Corrosion behavior of aluminum-boron composites in aqueous chloride solutions
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SEDRIKS, J . A. S. GREEN, AND D. L. NOVAK
A study has b e e n made of the c o r r o s i o n b e h a v i o r of diffusion bonded 2024 a l u m i n u m a l l o y u n i d i r e c t i o n a l b o r o n f i l a m e n t c o m p o s i t e s in aqueous c h l o r i d e s o l u t i o n s . C o m p a r e d with the 2024 a l l o y , the c o m p o s i t e s suffer g r e a t e r l o c a l i z e d c o r r o s i o n , both in the p r e s e n c e and a b s e n c e of applied s t r e s s , when the e n v i r o n m e n t is in contact with t r a n s v e r s e s e c t i o n s u r f a c e s ( i . e . s u r f a c e s c o n t a i n i n g exposed b o r o n f i l a m e n t ends and diffusion bonds). The e l e c t r o c h e m i c a l b e h a v i o r of such s u r f a c e s i n d i c a t e s that the lowered c o r r o s i o n r e s i s t a n c e is not due to g a l v a n i c a c t i o n b e t w e e n the f i l a m e n t and m a t r i x , but r e s u l t s f r o m a n i n c r e a s e in the n u m b e r of anodic s i t e s , the l a t t e r b e i n g a s s o c i a t e d with the f i l a m e n t - m a t r i x i n t e r f a c e s and the diffusion bonds b e t w e e n the a l l o y foils.
O F the r e c e n t l y developed m e t a l - m a t r i x c o m p o s i t e s , d i f f u s i o n - b o n d e d a l u m i n u m a l l o y - b o r o n f i l a m e n t sheet m a t e r i a l a p p e a r s to be n e a r i n g c o m m e r c i a l u t i l i z a t i o n . Despite t h i s , r e l a t i v e l y few 1-3 c o r r o s i o n s t u d i e s of c o m p o s i t e m a t e r i a l s have b e e n conducted, and it has b e e n pointed out that, s i n c e b o r o n p o s s e s s e s s o m e e l e c t r i c a l c o n d u c t i v i t y , the p o s s i b i l i t y of g a l v a n i c c o r r o s i o n o c c u r r i n g between the f i l a m e n t s and the m a t r i x c a n not be r u l e d o u t ) The a i m of this i n v e s t i g a t i o n was to e x p l o r e the c o r r o s i o n b e h a v i o r of a l u m i n u m a l l o y - b o r o n f i l a m e n t c o m p o s i t e s in aqueous salt s o l u t i o n s , both in the p r e s ence and a b s e n c e of applied s t r e s s , and in p a r t i c u l a r to e s t a b l i s h w h e t h e r s i g n i f i c a n t galvanic effects do o c c u r b e t w e e n the b o r o n f i l a m e n t s and the s u r r o u n d i n g m e t a l m a t r i x . A 2024 a l u m i n u m alloy was s e l e c t e d as the m a t r i x m a t e r i a l , and to expedite the study, heat t r e a t m e n t s w e r e chosen which m a x i m i z e s u s c e p t i b i l ity to i n t e r g r a n u l a r c o r r o s i o n in this a l l o y . The c o r r o s i o n b e h a v i o r of the alloy and the 2024-B c o m p o s i t e s was c o m p a r e d a f t e r such heat t r e a t m e n t s .
P a r a l l e l - s i d e d t e n s i l e s p e c i m e n s ( i . e . c o n t a i n i n g no r e d u c e d section) w e r e p r e p a r e d both for m e c h a n i c a l t e s t i n g and for the e v a l u a t i o n of c o r r o s i o n b e h a v i o r in the p r e s e n c e of s
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