Precision forging of a high strength superplastic zinc-aluminum alloy
- PDF / 1,691,919 Bytes
- 6 Pages / 613 x 788.28 pts Page_size
- 72 Downloads / 182 Views
S U P E R P L A S T I C a l l o y s have a c h a r a c t e r i s t i c a l l y low flow s t r e s s when they a r e d e f o r m e d at low s t r a i n r a t e s . T h i s flow s t r e s s i n c r e a s e s r a p i d l y with s t r a i n r a t e and at s t r a i n r a t e s in the r a n g e n o r m a l l y e m ployed in c o m m e r c i a l hot working, the f o r m i n g loads r e q u i r e d a r e s i m i l a r to those which m u s t be applied to comrentional a l l o y s . With the d e v e l o p m e n t of s u p e r p l a s t i c alloys which have good m e c h a n i c a l and p h y s i cal p r o p e r t i e s at a m b i e n t t e m p e r a t u r e s , it has become d e s i r a b l e to e v a l u a t e e c o n o m i c t e c h n i q u e s for p r o d u c i n g p r e c i s i o n forged p a r t s u t i l i z i n g the s u p e r p l a s t i c p r o p e r t i e s of these a l l o y s . It has b e e n suggested that e c o n o m i c a l slow speed f o r g i n g p r o c e s s e s could be developed for s u p e r p l a s t i c a l l o y s in c e r t a i n a p p l i c a t i o n s . The d i s a d v a n t a g e of longer f o r m i n g t i m e s would be outweighed by the lower cost of tooling and p r e s s e q u i p m e n t which is made p o s s i b l e by the s i g n i f i c a n t r e d u c t i o n s in f o r g i n g loads. A n u m b e r of f o r g i n g e x p e r i m e n t s c a r r i e d out with the eutectoid z i n c - a l u m i n u m alloy have b e e n r e p o r t e d . T h i s alloy can r e a d i l y be produced in an u l t r a f i n e g r a i n s t r u c t u r e and d e f o r m s under low s t r e s s e s at t e m p e r a t u r e s j u s t below the t r a n s f o r m a t i o n at 527~ (275~ P r o c e s s e s such as those d e s c r i b e d by F i e l d s , 1 Stewart, 2 and F e n g 3 a r e e x t e n s i o n s of c o m p r e s s i o n m o l d i n g p r a c t i c e c a r r i e d out in the p l a s t i c s i n d u s t r y . Other e x p e r i m e n t s in which z i n c - a l u m i n u m dies for coining o p e r a t i o n s w e r e produced by hobbing a r e d e s c r i b e d by S a l l e r and Duncan. 4 The most e x t e n s i v e work on closed die f o r g i n g is that by Stewart. 2 He p e r f o r m e d a n u m b e r of u p s e t t i n g and f o r g i n g o p e r a tions on z i n c - a l u m i n u m - c o p p e r alloys over a r a n g e of f o r g i n g speeds and t e m p e r a t u r e s . U s i n g p r e s s u r e s of up to 60,000 p s i (414 MPa), he showed that e x c e l l e n t die f i l l i n g could be obtained even in v e r y thin web s e c t i o n s . In addition, v e r y s m a l l draft a n g l e s could be used and s h a r p c o r n e r s were r e a d i l y produced on the p a r t s . All of S t e w a r t ' s e x p e r i m e n t s were c a r r i e d out on a h y d r a u l i c p r e s s at v e r y low s t r a i n - r a t e s . Closed die forging of a Pb-Sn-Zn ternary eutectoid alloy was carried out by Moles 6 using dies which had been prepared for conventional hot forging of gas turbine blades. He showed that forging
Data Loading...
