t h r e e A1-Mg a l l o y s i n v e s t i g a t e d , t h e p r e l i m i n a r y a g e i n g t r e a t m e n t s l e a d i n g t o c l u s t e r i n g i n A1-Mg 1 % a n d 5%, a n d t o t h e f i r s t s t a g e s of G u i n i e r , - P r e s - t o n z o n e s f o r m a t i o n i n A l - M g 1 3 % . Due t o the p o o r r e p r o d u c i b i l i t y of t h e p e a k s , i t i s not p o s s i b l e t o d e f i n e c r i t i c a l c o n d i t i o n s f o r t h e i r a p p e a r a n c e o r t o d e r i v e c o n -
c l u s i o n s a b o u t t h e i n f l u e n c e of m a g n e s i u m c o n t e n t o r of a g e i n g c o n d i t i o n s o n t h e i n t e r n a l f r i c t i o n s p e c t r u m .
C9-270 JOURNAL DE PHYSIQUE
- F r o m t h e d e c r e a s e of t h e p e a k h e i g h t f o r s u c c e s s i v e h e a t i n g r u n s a n d f r o m t h e t i m e d e p e n d e n c e of Q - I d u r i n g i s o t h e r m a l t e s t i n g i n t h e v i c i n i t y of t h e p e a k t e m p e - r a t u r e , i t m a y b e d e d u c e d t h a t t h e o b s e r v e d m a x i m u m i n d a m p i n g i s r e l a t e d with d e f e c t s ( m a y b e M g a t o m s - v a c a n c y c l u s t e r s / 4 - 7 / ) , a b l e t o d i f f u s e i n t h e t e m p e - r a t u r e r a n g e i n v e s t i g a t e d .
- It s e e m s p r e m a t u r e a t p r e s e n t t i m e t o d e r i v e c o n c l u s i o n s f r o m t h e o b s e r v e d i n - d e p e n d e n c e of t h e p e a k t e m p e r a t u r e s with f r e q u e n c y (1 H z a n d 2 , 4 H z ) , a s i t i s p o s s i b l e t h a t t h e v a r i a t i o n of Q - I with t i m e i n t h e v i c i n i t y of t h e p e a k t e m p e r a t u r e m a y m a s k t h e f r e q u e n c y d e p e n d e n c e . E x p e r i m e n t s with g r e a t e r f r e q u e n c y r a t i o a r e n e e d e d t o c l a r i f y t h i s point.
- F o r A1-Mg 1 3 % , i t m a y b e d e r i v e d f r o m e l a s t i c m o d u l u s m e a s u r e m e n t s a b o v e 300 K, t h a t a change i n s t r u c t u r a l s t a t e i s p r o d u c e d by low t e m p e r a t u r e i n t e r n a l f r i c t i o n m e a s u r e m e n t s . T h e n a t u r e of t h i s c h a n g e i s not i d e n t i f i e d a t p r e s e n t t i m e . We i n t e r p r e t t h e p e a k s o b s e r v e d i n t h e A1-Mg a l l o y s t o b e a s s o c i a t e d with l o c a l c h a n g e i n m i c r o s t r u c t u r a l s t a t e i n d u c e d by t h e m o v e m e n t of d i s l o c a t i o n s . S e v e r a l p r o c e s s e s m a y b e c o n s i d e r e d a s f o r e x a m p l e p a r t i a l d i s s o l u t i o n of t h e c l u s t e r s /13/, r e o r i e n t a t i o n of t h e z o n e s u n d e r s t r e s s /14/, t h e r m a l l y a c t i v a t e d unpinning of t h e d i s l o c a t i o n s f o l l o w e d by a r e d i s t r i b u t i o n of t h e s o l u t e - v a c a n c y c o m p l e x e s a t h i g h e r t e m p e r a t u r e / 1 5 / . F u r t h e r e x p e r i m e n t s , a m o n g o t h e r s i n t e r n a l f r i c t i o n m e a s u r e m e n t s a t h i g h e r f r e q u e n c y a n d with l o w e r v i b r a t i o n a l s t r a i n a m p l i t u d e a r e r e q u i r e d t o i d e n t i f y t h e m e c h a n i s m r e s p o n s i b l e f o r t h e low t e m p e r a t u r e p e a k s i n a g e d A1-Mg a l l o y s .
G r a t e f u l a c k n o w l e d g e m e n t i s g i v e n t o P r o f . J . C. B a u w e n s , P r o f e s s e u r B l t U n i v e r s i - tC d e B r u x e l l e s , f o r s u p p o r t i n g t h i s w o r k .
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