The addition of bismuth to aluminum-magnesium alloys to prevent embrittlement by sodium
- PDF / 1,059,319 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 61 Downloads / 164 Views
T A L B O T A N D C . E. RANSLEY
The addition of s m a l l q u a n t i t i e s of b i s m u t h to a l u m i n u m - m a g n e s i u m alloys p r e v e n t s e m b r i t t l e m e n t by sodium, which is often p r e s e n t as an i m p u r i t y . The b e n e f i c i a l effect of b i s m u t h has been d e m o n s t r a t e d by v i s u a l o b s e r v a t i o n of c r a c k i n g d u r i n g r o l l i n g and by m e a s u r e m e n t of m e c h a n i c a l p r o p e r t i e s at high t e m p e r a t u r e . T h e s e o b s e r v a t i o n s were r e l a t e d to r e s u l t s obtained u s i n g a s p e c i a l hydrogen a b s o r p t i o n technique, which showed that for full p r o t e c t i o n the a t o m i c f r a c t i o n of b i s m u t h added m u s t equal or exceed the a t o m i c f r a c t i o n of s o d i u m . In p r e l i m i n a r y p r o d u c t i o n - s c a l e t r i a l s , an addition of 0.01 wt pct b i s m u t h to an a l u m i n u m - 5 wt pct m a g n e s i u m alloy was effective in e n s u r i n g good h o t - r o l l i n g c h a r a c t e r i s t i c s , d e s p i t e the p r e s e n c e of 0.0022 wt pct sodium, a d e g r e e of c o n t a m i n a t i o n u s u a l l y expected to cause s e v e r e c r a c k i n g d u r i n g r o l l i n g . No a d v e r s e effects of b i s m u t h on other p r o p e r t i e s have b e e n o b s e r v e d and s u b s e q u e n t i n t e n s i v e p r o duction use has c o n f i r m e d the efficacy of this method of t r e a t m e n t .
ALUMINUM
alloys with high m a g n e s i u m c o n t e n t s a r e e m b r i t t l e d by s o d i u m in t r a c e quantities.1 The effect on the h o t - w o r k i n g c h a r a c t e r i s t i c s is s p e c t a c u l a r . F o r example, an a l u m i n u m - 5 wt pct m a g n e s i u m alloy (e.g. to BS GE1477 s p e c i f i c a t i o n NP6), is s h a t t e r e d by e x t e n s i v e i n t e r n a l c r a c k i n g when hotr o l l e d if the s o d i u m content exceeds ~0.0025 wt pct and m i n o r c r a c k s develop with as little as 0.001 wt pct. C o n t a m i n a t i o n with s o d i u m is difficult to avoid in the n o r m a l m a n u f a c t u r i n g p r o c e s s e s . Sodium is a c o m m o n i m p u r i t y in p r i m a r y a l u m i n u m ingot used to p r e p a r e alloys and t h e r e a r e f u r t h e r s o u r c e s in fluxes and other m a t e r i a l s i n contact with the m e t a l when m o l t e n . As a r e s u l t , the sodium content u s u a l l y l i e s in the r a n g e 0.0005 to 0.004 wt pct. Methods u s e d to r e d u c e the l e v e l of c o n t a m i n a t i o n include: a) F l u s h i n g the m o l t e n m e t a l with c h l o r i n e or g a s e o u s c h l o r i n a t e d compounds. b) Allowing s e l e c t i v e oxidation of the s o d i u m at the m o l t e n m e t a l s u r f a c e with or without the a s s i s t a n c e of t u r b u l e n c e c r e a t e d by a s t r e a m of n i t r o g e n p a s s e d through the m e l t . c) Heavy fluxing with m a g n e s i u m chloride b a s e d fluxes. T h
Data Loading...
