U.S. patent application number 12/174845 was filed with the patent office on 2009-02-26 for anodized aluminum alloy material having both durability and low polluting property.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.). Invention is credited to Jun Hisamoto, Koji Wada.
Application Number | 20090050485 12/174845 |
Document ID | / |
Family ID | 40280399 |
Filed Date | 2009-02-26 |
United States Patent
Application |
20090050485 |
Kind Code |
A1 |
Wada; Koji ; et al. |
February 26, 2009 |
ANODIZED ALUMINUM ALLOY MATERIAL HAVING BOTH DURABILITY AND LOW
POLLUTING PROPERTY
Abstract
An anodized aluminum alloy material is formed of an aluminum
alloy having a Mg content between 0.1 and 2.0% by mass, a Si
content between 0.1 and 2.0% by mass, a Mn content between 0.1 and
2.0% by mass, and an Fe, a Cr and a Cu content of 0.03% by mass or
below and containing Al and unavoidable impurities as other
components, and is coated with an anodic oxide film. Parts of the
anodic oxide film at different positions with respect to thickness
of the anodic oxide film have different hardnesses, respectively,
and the difference in Vickers hardness between a part having the
highest hardness and a part having the lowest hardness is Hv 5 or
above.
Inventors: |
Wada; Koji; (Kobe-shi,
JP) ; Hisamoto; Jun; (Kobe-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(Kobe Steel, Ltd.)
Kobe-shi
JP
|
Family ID: |
40280399 |
Appl. No.: |
12/174845 |
Filed: |
July 17, 2008 |
Current U.S.
Class: |
205/50 |
Current CPC
Class: |
C22F 1/043 20130101;
C22F 1/04 20130101; C22C 21/00 20130101; C22F 1/05 20130101; C25D
11/04 20130101; C22F 1/047 20130101; C22C 21/08 20130101; C22C
21/02 20130101 |
Class at
Publication: |
205/50 |
International
Class: |
C25D 11/02 20060101
C25D011/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 22, 2007 |
JP |
2007-216239 |
Claims
1. An anodized aluminum alloy material formed of an aluminum alloy
having a Mg content between 0.1 and 2.0% by mass, a Si content
between 0.1 and 2.0% by mass, a Mn content between 0.1 and 2.0% by
mass, and an Fe, a Cr and a Cu content of 0.03% by mass or below
and containing Al and unavoidable impurities as other components,
and coated with an anodic oxide film; wherein parts of the anodic
oxide film at different positions with respect to thickness of the
anodic oxide film have different hardnesses, respectively, and
difference in Vickers hardness between a part having the highest
hardness and a part having the lowest hardness is Hv 5 or
above.
2. The anodized aluminum alloy material according to claim 1,
wherein the hardness of the part having the lowest hardness of the
anodic oxide film is Hv 365 or above.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an aluminum alloy material
and, more particularly, to an anodized aluminum alloy material
intended for forming members of the vacuum chambers of apparatuses
for manufacturing semiconductor devices and liquid crystal devices,
such as CVD systems, PVD systems, ion-implanting systems,
sputtering systems and dry etching systems, and those placed in the
vacuum chambers.
[0003] 2. Description of the Related Art
[0004] Reactive gases, etching gases, and corrosive gases
containing halogen as a cleaning gas are supplied into the vacuum
chambers of apparatuses for manufacturing semiconductor devices and
liquid crystal devices, such as CVD systems, PVD systems,
ion-implanting systems, sputtering systems and dry etching systems.
Therefore, the vacuum chambers are required to have corrosion
resistance to corrosive gases (hereinafter, referred to as
"corrosive gas resistance"). Since a halogen plasma is often
produced in the vacuum chamber, resistance to plasmas (hereinafter,
referred to as "plasma resistance") is also important (refer to
JP-A Nos. 2003-34894 and 2004-225113). Recently, aluminum and
aluminum alloy materials have been used for forming the members of
the vacuum chamber because aluminum and aluminum alloy materials
are light and excellent in thermal conductivity.
[0005] Since aluminum and aluminum alloy materials are not
satisfactory in corrosive gas resistance and plasma resistance,
various surface quality improving techniques for improving those
properties have been proposed. However, those properties are still
unsatisfactory and further improvement of those properties is
desired.
[0006] Coating an aluminum or an aluminum alloy material with a
hard anodic oxide film having a high hardness is effective in
improving plasma resistance. The hard anodic oxide film is
resistant to the abrasion of a member by a plasma having high
physical energy and hence is capable of improving plasma resistance
(refer to JP-A 2004-225113).
[0007] Although the plasma resistance may be improved simply by
coating an aluminum or an aluminum alloy material with a hard
anodic oxide film, the hard anodic oxide film is liable to crack.
Once cracks penetrate the anodic oxide film, the corrosive gas
reaches the aluminum or the aluminum alloy body of the anodized
aluminum or aluminum alloy member through the cracks penetrating
the anodic oxide film (hereinafter, referred to as "through
cracks") and the aluminum or the aluminum alloy material is
corroded.
[0008] Therefore, an anodic oxide film having not only a high
hardness, but also durability (crack resistance and corrosive gas
resistance) is desired.
[0009] When the Fe content of an aluminum alloy is reduced with a
view to suppress the contamination of a semiconductor wafer or a
substrate for a liquid crystal display with Fe, an anodic oxide
film having a low Fe content can be formed. However, such an anodic
oxide film is harder, and the crack resistance and durability of
such an anodic oxide film are worse. Therefore, this field desires
improving durability (crack resistance and corrosive gas
resistance) without enhancing polluting property.
SUMMARY OF THE INVENTION
[0010] The present invention has been made in view of the foregoing
problems and it is therefore an object of the present invention to
provide an anodized aluminum alloy having a high hardness,
durability and low polluting property.
[0011] An anodized aluminum alloy material in a first aspect of the
present invention is formed of an aluminum alloy having a Mg
content between 0.1 and 2.0% ("%" signifies "mass %" herein unless
otherwise specified), a Si content between 0.1 and 2.0%, a Mn
content between 0.1 and 2.0%, and an Fe, a Cr and a Cu content of
0.03% or below and containing Al and unavoidable impurities as
other components, and is coated with an anodic oxide film; wherein
parts of the anodic oxide film at different positions with respect
to the thickness of the anodic oxide film have different
hardnesses, respectively, and the difference in Vickers hardness
between a part having the highest hardness and a part having the
lowest hardness is Hv 5 or above.
[0012] The anodized aluminum alloy material has a high hardness,
durability and low polluting property.
[0013] In the anodized aluminum alloy material in the first aspect
of the present invention, the hardness of the part having the
lowest hardness of the anodic oxide film is Hv 365 or above, which
leads to improvement of plasma resistance.
[0014] The aluminum alloy forming the anodized aluminum alloy
material has a Mg content between 0.1 and 2.0%, a Si content
between 0.1 and 2.0%, a Mn content between 0.1 and 2.0%, and an Fe,
a Cr and a Cu content of 0.03% or below and contains Al and
unavoidable impurities as other components, the anodized aluminum
alloy material is coated with the anodic oxide film, parts of the
anodic oxide film at different positions with respect to the
thickness of the anodic oxide film have different hardnesses,
respectively, and the difference in Vickers hardness between a part
having the highest hardness and the part having the lowest hardness
of the anodic oxide film is Hv 5 or above. Therefore, the anodized
aluminum alloy material has a high hardness, durability and low
polluting property.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] The present invention will be described in terms of
preferred embodiments thereof.
[0016] Composition of Aluminum Alloy Forming Anodized Aluminum
Alloy Material
[0017] An anodized aluminum alloy material according to the present
invention is formed of an aluminum alloy having a Mg content
between 0.1 and 2.0%, a Si content between 0.1 and 2.0%, a Mn
content between 0.1 and 2.0%, and an Fe, a Cr and a Cu content of
0.03% or below and containing Al and unavoidable impurities as
other components, and is coated with an anodic oxide film. Parts of
the anodic oxide film at different positions with respect to the
thickness of the anodic oxide film have different hardnesses,
respectively, and the difference in Vickers hardness between a part
having the highest hardness and a part having the lowest hardness
is Hv 5 or above. Thus the anodized aluminum alloy material has a
high hardness, durability and low polluting property.
[0018] Reasons for determining the foregoing composition will be
described.
[0019] The inventors of the present invention placed restrictions
on the Fe, the Cr and the Cu content of the aluminum alloy so that
a workpiece of a semiconductor or the like may not be contaminated.
Effect of limiting the Fe content at a low level on increasing the
hardness of the anodic oxide film and ensuring plasma resistance
was utilized positively and studies were made to find out measures
for preventing the growth of cracks formed in the anodic oxide film
to the aluminum alloy body of the anodized aluminum alloy material.
It was found through the studies that the growth of cracks formed
in the anodic oxide film to the aluminum alloy body of the anodized
aluminum alloy material can be prevented by properly determining
process conditions for forming the anodic oxide film such that
parts of the anodic oxide film at different positions with respect
to the thickness of the anodic oxide film have different
hardnesses, respectively, and the difference in Vickers hardness
between a part having the highest hardness and a part having the
lowest hardness is Hv 5 or above. Thus the penetration of a gas
through the anodic oxide film to the aluminum alloy material was
suppressed and general durability was ensured. Details of a
mechanism of the composition capable of solving the foregoing
problems have not been elucidated. However, it is inferred that
stress causing a crack to grow is absorbed by a part having a low
hardness of the anodic oxide film and, consequently, the crack
cannot grow to the aluminum alloy body of the anodized aluminum
alloy material.
[0020] The present invention will be described in detail.
[0021] Components of Aluminum Alloy
[0022] Although details of a mechanism is not clearly known, it is
inferred that an anodic oxide film is strengthened when a
Mg.sub.2Si compound, and an Al--Mn--Si compound or an Al--Mn
compound are combined with Mg, Si and Mn contained in an aluminum
alloy.
[0023] Mg Content: 0.1 to 2.0%
[0024] Magnesium (Mg) is an element necessary for producing a
Mg.sub.2Si compound. A Mg.sub.2Si compound is produced scarcely and
a desired effect on improving the durability of the anodic oxide
film cannot be achieved when the Mg content is below 0.1%. Coarse
grains of a Mg.sub.2Si compound are formed to obstruct formation of
a normal anodic oxide film when the Mg content is above 2.0%.
Therefore, a proper Mg content is between 0.1 and 2.0%, preferably,
0.8%.
[0025] Si Content: 0.1 to 2.0%
[0026] Silicon (Si), as well as Mg, is an element necessary for
producing a Mg2Si compound. A Mg.sub.2Si compound is produced
scarcely and a desired effect on improving the durability of the
anodic oxide film cannot be achieved when the Si content is below
0.1%. Coarse grains of a Mg.sub.2Si compound are formed to obstruct
formation of a normal anodic oxide film when the Si content is
above 2.0%. Therefore, a proper Si content is between 0.1 and 2.0%,
preferably, 1.2%.
[0027] Mn Content: 0.1 to 2.0%
[0028] Manganese (Mn) is an element necessary for producing an
Al--Mn--Si compound or an Al--Mn compound. An Al--Mn--Si compound
or an Al--Mn compound is produced scarcely and a desired effect on
improving the durability of the anodic oxide film cannot be
achieved when the Mn content is below 0.1%. Coarse grains of the
compound are formed to obstruct formation of a normal anodic oxide
film when the Mn content is above 2.0%. Therefore, a proper Mn
content is between 0.1 and 2.0%, preferably, 1.6%.
[0029] Fe, Cr and Cu Contents: 0.03% or Below Each
[0030] Electricity for an anodizing process is used for ionizing Al
and for generating oxygen through the electrolysis of water. If the
ratio of an amount of electricity for producing oxygen is high, the
ratio of an amount of electricity for the ionization of Al
decreases is low, aluminum oxide cannot be efficiently produced and
film formation rate decreases. When the aluminum alloy contains Fe,
Cr and Cu, generation of oxygen starts from those elements and the
ratio of the amount of electricity for oxygen generation increases
and, consequently, the film forming rate decreases. If each of the
Fe, the Cr and the Cu content is above 0.03%, Fe, Cr and Cu are
emitted from the aluminum alloy body and the anodic oxide film into
a gas and a workpiece of a semiconductor or the like is
contaminated. Therefore, each of the Fe, the Cr and the Cu content
is 0.03% or below, preferably, 0.01% or below.
[0031] Al and Unavoidable Impurities as Other Elements
[0032] Substantially, Al is only the other element. However, the
aluminum alloy contains, in addition to Fe, Cr and Cu, unavoidable
impurities including Ni, Zn, B, Ca, Na and K in unavoidably low
contents. Preferably, the total of the unavoidable impurity
contents other than the Fe, the Cr and the Cu content is 0.1% or
below.
[0033] A crystalline pattern is formed in the anodic oxide film and
anodic oxide film has an irregular color tone if the aluminum alloy
grains are coarse. Titanium (Ti) may be added to the aluminum alloy
to prevent the growth of coarse aluminum alloy grains. An
excessively low Ti content does not have a grain size control
effect. An excessively high Ti content causes pollution. When Ti is
added to the aluminum alloy, a lower limit Ti content is 0.01%,
preferably, 0. 015%, and an upper limit Ti content is 0.03%,
preferably, 0.025%.
[0034] Method of Manufacturing Aluminum Alloy Material
[0035] A method of manufacturing an aluminum alloy material will be
described.
[0036] An aluminum alloy ingot having the foregoing composition is
made by an ordinary casting process, such as a continuous casting
process, a semi-continuous casting process (DC casting process) or
the like. Then, the aluminum alloy ingot is subjected to a
homogenizing heat treatment, namely, a soaking process. An anodic
oxide film excellent in durability is formed by processing the
aluminum alloy ingot by the soaking process at a temperature,
namely, homogenizing temperature or soaking temperature, of
500.degree. C. or above. An anodic oxide film having still more
excellent in durability can be formed by processing the aluminum
alloy ingot by the homogenizing treatment at a homogenizing
temperature above 550.degree. C. Burning occurs to deteriorate the
surface quality of the aluminum alloy ingot when the homogenizing
temperature is above 600.degree. C. Therefore, it is recommended
that the homogenizing temperature is in the range of 500.degree. C.
(preferably, a temperature not lower than 550.degree. C.) to
600.degree. C. although the effect of the homogenizing temperature
on the formation of the anodic oxide film is not yet ascertained,
it is inferred that the homogenizing temperature participates in
producing an Al--Mn--Si compound or an Al--Mn compound as mentioned
above.
[0037] The aluminum alloy ingot processed by the homogenizing heat
treatment is processed by a proper plastic working process, such as
a rolling process, a forging process or an extrusion process, to
obtain an aluminum alloy material. Then, the aluminum alloy
material is subjected to a solution process, a quenching process
and an artificial aging process (hereinafter, referred to also
simply as "aging process"). Then, the aluminum alloy material is
formed in a suitable shape by machining to obtain an aluminum alloy
material. An aluminum alloy slab obtained by processing the
aluminum alloy ingot may be subjected to the solution process, the
quenching process and the aging process to obtain an aluminum alloy
material. The solution process, the quenching process and the aging
process may be, for example, a solution process at a temperature
between 515.degree. C. and 550.degree. C., a water quenching
process and an aging process at 170.degree. C. for 8 h or at
155.degree. C. to 165.degree. C. for 18 h forming an ordinary T6
process.
[0038] Anodic Oxide Film
[0039] An anodic oxide film coating the aluminum alloy material
will be described. An anodic oxide film forming method is executed
by properly determining conditions for electrolysis including the
composition and concentration of an electrolyte, voltage, current
density, waveforms of current and voltage, and temperature for
electrolysis. Electrolysis for anodization needs to use an
anodizing solution containing at least one of elements including C,
S, N, P and B. For example, it is effective to use an aqueous
solution containing at least one of oxalic acid, formic acid,
sulfamic acid, phosphoric acid, phosphorous acid, boric acid,
nitric acid or its compound, and phthalic acid or its compound.
There is not any particular limit to the thickness of the anodic
oxide film. The thickness of the anodic oxide film is between about
0.1 and about 200 .mu.m, preferably, between 0.5 and 70 .mu.m, more
desirably, between about 1 and about 50 .mu.m.
[0040] As mentioned above, parts of the anodic oxide film at
different positions with respect to the thickness of the anodic
oxide film have different hardnesses, respectively, and the
difference in Vickers hardness between a part having the highest
hardness and a part having the lowest hardness is Hv 5 or above.
Therefore, the anodic oxide film has a high hardness, and is
capable of suppressing the growth of cracks and excellent in crack
resistance. Since the anodic oxide film is excellent in crack
resistance, penetration of gases through the anodic oxide film to
the aluminum alloy body is suppressed and general durability is
ensured. If the difference in Vickers hardness between a part
having the highest hardness and a part having the lowest hardness
is below Hv 5, the behavior of the anodic oxide film is equal to
that of an anodic oxide film having a substantially uniform
thickness with respect to a direction parallel to the width, it is
difficult for the anodic oxide film to suppress the growth of
cracks. Consequently, the anodic oxide film has low crack
resistance and low corrosive gas resistance.
[0041] According to the present invention, the anodic oxide film
should have at least two parts at different positions with respect
to the thickness of the anodic oxide film having different
hardnesses. The number of such parts is not limited to any number,
provided that the number is two or greater. The hardness of the
anodic oxide film may discontinuously change or may continuously
change in a slope.
[0042] From the viewpoint of suppressing the growth of cracks
created in the anodic oxide film, it is considered that the part
having the lowest hardness has the lowest possible Vickers
hardness. However it is desirable, from the viewpoint of ensuring
resistance to the abrasive effect of the physical energy of plasma,
that the part has a hardness of Hv 365 or above.
[0043] An aluminum alloy material coated with the anodic oxide film
(hereinafter, referred to as "anodized aluminum alloy material") is
suitable for forming members to be used in a high-temperature
corrosive atmosphere. The anodized aluminum alloy material is
particularly suitable for forming a vacuum chamber for a plasma
processing apparatus included in a semiconductor device
manufacturing system or the like, and parts placed in the vacuum
chamber, such as electrodes, which are exposed to a corrosive gas
in a high-temperature atmosphere and are required to have a low
contaminating property of contaminating workpieces.
[0044] An anodic oxide film having parts at different positions
with respect to the thickness of the anodic oxide film respectively
having different hardnesses can be formed by a method that changes
the temperature of an anodizing solution intermittently or
continuously during an anodizing process, or a method that
interrupts an anodizing process using an anodizing solution, takes
out the aluminum alloy material from the anodizing solution, and
resumes an anodizing process using an anodizing solution of a
different composition and/or a different temperature. Those methods
can form an anodic oxide film having parts at different positions
with respect to the thickness respectively having different
hardnesses. An anodizing solution of a lower temperature is more
effective in suppressing the chemical dissolution of an anodic
oxide film during the anodizing process and in forming a hard
anodic oxide film.
[0045] As mentioned above, when the Fe content of an aluminum alloy
is reduced to 0.03% or below with a view to suppress the
contamination of a workpiece, such as a semiconductor wafer, the Fe
content of an anodic oxide film can be reduce to 500 ppm or below.
The Fe content of an anodic oxide film can be reduce to 150 ppm or
below when the Fe content of the aluminum alloy is reduced to 0.01%
or below.
[0046] As mentioned above the anodized aluminum alloy material has
a high hardness and is satisfactory in durability (crack resistance
and corrosive gas resistance) and low contaminating property.
EXAMPLES
[0047] Examples of the present invention will be described.
Examples described herein do not place any limit to the present
invention and changes that may be made therein without departing
from foregoing and the following gist are within the technical
scope of the present invention.
[0048] Aluminum alloy ingots of 220 mm in width, 250 mm in length
and 100 mm in thickness having the compositions of examples of the
present invention, namely, Samples Nos. 1, 2,4 and 5, and
comparative examples, namely, samples Nos. 3 and 6 to 14 shown in
Table 1 were formed by casting and were cooled at a cooling rate in
the range of 10 to 15 .degree. C./s. The aluminum alloy ingots were
cut and ground to obtain aluminum alloy slabs of 220 mm in width,
150 mm in length and 60 mm in thickness. The aluminum alloy slabs
were processed by a soaking process at 540.degree. C. for 4 h. The
soaked aluminum alloy slabs of 60 mm in thickness were subjected to
a hot rolling process to obtain aluminum alloy plates of 6 mm in
thickness. Sample alloy plates were obtained by processing the
aluminum alloy plates by a solution treatment at a temperature in
the range of 510.degree. C. to 520.degree. C. for 30 min, a water
quenching process, and an aging process at a temperature in the
range of 160.degree. C. to 180.degree. C. for 8h. Specimens of 25
mm.times.35 mm (rolling direction) and 3 mm in thickness were cut
out from the alloy plates. The surfaces of the specimens were
ground in a surface roughness of Ra 1.6.
TABLE-US-00001 TABLE 1 Durability Polluting property Content
Corroded Fe Cr Cu (% by mass) Hardness area ratio content content
content Specimen No. Mg Si Mn Fe Cr Cu difference (%) Judgment
(ppm) (ppm) (ppm) Judgment 1 Ex. 0.8 1.2 1.6 0.008 0.009 0.007 10 0
.circleincircle. 150 190 130 .circleincircle. 2 Ex. 0.8 1.2 1.6
0.008 0.009 0.007 5 2 .largecircle. 150 190 130 .circleincircle. 3
Comp. 0.8 1.2 1.6 0.008 0.009 0.007 4 10 X 160 180 150
.circleincircle. ex. 4 Ex. 0.1 0.1 0.1 0.029 0.028 0.027 10 3
.largecircle. 490 480 480 .largecircle. 5 Ex. 1.9 2.0 1.8 0.027
0.028 0.028 10 3 .largecircle. 470 480 490 .largecircle. 6 Comp.
0.09 0.8 1.1 0.006 0.008 0.009 10 11 X 120 170 190 .circleincircle.
ex. 7 Comp. 2.1 0.8 1.0 0.007 0.009 0.008 10 18 X 130 180 170
.circleincircle. ex. 8 Comp. 1.0 0.08 0.7 0.009 0.007 0.008 10 9 X
170 150 160 .circleincircle. ex. 9 Comp. 1.0 2.1 0.8 0.008 0.006
0.009 10 20 X 160 130 180 .circleincircle. ex. 10 Comp. 0.9 1.1
0.09 0.008 0.009 0.006 10 10 X 150 180 130 .circleincircle. ex. 11
Comp. 1.1 0.9 2.1 0.009 0.008 0.007 10 19 X 180 160 140
.circleincircle. ex. 12 Comp. 0.9 1.0 0.9 0.031 0.007 0.008 10 0
.circleincircle. 520 140 180 X ex. 13 Comp. 1.0 1.0 0.9 0.008 0.032
0.009 10 0 .circleincircle. 170 530 190 X ex. 14 Comp. 1.0 0.9 0.9
0.007 0.009 0.031 10 0 .circleincircle. 140 190 510 X ex. Second
anodic oxide film First anodic oxide film Tempera- Thick- Hard-
Temperature Voltage Thickness Hardness ture Voltage ness ness
Specimen No. Anodizing solution (.degree. C.) (V) (.mu.m) (Hv)
Anodizing solution (.degree. C.) (V) (.mu.m) (Hv) 1 Oxalic acid
solution 10 60 15 380 Oxalic acid solution 5 60 15 390
(Concentration: 25 g/l) (Concentration: 25 g/l) 2 Oxalic acid
solution 8 60 15 385 Oxalic acid solution 5 60 15 390
(Concentration: 25 g/l) (Concentration: 25 g/l) 3 Oxalic acid
solution 7 60 15 386 Oxalic acid solution 5 60 15 390
(Concentration: 25 g/l) (Concentration: 25 g/l) 4 Oxalic acid
solution 10 60 15 365 Oxalic acid solution 5 60 15 375
(Concentration: 25 g/l) (Concentration: 25 g/l) 5 Oxalic acid
solution 10 60 15 365 Oxalic acid solution 5 60 15 375
(Concentration: 25 g/l) (Concentration: 25 g/l) 6 Oxalic acid
solution 10 60 15 380 Oxalic acid solution 5 60 15 390
(Concentration: 25 g/l) (Concentration: 25 g/l) 7 Oxalic acid
solution 10 60 15 380 Oxalic acid solution 5 60 15 390
(Concentration: 25 g/l) (Concentration: 25 g/l) 8 Oxalic acid
solution 10 60 15 380 Oxalic acid solution 5 60 15 390
(Concentration: 25 g/l) (Concentration: 25 g/l) 9 Oxalic acid
solution 10 60 15 380 Oxalic acid solution 5 60 15 390
(Concentration: 25 g/l) (Concentration: 25 g/l) 10 Oxalic acid
solution 10 60 15 380 Oxalic acid solution 5 60 15 390
(Concentration: 25 g/l) (Concentration: 25 g/l) 11 Oxalic acid
solution 10 60 15 380 Oxalic acid solution 5 60 15 390
(Concentration: 25 g/l) (Concentration: 25 g/l) 12 Oxalic acid
solution 10 60 15 360 Oxalic acid solution 5 60 15 370
(Concentration: 25 g/l) (Concentration: 25 g/l) 13 Oxalic acid
solution 10 60 15 380 Oxalic acid solution 5 60 15 390
(Concentration: 25 g/l) (Concentration: 25 g/l) 14 Oxalic acid
solution 10 60 15 380 Oxalic acid solution 5 60 15 390
(Concentration: 25 g/l) (Concentration: 25 g/l) (Note) Examples are
abbreviated to Exs. and Comparative examples to Comp. exs.
[0049] Each of the specimens was immersed in a 10% NaOH solution of
60.degree. C. for 2 min, the specimen was rinsed with water, the
specimen was immersed in a 20% HNO.sub.3 solution of 20.degree. C.
for 2 min, and then the specimen was rinsed with water to clean the
surface thereof. Then, a first anodic oxide film was formed on a
surface of the specimen and a second anodic oxide film was formed
on the first anodic oxide film by an anodizing process. Process
conditions for the anodizing process are shown in Table 1. The
first and the second anodic oxide film were formed in a thickness
of 15 .mu.m using a processing solution having an oxalic
concentration of 25 g/L (the letter "L" represents "liter"). Bath
voltage was fixed at 60 V. The difference between the anodizing
conditions respectively for the forming the first and the second
anodic oxide film was only the temperature of the processing
solution. The temperature of the processing solution for forming
the first anodic oxide film was higher than that for forming the
second anodic oxide film.
[0050] The Fe, the Cr and the Cu content of the anodized aluminum
alloy specimens (hereinafter referred to simply as "specimens")
were measured, the hardness of the anodic oxide films was measured,
and the durability of the anodic oxide films was tested.
[0051] Measurement of Fe, Cr and Cu Contents of Anodic Oxide
Film
[0052] Contaminating properties of the specimens were evaluated.
The specimen was immersed in 100 ml of a 7% hydrochloric acid
solution to dissolve the anodic oxide film to the extent that the
aluminum alloy body is not exposed. The weight W (g) of the
dissolved anodic oxide film was determined by calculating the
difference in weight between the weight of the hydrochloric acid
solution before the dissolution of the anodic oxide film and that
of the same after the dissolution of the anodic oxide film. Then,
the Fe, the Cr and the Cu content of the hydrochloric acid solution
were determined through the ICP analysis of the hydrochloric acid
solution, and the respective weights W.sub.Fe, W.sub.Cr and
W.sub.Cu (g) of Fe, Cr and Cu contained in 100 ml of the
hydrochloric acid were calculated. Then, the Fe, the Cr and the Cu
content of the anodic oxide film, namely, W.sub.Fe/W W.sub.Cr/W and
W.sub.Cu/W, were calculated. The contaminating property of the
specimen was evaluated by the Fe, the Cr and the Cu content of the
anodic oxide film on the basis of the following criterion. Results
of evaluation are shown in Table 1.
[0053] Criterion for Contaminating Property Evaluation
[0054] Double circle: All the Fe, the Cr and the Cu content are 300
ppm or below
[0055] Circle: At least one of the Fe, the Cr and the Cu content is
above 300 ppm and 500 ppm or below and other elements are 300 ppm
or below
[0056] Cross: At least one of the Fe, the Cr and the Cu content is
above 500 ppm
[0057] Results of Evaluation of Polluting Property
[0058] As shown in Table 1, some of the Fe, the Cr and the Cu
content of the anodic oxide films of the specimens Nos. 12 to 14 of
the comparative examples was above 500 ppm. All of the Fe, the Cr
and the Cu content of the specimens Nos. 1, 2, 4 and 5 of the
examples and the specimens Nos. 3 and 6 to 11 of the comparative
examples were satisfactorily as low as 500 ppm or below. As shown
in Table 1, all of the Fe, the Cr and the Cu content of the
specimens Nos. 1 and 2 of the examples and the specimens Nos. 3 and
6 to 11 of the comparative examples were very low values of 300 ppm
or below and those examples and comparative examples were very
satisfactory.
[0059] Measurement of Hardness of Anodic Oxide Film
[0060] Each specimen was embedded in a resin, a cross section of
the specimen including sections of the anodic oxide film and the
aluminum alloy body was polished. The hardness of the polished
section of the anodic oxide film was measured by a measuring method
specified in Z2244 (1998), JIS.
[0061] Results of Measurement
[0062] In each of the specimens Nos. 1, 2, 4 and 5 of the examples
and the specimens Nos. 3 and 6 to 14 of the comparative examples,
the second anodic oxide film has a hardness higher than that of the
first anodic oxide film. Such a hardness difference between the
first and the second anodic oxide film was caused by a condition
that the temperature of the anodizing solution used for forming the
second anodic oxide film was lower than that of the anodizing
solution used for forming the first anodic oxide film. The
difference in hardness between the first and the second anodic
oxide film of the specimen No. 2 of the example was Hv 5. Such a
hardness difference was caused by a condition that the temperature
of the anodizing solution used for forming the second anodic oxide
film was 5.degree. C. and that of the anodizing solution used for
forming the first anodic oxide film was 8.degree. C. The difference
in hardness between the first and the second anodic oxide film of
the specimen No. 3 of the comparative example was Hv 4. Such a
hardness difference was caused by a condition that the temperature
of the anodizing solution used for forming the second anodic oxide
film was 5.degree. C. and that of the anodizing solution used for
forming the first anodic oxide film was 7.degree. C. The difference
in hardness between the first and the second anodic oxide film of
each of the specimens Nos. 1, 4 and 5 of the other examples and the
SPECIMENS Nos. 6 to 14 of the other comparative examples was Hv 10.
Such a hardness difference was caused by a condition that the
temperature of the anodizing solution used for forming the second
anodic oxide film was 5.degree. C. and that of the anodizing
solution used for forming the first anodic oxide film was
10.degree. C. Thus the anodic oxide film can be formed in an
optional hardness by controlling the temperature of the anodizing
solution. As shown in Table 1, the respective hardnesses of the
anodic oxide films excluding the anodic oxide film of the specimen
No. 12 of the comparative example were Hv 365 or above. Therefore,
the plasma resistance of the anodic oxide films excluding the
anodic oxide film of the specimen no. 12 of the comparative example
is satisfactory.
[0063] Test of Durability of Anodic Oxide Film
[0064] A durability test included a crack resistance test at a
first stage and a corrosive gas resistance test at a second stage.
In the crack resistance test, a specimen was heated at 450.degree.
C. for 1 h in a test vessel of an atmospheric atmosphere, and then
the specimen taken out from the test vessel was dipped in water of
27.degree. C. for quenching. The specimen tested by the crack
resistance test was subjected to two corrosive gas resistance test
cycles. Each corrosive gas resistance test cycle held the specimen
in a 5% Cl.sub.2--Ar gas atmosphere of 400.degree. C. for 4 h.
Then, the corroded area ratio of the surface of the specimen was
calculated by using and expression: (Corroded area ratio) {(Area or
corroded parts)/(Area of the surface of the specimen)}.times.100.
The specimens were evaluated on the basis of the following
criterion. Results of evaluation are shown in Table 1.
[0065] Criterion for Durability Evaluation
[0066] Double circle: Corroded area ratio 0%
[0067] Circle: Corroded area ratio: 0 to 3%
[0068] Cross: Corroded area ratio: Above 3%
[0069] Results of Durability Evaluation
[0070] As shown in Table 1, the specimens Nos. 3 and 6 to 11 of the
comparative examples were unacceptable. The specimens Nos. 1, 2, 4
and 5 of the examples and the specimens Nos. 12 to 14 of the
comparative examples were satisfactory in durability. As shown in
Table 1, the specimen No. 1 of the example and the specimen Nos. 12
to 14 of the comparative examples were very satisfactory in
durability.
[0071] It is known from the synthetic conclusion based on the
measured data on the Fe, the Cr and the Cu content of the anodic
oxide films, the measured data on the hardness of the anodic oxide
films, and the results of the durability tests of the anodic oxide
films that only the specimens Nos. 1, 2, 4 and 5 of the examples
meet all the criterions. The specimens Nos. 1, 2, 4 and 5 of the
examples meeting all the criterions are have a high hardness and
are satisfactory in both durability and low polluting property.
* * * * *