U.S. patent application number 13/796448 was filed with the patent office on 2014-09-18 for colored, corrosion-resistant aluminum alloy substrates and methods for producing same.
The applicant listed for this patent is Albert Askin, Thomas Levendusky, Luis Fanor Vega. Invention is credited to Albert Askin, Thomas Levendusky, Luis Fanor Vega.
Application Number | 20140262790 13/796448 |
Document ID | / |
Family ID | 49887336 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140262790 |
Kind Code |
A1 |
Levendusky; Thomas ; et
al. |
September 18, 2014 |
COLORED, CORROSION-RESISTANT ALUMINUM ALLOY SUBSTRATES AND METHODS
FOR PRODUCING SAME
Abstract
A silicon polymer treatment with included pigments for anodized
aluminum objects such as wheels. Titanium dioxide may be dispersed
in polysiloxane or polysilazane to form a white polymer treatment
on the object. Other beneficial components, such as corrosion
inhibitors may be included in the polymer matrix.
Inventors: |
Levendusky; Thomas;
(Greensburg, PA) ; Askin; Albert; (Lower Burrell,
PA) ; Vega; Luis Fanor; (Cheswick, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Levendusky; Thomas
Askin; Albert
Vega; Luis Fanor |
Greensburg
Lower Burrell
Cheswick |
PA
PA
PA |
US
US
US |
|
|
Family ID: |
49887336 |
Appl. No.: |
13/796448 |
Filed: |
March 12, 2013 |
Current U.S.
Class: |
205/50 ;
205/112 |
Current CPC
Class: |
C25D 11/246 20130101;
C25D 11/04 20130101; C23C 18/1245 20130101; C23C 18/1254 20130101;
C25D 11/08 20130101; C25D 11/24 20130101; C25D 9/06 20130101; C23C
18/122 20130101 |
Class at
Publication: |
205/50 ;
205/112 |
International
Class: |
C25D 9/06 20060101
C25D009/06 |
Claims
1. A treatment for anodized aluminum alloy object having a porous
oxide layer formed on a base layer of the aluminum alloy,
comprising: a liquid including a silicon monomer, the liquid having
a viscosity permitting infiltration into the porous oxide layer
when applied thereto and capable of reacting with the oxide layer
to chemically bond with molecules of the oxide layer, the monomer
capable of polymerizing within the porous oxide layer yielding a
polymer interlocked with the oxide layer; a pigment dispersed
within the liquid, the pigment capable of being bound within the
polymer and imparting a color to the object.
2. The treatment of claim 1, wherein the polymer is a
polysiloxane.
3. The treatment of claim 1, wherein the polymer is a
polysilazane.
4. The treatment of claim 1, wherein the pigment is titanium
dioxide.
5. The treatment of claim 1, wherein a portion of the pigment
particles enter the porous oxide layer prior to polymerization.
6. The treatment of claim 1, wherein a portion of the pigment
particles bound within the polymer are too large to enter the pores
of the oxide layer.
7. The treatment of claim 1, wherein the pigment includes particles
that are small enough to enter the porous oxide layer and particles
that are too large to enter the pores of the oxide layer.
8. The treatment of claim 1 wherein the silicon monomer is
dispersed in butanol.
9. The treatment of claim 1 further comprising a corrosion
inhibitor that is dispersed in the liquid and which is fixed in the
polymer after polymerization.
10. A method for treating an anodized aluminum object having a
porous oxide layer thereof, comprising the steps of: (A) obtaining
a liquid containing a silicon monomer; (B) obtaining a finely
divided solid pigment (C) mixing the pigment in the liquid to form
a mixture with the monomer; (D) applying the mixture to a surface
of the object; (E) allowing the liquid to infiltrate the porous
oxide layer; (F) polymerizing the monomer to yield a polymer
interlocked with the oxide layer and with pigment particles fixed
therein.
11. The method of claim 10, further comprising the step of
anodizing prior to the step (D) of applying, the anodizing step
being conducted on the aluminum alloy electrochemically, using a
solution having phosphoric acid and sulfuric acid.
12. The method of claim 11, wherein the step of anodizing results
in an oxide zone having sulphates and phosphates.
13. The method of claim 10, wherein the polymer formed by the step
of polymerizing is a polysiloxane.
14. The method of claim 10, wherein the polymer formed by the step
of polymerizing is a polysiloxane.
15. An object formed from aluminum alloy, comprising: a porous
oxide layer formed upon a surface of the aluminum alloy; a layer of
silicon-containing polymer interlocked with the oxide layer, the
polymer containing pigment particles therein that impart a color to
the object.
16. The object of claim 15, wherein the pigment particles are
titanium dioxide and the color imparted is white.
17. The object of claim 15, wherein the aluminum alloy is selected
from the group consisting of series 2XXX, 3XXX, 5XXX, 6XXX and 7XXX
aluminum alloys.
18. The object of claim 15, wherein the object is a wheel.
19. The object of claim 18, wherein the wheel is for an
aircraft.
20. The treatment of claim 1, wherein the silicon monomer is
dispersed in at least one of normal and tertiary butyl acetate.
Description
BACKGROUND
[0001] Metallic substrates, including aluminum and aluminum alloys,
may be anodized to increase corrosion and wear resistance of the
substrate. Anodizing is an electrolytic passivation process used to
increase the thickness and density of the natural oxide layer on
the surface of metal parts. Anodic films can also be used for a
number of cosmetic effects, either via thick porous coatings that
can absorb dyes or via thin transparent coatings that add
interference effects to reflected light. Anodic films are generally
stronger and more adherent than most paints and platings, making
them less likely to crack and peel. Anodic films are most commonly
applied to protect aluminum alloys, although processes also exist
for titanium, zinc, magnesium, and niobium.
[0002] Conventional anodizing processes, resultant anodized
substrates and coloring techniques have limitations with respect to
corrosion and wear resistance and color selection. Some protective
compounds applied to the anodized surfaces give rise to other
limitations. As a result, alternative approaches for coloring and
finishing anodized surfaces remain desirable.
SUMMARY OF THE INVENTION
[0003] The present disclosure relates to treatments for aluminum
alloys. In an embodiment of the present disclosure a treatment for
anodized aluminum alloy object having a porous oxide layer formed
on a base layer of the aluminum alloy, has a liquid including a
silicon monomer. The liquid has a viscosity permitting infiltration
into the porous oxide layer when applied thereto and capable of
reacting with the oxide layer to chemically bond with molecules of
the oxide layer. The monomer is capable of polymerizing within the
porous oxide layer yielding a polymer interlocked with the oxide
layer. A pigment dispersed within the liquid is capable of being
bound within the polymer and imparting a color to the object.
[0004] In another embodiment, the polymer is a polysiloxane.
[0005] In another embodiment, the polymer is a polysilazane.
[0006] In another embodiment, the pigment is titanium dioxide.
[0007] In another embodiment, a portion of the pigment particles
enter the porous oxide layer prior to polymerization.
[0008] In another embodiment, a portion of the pigment particles
bound within the polymer are too large to enter the pores of the
oxide layer.
[0009] In another embodiment, the pigment includes particles that
are small enough to enter the porous oxide layer and particles that
are too large to enter the pores of the oxide layer.
[0010] In another embodiment, the silicon monomer is dispersed in
butanol.
[0011] In another embodiment, a corrosion inhibitor is dispersed in
the liquid and is fixed in the polymer after polymerization.
[0012] In another embodiment, a method for treating an anodized
aluminum object having a porous oxide layer, includes the steps of
obtaining a liquid containing a silicon monomer; obtaining a finely
divided solid pigment; mixing the pigment in the liquid to form a
mixture with the monomer; applying the mixture to a surface of the
object; allowing the liquid to infiltrate the porous oxide layer;
polymerizing the monomer to yield a polymer interlocked with the
oxide layer and with pigment particles fixed therein.
[0013] In another embodiment, the method includes the step of
anodizing prior to the step of applying, the anodizing step being
conducted on the aluminum alloy electrochemically, using a solution
having phosphoric acid and sulfuric acid.
[0014] In another embodiment, the step of anodizing results in an
oxide zone having sulphates and phosphates.
[0015] In another embodiment, the polymer formed by the step of
polymerizing is a polysiloxane.
[0016] In another embodiment, the polymer formed by the step of
polymerizing is a polysiloxane.
[0017] In another embodiment, an object formed from aluminum alloy
has a porous oxide layer formed upon a surface of the aluminum
alloy. A layer of silicon-containing polymer is interlocked with
the oxide layer. The polymer contains pigment particles therein
that impart a color to the object.
[0018] In another embodiment, the pigment particles are titanium
dioxide and the color imparted is white.
[0019] In another embodiment, the aluminum alloy is selected from
the group consisting of series 2XXX, 3XXX, 5XXX, 6XXX and 7XXX
aluminum alloys.
[0020] In another embodiment, the object is a wheel.
[0021] In another embodiment, the wheel is for an aircraft.
In another embodiment, the silicon monomer of the coating is
dispersed in normal or tertiary butyl acetate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a schematic, cross-sectional view an anodized
aluminum alloy base having a sulfate-phosphate oxide zone treated
with a surface layer in accordance with an embodiment of the
present disclosure.
[0023] FIG. 2 is a schematic view of various reaction mechanisms
that may occur in accordance with a sulfate-phosphate oxide zone
and a silicon-based polymer.
[0024] FIGS. 3A and 3B are scanning electron microscope (SEM)
images at 6000.times. magnification.
[0025] FIG. 4 is a flow chart illustrating methods of producing
aluminum alloys having a sulfate-phosphate oxide zone and corrosion
resistant substrates.
[0026] FIG. 5 is a SEM image of a conventionally anodized aluminum
alloy surface.
[0027] FIG. 6A is a SEM image of a cross-section of a surface of an
anodized and treated aluminum alloy in accordance with an
embodiment of the present disclosure and FIG. 6B is an enlarged
view of the surface of the fiberous oxide network of the surface of
alloy of FIG. 6A.
[0028] FIG. 7A is photograph of an anodized aluminum alloy that has
been painted with a two coat paint system, scribed, frozen, then
subjected to pressurized steam.
[0029] FIG. 7B is photograph of an anodized aluminum alloy that was
coated in accordance with an embodiment of the present disclosure,
scribed, frozen, then subjected to pressurized steam.
[0030] FIGS. 8 and 9 are graphs of fatigue life for alloy samples
treated in accordance with the present disclosure as compared to
those which are not.
DETAILED DESCRIPTION
[0031] Reference is now made to the accompanying drawings, which
assist in illustrating various features of the instant application.
In one approach, the instant application relates to aluminum alloys
having a sulfate-phosphate oxide zone. One embodiment of an
aluminum alloy having a sulfate-phosphate oxide zone is illustrated
in FIG. 1. In the illustrated embodiment, an aluminum alloy base 10
includes a sulfate-phosphate oxide zone 20. In general, and as
described in further detail below, the aluminum alloy base 10 may
be modified with a mixed electrolyte (e.g., sulfuric acid plus
phosphoric acid) to produce the sulfate-phosphate oxide zone 20
(indicated by shading lines slanting downwardly from left to
right). The sulfate-phosphate oxide zone 20 may promote, among
other things, adhesion of polymers to the aluminum alloy base 10,
as described in further detail below.
[0032] The aluminum alloy base 10 may be any material adapted to
have a sulfate-phosphate oxide zone formed therein via
electrochemical processes. As used herein, "aluminum alloy" means a
material including aluminum and another metal alloyed therewith,
and includes one or more of the Aluminum Association 2XXX, 3XXX,
5XXX, 6XXX and 7XXX series alloys. The aluminum alloy base 10 may
be from any of a forging, extrusion, casting or rolling
manufacturing process. In one embodiment, the aluminum alloy base
10 comprises a 6061 series alloy. In one embodiment, the aluminum
alloy base 10 comprises a 6061 series alloy with a T6 temper. In
one embodiment, the aluminum alloy base 10 comprises a 2014 series
alloy. In one embodiment, the aluminum alloy base 10 comprises a
7050 series alloy. In one embodiment, the aluminum alloy base 10
comprises a 7085 series alloy. In one embodiment, the aluminum
alloy base 10 is a wheel product (e.g., a rim that is employed on
an aircraft or a vehicle). In one embodiment, the aluminum alloy
base 10 is a building product (e.g., aluminum siding or composite
panel).
[0033] In the illustrated embodiment, the aluminum alloy base 10
includes a sulfate-phosphate oxide zone 20. As used herein,
"sulfate-phosphate oxide zone" means a zone produced from
electrochemical oxidation of the aluminum alloy base 10, and which
zone may include elemental aluminum (Al), sulfur (S), phosphorus
(P) and/or oxygen (O) and compounds thereof. In one embodiment, and
as described in further detail below, the sulfate-phosphate oxide
zone 20 may be produced from an electrolyte comprising both
sulfuric acid and phosphoric acid.
[0034] The sulfate-phosphate oxide zone 20 generally comprises an
amorphous morphology that includes a plurality of sulfate-phosphate
oxide pores (not illustrated). As used herein, "sulfate-phosphate
oxide pores" means pores of the sulfate-phosphate oxide zone 20
that include elemental Al, O, S and/or P or compounds thereof and
proximal a surface thereof. As described in further detail below,
such sulfate-phosphate oxide pores may facilitate increased
adhesion between polymers and the sulfate-phosphate oxide zone 20
via chemical interaction between the polymer and one or more of the
Al, O, S, and P elements located on a surface thereof or proximal
thereto.
[0035] The sulfate-phosphate oxide zone 20 may include an amorphous
and porous morphology, which may facilitate increased adhesion
between a polymer and the aluminum alloy via an increased surface
area, porosity/roughness. Conventionally anodized surfaces
generally include columnar morphology (e.g., for a Type II,
sulfuric acid-only anodized surface), or a nodal morphology (e.g.,
for a phosphoric acid-only anodized surface) (see FIG. 5).
Conversely, the porous, amorphous morphology of the
sulfate-phosphate oxide zone 20 generally exhibits a more open
porosity and an increased surface area relative to conventionally
anodized surfaces. The sulphate-phosphate zone could be described
as a fibrous region having spacing and interstices therein (see
FIG. 6B). This greater porosity and surface area may contribute to
increased adhesion between polymer coatings and the aluminum alloy
base 10.
[0036] Increased adhesion of polymers to the aluminum alloy base 10
may be realized by controlling/selecting the pore size of the
sulfate-phosphate oxide pores. For example, the pore size of the
sulfate-phosphate oxide pores may be selected to facilitate flow of
certain polymers therein, e.g., by creating sulfate-phosphate oxide
pores having an average pore size that coincides with the radius of
gyration of the polymer to be used to treat the aluminum alloy base
10. In one embodiment, the average pore size of the
sulfate-phosphate oxide pores may be in the range of from about 10
nm to about 15 nanometers, and the polymer may be a
silicon-containing polymer, such as polysilazane and polysiloxane
polymers. Since this average pore size range is coincidental to the
radius of gyration of such polymers, these polymers (or their
precursors) may readily flow into the sulfate-phosphate oxide
pores. In turn, the polymers may readily bond with the
sulfate-phosphate oxides associated therewith (e.g., during curing
of the polymer, described in further detail below).
[0037] As used herein, "average pore size" means the average
diameters of the sulfate-phosphate oxide pores of the
sulfate-phosphate oxide zone as measured using microscopic
techniques. As used herein, "radius of gyration" means the mean
size of the polymer molecules of a sample over time, and may be
calculated using an average location of monomers over time or
ensemble:
R g 2 = def 1 N k = 1 N ( r k - r mean ) 2 ##EQU00001##
where the angular brackets . . . denote the ensemble average.
[0038] To promote chemical interaction between surfaces of the
sulfate-phosphate oxide zone and the polymer, the ratio of sulfur
atoms to phosphorus atoms may be tailored. In one embodiment, the
polymer is a silicon-based polymer and the ratio of sulfur atoms to
phosphorus in the sulfate-phosphate oxide zone 20 is at least about
5:1 (S:P), such as at least about 10:1 (S:P), or even at least
about 20:1 (S:P). In this embodiment, the ratio of sulfur atoms to
phosphorus atoms in the sulfate-phosphate oxide zone 20 may not
exceed about 100:1 (S:P), and preferably not greater than about
75:1 (S:P).
[0039] The thickness of the sulfate-phosphate oxide zone 20 may be
tailored so as to produce a zone having sufficient surface area for
bonding with a polymer. In this regard, the sulfate-phosphate oxide
zone 20 of the corrosion resistant substrate 1 generally has a
thickness of at least about 5 microns (0.00020 inch), such as a
thickness of at least about 6 microns (0.00024 inch). The
sulfate-phosphate oxide zone generally has a thickness of not
greater than about 25 microns (about 0.001 inch), such as, not
greater than about 17 microns (about 0.00065 inch).
[0040] As noted above, aluminum alloys with surfaces having
sulfate-phosphate oxides may be utilized to produce wear/corrosion
resistant aluminum alloy products. One embodiment of a
wear/corrosion resistant substrate is illustrated in FIG. 1. In the
illustrated embodiment, a silicon-containing polymer zone 30 coats
the sulfate-phosphate oxide zone 20. The silicon-containing polymer
zone is partially infused into and structurally integrated with at
least a portion of the sulfate-phosphate oxide zone 20, and thus
defines a mixed zone 40. Mixed zone 40 includes both
sulfate-phosphate oxides and silicon-containing polymer. A
polymer-free zone 60 may make up the remaining portion of the
sulfate-phosphate oxide zone 20. A coating 50 may make up the
remaining portion of the silicon-containing polymer zone 30. The
coating 50 is located on an outer surface of the aluminum alloy
base 10, and, since the coating 50 is integral with the
sulfate-phosphate oxide zone 20 via the mixed zone 40, the coating
50 may be considered integral with the aluminum alloy base 10 via
the mixed zone 40. In turn, increased adhesion between the coating
50 and the aluminum alloy base 10 may be realized relative to
conventional painted products.
[0041] As noted above, the sulfate-phosphate oxide zone 20
generally is porous. Thus, various amounts of silicon-containing
polymer may be contained within the pores of the sulfate-phosphate
oxide zone 20. This interface facilitates adhesion between the
sulfate-phosphate oxide zone 20 and the coating 50. Chemical
bonding between the silicon-containing polymer and the
sulfate-phosphate oxide zone 20 is believed to provide adhesive
qualities with respect to electrochemically treated aluminum
substrates due to, for example, the molecular size and structure of
the formed Al--O--P--O--Si compounds. This is disclosed in U.S.
Pat. No. 7,732,068 to Levendusky et al., entitled Corrosion
Resistant Aluminum Alloy Substrates and Methods of Producing Same,
which is incorporated by reference in its entirety herein. It is
believed that the Al--O--P--O--Si molecular structure is more
stable than the molecular arrangements achieved with conventional
anodizing processes (e.g., Al--O--Si, Al--O--P, Al--O--S,
independently, and Al--O--S--O--Si). For example, the substrate 1
may be able to pass the ASTM D3359-02 (Aug. 10, 2002) tape adhesion
test, in both dry and wet conditions. Examples of chemical
reactions that may occur between polymers and the sulfate-phosphate
oxides are illustrated in FIG. 2. Starting from their original
colloid compositions, the chemical reactions that occur upon
contact with water and subsequent curing may lead to a sequence of
hydration and condensation reactions with the evolution of water,
resulting in one or more new chemical structures within the
sulfate-phosphate oxide zone involving sulfate-phosphate oxides and
a silicon-based polymer. For example, the end products 70, 80
illustrated in FIG. 2 may be produced.
[0042] As used herein, "silicon-containing polymer" means a polymer
comprising silicon and that is suited for integrating with at least
a portion of the sulfate-phosphate oxide zone 20 (e.g., via
chemical bonding and/or physical interactions). In this regard, the
silicon-containing polymer should have a radius of gyration that is
coincidental with the average pore size of the sulfate-phosphate
oxide zone 20. Furthermore, since the silicon-containing polymer
zone 30 may act as a barrier between outside environments and the
aluminum alloy base 10, the silicon-containing polymer should
generally be fluid impermeable. For appearance purposes, the
silicon-containing polymer may be translucent, or even transparent,
so as to facilitate preservation of the original specularity and
aesthetic appearance of the finished product. As described more
fully below, the silicon-containing polymer made be used as a
binder for pigment particles which confer a selected color on the
aluminum alloy substrate to which they are applied. Particularly,
useful silicon-containing polymers having many of the above
qualities include polysiloxanes (Si--O--Si) and polysilazanes
(Si--N--Si). Polysiloxane polymers are available from, for example,
SDC Coatings of Irvine, Calif., U.S.A. Polysilazane polymers are
available from, for example, from AZ Electronic Materials USA of
Charlotte, N.C., U.S.A.
[0043] The selection of siloxane polymers versus silazane polymers
may be dictated by the desired performance characteristics of the
final product. Due to the dispersive nature of the siloxane
precursor, which involves condensation during reaction with the
sulfate-phosphate oxide zone 20, the resulting coefficient of
thermal expansion of the polysiloxane compound may induce residual
stresses at the surface of the coating 50, which may translate into
surface fissures and/or cracks in the finished product. To avoid
fissures and cracks with coatings 50 comprising polysiloxane, the
thickness of the coating 50 may be restricted to not greater than
10 microns, or even not greater than 8 microns. For enhanced
corrosion resistance, the barrier properties of the coating 50 may
need to be increased via, for example, increased thickness.
Substrates including coatings 50 produced from polysilazanes may
have higher thicknesses than coatings produced with polysiloxanes
and have similar fluid impermeable characteristics. It is believed
that the flexibility and chemical composition of polysilazanes
allow the production of end product 80, illustrated in FIG. 2,
which allows longer molecular chain lengths, and increased coating
thicknesses with little or no cracking (e.g., fissure-free,
crack-free surfaces). In one embodiment, the coating 50 is
sufficiently thick to produce a corrosion resistant substrate. The
corrosion resistant substrate may be corrosion resistant while
retaining a smooth surface and a glossy appearance (e.g., due to
transparency of the coating 50 in combination with the appearance
of the mixed zone 40). As used herein, "corrosion resistant
substrate" means a substrate having an aluminum alloy base, a
sulfate-phosphate oxide zone 20, and a silicon-containing polymer
zone 30, and which is able to pass a 240 hour exposure to
copper-accelerated acetic acid salt spray test, as defined by ASTM
B368-97 (2003)e1 (hereinafter the "CASS test"). In one embodiment,
the corrosion resistant substrate is capable of substantially
maintaining a glossy and translucent appearance while passing the
CASS test. In this regard, the silicon-containing polymer may
comprise a polysilazane and the coating 50 may have a thickness of
at least about 8 microns. In one embodiment, the coating 50 has a
thickness of at least about 35 microns. In one embodiment, the
coating 50 has a thickness of at least about 40 microns. In one
embodiment, the coating 50 has a thickness of at least about 45
microns. In one embodiment, the coating 50 has a thickness of at
least about 50 microns. In some embodiments, the coatings 50 may
exhibit little or no cracking. In this regard, it is noted that
polysilazane has a coefficient of thermal expansion that is closer
to the coefficient of thermal expansion of the aluminum alloy base
10 than polysiloxane coatings. For example, coatings comprising
polysilazane may have a coefficient of thermal expansion of at
least about 8.times.10.sup.-5/.degree. C. and aluminum-based
substrates may comprise a coefficient of thermal expansion of about
22.8.times.10.sup.-6/.degree. C. Hence, the ratio of the
coefficient of thermal expansion of the polysilazane coating to the
coefficient of thermal expansion of the substrate may be not
greater than about 10:1, such as not greater than about 7:1, or not
greater than 5:1, or not greater than about 4:1, or not greater
than about 3.5:1. Thus, in some instances, the coating 50 may
comprise a coefficient of thermal expansion that is coincidental to
a coefficient of thermal expansion of the aluminum alloy base 10
and/or the sulfate-phosphate oxide zone 20 thereof. Hence, coatings
50 including polysilazane may act as an impermeable or
near-impermeable barrier between the aluminum alloy base 10 and
other materials, while maintaining a glossy appearance and a smooth
outer surface. Nonetheless, the polysilazane coatings generally
should not be too thick, or the coating may crack. In one
embodiment, the coating 50 comprises polysilazane and has a
thickness of not greater than about 90 microns, such as a thickness
of not greater than about 80 microns.
[0044] As noted above, the coating 50 may have sufficient thickness
to facilitate production of a corrosion resistant substrate and the
corrosion resistant substrate may be capable of passing the CASS
test. In other embodiments, the corrosion resistance of the coating
50 may be a lesser consideration in the final product design. Thus,
the thickness of the coating 50 may be selected based on the
requisite design parameters. In one embodiment, the coating 50
comprises polysiloxane and has a thickness of not greater than
about 10 microns, such as a thickness of not greater than about 8
microns.
[0045] Polymers other than silicon-based polymers may be used to
produce a polymer-containing zone. Such polymers should posses a
radius of gyration that is coincidental to the average pore size of
the sulfate-phosphate oxide zone 20. Materials other than polymers
may also be used to facilitate production of wear resistant and/or
corrosion resistant substrates. For example, the sulfate-phosphate
oxide zone 20 may optionally include dye and/or a nickel acetate
preseal. With respect to dyes, ferric ammonium oxalate, metal-free
anthraquinone, metalized azo complexes or combinations thereof may
be utilized to provide the desired visual effect.
[0046] As noted above, the formation of anodic oxide layers on
aluminum, utilizing direct current (DC) or alternating current (AC)
anodizing, is known in the aluminum finishing industry. These
anodic oxide layers are formed by immersion in aqueous
electrolytes--including acids such as phosphoric, sulfuric and
chromic acid. Depending upon processing parameters, the resultant
anodic oxide can range in thickness from about 0.1 to about 50
microns. The anodic oxides formed on aluminum alloys (e.g., 1xxx,
2xxx, 3xxx, 5xxx, 6xxx, 7xxx & 8xxx) have colors that range
from clear to gray. The range of colors of the anodic oxides is
dependent upon alloy composition and anodizing process variables.
Aqueous solutions of organic dyes (i.e., available from suppliers
such as AZ Electronic Materials, Inc) can be used to produce a wide
array of colors--ranging from red to violet. Immersion of anodic
oxides into aqueous solutions of organic dyes results in colors
being adsorbed into the oxide. After the colors are adsorbed, the
subsequent colored oxide can be processed in aqueous solutions of
de-ionized water or metal salts, such as nickel acetate, operated
at elevated temperatures (>200 F).
[0047] Traditionally, the color white was not commonly available
for a colored anodic oxide surface on aluminum alloys. This may be
due to the unavailability of a white, aqueous-based dye solution
and/or that titanium dioxide, a white pigment, may have a particle
size larger than the pore openings in the conventional anodic oxide
layer (see FIG. 5). Both of these factors may have prevented the
development of a white anodic layer. An aspect of the present
disclosure is an approach that achieves a white color that is fixed
(i.e., locked) into the anodic oxide layer of an anodized aluminum
alloy.
[0048] As noted above, a new method in accordance with the present
disclosure and as referred to in U.S. Pat. No. 7,732,068 to
Levendusky et al utilizes a different means of sealing the pores of
the anodic oxide, viz., by means of a silicon-containing,
non-aqueous solution, with an inherent viscosity low enough to
enter the pores of the anodic oxide. The silicon containing
solution is applied to the surface of the anodic layer, e.g., by
dipping or spraying, with spraying being a convenient and effective
method. After application to the anodized surface, this
silicon-containing solution (e.g., siloxane or silazane) chemically
reacts with the elemental components of the anodic oxide formed by
the electrolyte composition, as described above and in U.S. Pat.
No. 7,732,068. The presence of elemental phosphorous in the oxide
layer promotes the formation of covalent chemical bonds with the
silicon-containing solution. The silicon-containing solution has a
low viscosity due to the low-molecular weight (i.e., short chain
lengths) of the silicon-containing oligomer in the non-aqueous
solution. As the reaction between the silicon solution and the
anodic oxide proceeds, the molecular chains increase in length,
resulting in an increase in the molecular weight of the
silicon-containing polymer in the pores of the anodic oxide. The
molecular weight increases until the pores of the oxide are
completely filled with a chemically-bound silicon polymer. The
phosphorous and aluminum in the oxide layer react with the silicon
solution to form a covalently bound structure that extends across
the entire pore opening in the oxide layer. This new composition
consequently seals the pores of the anodic oxide. Since the
covalent chemical bonds are formed with components of the anodic
oxide, the sealant is fixed (i.e., locked) into the pores of the
oxide.
[0049] An aspect of the present disclosure is the recognition that
the foregoing method and composition has advantages over
conventional aqueous sealing of anodic aluminum oxides. The first
of these is that other materials, such as finely dispersed
pigments, as well as thermal and radiation stabilizers, can be
incorporated into the low viscosity silicon solution. These
materials can be added at levels that do not increase the viscosity
of the silicon solution to levels that prohibit the solution from
entering the pores of the anodic oxide. For example, titanium
dioxide may be added to the silicon solution. This is a departure
from compositions and methods where titanium dioxide is added to
organic coatings (e.g., white paints) and then applied over
anodized articles in a secondary step after the oxide is formed and
sealed. In the case of an organic based paint, the molecular weight
of the organic coating is too large to enter the pores of the
anodic oxide and bridges the pore opening. Since a layer of white,
organic-based paint would not be chemically bound to the oxide
surface, it would not be locked into the oxide layer and therefore
would be easier to remove, e.g., in response to environmental
factors, such as abrasion.
[0050] A white, finely dispersed titanium dioxide pigment may be
incorporated into the silicon solution of the present disclosure
without increasing the viscosity of the mixture of pigment and
silicon solution to a level disabling entry of the silicon solution
into the pores of the oxide, in particular, the porous fibrous
oxide network with interstices, e.g., as shown in FIG. 6B. As used
herein, "pores" in the fibrous oxide zone of the present disclosure
includes the interstices therein. Titanium dioxide may be obtained
in a variety of particle sizes and typically a given sample has a
range of particle sizes. In accordance with one embodiment of the
present disclosure, if the particle size of the titanium dioxide in
the silicon solution is smaller than the pore size of the fibrous
oxide layer formed in accordance with the present disclosure of the
anodized aluminum alloy, it may enter the pores of this fibrous
network along with the silicon solution. The particle sizes of
other particles of the titanium dioxide may be larger than certain
pores, and they do not enter the pores, but are still distributed
and are visible in the silicon containing polymer. Any given sample
of titanium dioxide typically has a range of particle sizes from
larger to smaller than the pore size of the oxide layer of the
anodized alloy, e.g., larger than the pores associated with the
columnar layer (see FIG. 5), but smaller than the pores of the
porous fibrous oxide network shown in FIG. 6B. In each case, the
silicon solution enters the pores and does not bridge the pore
opening. When the silicon-solution reacts with the composition of
the anodic oxide to form a covalently-bound, sealed oxide, the
titanium-dioxide pigment particles (both those that are small
enough to enters the pores of the fibrous oxide layer and those
that do not enter the pores are dispersed in (surrounded by) the
silicon-containing sealant and the pigment is effectively fixed
(i.e., locked and chemically bound) into the oxide layer by the
polymerization of the silicon-containing sealant.
[0051] The foregoing dynamic is supported and enhanced by the
morphology of the titanium dioxide, in that finely divided
pigments, such as titanium dioxide, typically have a mesoporous
structure. Mesoporous materials have a large degree of porosity and
correspondingly large surface area. When finely divided materials
are added to the silicon solution, the components of the solution
can be both adsorbed and absorbed into the mesoporous material.
This permits ingress of the silicon monomers/oligomers, and
optionally other additives of the silicon solution--if present,
into the porous, finely divided pigment particles. When the silicon
monomers/oligomers polymerize, the pigment particles are strongly
bound into the polymer matrix.
[0052] In accordance with another aspect of the present disclosure,
other materials and components, such as corrosion inhibitors like
benzotriazole or piperidine derivatives, may be mixed with the
silicon solution and subsequently bound within the polymer matrix
after curing. The additional components may adsorbed or absorbed
into the mesoporous material, prior to being locked into the
polymerized silicon network. These materials can then be present in
the polymerized silicon network that is fixed to the anodic oxide
through covalent bonding. For example, upon damage to the
polymerized silicon polymer, included corrosion inhibitors would be
available to reduce and/or retard the formation of corrosion
products on the aluminum article.
[0053] The present disclosure recognizes that an anodic oxide can
be colored white by use of a chemically-bound silicon sealant that
incorporates fine, dispersed titanium dioxide. The white color is
locked to the anodized surface upon curing since the titanium
dioxide is dispersed within the silicon-containing sealant which is
fixed to the anodic oxide by polymerization. This approach may be
applied to pigments other than white pigments, e.g., green imparted
by copper phthalocyanide, or yellow imparted due to the inclusion
of cadmium sulphide, provided that the pigment particle size and
the amount of pigment and/or additive does not increase the
viscosity of the silicon-containing solution to the point where the
solution will not be able to enter the porous anodic oxide. The
increase in viscosity is analogous to increasing the radius of
gyration of the silicon compound in the silicon solution such that
it becomes too large to enter the pores in the anodic oxide. In
accordance with an embodiment of the present disclosure, the
viscosity of the silicon solution is preferably less than that
which prevents entry of the silicon-solution into the oxide
pores.
[0054] FIGS. 3A and 3B show scanning electron microscope (SEM)
micrographs 90, 100 of different portions of an anodized aluminum
alloy object 92, 102 that has been coated with a silicon-containing
sealant 94, 104, i.e., a polysilazane polymer with dispersed
titanium dioxide particles. This formulation is applied by
air-assisted spraying onto the surface of the alloy panel. The
panel is allowed to dry for a sufficient time to flash-off solvents
in the formulation, e.g., from 10 minutes to >60 minutes. The
panel is then cured in a thermal oven from 15 to >60 minutes at
temperatures ranging from about 100 F to 400 F. As shown, the
coating has a polymer matrix 96, 106 containing titanium dioxide
particles 98, 108. The distribution of the titanium dioxide
particles in FIGS. 3A and 3B differ, with the coating in FIG. 3A
exhibiting a higher concentration of titanium dioxide particles in
the fibrous oxide transition zone of the anodized surface than that
present in FIG. 3B, which shows more evenly dispersed titanium
dioxide particles 108 and a lower concentration near the transition
zone 109. This variation illustrates that a given sample of
titanium dioxide that is mixed with a silicon sealant as described
herein would be anticipated to have a range of particle sizes, with
some small enough to enter the porous oxide layer of the anodized
surface and some too large to enter. Moreover, the distribution of
the titanium dioxide (or other pigment) will have variations over
its extent. In addition, the porosity of the anodized surface may
vary. Regardless of the size of the titanium dioxide particles
(typically within the range of (500 naometers to 2000 nanometers),
the homogeneity of their distribution in the sealant, or the pore
sizes and distribution, when polymerization of the sealant occurs,
the pigment is captured within the polymer matrix and the polymer
matrix grips to the anodized surface of the object due to its
infusion into the pores thereof and infusion into the mesoporous
surface of the pigments particles that have entered the oxide pores
and those that have not entered the pores prior to polymerization.
When the polymerized layer of sealant is viewed from the exterior,
the whiteness of the titanium dioxide particles confers a white
color on the sealant coating and the coated object.
[0055] A method for producing a colored, corrosion resistant
substrate in accordance with an embodiment of the present
disclosure is illustrated in FIG. 4. In the illustrated embodiment,
the method includes the steps of producing a sulfate-phosphate
oxide zone on a surface of the aluminum alloy base (220) and
forming a silicon-containing polymer zone on the sulfate-phosphate
oxide zone (240). The method may optionally include the steps of
pretreating an aluminum alloy base (210) and/or applying a dye to
the sulfate-phosphate oxide zone (230). The aluminum alloy base,
the sulfate-phosphate oxide zone and the silicon-containing polymer
zone may be any of the above-described aluminum alloy bases,
sulfate-phosphate oxide zones and silicon-containing polymer zones,
respectively.
[0056] In one embodiment, and if utilized, a pretreating step (210)
may comprise contacting the aluminum alloy base with a pretreating
agent (212). For example, the pretreating agent may comprise a
chemical brightening composition (214). As used herein, "chemical
brightening composition" means a solution that includes at least
one of nitric acid, phosphoric acid, sulfuric acid, and
combinations thereof. For example, the methodologies disclosed in
U.S. Pat. No. 6,440,290 to Vega et al. may be employed to pretreat
an aluminum alloy base with a chemical brightening composition. In
one approach, and with respect to 6XXX series alloys, a phosphoric
acid-based solution with a specific gravity of at least about 1.65,
when measured at 80.degree. F. (about 26.7.degree. C.) may be used,
such as a phosphoric acid with a specific gravities in the range of
from about 1.69 to about 1.73 at the aforesaid temperature. A
nitric acid additive may be used to minimize a dissolution of
constituent and dispersoid phases on certain Al--Mg--Si--Cu alloy
products, especially 6XXX series forgings. Such nitric acid
concentrations dictate the uniformity of localized chemical attacks
between Mg2Si and matrix phases on these 6XXX series Al alloys. As
a result, end product brightness may be positively affected in both
the process electrolyte as well as during transfer from process
electrolyte to a rinsing substep (not illustrated). In one
approach, the nitric acid concentrations may be about 2.7 wt. % or
less, with more preferred additions of HNO3 to that bath ranging
between about 1.2 and 2.2 wt. %. For 6XXX series aluminum alloys,
improved brightening may occur in those alloys whose iron
concentrations are kept below about 0.35% in order to avoid
preferential dissolution of Al--Fe--Si constituent phases. For
example, the Fe content of these alloys may be kept below about
0.15 wt % iron. At the aforementioned specific gravities, dissolved
aluminum ion concentrations in these chemical brightening baths
should not exceed about 35 g/liter. The copper ion concentrations
therein should not exceed about 150 ppm.
[0057] In another approach, the pretreating agent may include an
alkaline cleaner (216). As used herein, "alkaline cleaner" means a
composition having a pH of greater than approximately 7. In one
embodiment, an alkaline cleaner has a pH of less than about 10. In
one embodiment, an alkaline cleaner has a pH in the range of from
about 7.5 to about 9.5. In one embodiment, the alkaline cleaner
includes at least one of potassium carbonate, sodium carbonate,
borax, and combinations thereof. In another embodiment, an alkaline
cleaner has a pH of at least about 10.
[0058] In one embodiment, the pretreating step (210) includes
removing contaminants from a surface of the aluminum alloy base.
Examples of contaminants include grease, polishing compounds, and
fingerprints. After the pretreating step (210), such as via
chemical brighteners or alkaline cleaners, described above, the
absence of contaminants on the surface of the aluminum alloy base
may be detected by determining the wetability of a surface of the
aluminum alloy base. When a surface of the aluminum alloy base wets
when subjected to water, it is likely substantially free of surface
contaminants (e.g., an aluminum alloy substrate that has a surface
energy of at least about 72 dynes/cm).
[0059] Turning now to the step of producing a sulfate-phosphate
oxide zone step (220), the sulfate-phosphate oxide zone may be
produced via any suitable technique. In one embodiment, the
sulfate-phosphate oxide zone is produced by electrochemically
oxidizing a surface of the aluminum alloy base (222). As used
herein, "electrochemically oxidizing" means contacting the aluminum
alloy base with a electrolyte containing both (a) sulfuric acid and
(b) phosphoric acid, and applying an electric current to the
aluminum alloy base while the aluminum alloy base is in contact
with the electrolyte.
[0060] The ratio of sulfuric acid to phosphoric acid within the
electrolyte (sometimes referred to herein as a "mixed electrolyte")
should be tailored/controlled so as to facilitate production of
suitable sulfate-phosphate oxide zones (224). In one embodiment,
the weight ratio of sulfuric acid (SA) to phosphoric acid (PA) in
the electrolyte is at least about 5:1 (SA:PA), such as a weight
ratio of at least about 10:1 (SA:PA), or even a weight ratio of at
least about 20:1 (SA:PA). In one embodiment, the weight ratio of
sulfuric acid to phosphoric acid in the electrolyte is not greater
than 100:1 (SA:PA), such as a weight ratio of not greater than
about 75:1 (SA:PA). In one embodiment, the mixed electrolyte
comprises at least about 0.1 wt % phosphoric acid. In one
embodiment, the mixed electrolyte comprises not greater than about
5 wt % phosphoric acid. In one embodiment, the mixed electrolyte
comprises not greater than about 4 wt % phosphoric acid. In one
embodiment, the mixed electrolyte comprises not greater than about
1 wt % phosphoric acid. In one embodiment, the phosphoric acid is
orthophosphoric acid.
[0061] The current applied to the mixed electrolyte should be
tailored/controlled so as to facilitate production of suitable
sulfate-phosphate oxide zones (226). In one embodiment,
electrochemically oxidizing step (222) includes applying
electricity to the electrolyte at a current density of at least
about 8 amps per square foot (asf), which is about 0.74 amps per
square meter (asm). In one embodiment, the current density is at
least about 12 asf (about 1.11 asm). In one embodiment, the current
density is at least about 18 asf (about 1.67 asm). In one
embodiment, the current density is not greater than about 24 asf
(about 2.23 asm). Thus, the current density may be in the range of
from about 8 asf to about 24 asf (0.74-2.23 asm), such as in the
range of from about 12 asf to about 18 asf (1.11-1.67 asm).
[0062] The voltage applied to the mixed electrolyte should also be
tailored/controlled so as to facilitate production of suitable
sulfate-phosphate oxide zones (228). In one embodiment, the
electrochemically oxidizing step (222) includes applying
electricity to the electrolyte at a voltage of at least about 6
volts. In one embodiment, the voltage is at least about 9 volts. In
one embodiment, the voltage is at least about 12 volts. In one
embodiment, the voltage is not greater than about 18 volts. Thus,
the voltage may be in the range of from about 6 volts to about 18
volts, such as in the range of from about 9 volts to about 12
volts.
[0063] The temperature of the electrolyte during the
electrochemically oxidizing step (222) should also be
tailored/controlled so as to facilitate production of a suitable
sulfate-phosphate oxide zone. In one embodiment, the
electrochemically oxidizing step (222) includes heating the
electrolyte to and/or maintaining the electrolyte at a temperature
of at least about 75.degree. F. (about 24.degree. C.), such as a
temperature of at least about 80.degree. F. (about 27.degree. C.).
In one embodiment, the temperature of the electrolyte is at least
about 85.degree. F. (about 29.degree. C.). In one embodiment, the
temperature of the electrolyte is at least about 90.degree. F.
(about 32.degree. C.). In one embodiment, the electrochemically
oxidizing step (222) includes heating the electrolyte and/or
maintaining the electrolyte at a temperature of not greater than
about 100.degree. F. (about 38.degree. C.). Thus, the temperature
of the electrolyte may be in the range of from about 75.degree. F.
(about 24.degree. C.) to about 100.degree. F. (38.degree. C.) step
(229), such as in the range of from about 80.degree. F. (about
27.degree. C.) to about 95.degree. F. (35.degree. C.), or a range
of from about 85.degree. F. (about 29.degree. C.) to about
90.degree. F. (about 32.degree. C.).
[0064] In a particular embodiment, the electrochemically oxidizing
step (222) includes utilizing a mixed electrolyte having: (i) a
weight ratio of sulfuric acid to phosphoric acid of about 99:1
(SA:PA), and (ii) a temperature about 90.degree. F. (about
32.degree. C.). In this embodiment, the current density during
electrochemically oxidizing step (222) is at least about 18 asf
(about 1.11 asm).
[0065] After the sulfate-phosphate oxide zone is produced (220),
the method may optionally include the step of presealing the
sulfate-phosphate oxide zone (not illustrated) prior to or after
the applying a dye step (230) and/or prior to the forming a
silicon-containing polymer zone (240). In one approach, at least
some, or in some instances all or nearly all, of the pores of the
sulfate-phosphate oxide zone may be sealed with a sealing agent,
such as, for instance, an aqueous salt solution at elevated
temperature (e.g., boiling water) or nickel acetate.
[0066] Moving to the applying a dye step (230), in one embodiment
the applying a dye step (230) comprises applying at least one of
ferric ammonium oxalate, metal-free anthraquinone, metalized azo
complexes or combinations thereof to at least a portion of a
sulfate-phosphate oxide zone. The dye may be applied via any
conventional techniques. In one embodiment, the dye is applied by a
spray coating or dip coating.
[0067] In the event that a dye is not desired or, alternatively,
after the step of applying colored dye (230), titanium dioxide
dispersed in a polymerizable, silicon-containing solution, such as
a polysiloxane or polysilazane precursor may be applied (232) to
the aluminum alloy base in order to achieve a white color. In the
event that another treatment is desired, e,g, to achieve corrosion
protection, an anti-corrosion agent, e.g., benzotriazole may be
added to the silicone containing solution, either alone or in
combination with the titanium dioxide and applied to the alloy
(234). As a further alternative, the silicon-containing solution
may be applied (240) to the alloy without additives to form a
silicone-containing polymer zone on the alloy. In either case, the
silicon-containing solution is applied, e.g., as a colloid/sol
on/in at least a portion of the sulfate-phosphate oxide zone
20--see FIG. 1 and cured (244). In one embodiment, the colloid is a
sol and the curing step (244) results in the formation of a gel
comprising the silicon-containing polymer zone. The applying step
(240) may be accomplished via any conventional process, such as
spraying, dipping, or painting with an applicator. Likewise, the
curing step (244) may be accomplished via any conventional process,
such as thermal curing in electric or gas-fired ovens. In one
embodiment, the applying step (240) is accomplished by one or more
of spray coating or dip coating, spin coating or roll coating. In
another embodiment, the applying step (240) is accomplished by
vacuum deposition from liquid and/or gas phase precursors. The
silicon-containing polymer zone may be formed on a dyed
sulfate-phosphate oxide zone or an undyed sulfate-phosphate oxide
zone.
[0068] Colloids used to form the silicon-containing polymer zone
generally comprise particles suspended in a liquid. In one
embodiment, the particles are silicon-containing particles (e.g.,
precursors to the silicon-containing polymer). In one embodiment,
the particles have a particle size in the range of from about 1.0
nm to about 1.0 micron. In one embodiment, the liquid is
aqueous-based (e.g., distilled H2O). In another embodiment, the
liquid is organic based (e.g., alcohol). In a particular
embodiment, the liquid comprises at least one of methanol, ethanol,
or combinations thereof. In another embodiment the liquid is
butanol or butyl acetate. In one embodiment, the colloid is a
sol.
[0069] The viscosity of the colloid may be tailored based on
deposition method. In one embodiment, the viscosity of the colloid
is about equal to that of water. In this regard, the particles of
the colloid may more freely flow into the fibrous network of the
porous sulfate-phosphate oxide zone. During or concomitant to the
applying step (240), the colloid may flow into the pores of the
sulfate-phosphate oxide zone, and may thus seal the pores by
condensation of the colloid to a gel state (e.g., via heat). Water
released during this chemical reaction may induce oxide hydration
and, therefore, sealing of the pores. In a particular embodiment,
the colloid may flow into a substantial amount of (e.g., all or
nearly all) the pores of the sulfate-phosphate oxide zone. During
the curing step (244), the silicon-containing polymer is formed and
seals a substantial amount of the unsealed pores of the
sulfate-phosphate oxide zone. In this embodiment, the curing step
(244) may include applying a temperature of from about 90.degree.
C. (about 194.degree. F.) to about 170.degree. C. (about
338.degree. F.). In one embodiment, the curing step may include
applying a temperature of from about 138.degree. C. (about
280.degree. F.) to about 160.degree. C. (about 320.degree. F.).
[0070] In one embodiment, the curing step (244) results in the
production of a polysiloxane coating (e.g., via gelation of the
colloid). In one embodiment, the curing step (244) results in the
production of a coating comprising polysilazane. The cured polymer
may have titanium dioxide particle inclusion and/or other
components, such as anti-corrosion agents. The colloid may include
silane precursors, such as trimethoxy methyl silanes, or silazane
precursors, such as methyldichlorine or aminopropyltriethoxysilane
reacted with ammonia via ammonolysis synthesis. As noted above, the
use of polysilazanes versus polysiloxanes is primarily a function
of the desired corrosion resistance and film thickness of the final
product.
[0071] FIG. 5 shows the pore structure of a aluminum alloy surface
S that has been anodized using traditional methods with sulphuric
acid. In general the pores P are too small to allow the entry of
typical commercial titanium dioxide pigment particles.
[0072] FIG. 6A shows a SEM image of a cross-section of a surface of
an anodized and coated aluminum alloy 110 in accordance with an
embodiment of the present disclosure. The alloy 110 has developed a
fibrous sulphate-phosphate oxide zone 120 which is coated by a
silicone-containing polymer sealant 130 as described above. FIG. 6B
is an enlarged view of the surface of the fiberous oxide zone 120
of the alloy 110 of FIG. 6A. As can be appreciated, the fibrous
oxide zone 120 of FIG. 5B has greater and larger porosity that the
pores P shown in the alloy surface S of the alloy of FIG. 5 and
therefore is able to absorb and adsorb both the polymer sealant 130
and titanium dioxide pigment particles that are present in the
sealant 130.
[0073] FIGS. 7A and 7B show the results of testing anodized
aluminum panels 301, 303, with panel 301 having a painted surface
310 and panel 303 having a surface 320 sealed with a silicon
polymer that is prepared and applied in accordance with an
embodiment of the present disclosure. The panel 301 was painted
with an epoxy primer with strontium chromate pigment and then
subsequently over-coated with a gray-pigmented urethane top coat.
The panel 303 was coated with a silicon-containing coating in
accordance with the present disclosure. More particularly, panel
303 was prepared by forming an oxide in mixed electrolyte described
above, sealing with a polysilazane formulation having dispersed
titanium dioxide particles and then cured for 30 minutes at 250-300
F. After the surfaces 310 and 320 were allowed to dry/cure, each
was immersed in tap water at the temperature of 100 F for 4 hours.
The panels were then removed and scribed with an "X" (partially
enhanced to be made visible by dashed lines in FIG. 5A) by a sharp
edge that cut down to the alloy substrate. The panels were then
placed in a freezer for 3 hours at -20 F. The panels were removed
from the refrigerator and subjected to a direct high pressure steam
blast directed at the scribed area. The painted panel exhibited
adhesion loss in the area 312 shown, resulting in a flap 314 of
loose paint. In contrast, the panel 303 sealed with the
silicon-containing coating (and having a white tint owing to the
inclusion of titanium dioxide showed no adhesion loss.
[0074] Fatigue testing results for alloy 2014-T6 and 7050-T7,
uncoated and coated by traditional methods compared to those coated
in accordance with the present disclosure are shown in FIGS. 8 and
9. As can be appreciated the bars representing fatigue results for
those samples coated in accordance with the present disclosure (the
last two bars of FIG. 8, labeled R991, and the second and seventh
bar of FIG. 9, labeled R-991 with sealant) are significantly better
than those of the other samples tested and identified in the
respective graphs. Based upon the testing conducted, the coating of
the present disclosure improves fatigue resistance of alloys
treated thereby.
[0075] While various embodiments of the present application have
been described above detail, it is apparent that modifications and
adaptations of those embodiments will occur to those skilled in the
art. For example, the present disclosure mentions applicability of
the disclosed technology to the 2XXX, 3XXX, 5XXX, 6XXX and 7XXX
Series alloys, but the present disclosure would be applicable to
other aluminum alloys. It is therefore understood that such
modifications and adaptations are within the spirit and scope of
the present invention.
* * * * *