Solution treatment of cast al-4.5 pct Cu alloy
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K i n e t i c s a r e d e s c r i b e d of d i s s o l u t i o n of n o n e q u i l i b r i u m second phase d u r i n g solution t r e a t m e n t of A1-4.5 pct Cu alloy. A s i m p l e n u m e r i c a l a n a l y s i s is p r e s e n t e d and c o m p a r e d with p r e v i o u s a n a l y s e s of T a n z i l l i and Heckel, T e l e s h o v and Z o l o t o r e v s k y , and Singh and F l e m i n g s . R e s u l t s of e x p e r i m e n t s a r e c o m p a r e d with t h e o r i e s p r e s e n t e d and it is shown that effective diffusion d i s t a n c e i n c r e a s e s n e a r the end of solution t r e a t m e n t when solute m u s t diffuse over d i s t a n c e s g r e a t e r than half the s e c o n d a r y d e n d r i t e a r m spacing.
HIGH s t r e n g t h
c a s t i n g a l l o y s r e q u i r e solution t r e a t go = volume f r a c t i o n of the second phase at t = 0 m e n t to develop o p t i m u m m e c h a n i c a l p r o p e r t i e s . StudD = diffusion coefficient at the solution t e m p e r a i e s on s e v e r a l alloys have shown that usual c o m m e r c i a l t u r e , sq am per sea s o l u t i o n t r e a t m e n t s do not fully solutionize c a s t s t r u c lo = one half s e c o n d a r y d e n d r i t e s p a c i n g , cm t u r e s , and that heat t r e a t m e n t s at higher t e m p e r a t u r e s a n d longer t i m e s i m p r o v e the m e c h a n i c a l p r o p e r t i e s . 1-3 t = t i m e of solution t r e a t m e n t , sec An analogous s i t u a t i o n e x i s t s in wrought m a t e r i a l s . a - CM - Co C o m m e r c i a l t h e r m a l and m e c h a n i c a l t r e a t m e n t s do not, C# in g e n e r a l , fully h o m o g e n i z e high s t r e n g t h wrought a l loys. 4-~ A n t e s , L i p s o n , and R o s e n t h a l 4 and, m o r e r e C M = m a x i m u m solubility at solution t e m p e r a c e n t l y , Singh and F l e m i n g s 5'6 have shown that s u b t u r e , g per cu am s t a n t i a l i m p r o v e m e n t s in both s t r e n g t h and ductility Co = i n i t i a l c o m p o s i t i o n , g per cu cm of wrought high s t r e n g t h a l u m i n u m a l l o y s can be obt a i n e d by p r o c e s s i n g t e c h n i q u e s which fully h o m o g e n i z e CI~ = c o m p o s i t i o n of /3 p h a s e , g per cu c m the s t r u c t u r e . The i m p r o v e d homogeneity of these m a The c r i t i c a l t i m e for complete s o l u t i o n i z i n g , t c , is t e r i a l s then m a k e s it p o s s i b l e to i n c r e a s e s t r e n g t h obtained by s e t t i n g g = 0 and s o l v i n g Eq. [1] for t: through an i n c r e a s e in s o l u t e , while s t i l l r e t a i n i n g a d e quate ductility. 4l~ go + a tc = ~ In a [2] ANALYSES OF SOLUTION T R E A T M E N T S e v e r a l a n a l y s e s which d e s c r i b e solution k i n e t i c s of cast structures containing a noneqnilibrium second phase have r e c e n t l y b e e n given. Each a s s u m e s that the p r e c i p i t a t e d i s s o l u t i o n is l i m i t e d by diffusion of solute in the p r i
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