Hydrogen embrittlement in a Mg-Al alloy
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EXPERIMENTAL The s t u d i e s w e r e c a r r i e d out on the h i g h - p u r i t y b i n c r y a l l o y c o n t a i n i n g 7.5 wt p e t A1 which was u s e d in the p r e v i o u s s t u d i e s . ' ' 2 T h r e e t y p e s of s p e c i m e n s w e r e m a c h i n e d f r o m sheet, n a m e l y : i) t e n s i l e s p e c i m e n s of d i m e n s i o n s 7.5 c m • 0.65 c m • 0.05 cm, with a gage s e c t i o n of 5.10 c m • 0.5 c m . ii) e d g e - n o t c h e d t e n s i l e s p e c i m e n s 8.9 e m • 2.85 c m • 0.125 c m with a 45 d e g notch e x t e n d i n g to a depth of 0.5 c m at one e d g e ; t h i s t y p e of t e s t p i e c e w a s u s e d in previous experiments. 2 iii) bend s p e c i m e n s of d i m e n s i o n s 7.5 c m • 0.25 c m • 0.25 c m , a l s o u s e d p r e v i o u s l y . T h e bend s p e c i m e n s w e r e h e a t t r e a t e d to p r o d u c e c o a r s e g r a i n s , and then s o l u t i o n t r e a t e d at 385~ f o r 4 h and w a t e r quenched. Both t y p e s of t e n s i l e s p e c i m e n s w e r e s o l u t i o n t r e a t e d and quenched f r o m 385~C, p r o ducing a g r a i n s i z e c o r r e s p o n d i n g to ASTM 8. P r i o r to t e s t i n g , the s u r f a c e s w e r e c l e a n e d by e t c h i n g with a D. G. CHAKRAPANt, formerly a Research Assistant in the Department of Metallurgy and Mining .Engineering, University of Illinois, tL, is now Corrosion-Control Analyst with the Physical Plant at that University. E. N. PUGH ~sProfessor of Metallurgical EngineerLn_gand a member of the Materials Research Laboratory at the University of Illinois, Urbana, IL 61801. Manuscript submitted June 13, 1975,
METALLURGICAL TRANSACTIONS A
s o l u t i o n c o n t a i n i n g 60 pct e t h y l e n e glycol, 20 pet g l a c i a l a c e t i c acid, 19 p c t w a t e r and 1 p c t c o n c e n t r a t e d n i t r i c acid. T y p e i) t e n s i l e s p e c i m e n s w e r e i m m e r s e d (uns t r e s s e d ) at r o o m t e m p e r a t u r e in the aqueous NaCt-K~CrO4 s o l u t i o n u s e d in the e a r l i e r s t r e s s c o r r o s i o n s t u d i e s . I ,z Only the g a u g e l e n g t h s w e r e e x p o s e d , the r e m a i n i n g s u r f a c e s b e i n g c o a t e d with L a c o m i t . C o r r o s i o n p o t e n t i a l s w e r e m e a s u r e d by m e a n s of a s a t u r a t e d c a l o m e l e l e c t r o d e i m m e r s e d in a s a t u r a t e d KCI solution, using an A g a r b r i d g e . A f t e r i m m e r s i o n , the s p e c i m e n s w e r e r i n s e d with d i s t i l l e d w a t e r and m e t h a n o l , and then d r i e d . S a m p l e s , 1.2 c m • 0.5 cm, w e r e cut f r o m the gage l e n g t h s of s p e c i m e n s i m m e r s e d f o r v a r i o u s t i m e s and a n a l y z e d f o r h y d r o g e n c o n c e n t r a t i o n by Leco T e c h n i c a l S e r v i c e s L a b o r a t o r y (St. J o s e p h , Michigan), using the i n e r t g a s f u s i o n m e thod. H y d r o g e n a n a l y s i s w a s a l s o c a r r i e d out on s p e c i m e n s i m m e r s
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