U.S. patent application number 10/258893 was filed with the patent office on 2003-08-14 for method for treating or pre-treating components comprising aluminum surfaces.
Invention is credited to Busch, Edgar, rg Hieke, J?ouml, Jaschke, Harald, Klocke, Christoph, Kolberg, Thomas, Rutka, Alfred, Schubach, Peter.
Application Number | 20030150527 10/258893 |
Document ID | / |
Family ID | 7644139 |
Filed Date | 2003-08-14 |
United States Patent
Application |
20030150527 |
Kind Code |
A1 |
Busch, Edgar ; et
al. |
August 14, 2003 |
Method for treating or pre-treating components comprising aluminum
surfaces
Abstract
The invention relates to a method for treating or pre-treating
parts, profiles, strips, or wires comprising surfaces of aluminium,
or alloys containing aluminium optionally in the presence of
surfaces consisting of other metals or alloys with an acidic,
aqueous solution containing fluoride and phosphate. Said method is
characterised in that the fluoride is present at least partially as
a free fluoride in the solution and that in the bath of phosphating
solution, the content of free fluoride is maintained within a
concentration range of between 5 and 500 mg/l F.sub.free and that
of aluminium is maintained within a concentration range that is
less than or equal to 100 mg/l Al ions (including complexed Al). To
achieve this, increases in the aluminium content are reduced to
contents of less than or equal to 100 mg/l Al ions in the bath,
using a precipitation container outside the phosphating bath by
circulating the phosphating solution from the phosphating bath to
the precipitation container and vice versa.
Inventors: |
Busch, Edgar; (Frankfurt am
Main, DE) ; Hieke, J?ouml;rg; (Eschborn, DE) ;
Kolberg, Thomas; (Heppenheim, DE) ; Schubach,
Peter; (Nidderau/Windecken, DE) ; Jaschke,
Harald; (Jetzendorf, DE) ; Klocke, Christoph;
(Munchsdorf, DE) ; Rutka, Alfred; (Mering,
DE) |
Correspondence
Address: |
FULBRIGHT & JAWORSKI, LLP
666 FIFTH AVE
NEW YORK
NY
10103-3198
US
|
Family ID: |
7644139 |
Appl. No.: |
10/258893 |
Filed: |
April 4, 2003 |
PCT Filed: |
May 19, 2001 |
PCT NO: |
PCT/EP01/05756 |
Current U.S.
Class: |
148/254 ;
148/275 |
Current CPC
Class: |
C23C 22/73 20130101;
C23C 22/365 20130101; C23C 22/36 20130101 |
Class at
Publication: |
148/254 ;
148/275 |
International
Class: |
C23C 022/36 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2000 |
DE |
100 26 850.1 |
Claims
1. Method for the treatment or pretreatment of parts, sections,
strips or wires with surfaces of aluminium or of alloys containing
aluminium--if applicable in the presence of surfaces of further
metals or alloys--with an acid aqueous solution containing fluoride
and phosphate, characterised in that the fluoride is at least
partly present in the solution as free fluoride, and in that, in
the bath of the phosphatizing solution, the free-fluoride content
is maintained at a concentration in the range from 5 to 500 mg/l
F.sub.free, and the aluminium content is maintained at a
concentration in the range of .ltoreq.100 mg/l Al ions (including
complex-bound Al) by virtue of the fact that increasing aluminium
contents, in a precipitation tank outside the phosphatizing bath,
are decreased to contents .ltoreq.100 mg/l Al ions in the bath by
circulating the phosphatizing solution from the phosphatizing bath
to the precipitation tank and back.
2. Method according to claim 1, modified in that, in a separate
zone of the phosphatizing bath, increasing aluminium contents in
the phosphatizing solution are decreased to contents .ltoreq.100
mg/l Al ions.
3. Method according to claim 1 or 2, characterised in that, in the
tank or in the separate zone of the bath, aluminium is precipitated
in the phosphatizing solution by adding alkali ions, fluoride
complexes and/or fluoride ions, in particular by means of Na or K
ions or by means of at least one easily dissociating fluoride such
as, for example, NaF, NH.sub.4F, NaHF.sub.2 or KF.
4. Method according to one of the preceding claims, characterised
in that the alkali ion content in the bath is maintained at a
concentration in the range from 1 to 20 g/l.
5. Method according to one of the preceding claims, characterised
in that the free-fluoride concentration in the precipitation tank
or in the separate zone of the bath container is 5 to 500 mg/l free
fluoride.
6. Method according to one of the preceding claims, characterised
in that the dwell time of the phosphatizing solution in the
precipitation tank or in the separate precipitation zone is up to 1
h.
7. Method according to one of the preceding claims, characterised
in that, prior to pickling/phosphatizing, the parts, sections,
strips and/or wires to be treated or pretreated are cleaned, rinsed
and, if appropriate and separately from the rinsing and cleaning
stages, brought into contact with an activating solution, for
example on the basis of colloidally dispersed titanium
phosphate.
8. Method according to one of the preceding claims, characterised
in that, after pickling/phosphatizing, the treated or pretreated
parts, sections, strips and/or wires are rinsed and/or passivated,
in particular by means of a passivating solution on the basis of a
chromate-containing compound, titanium fluoride, zirconium
fluoride, silane, self-organizing molecules for example on the
basis of phosphonate, a polymer soluble and/or dispersible in
solvent, a soluble rare-earth compound--in particular a soluble
cerium-containing compound, with the term rare-earth element also
including scandium, yttrium and lanthanum.
9. Method according to one of the preceding claims, characterised
in that the treated or pretreated and/or passivated parts,
sections, strips and/or wires are dried after
pickling/phosphatizing or after passivation.
10. Method according to one of the preceding claims, characterised
in that the precipitation of the aluminium is effected under normal
pressure and at a temperature in the range from room temperature to
70.degree. C.
11. Method according to one of the preceding claims, characterised
in that the formation of the conversion or passivation layer is
effected under normal pressure and at a temperature from room
temperature to 70.degree. C.
12. Method according to one of the preceding claims, characterised
in that the treated or pretreated and/or passivated parts,
sections, strips and/or wires are coated with a lacquer, with
another kind of organic coating, with a film and/or with an
adhesive layer, if applicable printed and if applicable reshaped,
where the metal parts coated in this way can in addition be bonded,
welded and/or otherwise connected together with other parts.
13. Use of the products produced in accordance with the method
according to claims 1 to 12 in the automotive industry, in the
aeronautical industry, in apparatus and machine construction, in
the furniture industry, in the building trade, for household
appliances, electrical appliances, measuring instruments, control
devices, testing devices, construction elements, housings,
panellings, shelf systems, racks, frames, dividers, partitions,
trim panels, lighting fixtures, crash barriers, radiator or fence
elements as well as small parts, in particular for car body parts
or car bodies.
Description
[0001] The invention relates to a method for the treatment or
pretreatment of parts with aluminium surfaces.
[0002] Phosphatizing methods for aluminium and aluminium alloys are
known in principle. In industrial practice, fluoride-modified
phosphatizing methods with at least 150 mg/l free fluoride have
proved to be particularly successful. These methods are important
in particular in the automotive industry and are chiefly used when
a mix of substrates of various metals or alloys is passed through
the plants.
[0003] However, these methods have the serious disadvantages that
due to the high fluoride content comparatively large amounts of
cryolite (Na.sub.3AlF.sub.6) and/or related precipitates are
precipitated in the phosphatizing bath, and that parts of the
precipitates are also precipitated on the phosphatized surface
without being removable therefrom by means of simple rinsing
operations, with an increased roughness being produced on the
pretreated surface which, even after the subsequent application of
lacquer, has a disturbing effect with its roughness.
[0004] DE-A1-197 35 314 describes a method for the pretreatment of
components with aluminium surfaces--if applicable in the presence
of magnesium, steel and/or zinc surfaces--in a phosphatizing plant
in which the components are degreased by means of a degreasing
solution, are phosphatized by treatment with a phosphatizing
solution containing fluoride, and are subsequently passivated by
treatment with a passivating solution. The proportion of the
aluminium and/or magnesium surface with respect to the entire
surface of the components to be treated is at least 10% in this
connection. The fluoride should be added to the phosphatizing
solution exclusively as complex-bound fluoride, and the
free-fluoride ion content formed therefrom in the phosphatizing
solution for phosphatizing the steel and/or zinc surfaces without
phosphatizing the aluminium and/or magnesium surfaces should be
maintained at less than 100 mg/l. The passivating solution should
also be composed in such a way that it passivates the phosphatized
steel and/or zinc surfaces and forms a conversion layer on the
aluminium and/or magnesium surfaces.
[0005] However, this method has the disadvantage that it can only
be used with comparatively small surface proportions in terms of
aluminium surfaces, mostly only up to approximately 20% by surface
of all the surfaces to be treated, with respect to the mix of
substrates. In addition it has the disadvantages that cryolite
and/or related precipitates are still formed in the pretreatment
bath, and that with an increased aluminium content of the
phosphatizing solution the layer-forming reactions, in particular
on iron and steel surfaces, are impaired so that the entire mix of
substrates of various metal and alloy surfaces can no longer be
coated well in the bath in a uniform manner.
[0006] It is an object of the invention to overcome the
disadvantages of the prior art and propose in particular a method
for phosphatizing aluminium and alloys containing aluminium, which
method, even with increased proportions of aluminium-containing
surfaces of the components to be treated or to be pretreated,
allows the application of a good conversion layer that is also
applicable on an industrial scale and/or a corresponding
passivation layer on the surfaces of aluminium or alloys containing
aluminium--if applicable in a mix of substrates of various metals
or alloys.
[0007] The object is achieved by means of a method for the
treatment or pretreatment of parts, sections, strips or wires with
surfaces of aluminium or alloys containing aluminium--if applicable
in the presence of surfaces of further metals or alloys--with an
acid aqueous solution containing fluoride and phosphate, which
method is characterised in that the fluoride is at least partly
present in the solution as free fluoride, and in that, in the bath
of the phosphatizing solution
[0008] the free-fluoride content is maintained at a concentration
in the region from 5 to 500 mg/l F.sub.free, and
[0009] the aluminium content is maintained at a concentration in
the region of .ltoreq.100 mg/l Al ions (including complex-bound
Al)
[0010] by virtue of the fact that increasing aluminium contents, in
a precipitation tank outside the phosphatizing bath, are decreased
to contents .ltoreq.100 mg/l Al ions in the bath by circulating the
phosphatizing solution from the phosphatizing bath to the
precipitation tank and back.
[0011] Alternatively or at the same time, it can be ensured in the
case of the method in accordance with the invention that in a
separate zone of the phosphatizing bath increasing aluminium
contents in the phosphatizing solution are decreased to contents
.ltoreq.100 mg/l Al ions.
[0012] As a result of the pickling attack, aluminium is solubilized
at the metallic surface, and an aluminium content is absorbed into
the phosphatizing solution. A certain aluminium content may,
however, also get into the phosphatizing solution from other
sources, for example from chemicals introduced into the rinsing
solution. The aluminium content can mainly be decreased or
completely be decreased by precipitation, but in part also by
complex formation. The content of free fluoride in the
phosphatizing solution is preferably maintained in a range from 6
to 120 mg/l, in particular preferably in a range from 10 to 80
mg/l, and especially preferably in a range from 20 to 50 mg/l. The
aluminium content in the phosphatizing solution is preferably
maintained at values .ltoreq.80 mg/l, in particular preferably
.ltoreq.60 mg/l, and especially preferably .ltoreq.30 mg/l.
[0013] The method in accordance with the invention is distinguished
by virtue of the fact that in the precipitation tank or in the
separate zone of the bath aluminium is precipitated in the
phosphatizing solution by adding alkali ions, fluoride complexes
and/or fluoride ions, in particular by means of Na or K ions or by
means of at least one easily dissociating fluoride such as, for
example, NaF, NH.sub.4F, NaHF.sub.2 or KF. The AlF.sub.x complex
may be present in an already precomplexed form in this case. It is
advantageous to control the method in accordance with the invention
in such a way that despite the addition of F the content of free
fluoride in the bath is not increased. The alkali ion contents in
the phosphatizing bath preferably amount to 1 to 20 g/l and are
preferably also maintained in this range, in particular in the
range from 3 to 10 g/l. In principle, the alkali ion content may
also lie far above the concentration of 20 g/l, for example at 30
g/l. In many cases, however, given such a high alkali
concentration, instability of the bath may occur. In the case of a
mixture of various alkali ions one beside the other, a dominant
sodium and/or potassium ion content is preferred.
[0014] This leads to the fact that the precipitated cryolite and
the related precipitates, such as K.sub.2NaAlF.sub.6, for example,
do not occur or hardly occur any more in the phosphatizing bath,
but largely or (almost) exclusively in the separate zone of the
bath or in the precipitation tank. As a result, the precipitates
can no longer settle or hardly settle any more on the surface to be
coated.
[0015] Advantageously, the free-fluoride concentration of the
phosphatizing solution in the phosphatizing bath is 8 to 80 mg/l
and in particular is 10 to 50 mg/l; and the concentration in the
precipitation tank or in the separate zone of the bath container is
5 to 500 mg/l free fluoride, in particular 20 to 200 mg/l, and
especially preferably 30 to 120 mg/l. It is therefore also
preferable to maintain these contents at these concentrations.
Since below 5 mg/l usually there is no pickling attack against
aluminium by free fluoride, and since this pickling attack is
needed, as the subsequent passivation for example alone by means of
chromate-containing compounds, titanium fluoride, zirconium
fluoride, a soluble rare-earth compound--in particular a
cerium-containing compound, where scandium, yttrium and lanthanum
are included by the term rare-earth element--on the basis of
silane, self-organizing molecules on the basis of phosphonate, a
polymer soluble and/or dispersible in solvent is not sufficient for
passivation, a small minimum free-fluoride content in the
phosphatizing solution is required. On the other hand, in many
cases a closed phosphate layer is formed on the metallic surfaces
from the phosphatizing bath at contents above 120 mg/l free
fluoride, if the content with respect to cations co-precipitated
with the phosphate, such as Zn, Cu, Ni, Fe, Mn etc., is not very
small. The formation of a phosphate layer on the aluminium surfaces
for reasons of protection against corrosion is not absolutely
necessary. Therefore, a free-fluoride content above 120 mg/l will
not usually be chosen, although in accordance with the invention it
is also possible to operate above this value, because it causes
additionally a higher consumption of chemicals and a larger amount
of precipitated sludge of cryolite and/or related precipitates.
Moreover, a difference in the free-fluoride concentration between
the phosphatizing bath and the precipitation tank or separate zone
in the bath of 30 to 60 mg/l should preferably be adjusted and
maintained.
[0016] In many cases, the method in accordance with the invention
will be utilized in such a way that the dwell time of the
phosphatizing solution in the precipitation tank or in the separate
precipitation zone is up to 1 h, often up to 0.5 h. The volume flow
from the bath to the precipitation tank and back is adjusted in
accordance with the chosen volumes or partial volumes as well as
the desired aluminium content in the phosphatizing bath.
[0017] The term "part" for the purposes of this application
includes all kinds and shapes of sheets, strips and sections,
moulded articles, semifinished products, components, assemblies
etc.
[0018] In the case of the method in accordance with the invention,
the parts, sections, strips and/or wires to be treated or
pretreated are usually cleaned, rinsed and, if appropriate and
separately from the rinsing and cleaning stages, brought into
contact with an activating solution, for example on the basis of
colloidally dispersed titanium phosphate, prior to
pickling/phosphatizing.
[0019] After pickling/phosphatizing, the treated or pretreated
parts, sections, strips and/or wires can be rinsed and/or
passivated, in particular by means of a passivating solution on the
basis of a chromate-containing compound, titanium fluoride,
zirconium fluoride, a soluble rare-earth compound--in particular a
cerium-containing compound, self-organizing molecules, for example
on the basis of phosphonate, on the basis of silane, a polymer
soluble and/or dispersible in solvent.
[0020] After pickling/phosphatizing or after passivation, the
treated or pretreated and/or passivated parts, sections, strips
and/or wires may be dried. In some cases, for example in the case
of immediately following electro-dipcoating, drying is not,
however, required.
[0021] The precipitation of the aluminium may be effected under
normal pressure and at a temperature in the range from room
temperature to 70.degree. C., in particular at a temperature in the
range from 40 to 60.degree. C. In the case of the method in
accordance with the invention, the formation of the conversion or
passivation layer may be effected under normal pressure and at a
temperature from room temperature to 70.degree. C., preferably at
35 to 60.degree. C. The pH value usually lies in the range from 2
to 4. In principle, the pH value of phosphatizing baths always lies
in the range around pH 3. At values of pH .gtoreq.4.0, the bath is
usually unstable, whilst at values of pH .ltoreq.2.0 the bath is so
stable that usually there is no good formation of layers, because
the displacement of the pH value at the freshly pickled metallic
surface is not sufficient for deposition of the conversion
layer.
[0022] Finally, the treated or pretreated and/or passivated parts,
sections, strips and/or wires can be coated with a lacquer, with
another kind of organic coating, with a film and/or with an
adhesive layer, if applicable printed and if applicable reshaped,
where the metal parts coated in this way can in addition be bonded,
welded and/or otherwise connected together with other parts.
[0023] The products produced in accordance with the invention can
be used in the automotive industry, in the aeronautical industry,
in apparatus and machine construction, in the furniture industry,
in the building trade, for household appliances, electrical
appliances, measuring instruments, control devices, testing
devices, construction elements, housings, panellings, shelf
systems, racks, frames, dividers, partitions, trim panels, lighting
fixtures, crash barriers, radiator or fence elements as well as
small parts, in particular for car body parts or car bodies.
[0024] FIG. 1 shows a flow diagram in which one possible principle
out of several principles of the separate aluminium deposition is
represented schematically.
[0025] Compared with methods described and practised so far, the
phosphatizing method in accordance with the invention has the
advantage that the sludge with its cryolite content and/or related
precipitates content is largely obtained in a separate
precipitation zone or in a separate precipitation tank and can be
disposed of from there. With the method in accordance with the
invention it is also possible to treat or pretreat different
metallic substrates in one mix, without the formation of layers,
for example on steel, being impaired as a result. On account of the
reduced free-fluoride contents in the phosphatizing solution, there
is also a reduced pickling attack against aluminium-containing
surfaces, which also gives rise to a correspondingly reduced
formation of sludge. It has also been possible to ensure by means
of the method in accordance with the invention that, on account of
only few particles being co-precipitated and deposited on the
phosphatized surface after the subsequent application of lacquer,
no disturbing markings such as roughness, streaking or other
irregularities could be detected.
[0026] Surprisingly, largely stable bath conditions with respect to
the free-fluoride content and aluminium content could be realized
in the phosphatizing bath as well as in the separate zone or in the
precipitation tank despite the very different concentrations of
these contents.
[0027] The subject-matter of the invention will be explained in
greater detail in the following with reference to an exemplifying
embodiment.
EXAMPLE
[0028] The following experiments were performed in order to
determine the suitable precipitation conditions for
aluminium-containing phosphatizing solutions in a phosphatizing
bath in accordance with the invention. Above all, the influences of
the concentrations of free fluoride, sodium as well as
complex-bound fluoride on the speed of the precipitation of
aluminium were examined in this connection.
1. Test Design
[0029] A computer-assisted test design was employed in order to be
able to recognize in a better way interactions of the significant
parameters that might possibly exist. The Stavex 4.3 program was
used.
2. Analyzers
[0030] Fluoride measurement: Orion Model 960 with ion-selective
electrode
[0031] Aluminium ICP.
[0032] A standard phosphatizing solution was prepared from p.a.
chemicals to have following composition:
[0033] Zn: 1.5 g/l
[0034] Mn: 1.0 g/l
[0035] Ni: 1.0 g/l
[0036] P.sub.2O.sub.5: 14.0 g/l
[0037] NO.sub.3: 3.0 g/l
[0038] SiF.sub.6: 1.0 g/l
[0039] FA: 2.0 free acid.
[0040] Proceeding from this solution, ions of SiF.sub.6 and Na as
well as the proportion of free fluoride were varied in further
preparations.
3. Practical Execution
[0041] 0.5 l of the phosphatizing solution described above was
poured into a plastics beaker, and the possibly desired higher
silicofluoride content was adjusted by means of a 24%
H.sub.2SiF.sub.6 solution, the correction of the free-acid content
being effected by adding NaOH. The Na content was adjusted by means
of NaNO.sub.3; the corresponding free-fluoride content was adjusted
by means of a dilute ammonium bifluoride solution. 20 mg/l
aluminium were added to the bath by means of a dilute aluminium
nitrate solution. After 0, 15, 30 and 60 minutes, the free fluoride
was measured, and a sample of the solution was discharged for the
determination of aluminium.
[0042] To prevent postprecipitation of the aluminium in the sample
drawn, the procedure was as follows: 5 ml of the sample filtered by
means of a membrane filter was added to a strongly hydrochloric
deionized-water solution and filled up to 50 ml by means of
deionized water. This solution was examined for its aluminium
content by means of ICP.
[0043] The results are compiled in Table 1.
1TABLE 1 Precipitation tests Content of F.sub.free in the Content
of Al in the F.sub.free Na SiF.sub.6 phosphatizing solution (mg/l)
phosphatizing solution (mg/l) Test (ppm) (g/l) (g/l) 0 min 15 min
30 min 60 min 0 min 15 min 30 min 60 min 5 days 1 40 3.0 1.00 39 25
27 27 20 20 20 20 20 2 80 3.0 1.00 78 53 52 58 20 20 19 19 3.5 3 40
7.0 1.00 39 28 27 28 20 19 19 19 4 4 80 7.0 1.00 80 50 46 44 20 1.5
1 0.5 5 40 3.0 3.00 46 44 44 44 20 19 19 19 20 6 80 3.0 3.00 79 19
36 54 20 19 18 19 2 7 40 7.0 3.00 40 16 17 22 20 19 20 19 2 8 80
7.0 3.00 79 54 48 148* 20 1 0.5 <0.5 9 60 5.0 2.00 60 34 40 106*
20 10 4.5 2 10 43 5.0 2.00 46 25 34 80* 20 18 11 5 11 77 5.0 2.00
73 67 42 37 20 19 17 13 12 60 3.3 2.00 59 43 39 28 20 19 19 19 3 13
60 6.7 2.00 59 52 51 33 20 15 7.5 3.5 14 60 5.0 1.15 61 32 25 21 20
19 2 1 15 60 5.0 2.85 59 29 25 27 20 4 2 1 *Measurement error, as
no free fluoride was added during the test.
[0044] In Test 1 no precipitation of aluminium was observed over
the period of 5 days. Tests 4, 8 and 15 revealed a drastic
reduction in the aluminium content even within 15 minutes.
Increased alkali contents are preferred in conjunction with
increased free-fluoride contents. SiF.sub.6 was added because of
the stability of the phosphatizing solution and for usability for a
mix of various kinds of metallic surfaces, in particular to avoid
stippling on zinc-plated or zinc-containing surfaces.
[0045] Upon evaluation of the values found in Example 1, the
following exemplifying calculation can be made:
4. Exemplifying Calculation of the Volume Flows or of the Reaction
Vessel
[0046]
2 Phosphatizing bath 200 m.sup.3 Partial stream for precipitation
100 m.sup.3 in a precipitation tank Feed of Al per hour 10 ppm
[0047] This feed corresponds to about 40 car bodies per hour with
an aluminium-surface proportion of 50% and a pickling attack of
approximately 1 g/m.sup.2 during the contact time.
[0048] Calculation formula for the stationary concentration of
aluminium in the phosphatizing solution:
[0049] Al(ppm)=(((200 m.sup.3-partial stream).times.conc. Al in ppm
after 1 h+(partial stream.times.rest Al in ppm after
precipitation))/200)+Al in ppm from feed via pickling attack/h.
[0050] Hence it was concluded that it is necessary for the volume
flow, which is to be treated, to be at least 0.5 basin volumes per
hour in order to be able to detect a sufficiently high proportion
of dissolved aluminium. With an average dwell time of 30 min, this
results in a volume of the reaction bath of 50 m.sup.3. A residual
aluminium content in the outlet of the treatment bath of
approximately 5 ppm results in a theoretical stationary aluminium
content in the treatment bath of approximately 25 ppm. However,
since a partial precipitation of the aluminium can also be expected
in the treatment bath (see for example Test 3 from Table 1), the
actual content in terms of dissolved aluminium will adopt a lower
value. Approximately 20% of all the precipitates are obtained in
the phosphatizing bath and provided an Al content of approximately
20 ppm in the phosphatizing solution of the bath in the stationary
condition. Approximately 80% of all the precipitates were
precipitated in the precipitation tank.
* * * * *