The mechanisms of anneal hardening in Cu-Al alloys
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c a n be a p p l i e d to d e r i v e the c o m p o s i t i o n and p r o c e s s i n g v a r i a b l e s which d e t e r m i n e the p r a c t i c a l u s e of t h i s s t r e n g t h e n i n g effect. W h e r e a s m o s t p r e c e d i n g i n v e s t i g a t i o n s of a n n e a l h a r d e n i n g of Cu-A1 a l l o y s w e r e c a r r i e d out b y i s o c h r o n a l h e a t t r e a t m e n t , the p r e s e n t w o r k i s m a i n l y b a s e d on i s o t h e r m a l annealing. Also, s i n c e s o m e a n n e a l i n g p r o c e s s e s and r e s u l t i n g p r o p e r t y c h a n g e s o c c u r at r o o m t e m p e r a t u r e a f t e r d e f o r m a t i o n (as w a s shown f o r C u - Z n in Ref. 7 and f o r Cu-A1 in t h e p r e s e n t w o r k ) the s p e c i m e n s u s e d in t h i s w o r k w e r e s t o r e d in liquid n i t r o g e n w h e n e v e r p o s s i b l e to m i n i m i z e the d a n g e r of f a i l i n g to o b s e r v e the low t e m p e r a t u r e aging p h e n o m e n a . The p a r a m e t e r s m e a s u r e d h e r e w e r e t e n s i l e p r o p e r t i e s , Young's m o d u l u s and e l e c t r i c a l r e sistivity.
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A Cu-16.1 at. pct A1 alloy was produced from high purity Cu (99.9998 pct) and A1 (99.999 pct) by vacuum induction m e l t i n g in an a l u m i n a c r u c i b l e and c a s t i n g into 11 • 8 x 1 c m Cu c h i l l m o l d s . The ingots w e r e h o m o g e n i z e d in e v a c u a t e d q u a r t z t u b e s f o r 6 d a y s at 850~ and then a i r c o o l e d . 1 m m and 0.2 m m s h e e t s p e c i m e n s with an a v e r a g e g r a i n s i z e of 30 t~m w e r e o b t a i n e d by c o l d r o l l i n g and c o n t r o l l e d r e c r y s t a l l i z a t i o n at 500~ Rod s p e c i m e n s 6 m m diana w e r e a l s o p r e p a r e d by hot swaging. The s u b s e q u e n t t r e a t m e n t c o n s i s t e d of a n n e a l i n g f o r 30 m i n at 450~ quenching into CaCI" 6H20 b r i n e at - 4 0 c C , which e n s u r e s that a m i n i m u m d e g r e e of SRO i s obtained, 14 and i m m e d i a t e c o o l i n g in liquid n i t r o g e n , w h e r e the s p e c i m e n s w e r e k e p t b e t w e e n a l l s u b s e q u e n t t r e a t m e n t s and m e a s u r e m e n t s . T e n s i l e s p e c i m e n s w e r e o b t a i n e d f r o m the 1 m m s h e e t a f t e r 50 p e t r e d u c tion. The s a m p l e s w e r e s t a m p e d out of the 0.5 ram s h e e t with 30 m m gage length, 3.2 m m wide. Rod s p e c i m e n s f o r m e a s u r e m e n t s of Young's m o d u l u s w e r e c o l d d r a w n f r o m 6 to 4 m m diana in t h r e e p a s s e s , the r e d u c tion in a r e a b e i n g 55 p c t . F o r e l e c t r i c a l r e s i s t i v i t y m e a s u r e m e n t s 0.1 m m s h e e t s p e c i m e n s w e r e p r o d u c e d by c o l d r o l l i n g the 0.2 m m s h e e t and s t a m p i n g out with a d i e which y i e l d e d a s t r i p with four t a b s for a t t a c h m e n t of c u r r e n t and v o l t a g e l e a d s . I m m e d i
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