Serrated flow in aluminum 6061 alloy
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flow is often o b s e r v e d in t e n s i l e d e f o r m a t i o n of s u b s t i t u t i o n a l alloys such as C u - S n , 1 ~ b r a s s , 2 and s o m e a l u m i n u m alloys.l'2 We s h a l l c o n c e n t r a t e on R u s s e l l ' s 1 Type A and B, as defined in F i g . 1. S e v e r a l a u t h o r s have studied the s t r a i n i n c r e m e n t s a s s o c i a t e d with these two f o r m s of load drops S by a t taching e x t e n s o m e t e r s to the s p e c i m e n s , 2'4 or by v i s u a l o b s e r v a t i o n of s u r f a c e s t r a i n m a r k i n g s . T h e s e s t u d i e s have shown that Type A s e r r a t i o n s a r e a s s o ciated with Liiders bands that n u c l e a t e r e p e a t e d l y at the s a m e end of the s p e c i m e n gage length and p r o p a gate to the other end u n d e r i n c r e a s i n g load. 2'4'8 Type B s e r r a t i o n s c o n v e r s e l y r e p r e s e n t bands that f o r m but do not p r o p a g a t e . 1'2'7 Some a u t h o r s 1'2'5 r e p o r t that Type B bands f o r m s u c c e s s i v e l y ahead of each o t h e r , which is e q u i v a l e n t to the d i s c o n t i n u o u s p r o p a g a t i o n of a s i n g l e band, while o t h e r s state that they n u c l e a t e at r a n d o m over the gage length, 7 or that the bands form independently. In this work a technique involving photoelastic coatings was used to obtain additional e x p e r i m e n t a l i n f o r m a t i o n that could shed light on the n a t u r e of these s e r r a t i o n s . E X P E R I M E N T A L TECHNIQUES 6061 a l u m i n u m alloy was u s e d . The heat t r e a t m e n t , g r a i n size and c r o s s h e a d speed w e r e v a r i e d to p r o duce e i t h e r Type A or B s e r r a t i o n s on r o o m t e m p e r a t u r e l o a d - t i m e c u r v e s . The s p e c i m e n s were flat, with 2 in. (51 mm) gage length and 0.125 (3.2 mm) t h i c k n e s s . P h o t o e l a s t i c coatings w e r e c e m e n t e d to these s p e c i m e n s . When these coatings w e r e i l l u m i nated by p o l a r i z e d white light and viewed through a r e f l e c t i o n p o l a r i s c o p e , the p l a s t i c s t r a i n p a t t e r n in the s p e c i m e n could be viewed over the gage s e c t i o n . The f o r m a t i o n and m o v e m e n t of bands w e r e r e corded on motion p i c t u r e f i l m , s y n c h r o n i z e d with the I n s t r o n C h a r t R e c o r d e r by a t i m e r included in the p i c t u r e f r a m e . The e l a s t i c m o d u l u s of both the P. R. CETLIN, formerly Graduate Student, University of Florida, Gainesville, Fla. 32601, is now at Instituto de Pesquisas Radioativas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil. A. $. GIJLE(~ is Visiting Assistant Professor, University of Florida, on leave from Technical University of lstanbul, Istanbul, Turkey. R. E. REEDHILL is Professor, Department of Materials Science and Engineering, University of Florida. Manuscript submitted May 15, 1972. METALLURGICALTRANSACTIONS
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