U.S. patent application number 10/078693 was filed with the patent office on 2002-10-31 for anodizing process, with low environmental impact, for a woodpiece of aluminum or aluminum alloys.
This patent application is currently assigned to Alenia Aeronautica S.p.A.. Invention is credited to Dattilo, Alessandro, Romano, Carlo, Tamiro, Salvatore.
Application Number | 20020157961 10/078693 |
Document ID | / |
Family ID | 11458586 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020157961 |
Kind Code |
A1 |
Dattilo, Alessandro ; et
al. |
October 31, 2002 |
Anodizing process, with low environmental impact, for a woodpiece
of aluminum or aluminum alloys
Abstract
The process for anodizing a workpiece of aluminum or aluminum
alloys provides for the use of the workpiece as the anode of an
electrolytic cell in the presence of an aqueous acid solution which
contains from 10 to 200 g sulfuric acid and from 5 to 200 g
L(+)-tartaric acid.
Inventors: |
Dattilo, Alessandro; (Santa
Maria Capua Vetere (Caserta), IT) ; Tamiro, Salvatore;
(Mompantero (Torino), IT) ; Romano, Carlo;
(Pomigliano D'Arco (Napoli), IT) |
Correspondence
Address: |
COOK, ALEX, MCFARRON, MANZO,
CUMMINGS & MEHLER, LTD.
Suite 2850
200 W. Adams Street
Chicago
IL
60606
US
|
Assignee: |
Alenia Aeronautica S.p.A.
|
Family ID: |
11458586 |
Appl. No.: |
10/078693 |
Filed: |
February 19, 2002 |
Current U.S.
Class: |
205/328 |
Current CPC
Class: |
C25D 11/06 20130101 |
Class at
Publication: |
205/328 |
International
Class: |
C25D 011/04; C25D
011/08 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 20, 2001 |
IT |
TO2001A000149 |
Claims
What is claimed is:
1. Process for anodizing a workpiece of aluminium or aluminium
alloys, which provides for the use of the workpiece as the anode of
an electrolytic cell in the presence of an aqueous acid solution,
wherein the aqueous acid solution contains from 10 to 200 g
sulphuric acid and from 5 to 200 g L(+)-tartaric acid.
2. Process according to claim 1, wherein the aqueous acid solution
contains from 20 to 80 g sulphuric acid and from 30 to 120 g
L(+)-tartaric acid per liter of solution.
3. Process according to either of the preceding claims, wherein the
solution is maintained, during the anodizing treatment, at a
temperature of between ambient temperature and 120.degree. C., and
preferably between 25 and 35.degree. C.
4. Process according to claim 1, wherein the electrolytic cell is
subjected to a voltage of between 1 and 120 V, and preferably of
between 10 and 30 V.
5. Process according to claim 1, wherein it has a duration of
between 5 and 120 minutes, and preferably of between 5 and 30
minutes.
6. Process according to claim 1, wherein it is preceded by a
cleaning, deoxidizing and rinsing treatment for the workpiece to be
anodized.
7. Process according to claim 1, wherein it is followed by a
rinsing and sealing treatment for the anodized workpiece.
Description
DESCRIPTION
[0001] The present invention relates to an anodizing process for a
workpiece (such as, for example, a part or a component of a system)
of aluminium or aluminium alloys, this definition being intended to
comprise pure or almost pure aluminium, as well as combinations
thereof in all percentages with other elements.
[0002] In greater detail, this process makes use of the
above-mentioned workpiece as the anode of an electrolytic cell in
the presence of an aqueous acid solution in order to form on the
surface of the workpiece a coating of aluminium oxide.
[0003] This coating results in better properties concerning the
resistance to corrosion and the adhesion of paints, bonding agents
and other organic coatings suitable for improving the appearance or
the resistance to corrosion of the finished workpiece.
[0004] Conventionally, this acid solution substantially comprises
sulphuric acid at high concentrations or chromic acid, the latter
being the compound mainly used in the field of aeronautics.
[0005] The problem addressed by the present invention is to provide
an anodizing process having a lesser toxicological impact on the
environment in comparison with the known types, avoiding the use of
chromic acid whilst nevertheless obtaining anodized workpieces
having properties which are at least equivalent to those of
workpieces obtained by conventional means.
[0006] This problem is solved according to the invention by an
anodizing process of the type indicated in the introduction to the
present description and characterized in that the aqueous acid
solution contains from 10 to 200 g sulphuric acid and from 5 to 200
g L(+)-tartaric acid per liter of solution.
[0007] The process according to the invention has the advantage of
eliminating, or in any case greatly reducing, the production of
industrial waste, in particular waste containing compounds of
chromium, without causing the formation of other waste materials
having particular toxic or dangerous properties.
[0008] The process according to the invention further has the
advantage of having a cycle time which is approximately 40% short
of that of the analogous process which makes use of chromic acid,
producing anodized workpieces having properties at least equivalent
if not superior. Consequently, the process according to the
invention allows a considerable reduction in running costs to be
obtained in that it results in lower costs for the treatment of the
waste and involves a substantially lower rate of consumption for
the different chemicals used for replenishing the baths, which have
an operational life greater than those used in known processes.
[0009] The aqueous acid solution of the process according to the
invention preferably contains from 20 to 80 g sulphuric acid and
from 30 to 120 g L(+)-tartaric acid per liter of solution.
[0010] Again preferably, the aqueous solution is maintained, during
the anodizing treatment, at a temperature of between ambient
temperature and 120.degree. C. and, more preferably, between 25 and
35.degree. C.
[0011] The electrolytic cell, in which the process according to the
invention is carried out, is preferably subjected to a voltage of
between 1 and 120 V and, more preferably, of between 10 and 30
V.
[0012] The process according to the invention advantageously has a
duration of between 5 and 120 minutes and, preferably, of between 5
and 30 minutes.
[0013] The anodizing process is generally preceded by a cleaning
and/or deoxidizing treatment of the workpiece to be anodized and
can be followed by a sealing treatment and, optionally, rinsing for
the anodized workpiece. In principle, these treatments are of
conventional type and completely compatible with the present
invention and can be selected at will from treatments known to this
end by the person skilled in the art.
[0014] The workpiece advantageously has, upon completion of the
anodizing treatment, an oxidized surface coating having a thickness
of between a few micrometers and several tens of micrometers.
[0015] There now follow, merely by way of non-limiting,
illustrative example, examples of the anodizing process according
to the invention, as well as a comparative example performed by
conventional techniques.
EXAMPLE 1
[0016] Anodizing a 2000-Series Aluminium Alloy with
Sulphuric-Tartaric Acid
[0017] A workpiece (of a 2000-series aluminium alloy having
dimensions of 150.times.100.times.1 mm) was first subjected in a
conventional manner to cleaning and deoxidizing treatments, such as
de- greasing by immersion for approximately 10 minutes, rinsing by
immersion in drinking water for approximately 3 minutes,
pickling/deoxidation by immersion for approximately 10 minutes and
rinsing by immersion in drinking water, preferably followed by
further rinsing by immersion in deionized water for a total of
approximately 3 minutes.
[0018] The workpiece was then used as the anode of an
electrochemical cell, in which the cathode was constituted by
corrosion-resistant steel of the type AISI 321 and having a surface
area equal to or greater than that to be oxidized and in the
presence of an aqueous acid solution containing 45 g sulphuric acid
and 80 g L(+)-tartaric acid per liter of solution and was
maintained at a temperature of between 30 and 35.degree. C. The
workpiece was kept completely immersed in the acid solution.
[0019] The electrical voltage was increased from an initial value
of 0 V to a value of 18 V at a rate in the order of 3.6 V/min. The
final voltage value was maintained for 25 minutes, producing on the
workpiece, upon completion of the anodizing treatment, an oxidized
coating having a thickness of approximately 5 .mu.m.
[0020] The anodized workpiece was then subjected to treatments
which are conventional per se, such as rinsing with drinking water,
preferably followed by further rinsing with deionized water for an
overall immersion time of approximately 3 minutes and sealing by
immersion for approximately 45 minutes. The workpiece was then
dried with air, in particular at a low temperature, if good
properties of adhesiveness were required for the oxide.
[0021] The properties of this oxide are indicated in Table I.
EXAMPLE 2
Anodizing a 7000-Series Aluminium Alloy with Sulphuric-Tartaric
Acid
[0022] A workpiece (of a 7000-series aluminium alloy having
dimensions of 150.times.100.times.1 mm) was first subjected in a
conventional manner to cleaning and deoxidizing treatments, similar
to those described with reference to Example 1.
[0023] The workpiece was then used as the anode of an
electrochemical cell, in which the cathode was constituted by
corrosion-resistant steel of the type AISI 321 and having a surface
area equal to or greater than that to be oxidized and in the
presence of an aqueous acid solution containing 45 g sulphuric acid
and 80 g L(+)-tartaric acid per liter of solution and was
maintained at a temperature of between 30 and 35.degree. C. The
workpiece was kept completely immersed in the acid solution.
[0024] The electrical voltage was increased from an initial value
of 0 V to a value of 15 V at a rate in the order of 3 V/min. The
final voltage value was maintained for 25 minutes, producing on the
workpiece, upon completion of the anodizing treatment, an oxidized
coating having a thickness of approximately 5 .mu.m.
[0025] The anodized workpiece was then subjected to rinsing and
sealing treatments, which are conventional per se, similar to those
described with reference to Example 1.
[0026] The properties of the oxide coating obtained are indicated
in Table I.
EXAMPLE 3
Anodizing Plated or Pure Aluminium with Sulphuric-Tartaric Acid
[0027] A workpiece (of a plated aluminium alloy or pure aluminium
having dimensions of 150.times.100.times.1 mm) was first subjected,
in a conventional manner, to cleaning and deoxidizing treatments,
similar to those described with reference to Example 1.
[0028] The workpiece was then used as the anode of an
electrochemical cell, in which the cathode was constituted by
corrosion-resistant steel of the type AISI 321 and having a surface
area equal to or greater than that to be oxidized and in the
presence of an aqueous acid solution containing 45 g sulphuric acid
and 80 g L(+)-tartaric acid per liter of solution and was
maintained at a temperature of between 30 and 35.degree. C. The
workpiece was kept completely immersed in the acid solution.
[0029] The electrical voltage was increased from an initial value
of 0 V to a value of 15 V at a rate in the order of 3 V/min. The
final voltage value was maintained for 25 minutes, producing on the
workpiece, upon completion of the anodizing treatment, an oxidized
coating having a thickness of approximately 5 .mu.m.
[0030] The anodized workpiece was then subjected to rinsing and
sealing treatments, which are conventional per se, similar to those
described with reference to Example 1.
[0031] The properties of the oxide coating obtained are indicated
in Table I.
EXAMPLE 4 (FOR COMPARATIVE PURPOSES)
Anodizing with Chromic Acid
[0032] A workpiece (of a plated aluminium alloy or a pure aluminium
having dimensions of 150.times.100.times.1 mm) was first subjected
in a conventional manner to cleaning and deoxidizing treatments,
similar to those described with reference to Example 1.
[0033] The workpiece was then used as the anode of an
electrochemical cell, in which the cathode was constituted by
corrosion-resistant steel of the type AISI 321 and having a surface
area equal to or greater than that to be oxidized and in the
presence of an aqueous acid solution containing 65 g chromic acid
and was maintained at a temperature of between 35 and 40.degree. C.
The workpiece was kept completely immersed in the acid
solution.
[0034] The electrical voltage was increased from an initial value
of 0 V to a value of 40 V at a rate in the order of 5 V/min. The
final voltage value was maintained for 45 minutes, producing on the
workpiece, upon completion of the anodizing treatment, an oxidized
coating having a thickness of approximately 3 .mu.m.
[0035] The anodized workpiece was then subjected to rinsing and
sealing treatments, which are conventional per se, similar to those
described with reference to Example 1.
[0036] The properties of the oxide coating obtained are indicated
in Table I.
1TABLE I Prior art Chromic acid Prior art INVENTION Property Test
method (Example 4) Sulphuric acid (Examples 1, 2, 3) Weight of
oxide ASTM B 137 >32 mg/dm.sup.2 >32 mg/dm.sup.2 >40
mg/dm.sup.2 Corrosion resistance Tests in saline mist ac- No
corrosion points after No corrosion points after No corrosion
points after cording to Iso 7253 exposure for 500 hours exposure
for 500 hours exposure for 750 hours Impact test according to No
detachment of paint or ASTM D 2794 only slight cracking of paint
NOT APPLICABLE No detachment of paint Paint adhesion Adhesion
without condi- tioning according to ISO 100% adhesion 90% adhesion
100% adhesion 2409 Adhesion after condition- ing in water for 14
days 100% adhesion 80% adhesion 100% adhesion according to ISO 2409
Influence of oxide on Fatigue tests on cylindrical Reduction in
fatigue cycles Reduction in fatigue cy- fatigue life of base test
pieces at frequency of not greater than 25% Unsatisfactory cles not
greater than 15% metal 10-140 Hz, ratio R:0.1
[0037] A comparison of the results of the tests carried out on the
workpieces of the Examples according to the invention and the
Example for comparative purposes establishes that the process
according to the invention produces oxides having properties which
are superior to those of the oxides obtained with conventional
processes. Furthermore, the process according to the invention
offers environmental advantages associated with the different types
of product used, and has a duration which is substantially
shorter.
[0038] Of course, without altering the principle of the invention,
the details of implementation and the embodiments can vary
extensively in relation to the description, which is given purely
by way of example, without in any way departing from the scope
thereof. In particular, the aqueous acid solution could contain, in
addition to sulphuric acid and tartaric acid, any other components
or combinations of components which are compatible with those
substances.
* * * * *