[0001] The present invention relates to a novel conversion treatment solution for aluminum
and aluminum alloys which imparts an excellent corrosion resistance and paint adherence
to the surface of aluminum and aluminum alloys prior to their being painted and to
a process of treating surfaces with such a solution. The conversion treatment solution
is particularly well suited for application to the surface of, for example, the lid
material for beverage cans (i.e., can end stock) and the like.
[0002] Conversion treatment solutions for aluminum and aluminum alloys may be roughly classified
into chromate-type treatments and nonchromate-type treatments. Typical examples of
chromate-type treatments are chromic acid/chromate treatments and phosphoric acid/chromate
treatments. Chromic acid/chromate treatments came into practical application in about
1950, and are still widely used at present on, for example, the fin material of heat
exchangers. The principal components of this type of conversion treatment solution
are chromic acid (CrO₃) and hydrofluoric acid (HF), and an accelerator may also be
present. A film which contains some quantity of hexavalent chromium is formed.
[0003] The phosphoric acid/chromate conversion treatment is disclosed in United States Patent
Number 2,438,877. This conversion treatment solution is composed of chromic acid (CrO₃),
phosphoric acid (H₃PO₄), and hydrofluoric acid (HF). The principal component of the
resulting film is hydrated chromium phosphate (CrPO₄·4H₂O. Since this film does not
contain much if any hexavalent chromium, it is widely used at present as a paint undercoating
treatment for beverage cans and the associated lid stock.
[0004] Nonchromate-type treatments are recognized in the art as a distinct category from
the chromate-type treatment solutions explained above, and are exemplified by the
invention disclosed in Japanese Patent Application Laid Open [Kokai] Number 52-131937
[131,937/77]. The treatment solution disclosed therein comprises an acidic (pH approximately
1.0 to 4.0) aqueous coating solution which contains zirconium or titanium or a mixture
thereof as well as phosphate and fluoride. Treatment with the disclosed conversion
treatment solution produces on the aluminum surface a conversion film whose main component
is zirconium and/or titanium oxide. Although the absence of hexavalent chromium is
an advantage of the nonchromate-type treatment solution, this type of treatment solution
nevertheless suffers from a corrosion resistance and paint adherence inferior to those
for chromate-type treatments.
[0005] Aluminum alloy, in sheet or coil form, is widely used after painting for beverage
can lid material, i.e., can end stock. It is subjected to a conversion treatment in
order to raise the corrosion resistance and paint adherence, and the phosphoric acid/chromate
treatment is employed in almost all commercial can lid manufacturing in Japan.
[0006] The phosphoric acid/chromate conversion treatment of can end stock generally employs
a treatment solution which contains 10.0 to 40.0 g/L phosphate ion, 2.0 to 4.0 g/L
hexavalent chromium, and 0.7 to 1.5 g/L fluoride ion. At present, vinyl chloride paint
is generally used to coat can end stock. Thus, the production of can ends normally
includes a phosphoric acid/chromate treatment of aluminum alloy in coil or sheet form,
followed by coating with a vinyl chloride paint and then forming.
[0007] A beverage can thus normally consists of a can end formed from aluminum alloy coil
or sheet treated as described above and of a can body filled with, for example, juice
or beer. Depending on its contents, the can may be subject d to sterilization at relatively
high temperatures after filling. If it is, steam is formed from vaporization of the
contents, the steam penetrates through the paint film, and the permeated steam then
condenses at the interface between the paint film and conversion film. As a result,
sterilization tends to reduce the adherence of the paint film. In particular, when
a section of the can end is opened by the easy-open method, defects (enamel feathering)
can be generated in the opened region due to peeling or exfoliation of the paint film.
[0008] US-A-2 868 682 discloses aqueous solutions and a process for forming coatings particularly
on surfaces of aluminum, iron or alloys thereof. The solutions contain condensed phosphate
compounds in a concentration not exceeding about 0.5 % by weight based on condensed
phosphate of sodium compound (corresponding to a PO₄³⁻-value of a about 3.6 g/l) hexavalent
chromium within the range of from 0.42 to 13 g/l Cr⁶⁺ (0.08 to 2.5 % CrO₃), between
0.1 to 20 g/l fluoride expressed as sodiumbifluoride, and up to 16 g/l fluoborate
(preferably between 6 to 7 g/l) and optionally K₂TiF₆ and K₂ZrF₆ up to about 1 g/l.
[0009] Increasing the adhesion of paint to aluminum and its alloys, particularly aluminum
and its alloys used in forming beverage can ends to be used for cans requiring high
temperature sterilization of the contents, is the major problem addressed by this
invention.
[0010] As a concrete means for solving the problems described hereinbefore for the prior
art, the present invention introduces an aqueous conversion treatment solution for
aluminum and aluminum alloys that has a pH in the range from 1.0 to 3.0 and consists
essentially of, water and 5.0 to 40.0 grams per liter ("g/L") of phosphate ions, 1.0
to 4.0 g/L of hexavalent chromium (in the form of chromium containing anions), 0.1
to 2.0 g/L of fluoride ions, and a complex fluoride ion component selected from the
group consisting of (i) 4.0 to 15.0 g/L of fluosilicate ion, (ii) 0.5 to 3.0 g/L of
fluoborate ion, (iii) 2.0 to 8.0 g/L of fluozirconate ions, and (iv) 2.0 to 8.0 g/L
of fluotitanate ions. This conversion treatment solution is capable of forming a highly
paint-adherent conversion film which imparts an excellent corrosion resistance to
the surface of aluminum and aluminum alloys. In other words, the present invention
seeks to offer a conversion treatment solution which imparts an excellent corrosion
resistance and paint adherence to the surface of aluminum and aluminum alloy prior
to their being painted.
[0011] The conversion treatment solution of the present invention is an acidic treatment
solution which contains complex fluoride ion, phosphate ion, hexavalent chromium,
and fluoride ion as its essential components.
[0012] The complex fluoride ions are selected from fluosilicate (SiF₆⁻²) ions, fluotitanate
(TiF₆⁻²), fluozirconate (ZrF₆⁻²), and fluoborate (BF₄⁻²) ions, and may be added in
the form of fluosilicic acid, fluoboric acid, fluozirconic acid, fluotitanic acid,
or any soluble salt thereof. Mixtures of these ions may also be used. A range of 4.0
to 15.0 g/L is indicated for the fluosilicate ion. Values less than 4.0 g/L cannot
normally generate good paint adherence, while values exceeding 15.0 g/L may cause
substantial etching of an aluminum surface and prevent the formation of a satisfactory
film. A range of 0.5 to 3.0 g/L is indicated for the fluoborate ion. Values less than
0.5 g/L again cannot usually generate a good paint adherence, while values in excess
of 3 0 g/L increase waste water pollution and are uneconomical. A range of 2.0 to
8.0 g/L is indicated for fluozirconate ions, fluotitanate ions, or mixtures of these
two ions. Concentrations of these two complex fluoride ions that are less than 2.0
g/L cannot usually generate good paint adherence, while concentrations exceeding 8.0
g/L cause substantial etching and usually prevent the formation of a satisfactory
film.
[0013] Phosphoric acid (H₃PO₄) is the preferred source for the phosphate ion, and the phosphoric
acid content falls into the range of 5.0 to 40.0 g/L. When this value is less than
5.0 g/L, the resulting film will normally contain only small quantities of chromium
phosphate and the paint adherence may be inadequate. While good films are formed at
concentrations exceeding 40.0 g/L, the cost of the treatment solution is also increased
and the economics become less favorable.
[0014] Chromic acid (CrO₃) is the source for the hexavalent chromium, and the preferred
chromic acid content is that which will result in a concentration of its stoichiometric
equivalent as hexavalent chromium in the range from 1.0 to 4.0 g/L. Values less than
1 g/L result in an inferior corrosion resistance because a satisfactory conversion
film is not formed. Values in excess of 4.0 g/L can cause increased pollution from
and/or pollution abatement cost for waste water from the treatment solution and thus
create environmental and economic problems.
[0015] The fluoride ion content is an important component for controlling the film growth
rate of the conversion film. The fluoride ion source may be, for example, hydrofluoric
acid (HF), sodium fluoride (NaF), potassium fluoride (KF), and the like. The fluoride
ion concentration in the conversion solutions was determined as follows: An ion-selective
electrode (Fluorine F-125 electrode, reference HS-305DP from Toa Denpa Kogyo Kabushiki
Kaisha) and an ion meter (Type IM-40S from Toa Denpa Kogyo Kabushiki Kaisha) were
used. For calibration, standard solutions were prepared by adding a specified quantity
of hydrofluoric acid (for example, 0.1 g/L, 1 g/L, or 10 g/L) to 5 g/L chromic acid
and 15 g/L phosphoric acid and by adjusting the pH to 2.0 with phosphoric acid or
sodium hydroxide. (The fluoride ion concentration was assumed to correspond to the
total quantity of fluorine from hydrofluoric acid addition). The meter readings obtained
with these solutions of known fluoride ion concentration were then determined and
plotted against the fluoride ion concentrations to generate a calibration curve. The
pH of the conversion solution itself was adjusted to 2.0 using phosphoric acid or
sodium hydroxide and then measured using the fluorine ion meter, and the measured
value was converted to the fluoride ion concentration by reference to the calibration
curve.
[0016] The range for the fluoride ion concentration is 0.1 to 2.0 g/L. At values less than
0.1 g/L, the growth rate of the conversion film is slow, so that long treatment times
must be used in order to obtain satisfactory conversion films and the productivity
is therefore low. Rapid growth rates are encountered at values in excess of 2.0 g/L;
this results in large film weights and an undesirable loss of the metallic luster
of the workpiece. As a consequence, the concentration range is 0.1 to 2.0 g/L; the
particularly preferred range is 0.4 to 1.0 g/L.
[0017] The pH of this conversion treatment solution is in the range of 1.0 to 3.0 and may
conveniently be adjusted into that range through the use of an acid arbitrarily selected
from acids such as phosphoric acid, nitric acid, and hydrochloric acid or a base arbitrarily
selected from bases such as sodium hydroxide, ammonium hydroxide, and the like. A
pH below 1.0 causes substantial etching and therefore interferes with coat formation.
A pH in excess of 3.0 usually results in weak etching so that a uniform film cannot
be formed.
[0018] The use of the conversion treatment solution of the present invention in treatment
processes is another embodiment of this invention and will now be considered in more
detail. The conversion treatment solution of the present invention can be used as
a substitute for the currently widely used phosphoric acid/chromate treatment solutions.
A preliminary surface cleaning must usually be carried out when the conversion treatment
solution of the present invention is used for the conversion treatment of the surface
of aluminum or aluminum alloy. The cleaning method in this case may consist of treatment
with an acidic, alkaline, or solvent-based cleaning solution or some combination thereof.
As necessary or desired, the aluminum or aluminum alloy surface may be etched with
alkali or acid after cleaning. Either immersion or spray treatment may be used as
the method for treatment with solution according to the present invention. The weight
of the resulting conversion film is governed by such factors as the treatment temperature
and treatment time. The temperature of the treatment solution should preferably fall
into the range from room temperature (about 20 degrees Centigrade) to 70 degrees Centigrade
and more preferably falls into the range from 35 to 55 degrees Centigrade. Treatment
times in the range of 1 to 90 seconds are preferred. As with phosphoric acid/chromate
films, the conversion film weight is normally evaluated based on the deposition of
chromium, and optionally zirconium, and/or titanium. The quantity of deposition of
each of the three metals, when present at all, preferably falls within the range of
5 to 50 mg/m², and should be adjusted in accordance with the required degree of corrosion
resistance. The deposition of chromium, and optionally titanium, and/or zirconium
can be controlled by suitably adjusting the treatment temperature and treatment time.
[0019] The conversion film formed by the conversion treatment solution according to the
present invention when neither zirconium or titanium is present is believed to be
chemically and physically similar to the film formed by phosphoric acid/chromate treatments,
and is composed principally of hydrated chromium phosphate (CrPO₄·4H₂O). When either
fluotitanate or fluozirconate is included in the treatment solution, the conversion
film usually contains both hydrated chromium phosphate and zirconium oxide (ZrO₂)
and/or titanium oxide (TiO₂).
Examples
[0020] The conversion treatment solution of the present invention is explained in greater
detail below through the use of several illustrative examples. The first group of
examples are for solutions containing fluoborate or fluosilicate ions, and the effectiveness
of such solutions relative to comparison examples is reported in Table 1.
[0021] The substrate for these examples was an aluminum/magnesium alloy (described in detail
in Japanese Industrial Standard {hereinafter "JIS"} A5082). This aluminum alloy was
degreased and conversion treated using a small sprayer designed to give spraying conditions
identical to those currently encountered in typical spray treatments on commercial
continuous conversion treatment lines for the conversion treatment of aluminum alloy
coil. Chromium content in the coating deposited by the conversion process was measured
using a fluorescent X-ray analyzer (Model 3070E from
Rigaku Denki Kogyo). This conversion treated aluminum alloy sheet was then coated
with a can end paint of a poly {vinyl chloride} type to give a paint film thickness
of 12 to 14 micrometers, which was then baked at 200 degrees Centigrade for 10 minutes
before the sheets were subjected to the other tests reported in Table 1.
[0022] Salt-spray testing was conducted in order to evaluate the corrosion resistance. Salt-spray
testing was conducted in accordance with JIS Z-2371, and the value reported is the
time required for the appearance of blistering at a cross form cut in the paint film
on the painted test panel. Thus, longer times correspond to a better corrosion resistance.
Spray times of 2000 hours or more are generally now rated as excellent.
[0023] The paint adherence was evaluated as follows The painted test sheet was cut into
5 x 150 millimeter (hereinafter "mm") size rectangular strips, which were then hot-press-bonded
with polyamide film. The obtained test specimen was immersed in boiling deionized
water for 3 hours, and the peel strength was then evaluated in a 180° peel test. High
peel strength values correspond to a better paint adherence, and as a general rule
a value of 3.0 kilograms of force (hereinafter "kgf") per 5 mm width is rated as excellent.
[0024] Enamel feathering was evaluated in accordance with the Alcoa method, as described
on page 49 of the Lecture Notes from the 73rd Fall Meeting of
Keikinzoku Gakkai [Institute of Light Metals of Japan]. This evaluation is based on the maximum residual
paint film width after peeling. Thus, smaller residual paint film widths correspond
to a more desirable smaller amount of enamel feathering, and as a general rule residual
widths not exceeding 0.5 mm are rated as excellent.
Example 1
[0025] The surface of the aluminum alloy was cleaned by rinsing with a hot (70 degrees Centigrade)
4 % aqueous solution of a commercial strongly alkaline degreaser (FINE CLEANER™ 4418
from Nihon Parkerizing Company, Limited) and then with water. This was followed by
spraying for 5 seconds with conversion treatment solution 1 heated to 50 degrees Centigrade,
rinsing again with tap water, spraying with deionized water (specific resistance ≧
3,000,000 ohm-cm) for 10 seconds, and finally drying in a hot-air drying oven at 70
degrees Centigrade for 5 minutes. After drying, the conversion coated test panel was
painted as described above, and the corrosion resistance, paint adherence, and enamel
feathering were then evaluated.
Conversion treatment solution 1 contained 18.8 g/L of 40% fluosilicic acid (H₂SiF₆) = 7.4 g/L of SiF₆²⁻; 21.3 g/L
of 75 % phosphoric acid (H₃PO₄) = 15.5 g/L of PO₄³⁻; 5.8 g/L of chromic acid (CrO₃)
= 3.0 g/L of Cr⁶⁺; and 3.0 g/L of 20 % hydrofluoric acid (HF) = 0.6 g/L of F⁻; the
pH was adjusted to 2.0 with ammonium hydroxide after all the other ingredients had
been added.
Example 2
[0026] This was identical to Example 1, except that the Conversion treatment solution 2
used contained only 12.5 g/L of 40 % fluosilicic acid = 4.9 g/L of SiF₆²⁻, rather
than the larger amount in Conversion treatment solution 1.
Example 3
[0027] This was identical to Example 2, except that (i) the Conversion treatment solution
3 used contained only 2.9 g/L of chromic acid = 1.5 g/L of Cr⁶⁺, rather than the larger
amount in Conversion treatment solution 2 and (ii) the pH was adjusted to 1.5 with
hydrochloric acid rather than to 2.0 with ammonium hydroxide as in Conversion treatment
solution 2.
Example 4
[0028] This was identical to Example 1, except that the Conversion treatment solution 4
used contained 5.0 g/L of 20 % hydrofluoric acid = 1.0 g/L of F⁻, rather than the
smaller amount in Conversion treatment solution 1.
Example 5
[0029] This was identical to Example 1, except that the Conversion treatment solution 5
used contained 1.0 g/L of sodium fluoborate (NaBF₄) = 0.8 g/L of BF₄⁻, instead of
the fluosilicic acid used in Conversion treatment solution 1.
Example 6
[0030] This was identical to Example 5, except that (i) the Conversion treatment solution
6 used contained 2.0 g/L of sodium fluoborate (NaBF₄) = 1.6 g/L of BF₄⁻, rather than
the smaller amount in Conversion treatment solution 5 and (ii) the pH was adjusted
to 2.5 instead of 2.0.
Example 7
[0031] This was identical to Example 1, except that the samples were spray treated for 10
seconds at 40 degrees Centigrade rather than for 5 seconds at 50 degrees Centigrade
as in Example 1.
Example 8
[0032] This was identical to Example 1, except that the samples were spray treated for 10
seconds rather than for 5 seconds as in Example 1.
Comparison Example 1
[0033] This was identical to Example 1, except that the Conversion treatment solution 7
used contained only 6.3 g/L of 40 % fluosilicic acid = 2.5 g/L of SiF₆²⁻, rather than
the larger amount in Conversion treatment solution 1.
Comparison Example 2
[0034] This was identical to Example 1, except that the Conversion treatment solution 8
used contained 40.0 g/L of 40 % fluosilicic acid = 15.8 g/L of SiF₆²⁻, rather than
the smaller amount in Conversion treatment solution 1.
Comparison Example 3
[0035] The aluminum alloy was cleaned as in Example 1 and then spray-treated for 5 seconds
with a 5 % aqueous solution of a commercial phosphoric acid/chromate treatment concentrate
(ALCHROM™ K702 from Nihon Parkerizing Company, Limited) heated to 50 degrees Centigrade.
After this treatment, it was rinsed with water, dried, and painted as in Example 1,
and its performance was then evaluated.
Comparison Example 4
[0036] The aluminum alloy was cleaned as in Example 1 and then spray-treated for 30 seconds
with a 2 % aqueous solution of a commercial non-chromate treatment concentrate (PARCOAT™
K3761 from Nihon Parkerizing Company, Limited) heated to 50 degrees Centigrade. After
this treatment, it was rinsed with water, dried, and painted as in Example 1, and
its performance was then evaluated.
[0037] Another group of examples and comparison examples utilized solutions containing fluozirconate
or fluotitanate ions, as described in more detail below.
Example 9
[0038] This was identical to Example 1, except that the Conversion Solution 9 used contained
20.2 g/L of 20 % aqueous fluozirconic acid (H₂ZrF₆) = 4.0 g/L of ZrF₆⁻² instead of
the fluosilicic acid used in Conversion Solution 1 in Example 1.
Example 10
[0039] This was identical to Example 9, except that the Conversion Solution 10 used contained
12.6 g/L of 20 % aqueous fluozirconic acid (H₂ZrF₆) = 2.5 g/L of ZrF₆⁻² instead of
the larger amount of fluozirconic acid used in Conversion solution 9 in Example 9.
Example 11
[0040] This was identical to Example 9, except that the Conversion Solution 11 used (i)
contained 1.9 g/L of chromic acid = 1.0 g/L of Cr⁺⁶ instead of the larger amount of
chromic acid in Conversion Solution 1 in Example 1 and (ii) had a pH of 1.5 achieved
by adjustment with hydrochloric acid rather than a pH of 2.0 achieved by adjustment
with ammonia as in Conversion Solution 9.
Example 12
[0041] This was identical to Example 11, except that the Conversion Solution 11 used contained
5.8 g/L of chromic acid = 3.0 g/L of Cr⁺⁶ and 5.0 g/L of 20 % aqueous hydrofluoric
acid = 1.0 g/L of F ions instead of the smaller amounts of these two constituents
used in Conversion Solution 11 in Example 11.
Example 13
[0042] This was identical to Example 9, except that the Conversion Solution 13 used (i)
contained 20.3 g/L of aqueous fluotitanic acid = 4.0 g/L of TiF₆⁻² instead of the
fluo zirconic acid in Conversion Solution 9 in Example 9 and (ii) had a pH of 2.5
achieved by adjustment with sodium hydroxide rather than a pH of 2.0 achieved by adjustment
with ammonia as in Conversion Solution 9.
Example 14
[0043] This was identical to Example 9, except that the Conversion Solution 14 used contained
12.7 g/L of 20 % aqueous fluotitanic acid = 1.6 g/L of TiF₆⁻² and 12.6 g/L of 20 %
aqueous fluozirconic acid = 2.5 g/L of ZrF₆-
ions instead of the larger amount of fluozirconic acid, with no fluotitanic acid, used in Conversion
Solution 9 in Example 9.
Example 15
[0044] This was identical to Example 9, except that the samples were spray treated for 10
seconds at 40 degrees Centigrade rather than for 5 seconds at 50 degrees Centigrade
as in Example 9.
Example 16
[0045] This was identical to Example 9, except that the samples were spray treated for 10
seconds rather than for 5 seconds as in Example 9.
Comparison Example 5
[0046] This was identical to Example 9, except that the Conversion treatment solution 15
used contained only 5.0 g/L of 20 % fluozirconic acid = 1.0 g/L of ZrF₆²⁻, rather
than the larger amount in Conversion treatment solution 9.
Comparison Example 6
[0047] This was identical to Example 9, except that the Conversion treatment solution 16
used contained 50.0 g/L of 20 % fluozirconic acid = 15.8 g/L of ZrF₆²⁻, rather than
the smaller amount of fluozirconic acid in Conversion treatment solution 9.
[0048] Test results from this second group of examples are shown in Table 2, where Comparison
Examples 3 and 4 are repeated from Table 1.
Benefit of the Invention
[0049] As Tables 1 and 2 make clear, application of the conversion treatment solution of
the present invention affords an excellent corrosion resistance and paint adherence
as well as an excellent resistance enamel feathering.
1. An aqueous conversion coating solution that has a pH value from 1.0 to 3.0 and consists
essentially of
(A) an amount of phosphate ions that is stoichiometrically equivalent to from 5.0
to 40.0 g/L of phosphoric acid;
(B) from 1.0 to 4.0 g/L of hexavalent chromium;
(C) from 0.1 to 2.0 g/L of fluoride ions; and
(D) a complex fluoride ion component selected from the group consisting of:
(i) from 4.0 to 15.0 g/L of fluosilicate ions,
(ii) from 0.5 to 3.0 g/L of fluoborate ions,
(iii) from 2.0 to 8.0 g/L of fluozirconate ions, and
(iv) from 2.0 to 8.0 g/L of fluotitanate ions.
2. An aqueous solution according to claim 1, characterized in that it comprises from
0.4 to 1.0 g/L of fluoride ions.
3. A process for treating a surface of aluminum or an aluminum alloy, said process comprising
steps of forming a conversion coating on said surface and subsequently over-coating
the conversion coated surface with an organic protective coating, characterized in
that the conversion coating on said surface is formed by contacting said surface with
an aqueous solution having a pH values from 1.0 to 3.0 and consisting essentially
of :
(A) an amount of phosphate ions that is stoichiometrically equivalent to from 5.0
to 40.0 g/L of phosphoric acid:
(B) from 1.0 to 4.0 g/L of hexavalent chromium;
(C) from 0.1 to 2.0 g/L of fluoride ions; and
(D) a complex fluoride ion component selected from the group consisting of:
(i) from 4.0 to 15.0 g/L of fluosilicate ions,
(ii) from 0.5 to 3.0 g/L of fluoborate ions,
(iii) from 2.0 to 8.0 g/L of fluozirconate ions, and
(iv) from 2.0 to 8.0 g/L of fluotitanate ions.
4. A process according to claim 3, characterized in that said aqueous solution comprises
from 0.4 to 1.0 g/L of fluoride ions.
5. A process according to claim 4, characterized in that the conversion coating formed
contains chromium, and optionally zirconium and/or titanium atoms in an amount of
from 5 to 50 milligrams per square meter respectively.
6. A process according to claim 3, 4 or 5, characterized in that the conversion coating
is performed at a temperature in the range from 20 to 70 degrees-Centigrade.
7. A process according to claim 6, characterized in that the conversion coating is performed
at a temperature in the range from 35 to 55 degrees Centigrade for a contact time
in the range from 1 to 90 seconds.
1. Wäßrige Umwandlungs-Beschichtungslösung mit einem pH-Wert von 1,0 bis 3,0 und im wesentlichen
bestehend aus:
(A) einer Menge an Phosphat-Ionen, die 5,0 bis 40,0 g/l Phosphorsäure stöchiometrisch
äquivalent ist,
(B) 1,0 bis 4,0 g/l sechswertigen Chroms,
(C) 0,1 bis 2,0 g/l Fluorid-Ionen und
(D) einer komplexen Fluoridionen-Komponente, ausgewählt aus der Gruppe bestehend aus:
(i) 4,0 bis 15,0 g/l Fluorsilikat-Ionen,
(ii) 0,5 bis 3,0 g/l Fluorborat-Ionen,
(iii) 2,0 bis 8,0 g/l Fluorzirconat-Ionen und
(iv) 2,0 bis 8,0 g/l Fluortitanat-Ionen.
2. Wäßrige Lösung gemäß Anspruch 1, dadurch gekennzeichnet, daß sie 0,4 bis 1,0 g/l Fluorid-Ionen
umfaßt.
3. Verfahren zur Behandlung einer Oberfläche aus Aluminium oder einer Aluminium-Legierung,
wobei das Verfahren Stufen des Bildens einer Umwandlungs-Beschichtung auf der Oberfläche
und anschließendes Überschichten der durch Umwandlung beschichteten Oberfläche mit
einer organischen Schutz-Beschichtung umfaßt, dadurch gekennzeichnet, daß die Umwandlungs-Beschichtung
auf der Oberfläche durch In-Kontakt-Bringen der Oberfläche mit einer wäßrigen Lösung
mit einem pH-Wert von 1,0 bis 3,0 gebildet wird, und daß sie im wesentlichen besteht
aus:
(A) einer Menge an Phosphat-Ionen, die 5,0 bis 40,0 g/l Phosphorsäure stöchiometrisch
äquivalent ist,
(B) 1,0 bis 4,0 g/l sechswertigen Chroms,
(C) 0,1 bis 2,0 g/l Fluorid-Ionen und
(D) einer komplexen Fluoridionen-Komponente, ausgewählt aus der Gruppe bestehend aus:
(i) 4,0 bis 15,0 g/l Fluorsilikat-Ionen,
(ii) 0,5 bis 3,0 g/l Fluorborat-Ionen,
(iii) 2,0 bis 8,0 g/l Fluorzirconat-Ionen und
(iv) 2,0 bis 8,0 g/l Fluortitanat-Ionen.
4. Verfahren gemäß Anspruch 3, dadurch gekennzeichnet, daß die wäßrige Lösung 0,4 bis
1,0 g/l Fluorid-Ionen umfaßt.
5. Verfahren gemäß Anspruch 4, dadurch gekennzeichnet, daß die gebildete Umwandlungs-Beschichtung
Chrom- und ggf. Zirconium- und/oder Titan-Atome in einer Menge von jeweils 5 bis 50
mg/m² enthält.
6. Verfahren gemäß Anspruch 3, 4 oder 5, dadurch gekennzeichnet, daß das Umwandlungs-Beschichten
bei einer Temperatur im Bereich von 20 bis 70 °C durchgeführt wird.
7. Verfahren gemäß Anspruch 6, dadurch gekennzeichnet, daß das Umwandlungs-Beschichten
bei einer Temperatur im Bereich von 35 bis 55 °C bei einer Kontaktzeit im Bereich
von 1 bis 90 Sekunden durchgeführt wird.
1. Une solution aqueuse de revêtement par conversion qui a un pH de 1,0 à 3,0 et est
constituée essentiellement de :
(A) une quantité d'ions phosphates qui est stoechiométriquement équivalente à 5,0
à 40,0 g/l d'acide phosphorique ;
(B) 1,0 à 4,0 g/l de chrome hexavalent ;
(C) 0,1 à 2,0 g/l d'ions fluorures ; et
(D) un composant ion fluorure complexe choisi dans le groupe constitué par :
(i) 4,0 à 15,0 g/l d'ions fluosilicates,
(ii) 0,5 à 3,0 g/l d'ions fluoborates,
(iii) 2,0 à 8,0 g/l d'ions fluozirconates et
(iv) 2,0 à 8,0 g/l d'ions fluotitanates.
2. Une solution aqueuse selon la revendication 1, caractérisée en ce qu'elle comprend
de 0,4 à 1,0 g/l d'ions fluorures.
3. Un procédé pour le traitement d'une surface d'aluminium ou d'alliage d'aluminium,
ledit procédé comprenant les étapes de formation d'un revêtement par conversion sur
ladite surface, puis de recouvrement de la surface revêtue par conversion avec un
revêtement protecteur, caractérisé en ce que le revêtement par conversion sur ladite
surface est formé par contact de ladite surface avec une solution aqueuse ayant un
pH de 1,0 à 3,0 et constituée essentiellement de :
(A) une quantité d'ions phosphates qui est stoechiométriquement équivalentes à 5,0
à 40,0 g/l d'acide phosphorique ;
(B) 1,0 à 4,0 g/l de chrome hexavalent ;
(C) 0,1 à 2,0 g/l d'ions fluorures ; et
(D) un composant ion fluorure complexe choisi dans le groupe constitué par :
(i) 4,0 à 15,0 g/l d'ions fluosilicates,
(ii) 0,5 à 3,0 g/l d'ions fluoborates,
(iii) 2,0 à 8,0 g/l d'ions fluozirconates, et
(iv) 2,0 à 8,0 g/l d'ions fluotitanates.
4. Un procédé selon la revendication 3, caractérisée en ce que ladites solution aqueuse
comprend de 0,4 à 1,0 g/l d'ions fluorures.
5. Un procédé selon la revendication 4, caractérisée en ce que le revêtement formé par
conversion contient des atomes de chrome et facultativement de zirconium et/ou de
titane, respectivement en une quantité de 5 à 50 milligrammes par mètre carré.
6. Un procédé selon la revendication 3, 4 ou 5, caractérisé en ce que le revêtement par
conversion est réalisé à une température dans la gamme de 20 à 70°C.
7. Un procédé selon la revendication 6, caractérisé en ce que le revêtement par conversion
est réalisé à une température dans la gamme de 35 à 55°C pour une durée de contact
dans la gamme de 1 à 90 secondes.