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The effects of n e u t r o n i r r a d i a t i o n below 3.6 • 102z n e u t r o n s / c m ~ (>0.1 MeV) and 5.8 • 10 zz n e u t r o n s / c m 2 ( t h e r m a l , < 0.414 eV) on the m i c r o s t r u c t u r e and c r e e p - r u p t u r e p r o p e r t i e s at 50~ of the 5052 a l u m i n u m alloy were d e t e r m i n e d . I r r a d i a t i o n - i n d u c e d s t r e n g t h e n i n g is a t t r i b u t e d to the f o r m a t i o n of/3' Mg2Si p r e c i p i t a t e and d i s l o c a t i o n loops. Total c r e e p - r u p t u r e elongations before i r r a d i a t i o n w e r e over 25 pct, while i r r a d i a t e d s p e c i m e n s s t r a i n e d only about 1 pct. The loss of ductility was a c c o m p a n i e d by a p r o p e n s i t y for i n t e r g r a n u l a r fracture.

ALUMINUM

and its alloys have b e e n used e x t e n s i v e l y in w a t e r - c o o l e d r e s e a r c h and m a t e r i a l s t e s t i n g r e a c t o r s . The choice of a p a r t i c u l a r alloy has been d i c tated h i s t o r i c a l l y by c o n s i d e r a t i o n s of u n i r r a d i a t e d s t r e n g t h , ductility, c o r r o s i o n r e s i s t a n c e and w e l d a b i l ity. Only r e c e n t l y have the effects of n e u t r o n i r r a d i a tion damage on m e c h a n i c a l p r o p e r t i e s and on s w e l l i n g in a l u m i n u m alloys r e c e i v e d attention. The r e s u l t s of s t u d i e s on 1100 a l u m i n u m , t 8001 z alloy and m o r e r e c e n t l y on the t e r n a r y A1-Mg-Si 60613 alloy in the aged condition have shown that i r r a d i a t i o n g e n e r a l l y i n c r e a s e s s t r e n g t h and r e d u c e s ductility. The d u c t i l i t y loss in i r r a d i a t e d a l u m i n u m alloys is p a r t i c u l a r l y s e v e r e under slow s t r a i n r a t e t e s t i n g at t e s t t e m p e r a t u r e s n e a r 200~ although adequate d u c t i l i t y e x i s t s at about 50 to 100~ Of the a l u m i n u m alloys studied to date, 4 the A1-Mg-Si alloy (6061) c o n t a i n i n g a high c o n c e n t r a t i o n of MgzSi p r e c i p i t a t e p a r t i c l e s exhibits the b e s t r e s i s t a n c e to s w e l l i n g f r o m voids. The 5052 alloy, e s s e n t i a l l y A1-2.5 wt pct Mg, is a s o l i d - s o l u t i o n alloy which has b e e n e m p l o y e d in the c o n s t r u c t i o n of the c a l a n d r i a in the B r i t i s h SGHW R e actor S and in the tank of the A m e r i c a n Oak Ridge R e s e a r c h (ORR) R e a c t o r . However, s i l i c o n produced by the Z~Al(n, y)28A1, ZSA1 ~ ZSSi+ f3 r e a c t i o n s , p r i m a r i l y with t h e r m a l n e u t r o n s , c o n v e r t s the alloy into a t e r n a r y A1-Mg-Si alloy. We have shown e a r l i e r 6 that this t r a n s m u t a t i o n - p r o d u c e d Si r e a c t s with the Mg in solid solution in the 5052 alloy to produce a fine d i s t r i b u t i o n of/3' Mg2Si p r e c i p i t a t e . The c o n s e q u e n c e s of this r e a c tion together with the f a s t - n e u t r o n induced damage s t r u c t u r e