Dimensional changes in heat treating aluminum alloys
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the s o u r c e of p a r t of the d i m e n s i o n a l c h a n g e s o c c u r r i n g in s u b s e q u e n t s t e p s of the c o m p l e t e heat t r e a t i n g cycle, and also a r e the p r i m a r y f a c t o r in c a u s i n g d i m e n s i o n a l i n s t a b i l i t y that m a y a c c o m p a n y m e t a l removal operations. Significant t i m e - d e p e n d e n t d i m e n s i o n a l c h a n g e s a r e a t t r i b u t a b l e to the m e t a l l u r g i c a l s t r u c t u r e changes f r o m solution, p r e c i p i t a t i o n and t r a n s f o r m a t i o n ( m e t a s t a b l e to e q u i l i b r i u m p r e c i p i t a t e changes) of s o l u b l e alloy p h a s e s . T h e s e p r o c e s s e s a c c o u n t for both t r a n s i e n t and p e r m e n e n t d i m e n s i o n a l changes e n c o u n t e r e d in heat t r e a t i n g , and the n o n e q u i l i b r i u m s t a t e s r e m a i n i n g after c e r t a i n t y p e s of heat t r e a t m e n t m a y r e s u l t in s u b s e q u e n t d i m e n s i o n a l i n s t a b i l i t y . u puu~lsnea n t e r a t u r e c o n c e r n i n g d i m e n s i o n a l c h a n g e s in a l u m i n u m a l l o y s is r e l a t i v e l y s p a r s e and s c a t t e r e d in a n u m b e r of s o u r c e s . Kempf and Hopk i n s ' p u b l i s h e d i n f o r m a t i o n on the t e m p e r a t u r e - and t i m e - d e p e n d e n c e of v o l u m e t r i c and l i n e a r d i m e n s i o n a l changes f r o m p r e c i p i t a t i o n in s o l u t i o n heat t r e a t e d a l l o y s n o t i n g the effects of i n d i v i d u a l solute e l e m e n t s and t h e i r i n t e r a c t i v e effects in c o m p o s i t i o n s b a s e d on t y p i c a l t e r n a r y s y s t e m s and in c o m m e r c i a l a l l o y s . The r e l a t i o n s h i p to m e c h a n i c a l p r o p e r t i e s and the b a s i s for s t a b i l i z e d or " d e g r o w t h e d " t e m p e r s was clearly described. Dimensional changes of a binary A1-4 pct Cu alloy from precipitation and reversion treatments over a wide temperature range and for extended periods of heating were reported by Lankes and Wassermann. 2 The results were shown to be consistent with those calculated from the known phase transformations in this system. Correlations of measured densities with those computed from chemical compositions were made by Kunkle and Willey, s Kutner and Lange 4 and Helfrich and Dodd. 5 Dimensional changes observed at various stages of the solution-quench-precipitation sequences used to produce standard tempers of commercial alloys have b e e n r e p o r t e d by H u n s i c k e r 6 and L a k t i o n o v a , et aIJ R e s i d u a l s t r e s s e s induced by q u e n c h i n g , and effects of c o m p o s i t i o n , s e c t i o n s i z e and o p e r a t i n g p a r a m e t e r s , such as s o l u t i o n t e m p e r a t u r e , cooling r a t e and s u b s e q u e n t p r e c i p i t a t i o n heat t r e a t m e n t s , on t h e m w e r e r e v i e w e d by V a n H o r n s and A n j o t . 9
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