EP1290242B1 - Method for treating or pre-treating components comprising aluminium surfaces - Google Patents

Abstract

A method for treating or pre-treating parts, profiles, strips, or wires comprising surfaces of aluminum, or other metal surfaces with an acidic, aqueous solution containing fluoride and phosphate.

Description

The invention relates to a method for treating or pretreating parts with aluminum surfaces.

Phosphating processes for aluminum and aluminum alloys are fundamental known. In industrial practice, fluoride has been modified Phosphating process with at least 150 mg / l free fluoride especially proven. These processes are particularly important in the automotive industry are mainly used when a mix of substrates from different Metals or alloys are given by the plants.

However, these processes have the serious disadvantages that, owing to the high fluoride content, larger amounts of cryolite (Na ₃ AlF ₆ ) and / or related precipitation products are excreted in the phosphating bath and that portions of the precipitation products are also deposited on the phosphated surface without simple rinsing processes to be able to be removed from there, an increased roughness being produced on the pretreated surface, which also has a disruptive effect on its roughness after the subsequent coating.

DE-A1-197 35 314 describes a method for pretreating components with Aluminum surfaces - possibly in the presence of magnesium, steel and / or zinc surfaces - In a phosphating plant in which the components with a Degreasing solution degreased by treatment with a fluoride-containing Phosphating solution phosphated and then by treatment with a Passivation solution to be passivated. The proportion of aluminum or / and Magnesium surface on the entire surface of the components to be treated is at least 10%. Here, the fluoride of the phosphating solution The content should only be added as complex-bound fluoride the free fluoride ions formed therefrom in the phosphating solution Phosphating of the steel and / or zinc surfaces without phosphating the Aluminum and / or magnesium surfaces kept at less than 100 mg / l become. In addition, the passivation solution should be composed so that it the phosphated steel and / or zinc surfaces passivated and on the Aluminum or / and magnesium surfaces forms a conversion layer.

However, this method has the disadvantage that it is only comparatively small Area shares on aluminum surfaces, mostly only up to about 20% by area of all surfaces to be treated on the mix of substrates can. It also has the disadvantages that cryolite or / and related ones Precipitation products continue to be formed in the pretreatment bath and that the Layering reactions, especially on iron and steel surfaces in one increased aluminum content of the phosphating solution are affected, so that no longer the entire mix of substrates made of different metal and Alloy surfaces can be coated equally well in the bathroom.

EP-A2-0 454 361 describes a zinc phosphating process in which the body is involved metallic surfaces are immersed in a zinc phosphating bath, which is next to a fluoride complex has a content of simple fluoride in the range from 200 to 300 mg / L contains and in which the molar ratio of the contents of complex fluoride to simple fluoride ≥ 0.01, and then the body with a second zinc phosphating solution are sprayed, which contains simple Fluoride ≤ 500 mg / L, but a higher content than the first Zinc phosphating solution. An external precipitation container can be used here be used.

EP-A2-0 434 358 teaches a similar zinc phosphating process in which such bodies are brought into contact with a zinc phosphate solution only once with a solution of simple fluoride in the range of 200. up to 500 mg / L and at which the molar ratio of the contents Complex fluoride to simple fluoride is kept in the range of 0.01 to 0.5.

The object of the invention is to overcome the disadvantages of the prior art and in particular a process for phosphating aluminum and aluminum-containing To propose alloys, even with increased proportions of aluminum-containing Surfaces of the components to be treated or pre-treated a good conversion layer that can be applied on an industrial scale or / and one appropriate passivation layer on the surfaces of aluminum or Alloys containing aluminum - possibly in a mix of substrates different metals or alloys - allowed to apply.

• an freiem Fluorid im Konzentrationsbereich von 6 bis 120 mg/l F_frei und
• an Aluminium im Konzentrationsbereich kleiner oder gleich 100 mg/l Al-lonen (einschließlich komplexgebundenem Al)

gehalten werden, indem steigende Aluminium-Gehalte in einem Fällungsbehälter außerhalb des Phosphatierungsbades unter Zirkulation der Phosphatierungslösung vom Phosphatierungsbad zum Fällungsbehälter und zurück auf Gehalte kleiner oder gleich 100 mg/l Al-lonen im Bad abgesenkt werden.The object is achieved by a method for the treatment or pretreatment of parts, profiles, strips or wires with surfaces of aluminum or aluminum-containing alloys - if appropriate in the presence of surfaces of further metals or alloys - with a fluoride and phosphate-containing alloy acidic aqueous solution, characterized in that the fluoride is at least partially present as free fluoride in the solution and that the contents in the bath of the phosphating solution

• free fluoride in the concentration range from 6 to 120 mg / l F _free and
• on aluminum in the concentration range less than or equal to 100 mg / l Al ions (including complex-bound Al)

are kept by lowering increasing aluminum contents in a precipitation container outside the phosphating bath with circulation of the phosphating solution from the phosphating bath to the precipitation container and back to contents less than or equal to 100 mg / l Al ions in the bath.

Alternatively or simultaneously, the method according to the invention can be used for this be ensured that increasing levels of aluminum in the phosphating solution in a separate zone of the phosphating bath to contents less than or be reduced to 100 mg / l Al ions.

The pickling attack dissolves aluminum on the metallic surface, and an aluminum content is taken up in the phosphating solution. Someone specific Aluminum content can also be from other sources in the phosphating solution come like from registered chemicals of the rinse solution. The Aluminum content can be predominantly or entirely by precipitation, but also partially be lowered by complexation. The free fluoride content in the Phosphating solution is preferably in a range from 6 to 120 mg / l, particularly preferably in a range from 10 to 80 mg / l, very particularly preferably kept in a range of 20 to 50 mg / l. The aluminum content in the Phosphating solution is preferred especially at values ≤ 80 mg / l preferably ≤ 60 mg / l, very particularly preferably ≤ 30 mg / l.

The process according to the invention is also characterized in that aluminum is precipitated in the phosphating solution in the precipitation tank or in the separate zone of the bath by adding alkali metal ions, fluoride complexes and / or fluoride ions, in particular with Na or K Ion or with at least one easily dissociating fluoride such as NaF, NH ₄ F, NaHF ₂ or KF. The AlF _x complex can already be pre-complexed. It is advantageous to control the process according to the invention in such a way that, despite the F addition, there is no increase in the free fluoride content in the bath. The contents of alkali ions in the phosphating bath are preferably 1 to 20 g / l and are preferably also kept in this range, in particular 3 to 10 g / l. In principle, the alkali ion content can also be far above the concentration of 20 g / l, for example 30 g / l. With such a high alkali concentration, instability of the bath can occur in many cases. In the case of a mixture of different alkali ions next to one another, a dominant content of sodium and / or potassium ions is preferred.

This has the effect that the precipitated cryolite and the related precipitation products such as K ₂ NaAlF ₆ do not or hardly occur in the phosphating bath, but largely or (almost) exclusively in the separate zone of the bath or in the precipitation container. As a result, the precipitation products can no longer or hardly settle on the surface to be coated.

The concentration of free fluoride is advantageously Phosphating solution in the phosphating bath 8 to 80 mg / l and in particular 10 up to 50 mg / l or in the precipitation tank or in the separate zone of the bath tank 5 to 500 mg / l free fluoride, in particular 20 to 200 mg / l, particularly preferably 30 up to 120 mg / l. It is therefore also preferred to have these levels in these concentrations to keep. Since usually below 5 mg / l there is no pickling attack on aluminum by free Fluoride occurs and because this pickling attack is needed as the subsequent one Passivation e.g. with chromate-containing compounds, titanium fluoride, zinc fluoride, soluble rare earth compound - especially a cerium-containing compound, wherein Scandium, yttrium and lanthanum are contained in the term rare earth element -, on Based on silane, self-organizing molecules based on phosphonate, in solvent soluble or / and dispersible polymer alone not for passivation is sufficient, a low minimum level of free fluoride in the Phosphating solution required. On the other hand, in many cases Keep a closed phosphate layer above 120 mg / l free fluoride from the phosphating bath on the metallic surfaces if the content not very much on cations co-precipitated with the phosphate such as Zn, Cu, Ni, Fe, Mn etc. is low. The formation of a phosphate layer on the aluminum surfaces is not absolutely necessary for reasons of corrosion protection. Therefore, a Content of free fluoride above 120 mg / l is usually not chosen, although it is also possible to work according to the invention above this value because also higher chemical consumption and a larger amount of precipitated Sludge from cryolite and / or related precipitation products is caused. It is also preferred to have a concentration difference in free fluoride between the phosphating bath and the precipitation tank or separate zone in the bath adjust and maintain from 30 to 60 mg / l.

In many cases, the inventive method will be used so that the Residence time of the phosphating solution in the precipitation tank or in the separate one Precipitation zone is up to 1 h, often up to 0.5 h. The volume flow from the bathroom to the Precipitation container and back is according to the selected volumes or Partial volumes and the desired aluminum content in the phosphating bath set.

The term "part" in the sense of this application encompasses all types and forms of Sheets, strip and profile sections, shaped bodies, semi-finished products, components, Assemblies etc.

The parts, profiles, to be treated or pretreated are usually Tapes and / or wires in the method according to the invention before pickling / phosphating cleaned, rinsed and, if necessary, separated from the rinsing and Cleaning stages with an activation solution, e.g. based on colloidal distribution Titanium phosphate contacted.

The treated or pretreated parts, profiles, strips or / and. Wires can rinsed and / or passivated after pickling / phosphating, in particular with a passivation solution based on a chromate-containing compound, Titanium fluoride, zirconium fluoride, soluble rare earth compound - especially cerium-containing Connection, self-organizing molecules e.g. based on phosphonate, based Silane, solvent-soluble and / or dispersible polymer.

The treated or pretreated and / or passivated parts, profiles, strips or / and wires can be after pickling / phosphating or after Passivation can be dried. In some cases such as at the immediate subsequent electrodeposition, however, drying is not necessary.

The precipitation of the aluminum can be carried out under normal pressure and at a temperature in the Range from room temperature to 70 ° C, especially at one temperature in the range of 40 to 60 ° C. In the method according to the invention, the Formation of the conversion or passivation layer under normal pressure and at a temperature from room temperature to 70 ° C, preferably at 35 to 60 ° C. The pH is usually in the range of 2 to 4. The pH of Phosphating baths are always in the range around pH 3. at Values of pH ≥ 4.0 are usually unstable, while values of pH ≤ 4.0 2.0 the bath is so stable that usually no good layer formation occurs because the The pH value shift on the freshly pickled metallic surface does not increase a separation of the conversion layer is sufficient.

Finally, the treated or pretreated and / or passivated parts, Profiles, tapes and / or wires with a varnish, with a different organic Coating, coated with a film or / and with an adhesive layer, if necessary printed and possibly formed, the metal parts coated in this way additionally glued, welded together and / or with other parts can otherwise be connected.

The products thus produced according to the invention can be found in the Automotive industry, in the aviation industry, in apparatus and mechanical engineering, in the Furniture industry, construction, for household appliances, electrical appliances, measuring devices, Control devices, test devices, construction elements, housings, Cladding, shelves, frames, frames, room dividers, partitions, facings, Lighting fixtures, crash barriers, radiator or fence elements as well as small parts, especially for body parts or bodies.

FIG. 1 shows a flow diagram which shows one possible of several principles of separate aluminum deposition schematically.

The phosphating process according to the invention has been described in comparison with previously and practiced methods the advantage that the cryolite or / and related Sludge containing precipitation products largely in a separate Precipitation zone or in a separate precipitation container and from there can be disposed of. It is also with the method according to the invention possible to treat different metallic substrates in one mix or pretreatment without affecting the layer formation e.g. on Steel is coming. Due to the reduced levels of free fluoride in the Phosphating solution also occurs less pickling attack on those containing aluminum Surfaces that also cause a correspondingly lower sludge formation. In addition, it was possible to ensure with the method according to the invention that due to the fact that there is less and less precipitated on the phosphated surface deposited particles after the subsequent painting no annoying Markings such as Roughness, streaking or other irregularities were recognizable.

It was surprising that largely stable bath conditions with regard to the Free fluoride and aluminum content in the phosphating bath and in the separate zone or in the precipitation container despite the very different Concentrations of these levels were achieved.

The object of the invention is described below with reference to a Embodiment explained in more detail.

Example:

To find the suitable precipitation conditions for aluminum-containing To determine phosphating solutions in a phosphating bath according to the invention, the following tests were carried out. The influences of the Concentrations of free fluoride, sodium and complex bound fluoride investigated the rate of aluminum precipitation.

1. Experimental design

To better possibly existing interactions of the significant parameters To be able to recognize, was a computer-assisted test planning used. The Stavex 4.3 program was used.

2. Analysis devices

Fluoride measurement:

Orion Model 960 with ion-selective electrode

Aluminum:

ICP.

A standard phosphating solution with the following composition was prepared from pa chemicals: Zn 1.5 g / l Mn 1.0 g / l Ni 1.0 g / l P ₂ O ₅ 14.0 g / l NO ₃ 3.0 g / l SiF ₆ 1.0 g / l FS 2.0 Free acid.

Starting from this solution, ions of SiF ₆ and Na and the proportion of free fluoride were varied in further batches.

3. Practical implementation:

0.5 l of the phosphating solution described above was poured into a plastic beaker, and the desired higher content of silicofluoride was adjusted with a 24% H ₂ SiF ₆ solution, the correction of the free acid content using NaOH - Additional was made. The Na content was adjusted using NaNO ₃ , the corresponding free fluoride content was adjusted using a dilute ammonium bifluoride solution. Now 20 mg / l aluminum were added to the bath with a dilute aluminum nitrate solution. After 0, 15, 30 and 60 minutes the free fluoride was measured and a sample of the solution was taken for aluminum determination.

To prevent reprecipitation of the aluminum in the sample taken, proceed as follows: 5 ml of the sample filtered using a membrane filter were placed in a added strongly hydrochloric acid demineralized water solution and made up to 50 ml with demineralized water. This solution was examined for its aluminum content by means of ICP.

The results are summarized in Table 1.

In experiment 1, there was no precipitation of the aluminum over a period of 5 days. Experiments 4, 8 and 15 showed a drastic reduction in the aluminum content even within 15 minutes. Increased alkali levels are preferred in connection with increased levels of free fluoride. SiF ₆ was added because of the stability of the phosphating solution and because it can be used for a mix of different types of metallic surfaces, especially to avoid specks on galvanized or zinc-containing surfaces.

After evaluating the values found in Example 1, the following are exemplary Carry out calculation:

4. Exemplary calculation of the volume flows or the reaction vessel

phosphating 200 m ³ Partial stream for precipitation in a precipitation tank 100 m ³ Al entry per hour 10 ppm

This entry corresponds to approx. 40 bodies per hour with 50% aluminum surface area and a pickling attack of approx. 1 g / m ² during the contact time.

Calculation formula for the stationary concentration of aluminum in the phosphate solution: Al (ppm) = ((((200m 3 - partial flow) • conc. Al in ppm after 1 h + (partial flow • rest Al in ppm after precipitation)) / 200) + Al in ppm from entry via pickling attack / h.

From this it was concluded that it is necessary for the volume flow to be treated to be at least 0.5 pool volumes per hour in order to be able to detect a sufficiently high proportion of dissolved aluminum. With an average residence time of 30 min, this results in a volume of the reaction basin of 50 m ³ . A residual aluminum content in the outlet of the treatment pool of approx. 5 ppm results in a theoretical stationary aluminum content in the treatment bath of approx. 25 ppm. However, since a partial precipitation of the aluminum can also be expected in the treatment bath (see, for example, experiment 3 from table 1), the actual content of dissolved aluminum will set itself to a lower value: approx. 20% of the total precipitation products occur in the phosphating bath and resulted in approx. 20 ppm Al content in the phosphating solution of the bath in stationary condition. Approximately 80% of the total precipitation products failed in the precipitation container.

Claims (13)

1. 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, 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 6 to 120 mg/l F_free, and

   the aluminium content is maintained at a concentration in the range of ≤ 100 mg/l Al ions (including complex-bound A1)

   by virtue of the fact that increasing aluminium contents, in a precipitation tank outside the phosphatizing bath, are decreased to contents ≤ 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 ≤ 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, NH₄F, NaHF₂ 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 applicable 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, in which case the term rare-earth element is also to include 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°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°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.

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