The anisotropy of Al-4 Wt Pet Cu single crystals tested in plane-strain compression
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a r e c e n t study, 1 Hosford and Z e i s l o f t i n v e s t i g a t e d the effect of age h a r d e n i n g on a n i s o t r o p y of A1-4 wt pct Cu s i n g l e c r y s t a l s i n p l a n e - s t r a i n c o m p r e s s i o n . The resulting compressive stress-strain curves showed much l e s s a n i s o t r o p y than the c u r v e s for s i m i l a r l y t e s t e d s i n g l e - p h a s e c r y s t a l s ; the a n i s o t r o p y was m u c h l e s s t h a n that p r e d i c t e d by the T a y l o r 2 and Bishop and Hill 3 m o d e l s . T h e s e r e s u l t s w e r e e x p l a i n e d by p o s t u l a t i n g that the d i s p e r s e d O' p r e c i p i t a t e p l a t e lets m a i n t a i n e d c o m p a t i b i l i t y with the d e f o r m i n g m a t r i x by both d e f o r m i n g and r o t a t i n g ; the r e l a t i v e a m o u n t s of d e f o r m a t i o n (which r e q u i r e s e n e r g y and t h u s c o n t r i b u t e s to s t r e n g t h e n i n g ) and of r o t a t i o n (which does not c o n t r i b u t e to s t r e n g t h e n i n g ) would v a r y with o r i e n t a t i o n . Some o r i e n t a t i o n s a r e , t h e r e fore, s t r e n g t h e n e d m u c h m o r e by the p r e c i p i t a t e t h a n o t h e r s . T h u s , the p l a t e - l i k e s h a p e and {100} h a b i t of the 0' c a u s e s an a n i s o t r o p y of the s e c o n d p h a s e s t r e n g t h e n i n g which c o m b i n e s with the T a y l o r type a n i s o t r o p y of the m a t r i x c r y s t a l in such a way as to r e d u c e the o v e r a l l a n i s o t r o p y . The p r e s e n t w o r k was u n d e r t a k e n to study the n a t u r e of the a n i s o t r o p y in the s a m e alloy in both the s o l u t i o n - t r e a t e d condition, where no s t r e n g t h e n i n g f r o m p r e c i p i t a t e s would be expected, and the o v e r a g e d condition w h e r e the 0' p l a t e l e t s have grown into the e q u i l i b r i u m p r e c i p i t a t e , 0-CuA12. T h e 0 p r e c i p i t a t e i s n o n c o h e r e n t , g e n e r a l l y cuboidal o r s p h e r o i d a l in s h a p e . T h e r e f o r e , p r e c i p i t a t e s t r e n g t h e n i n g should be l e s s a n i s o t r o p i c than with 0'. EXPERIMENTAL
PROCEDURES
The binary AI-4 wt pct Cu alloy, obtained as a plate (i.i cm thick), was the same as that used earlier.1 Grains of up to i0 cm diam were grown by pulling b a r s cut f r o m the plate to ~'0.7 pct s t r a i n , followed by a n n e a l i n g i n a f o r c e d - a i r f u r n a c e at ~535°C for 2 d a y s , then r e p e a t i n g the cycle. T h e o r i e n t a t i o n s of the l a r g e r g r a i n s (>2 c m diam) w e r e d e t e r m i n e d by the Laue b a c k - r e f l e c t i o n t e c h n i q u e . Two s e t s of s i n -
gle c r y s t a l s p e c i m e n s (1.25 c m × 1.25 c m × 0.65 cm) were machined from suitably oriented grains. Table I shows the n o m i n a l o r i e n t a t i o n s and the d i v e r g e n c e of the s p e c i m e n s f r o m t h e s e o r i e n t a t i o
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