U.S. patent application number 11/768955 was filed with the patent office on 2009-01-01 for corrosion inhibiting additive.
Invention is credited to Sarah Arsenault, James T. Beals, Mark R. Jaworowski.
Application Number | 20090004486 11/768955 |
Document ID | / |
Family ID | 39772850 |
Filed Date | 2009-01-01 |
United States Patent
Application |
20090004486 |
Kind Code |
A1 |
Arsenault; Sarah ; et
al. |
January 1, 2009 |
CORROSION INHIBITING ADDITIVE
Abstract
A corrosion resistant article includes an aluminum substrate
having greater than 0.25 wt % zinc, and a protective coating on the
aluminum substrate. The protective coating includes a non-tungstate
anodic corrosion inhibitor and a cathodic corrosion inhibitor.
Inventors: |
Arsenault; Sarah; (Vernon,
CT) ; Beals; James T.; (West Hartford, CT) ;
Jaworowski; Mark R.; (Glastonbury, CT) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD, SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
39772850 |
Appl. No.: |
11/768955 |
Filed: |
June 27, 2007 |
Current U.S.
Class: |
428/457 ;
106/14.05 |
Current CPC
Class: |
C09D 5/084 20130101;
C23C 22/83 20130101; C23F 11/187 20130101; C09D 5/12 20130101; Y10T
428/31678 20150401; C23F 11/12 20130101; C23C 22/40 20130101; C23F
11/185 20130101; C23C 22/73 20130101 |
Class at
Publication: |
428/457 ;
106/14.05 |
International
Class: |
B32B 15/04 20060101
B32B015/04; C04B 9/02 20060101 C04B009/02 |
Claims
1. A corrosion resistant article comprising: an aluminum substrate
having greater than 0.25 wt % zinc; and a protective coating on the
aluminum substrate, the protective coating comprising a
non-tungstate anodic corrosion inhibitor and a cathodic corrosion
inhibitor.
2. The corrosion resistant article as recited in claim 1, wherein
the aluminum substrate includes greater than 5 wt % zinc.
3. The corrosion resistant article as recited in claim 2, wherein
the aluminum substrate includes about 5.1-6.1 wt % of the zinc.
4. The corrosion resistant article as recited in claim 1, wherein
the aluminum substrate includes about 2 wt % or less of copper.
5. The corrosion resistant article as recited in claim 4, wherein
the aluminum substrate includes about 1.2-2 wt % of the copper.
6. The corrosion resistant article as recited in claim 5, wherein
the aluminum substrate comprises about 0.3 wt % manganese, about
2.1-2.9 wt % magnesium, about 0.4 wt % silicon, about 0.5 wt %
iron, about 5.1-6.1 wt % of the zinc, about 0.18-0.35 wt %
chromium, about 0.2 wt % titanium, and a balance of aluminum.
7. The corrosion resistant article as recited in claim 1, wherein
the non-tungstate anodic corrosion inhibitor comprises at least one
of a vanadate compound or a molybdate compound.
8. The corrosion resistant article as recited in claim 7, wherein
the non-tungstate anodic corrosion inhibitor consists of zinc
molybdate.
9. The corrosion resistant article as recited in claim 1, wherein
the cathodic corrosion inhibitor comprises a Group IIIB Periodic
Table element.
10. The corrosion resistant article as recited in claim 9, wherein
the cathodic corrosion inhibitor consists of cerium citrate.
11. The corrosion resistant article as recited in claim 1, wherein
the protective coating comprises a conversion coating, primer,
paint, adhesive, or sealant.
12. The corrosion resistant article as recited in claim 1, wherein
the non-tungstate anodic corrosion inhibitor and the cathodic
corrosion inhibitor comprise about 1-50 wt % of the protective
coating.
13. A method of selecting a corrosion-inhibiting substance,
comprising: selecting a corrosion-inhibiting substance to include a
non-tungstate anodic corrosion inhibitor based upon an amount of at
least one alloying element in an aluminum alloy substrate that is
to be coated with the corrosion-inhibiting substance.
14. The method as recited in claim 13, wherein the at least one
alloying element comprises zinc, and further including selecting
the corrosion inhibiting substance to include the non-tungstate
anodic corrosion inhibitor based upon the amount of the zinc being
between greater than 0.25 wt % of the aluminum alloy.
15. The method as recited in claim 13, wherein the at least one
alloying element comprises zinc, and further including selecting
the corrosion inhibiting substance to include the non-tungstate
anodic corrosion inhibitor based upon the amount of the zinc being
between about 5.1 and 6.1 wt % of the aluminum alloy.
16. The method as recited in claim 13, including selecting the
non-tungstate anodic corrosion inhibitor to include at least one of
vanadium and molybdenum.
17. The method as recited in claim 16, including selecting the
non-tungstate anodic corrosion inhibitor to include zinc
molybdate.
18. The method as recited in claim 13, including selecting the
corrosion inhibiting substance to include a cathodic corrosion
inhibitor comprising at least one Group IIIB Periodic Table
element.
19. A corrosion-inhibiting substance comprising: a carrier fluid; a
cathodic corrosion inhibitor within the carrier fluid; and a
zinc-inert anodic corrosion inhibitor within the carrier fluid for
protecting aluminum alloys having greater than 0.25 wt % zinc.
20. The corrosion-inhibiting substance as recited in claim 19,
wherein the carrier fluid comprises at least one of water, alcohol,
primer, paint, adhesive, or sealant.
21. The corrosion-inhibiting substance as recited in claim 19,
wherein the zinc-inert anodic corrosion inhibitor consists of zinc
molybdate.
22. The corrosion-inhibiting substance as recited in claim 21,
wherein the cathodic corrosion inhibitor consists of cerium
citrate.
23. The corrosion-inhibiting substance as recited in claim 19,
comprising about 0.1 to 100 grams per liter of each of the cathodic
corrosion inhibitor and the zinc-inert anodic corrosion inhibitor
within the carrier fluid.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to corrosion inhibitors and, more
particularly, to a corrosion inhibitor that is effective for use on
aluminum alloys having relatively high amounts of zinc.
[0002] Components made from metallic alloys, such as aluminum
alloys, achieve higher strengths through inclusion of alloying
elements. However, the presence of these alloying elements tends to
make the alloy vulnerable to corrosion. Typically, the component
utilizes a protective coating containing a corrosion-inhibitor to
protect the underlying alloy from corrosion.
[0003] One type of corrosion-inhibitor includes hexavalent chromium
in the form of a barium or strontium chromate compound, for
example. Although effective, hexavalent chromium is commonly
recognized as a carcinogen and is therefore undesirable for use as
a coating.
[0004] Chrome-free corrosion-inhibitors have been used as an
alternative to hexavalent chromium inhibitors. For example,
chrome-free corrosion inhibitors utilize anodic and cathodic
corrosion inhibitors to resist corrosion of the underlying alloy.
One drawback of existing chrome-free corrosion inhibitors is that
they do not provide equal corrosion protection for all alloy
compositions.
[0005] New compositions of aluminum alloys are being developed and
are finding use in industries such as the aerospace industry.
Although conventional corrosion inhibitors, such as EcoTuff.RTM.,
have been effective in providing corrosion protection, an even
greater degree of corrosion protection is desired. Accordingly,
there is a need for a corrosion-inhibiting substance that provides
enhanced corrosion protection of aluminum alloys.
SUMMARY OF THE INVENTION
[0006] An example corrosion resistant article includes an aluminum
substrate having greater than 0.25 wt % zinc and a protective
coating on the aluminum substrate. For example, the protective
coating includes a non-tungstate anodic corrosion inhibitor and a
cathodic corrosion inhibitor.
[0007] An example corrosion-inhibiting substance for forming the
protective coating on the aluminum substrate includes a carrier
fluid, a cathodic corrosion inhibitor within the carrier fluid, and
a zinc-inert anodic corrosion inhibitor within the carrier fluid.
For example, the composition of the corrosion-inhibiting substance
may be selected based upon an amount of at least one alloying
element in an aluminum alloy substrate that is to be coated with
the corrosion-inhibiting substance. For example, the
corrosion-inhibiting substance includes a non-tungstate anodic
corrosion inhibitor based upon the aluminum alloy substrate having
greater than about 0.25 wt % zinc.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The various features and advantages of this invention will
become apparent to those skilled in the art from the following
detailed description of the currently preferred embodiment. The
drawings that accompany the detailed description can be briefly
described as follows.
[0009] FIG. 1 illustrates an example corrosion resistant
article.
[0010] FIG. 2 illustrates an example corrosion-inhibiting substance
for forming a protective coating.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0011] FIG. 1 illustrates selected portions of an example corrosion
resistant article 10, such as an aerospace component, or other type
of article. In this example, the corrosion resistant article
includes a substrate 12 and a protective coating 14 on the
substrate 12. The protective coating 14 resists corrosion of the
underlying substrate 12. Although a particular structure of the
protective coating 14 and substrate 12 is shown in the disclosed
example, it is to be understood that the disclosed configuration is
not limited to the example shown and may include additional layers
or coatings.
[0012] In this example, the substrate 12 is an aluminum alloy
having a relatively high amount of zinc. For example, the aluminum
alloy includes greater than 0.25 wt % zinc. In a further example,
the aluminum alloy includes greater than about 5 wt % zinc. In yet
a further example, the aluminum alloy includes about 5.1-6.1 wt %
zinc. The term "about" as used in this description relative to
numerical values such as compositions refers to possible variation
in the value, such as normally accepted variations or tolerances in
the art.
[0013] The composition of the protective coating 14, as will be
described below, is selected to provide corrosion protection for
the aluminum alloy substrate 12 having a relatively high amount of
zinc. For example, tungsten may react with zinc at the surface of a
zinc-containing substrate to the detriment of the corrosion
protection of the coating. For alloys such as aluminum 2024, the
amount of zinc is below 0.25 wt % and the amount of copper is above
3.0 wt %, which results in a copper-rich surface that is not
susceptible to reaction between tungsten and zinc. However, with
lower amounts of copper and higher amounts of zinc, such as in
aluminum 7075, there is a zinc-rich surface that is susceptible to
reacting with tungsten from a corrosion inhibitor. In the disclosed
example, the protective coating 14 is tungstate-free and thereby
the benefit of avoiding the reaction between the tungsten and
zinc.
[0014] In one example, the aluminum alloy of the substrate 12 is
aluminum 7075 and includes about 1.2-2.0 wt % copper, about 0.3 wt
% manganese, about 2.1-2.9 wt % magnesium, about 0.4 wt % silicon,
about 0.5 wt % iron, about 5.1-6.1 wt % zinc, about 0.18 to 0.35 wt
% chromium, about 0.2 wt % titanium, and a balance of aluminum. The
aluminum 7075 may include additional impurities or other elements
that do not materially affect the properties of the alloy, or
elements that are unmeasured or undetectable in the alloy.
Likewise, the substrate 12 may be another type of high zinc
aluminum alloy having greater than 0.25 wt % zinc.
[0015] In the illustrated example, the protective coating 14
includes a non-tungstate anodic corrosion inhibitor 16 and a
cathodic corrosion inhibitor 18 that protects the underlying
substrate 12 against corrosion. For example, the non-tungstate
anodic corrosion inhibitor suppresses metal oxidation reactions,
and the cathodic corrosion inhibitor 18 suppresses reduction
reactions.
[0016] In one example, the non-tungstate anodic corrosion inhibitor
includes at least one of a vanadate compound or a molybdate
compound. In a further example, the non-tungstate anodic corrosion
inhibitor is zinc molybdate. The cathodic corrosion inhibitor
includes at least one element selected from the Group IIIB Periodic
Table elements. In a further example, the cathodic corrosion
inhibitor includes cerium. For example, the cerium is in the form
of cerium citrate. In yet a further example, the non-tungstate
anodic corrosion inhibitor 16 includes only zinc molybdate, and the
cathodic corrosion inhibitor includes only the cerium citrate,
which may ensure that other elements of unknown reactivity are not
present within the protective coating 14.
[0017] The protective coating 14 may be used in any of a variety of
different forms. For example, the non-tungstate anodic corrosion
inhibitor 16 and the cathodic corrosion inhibitor 18 may be used as
an additive or pigment in adhesives, paints, primers, sealants, or
the like. In another example, the non-tungstate anodic corrosion
inhibitor 16 and the cathodic corrosion inhibitor 18 are used as an
additive in a conversion coating process for forming the protective
coating 14. In one example, the non-tungstate anodic corrosion
inhibitor 16 and the cathodic corrosion inhibitor 18 comprise about
1 to 50 wt % of the protective coating 14 with the remaining amount
comprising a matrix surrounding the corrosion inhibitors 16 and
18.
[0018] Referring to FIG. 2, the protective coating 14 may be formed
from a corrosion inhibiting substance 30 that is added to a primer,
paint, adhesive, sealant, conversion coating, or used as a directly
applied corrosion inhibitor, for example. The corrosion inhibiting
substance 30 includes a carrier fluid 32, a cathodic corrosion
inhibitor 34 within the carrier fluid 32, and a zinc-inert anodic
corrosion inhibitor 36 within the carrier fluid. Depending upon the
composition of the cathodic corrosion inhibitor 34, the zinc-inert
anodic corrosion inhibitor 36, and the carrier fluid 32, the
corrosion inhibitors 34 and 36 may exist as solid particles within
the carrier fluid 32 or as dissolved substances within the carrier
fluid 32.
[0019] In one example, the zinc-inert anodic corrosion inhibitor 36
is a corrosion inhibitor that is suitable for avoiding reaction
with zinc when exposed to an aluminum alloy having greater than
0.25 wt % zinc. For example, the zinc-inert anodic corrosion
inhibitor 36 includes a vanadate or molybdate compound. In a
further example, the compound is zinc molybdate. The cathodic
corrosion inhibitor 34 includes at least one element selected from
the Group IIIB Periodic Table elements. In a further example, the
cathodic corrosion inhibitor 34 includes cerium. For example, the
cerium is in the form of cerium citrate.
[0020] The amounts of the cathodic corrosion inhibitor 34 and the
zinc-inert anodic corrosion inhibitor 36 within the carrier fluid
32 depends upon the desired composition of the protective coating
14. In one example, the concentration of each of the corrosion
inhibitors 34 and 36 within the carrier fluid is about 0.1 to 100
grams per liter (0.01-13.3 ounces per gallon) of the carrier fluid
32. Given this description, one of ordinary skill in the art will
be able to determine suitable concentrations of the corrosion
inhibitors 34 and 36 for forming the protective coating 14 with a
desirable composition.
[0021] As indicated in the above examples, the corrosion inhibiting
substance 30 is selected to include the non-tungstate anodic
corrosion inhibitor 16 based upon the amount of the zinc within the
aluminum alloy of the substrate 12. In one non-limiting example to
demonstrate the effectiveness of the non-tungstate anodic corrosion
inhibitor 16 on high zinc aluminum alloys, specimens of aluminum
2024 and 7075 were coated with various compositions of
corrosion-inhibiting substances and subsequently evaluated for
corrosion. The specimens were coated with one or more of three
different corrosion inhibiting substances. As shown in Table 1
below, a cerium citrate cathodic inhibitor is indicated as
inhibitor 1, a zinc molybdate anodic inhibitor is indicated as
inhibitor 2, and a strontium tungstate anodic inhibitor is
indicated as inhibitor 3. The specimens were then tested according
to ASTM G85 Annex 5 and evaluated with a numerical rating between 1
and 10, where 10 indicates no corrosion and 0 indicates complete
corrosive failure. In other examples, other test conditions or
standards may be used.
[0022] As shown in Table 1, the corrosion-inhibiting combination of
all three corrosion inhibitors provides a rating of nine for the
2024 alloy. However, the corrosion-inhibiting combination of all
three corrosion inhibitors provides only a rating of six for
protecting the 7075 alloy. In this test, the combination of the
cerium citrate cathodic inhibitor 1 and the zinc molybdate anodic
inhibitor 2 provided a rating of nine for the 2024 alloy and a
rating of 8 for the 7075 alloy. Thus, the tungstate-containing
combination protects the 2024 alloy but does not protect the 7075
alloy as well, whereas the tungstate-free combination provides
corrosion protection for the 2024 alloy and the 7075 alloy.
TABLE-US-00001 TABLE 1 Inhibitor 1 + Inhibitor Alloy Inhibitor 1 +
Inhibitor 2 2 + Inhibitor 3 2024 9 9 7075 8 6
[0023] Although a combination of features is shown in the
illustrated examples, not all of them need to be combined to
realize the benefits of various embodiments of this disclosure. In
other words, a system designed according to an embodiment of this
disclosure will not necessarily include all of the features shown
in any one of the Figures or all of the portions schematically
shown in the Figures. Moreover, selected features of one example
embodiment may be combined with selected features of other example
embodiments.
[0024] The preceding description is exemplary rather than limiting
in nature. Variations and modifications to the disclosed examples
may become apparent to those skilled in the art that do not
necessarily depart from the essence of this disclosure. The scope
of legal protection given to this disclosure can only be determined
by studying the following claims.
* * * * *