THE
CORROSION
CERTAIN
MEDIA
RESISTANCE IN THE
OF ALUMINUM
CHEMICAL
1~. K . M a l a k h o v a , L. and R. G. Zinchenko
V.
ALLOYS
IN
INDUSTRIES
Zaitseva,
UDC 66.018.8:546.21
To extend the field of application of equipment m a d e f r o m the aluminum alloys AMg2, AMg3, AMg5, AMg6, and AMtsS, the North Donets B r a n c h of the S c i e n t i f i c - R e s e a r c h Institute of Chemical P l a n t has m a d e a study of the c o r r o s i o n r e s i s t a n c e of t h e s e a l l o y s . The a l u m i n u m equipment on 25 plants was inspected. T h e studies w e r e c a r r i e d out under industrial conditions. The t e s t s p e c i m e n s w e r e p r e p a r e d f r o m r o l l e d s h e e t b y the n o r m a l method (Table 1), s p e c i m e n s f r o m the m e t a l itself and f r o m welded joints being tested. Manual a r g o n - a r c welding was c a r r i e d out with a l t e r n a t i n g c u r r e n t using AMg5 w i r e . V L - 1 0 l a n thanated tungsten was u s e d as the infusible e l e c t r o d e . P l a t e s for the p r e p a r a t i o n of the t e s t s p e c i m e n s w e r e welded on a backing having a V - s h a p e d d r e s s e d edge. The joints w e r e butt-welded f r o m one side.* T h e s p e c i m e n s of b a s e m e t a l p l a c e d in the a p p a r a t u s had b e e n o p e r a t i n g under industrial conditions f r o m 1500 to 4500 h, those f r o m the welded joints up to 3000 h. The t e s t s r e v e a l e d m e d i a w h e r e aluminum alloys can be used s u c c e s s f u l l y and m e d i a which c a u s e the nonuniform and extensive c o r r o s i o n of aluminum alloys. F o r e x a m p l e , in solutions of c i t r i c acid the alloys a r e stable up to a concentration of 25% and a t e m p e r a t u r e of 50~ inclusive. When t r a c e s of iron (Fe ++ and Fe+++), which have a d e p o l a r i z i n g action, p a r t i c u l a r l y a t elevated t e m p e r a t u r e s (70~ a r e p r e s e n t in s o l u tion aluminum alloys undergo i r r e g u l a r c o r r o s i o n . In the p r e s e n c e of sulfuric acid extensive c o r r o s i o n of a l u m i n u m alloys was o b s e r v e d at 50~ in a w a s h - w a t e r c o l l e c t o r used in citric acid production, w h i c h a g r e e s with r e s u l t s in the l i t e r a t u r e [1], Aluminum alloys a r e used in the production of p o t a s s i u m n i t r a t e (under the o p e r a t i n g conditions of a d r u m d r i e r ) a t 130-150~ in dichloroethane (production of ion e x change r e s i n s ) , in aliphatic acids a t 50-60~ (production of alkyd r e s i n s ) , in 100% benzene containing t r a c e s of chlorobenzene at 4 0 80~ in monoethylene glycol a t r o o m t e m p e r a t u r e , in a m i x t u r e of a m m o n i u m hydrosulfite (820 g / l i t e r ) with a m m o n i u m sulfate (10 g / l i t e r ) a t 50~ (bisulfite production), in a m i x t u r e of acetic acid (10%) and acetic anhydride (25%) a t r o o m t e m p e r a t u r e (triacetate production), in 96% acetic anhydride, and m - d i h y d r o x y b e n z e n e ( r e active dyes production) at a m b i e n t t e m p e r a t u r e , in glacial acetic Fig. 1. I n t e r c r y s t a l l i t e c o r r o s i o n of AMg6 alloy (•
* All the welding w o r k was c a r r i e d out by the welding l a b o r a t o r y under the s u p e r v i s i o n of A. N. Kuzyukova.
TABLE
1
Principal component%%Impurities(%), not mom than
Alloy]!Mg
Mn
Si
I
,.
$~
2 18o 0,80
~
Till Be I
I-
-
3'21 0,40 0 t [ -- ]
o,o8 -
0tT1
TI
Mg
_f0870800201010
020
000!
--
0,10
-
Fe
S[
0:3610:21
0,28
--
Cu
0,10
0.10
Zn
0,20
0,20
0,20
ooolo, o ,o,8,,o,,o o, lo o, o o,,o 0,0710,00020,23 0,40 0, I0 0,20
--
-
--
T r a n s l a t e d f r o m K h i m i c h e s k o e i Neftyanoe M a s h i n o s t r o e n i e , No. 8, pp. 22-23, August, 1972.
9 1973 Consultants Bureau, a division of Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. All rights reserved. This article cannot be reproduced [or any purpose whatsoever without permission o[ the publisher. A copy o[ this article is available [rom the publisher for $15.00.
736
Fig. 2.
Scaling c o r r o s i o n of different alloys (x500): a) AMtsS alloy; b) AMg2 alloy.
acid (production of c h e m i c a l r e a g e n t s ) , and in the production of a m m o n i u m c a r b o n a t e (decanter and a m m o nium c a r b o n a t e v e s s e l ) . None of the alloys p a s s e d the t e s t s for adipic acid production (rate of c o r r o s i o n g r e a t e r than 1 g / m 2 9h) the p r i n c i p a l c o r r o s i v e m e d i a under these conditions being dicarboxylic acids at 50~C and m o i s t u r e . A p p r e c i a b l e c o r r o s i o n , p a r t i c t t l a r l y of the alloys containing m a g n e s i u m was found in a local plant for the production of dinitrochlorobenzene and m o n o c h l o r o b e n z e n e . W h e r e a s the r a t e of c o r r o s i o n of AMtsS alloy is 0.3 g / m 2 .h and the c o r r o s i o n is u n i f o r m , the r a t e of c o r r o s i o n of AMg6 alloy is 1.3 g / m 2 .h and the c o r r o s i o n is i n t e r c r y s t a l l i t e in nature (Fig. 1).* Since the b a s e m e t a l containing m a g n e s i u m was found to be u n s t a b l e , the welded joints of all the alloys welded with AMg5 w i r e underwent extensive c o r r o s i v e failure. Specimens t e s t e d in f o r m a l d e h y d e solution f r o m u r o t r o p i n e production have a low r a t e of c o r r o s i o n but the p r e s e n c e of localized c o r r o s i o n (points and pitting), and of scaling c o r r o s i o n on AMtsS and AMg2 a l l o y s , m e a n s that these alloys a r e not c o r r o s i o n - r e s i s t a n t (Fig. 2). The s p e c i m e n s showed good c o r r o s i o n r e s i s t a n c e in solutions f r o m the production of a m m o n i u m c a r bonate ( a b s o r b e r and s a t u r a t o r ) but owing to the insufficient h a r d n e s s of the alloys they had undergone a b r a s i v e w e a r by the a m m o n i u m c a r b o n a t e c r y s t a l s . In c h l o r a l k a l i production, w h e r e c a r b o n steel and s t a i n l e s s s t e e l a r e c o r r o d e d , s p e c i m e n s of the alloys tested a r e s a t i s f a c t o r i l y stable. T h e r e is no l o c a l i z e d c o r r o s i o n on the s u r f a c e and this could not be s e e n in m e t a l l o g r a p h i c investigations even on AMg6 alloy, which tends to undergo a type of i n t e r c r y s t a l l i t e c o r rosion. A f t e r testing in 98% nitric acid the b a s e m e t a l of the alloys was in a good s t a t e and the c o r r o s i o n was u n i f o r m but the welded joints had undergone i n t e r c r y s t a l l i t e failure. LITERATURE 1.
CITED
F. Todt, C o r r o s i o n and C o r r o s i o n P r o t e c t i o n [in Russian], K h i m i y a , Moscow (1966).
* The m e t a l l o g r a p h i c studies w e r e m a d e by V. I. Romanov.
737
