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Table I

Alloy

Zn

Cu

Pct by Wt Si

Fe

Mg

A B

38.9 39.3

0.008 0.94

0.004 0.004

0.006 0.009

0.001 0.001

Allotherslessthan 0.001 pct.

Authors' Reply

(a) 80

AI-40%Z~-=%du

AI- 4 0 % Z'n

70 I

N. SANO, S. HONMA, AND Y. MATSUSHITA

..,... ~

~ 0

Q

Q

~ 1 7 6

U~

6O Whiteway and M a s s o n a v e r a g e d the e l e c t r o m o t i v e f o r c e and the i n t e r n a l r e s i s t a n c e s e p a r a t e l y and c o m b i n e d them for the e q u i v a l e n t c i r c u i t . G e n e r a l l y s p e a k ing, however, the e s t i m a t i o n of the i n t e r n a l r e s i s t a n c e of a m a t e r i a l , in which the e l e c t r i c a l p o t e n t i a l d i f f e r s locally, is not as s i m p l e as they suggest. We think that t h e i r e s t i m a t i o n should be j u s t i f i e d exp e r i m e n t a l l y , c o m p a r i n g t h e i r data with that c o m p i l e d by a n o t h e r method, for e x a m p l e . Judging f r o m t h e i r data, we accept t h e i r e s t i m a t i o n . However, we f e a r that it will be a s s u m e d that the tube is applicable in all s i t u a t i o n s , a long tube wholly dipped in a r e f e r e n c e bath, for i n s t a n c e . On the c o n t r a r y , our method does not involve any q u e s t i o n a b l e e s t i m a t i o n and can be applied widely.

8 12 g S 8 4 ,T,

50 co , , l * , L , I l l l l

(b) SC AI- 40"/. Z~ 7(3

60

AI-4'O% Z~- I%C~,

9-Tensile Strength *-O.2 % Yield Strength

~ ' . . , . , ~ Elongation

-1, 50 a~

40

(,3

5o

N ~

16 8 12 :o

12 N Sano.S. Honma,andY Matsush]ta Met Trans., 1970,vol 1, pp. 301-03 13. C. R. Massonand S. G. Wh]teway:Can. Met Quart., 1967,vol.6. pp 199217.

4 ,T,

O,I ' ' II 2 5' lot ' '1

IOOO O.I

I

IO

IOO IOOO

0

AgiNg Time (Hours)

Fig. 1-Effect of aging time at (a) 25~ and (b) 95"C on the tensile properties of A1-Zn alloys.

On the Mechanical Properties of AI- 40 Pct Zn Alloys R. C. DORWARD

ALUMINUMalloys

c o n t a i n i n g zinc in the r a n g e 30 to 60 wt pct have r e c e i v e d c o n s i d e r a b l e attention recently, due to the p o s s i b i l i t y of spinodal d e c o m p o s i t i o n o c c u r r i n g in this s y s t e m . ~ It s e e m s r e a s o n a b l e to expect that this mode of d e c o m p o s i t i o n might give c o n s i d e r a b l e s t r e n g t h e n i n g b e c a u s e of the close spacing and s p a t i a l r e g u l a r i t y of " p r e c i p i t a t e s " f o r m e d by the p r o c e s s . Although C a h n ' s theory of spinodal h a r d e n i n g z does not a p p e a r to p r e d i c t e x p e r i m e n t a l l y o b s e r v e d s t r e n g t h s , 3'4 a m e c h a n i s m proposed by H i r s c h and Kelly 5 i n d i c a t e s that s i g n i f i c a n t s t r e n g t h e n i n g should o c c u r i n s p i n o d a l l y - d e c o m p o s e d s t r u c t u r e s having l a r g e v a r i a t i o n s i n s t a c k i n g - f a u l t e n e r g y a s s o c i a t e d with the c o m p o s i tion fluctuations. This theory should be p a r t i c u l a r l y a p r o p r o s to c o n c e n t r a