ES2215920T3 - PROCEDURE FOR THE TREATMENT OR PRE-TREATMENT OF PARTS WITH ALUMINUM SURFACES. - Google Patents

Abstract

Procedure for the treatment or pretreatment of parts, profiles, strips or wires with aluminum surfaces or alloys containing aluminum -eventually in the presence of surfaces of other metals or alloys- with an acidic aqueous solution containing fluoride and phosphate, characterized in that fluoride It is found, at least in part, as free fluoride in the solution and because the contents in the phosphate solution bath that are maintained in free fluoride in the concentration range are 6 to 120 mg / l of Flibre and in the Aluminum in the concentration range is less than or equal to 100 mg / l of Al ions (including Al bound to the complex), lowering the increasing contents of aluminum, in a precipitation vessel outside the phosphating bath, by circulating the phosphating solution from the phosphating bath to the precipitation and return container, to contents less than or equal to 100 mg of Al ions in bathroom.

Description

Procedure for treatment or pretreatment of parts with aluminum surfaces.

The invention relates to a method for the treatment or pretreatment of parts with surfaces of aluminum.

In principle, procedures of phosphating for aluminum and aluminum alloys. In practice industrial, it has been seen that they are particularly successful fluoride modified phosphating procedures with at least 150 mg / l free fluoride. These procedures are important in particular in the automotive industry and are used mostly, when a mixture of substrates of Different metals or alloys.

However, these procedures have the serious disadvantages, that, because of the high content in fluoride, from which they precipitate in the large phosphating bath amounts of cryolite (Na 3 AlF 6) or / and precipitates related, and also precipitate parts of the precipitates on the phosphated surface, without being removed from there through simple washing processes, forming a high roughness on the pretreated surface, which even after Subsequent varnishing has an annoying effect with its roughness.

The document DE-A1-197 35 314 describes a procedure for pretreatment of parts with surfaces of aluminum - eventually in the presence of magnesium surfaces, steel or / and zinc - in a phosphating facility, in which the parts are degreased with a degreasing solution, phosphated by treatment with a phosphating solution containing fluoride and then passivated with a passivation solution. The surface part of aluminum or / and magnesium with respect to the total area of the piece to be treated is in this case of at least 10% In this case, fluoride must be added to the solution phosphating exclusively as fluoride bound to the complex and the content of fluoride free ions that form in the phosphating solution to phosphate steel surfaces and / or zinc without phosphating the surfaces of aluminum or / and magnesium is maintained at less than 100 mg / l. In addition, the passivation solution It must be composed in such a way that passive surfaces phosphated steel or / and zinc and forming a conversion layer on the surfaces of aluminum or / and magnesium.

However, this process has the disadvantage of which can only be used on parts of surfaces comparatively small in terms of aluminum surfaces, usually only up to about 20% of the surface of all surfaces to be treated, with regarding the mixture of substrates. In addition, it has the disadvantages, that are also formed in the cryolite pretreatment bath or / and related precipitates and that the formation reactions of layers, in particular on iron and steel surfaces can be influence with a high aluminum content of the solution phosphating, such that the entire substrate mix of different surfaces of metals and alloys can no longer be coat well in the bathroom evenly.

The document EP-A2-0 454 361 describes a zinc phosphating procedure, in which the body with Metal surfaces are immersed in a zinc phosphating bath, which contains, in addition to a fluoride complex, a content in simple fluoride in the range of 200 to 300 mg / l, and in which the molar ratio of complex fluoride contents with respect to simple fluoride remains = 0.01, and in which after this the bodies are sprayed with a second phosphating solution of zinc, which has a simple fluoride content of = 500 mg / l, but which is a higher content than the first solution of zinc phosphating In this case you can use a container of external precipitation.

The document EP-A2-0 434 358 describes a process similar to zinc phosphating, in which such bodies are put only once in contact with a zinc phosphate solution, this solution having a simple fluoride content in the range of 200 to 500 mg / l and in which the molar ratio of complex fluoride contents with respect to simple fluoride are keeps in the range of 0.01 to 0.5.

The mission of the invention is to overcome disadvantages of the state of the art and in particular to propose a procedure for phosphating aluminum and alloys that they contain aluminum, which even with high proportions of surfaces containing aluminum of the parts to be treated  or to pretreat, allows the placement of a good layer of conversion, which is also applicable on an industrial scale or / and a corresponding passivation layer on the surfaces of aluminum or aluminum-containing alloys - eventually in a mixture of substrates of different metals or alloys.

The mission is solved through a procedure for the treatment or for the pretreatment of parts, profiles, strips or wires with aluminum surfaces or alloys that contain aluminum - eventually in the presence of surfaces of other metals or alloys - with an acidic aqueous solution that it contains fluoride and phosphate, characterized in that the fluoride is present in the solution, at least partially, as free fluoride and that the contents in the phosphate solution bath are they keep

- in free fluoride in the range of concentration is 6 to 120 mg / l of free F and

- in aluminum in the concentration range less than or equal to 100 mg / l of Al ions (including Al bound to the complex),

lowering the increasing contents in aluminum, in a precipitation vessel outside the bathroom phosphation, through the circulation of the phosphating solution from the phosphating bath to the precipitation and return container, up to contents less than or equal to 100 mg of Al ions in the bath.

Alternatively or simultaneously, you can ensure in the case of the process according to the invention that in a separate area of the phosphating bath increasing contents of aluminum in the phosphating solution are lowered to contents less than or equal to 100 mg / l of Al ions.

The stripping attack dissolves aluminum in the metal layer, and a content of aluminum in the phosphating solution. However, a content certain aluminum can come from other sources in the phosphating solution, such as p. ex. of chemical compounds introduced from the wash solution. It can decrease the aluminum content mainly or totally by precipitation, but partially also by complexation. The Free fluoride content in the phosphating solution is preferably maintained in a range of 6 to 120 mg / l, particularly preferred in a range of 10 to 80 mg / l, totally preferred in a range of 20 to 50 mg / l. The content in aluminum in the phosphating solution is maintained preferably in values ≤ 80 mg / l, particularly preferred ≤ 60 mg / l, totally preferred ≤ 30 mg / l.

The process according to the invention is also characterized in that in the precipitation vessel or in the area separated from the bath, aluminum is precipitated in the solution of phosphation by the addition of alkali ions, complexes of fluoride or / and fluoride ions, in particular with Na or K ions or with at least one slightly dissociated fluoride, such as p. ex. NaF, NH4F, NaHF2 or KF. The AlF_ {x} complex can be present in a precomplexed form in this case. It is advantageous, control the method according to the invention in such a way that Despite the addition of F, do not increase the free fluoride content in the bathroom. The alkaline ion contents in the bathroom phosphating are preferably 1 to 20 g / l and are maintained also preferably in this range, in particular from 3 to 10 g / l In principle, the alkali ion content may be also well above the concentration of 20 g / l, p. ex. to 30 g / l But at such an alkaline concentration it can appear in  Many cases a bathroom instability. In a mixture of different alkaline ions next to each other, a dominant content in sodium or / and potassium ions.

In this way it originates, from which the cryolite precipitate and related precipitates, such as p. ex. K_ {2} NaIF_ {6}, do not appear or just do it in the bathroom of phosphating, but mainly or (almost) exclusively in the area separated from the bath or in the precipitation vessel. This way, the precipitates can no longer or just do it in the surface to be coated.

Advantageously, the concentration in fluoride free of the phosphating solution in the phosphating bath is of 8 to 80 mg / l and in particular 10 to 50 mg / l or in the bath of precipitation or in the separate area of the bath container 5 to 500 mg / l of free fluoride, in particular 20 to 200 mg / l, totally preferred 30 to 120 mg / l. It is therefore preferred also to keep these contents in these concentrations. Since normally below 5 mg / l no stripping attack appears on the aluminum by means of free fluoride, and since this is necessary stripping attack, since the subsequent passivation, p. ex. with compounds containing chromate, titanium fluoride, fluoride of zinc, a rare earth soluble compound - in particular of a compound containing cerium, including scandium, yttrium and lanthanum in the concept of rare earth element-, based on silane, self-organizing molecules based on phosphonate, soluble polymer or / and dispersible in solvents is not sufficient for passivation, a minimum content of free fluoride in the solution is necessary Phosphating On the other hand it is formed in many cases, with contents above 120 mg / l of free fluoride, one layer closed phosphate from the phosphating bath on the metal surfaces, in case the cation content precipitates with phosphate, such as Zn, Cu, Ni, Fe, Mn, etc. lest very low The formation of a layer is not necessarily necessary of phosphate on the aluminum surface, for reasons of corrosion protection. Therefore, it is not normally chosen a free fluoride content above 120 mg / l, although you can also work according to the invention above this value, because it also causes a high consumption of products chemicals and a greater amount of cryolite precipitated sludge or / and related precipitates It is also preferred to set and maintain a difference in concentration of free fluoride between the bath phosphating and the precipitation vessel or separate area in the bath 30 to 60 mg / l.

It is used in such a way in many cases the procedure according to the invention, that the residence time of the phosphating solution in the precipitation vessel or in the separate area of precipitation is up to 1 h, often up to 0.6 h. The flow rate from the bath is adjusted accordingly to the precipitation vessel and return with respect to the volumes or partial volumes chosen, as well as the content desired in aluminum in the phosphating bath.

The term "part" in the sense of this application includes all types and forms of sheets, pieces of strips and profiles, molding bodies, semi-finished, components, unions etc.

Normally, parts, profiles, strips or / and wires to be treated or pretreated with the procedure according to the invention, before pickling / phosphating is cleaned, washed and eventually they get in touch, separately from the washing and purification steps, with an activation solution, e.g. ex. based on colloidally dispersed titanium phosphate.

Parts, profiles, strips or / and wires are they can wash or / and passivate after pickling / phosphating, in particular with a passivation solution based on a compound containing chromate, titanium fluoride, zirconium fluoride, rare earth soluble compound - in particular compound that contains cerium, self-organizing molecules, e.g. ex. based phosphonate, based on silane, soluble polymer or / and dispersible in solvents

Parts, profiles, strips or / and wires treated or pretreated or / and passivated can be dried after pickling / phosphating or after passivation. However, in Many cases do not require drying, such as p. ex. for him directly subsequent electro-immersion varnishing.

Aluminum precipitation can be performed at normal pressure and at a temperature in the temperature range ambient at 70 ° C, in particular at a temperature in the range of 40 to 60 ° C. In the process according to the invention, it can be carried out the formation of the conversion or passivation layer at normal pressure and at a temperature of room temperature to 70 ° C, preferably from 35 to 60 ° C. The pH value is normally found in the range from 2 to 4. In principle the pH value of the baths of phosphating is always in the range of around pH 3. At pH values ≥ 4.0 is the bath is normally unstable, while at pH values ≥ 2.0 the bath is so stable, that normally no layer formation appears, because the displacement of the pH value on the metal surface recently pickling is not enough for the deposition of the conversion layer

Finally, the pieces can be coated, profiles, strips or / and wires treated or pretreated or / and passivated with a varnish, with an organic coating of another type, with a sheet or / and with a layer of adhesive, eventually they are printed and eventually molded, being able to join, weld or / and join any way with each other metal parts so coated with Other pieces

Products manufactured according to the invention are used in the automobile industry, in the industry of the aviation, in the manufacture of apparatus and machines, in industry of furniture, in construction, for household appliances, appliances electrical, measuring devices, control devices, test devices, construction elements, housings, coatings, shelves, brackets, racks, dividers, walls of separation, plasters, lighting devices, protectors, elements of heating bodies or fences, as well as parts small, particularly for body parts or bodies.

Figure 1 shows a flow chart, which schematically represents a possible principle of the various Early deposition separates aluminum.

The phosphating procedure according to the invention has the advantage over procedures described and practiced so far, that the mud it contains cryolite or / and related precipitates is obtained mainly in a separate precipitation zone or in a separate vessel of precipitation, and from there it can be removed. Also, with the procedure according to the invention it is possible to treat or pretreat different metal substrates in a mixture, without altering the layer formation, p. ex. on steel Because of the bass free fluoride content in the phosphating solution, appears also a small stripping attack on surfaces that they contain aluminum, which also conditions a correspondingly low mud formation. It was also possible ensure with the process according to the invention, because only few particles are coprecipitated and deposited in the phosphated surface after subsequent application of varnish, no altering mark could be detected, such as p. ex. roughness, cracking or other irregularities.

Surprisingly, they were able to get very stable conditions of the bathroom with respect to the content of free fluoride and aluminum content, as well as in the area separate or in the precipitation vessel, despite the very different concentrations of these contents.

The purpose of the invention with an exemplary embodiment.

Example

The following experiments were performed to determine the appropriate precipitation conditions for phosphating solutions containing aluminum in a bath phosphating according to the invention. Regarding this, they were examined especially the influences of free fluoride concentrations,  sodium, as well as fluoride bound to complex, on the speed of the precipitation of aluminum.

1. Trial design

An assisted trial design was used with computer so you might be able to better recognize the interactions of significant parameters that could exist. The Stavex 4.3 program was used.

2. Analytical devices

Fluoride measurement: Orion model 900 with ion selective electrode.

Aluminum: ICP

From chemical products p. to. he prepared a standard phosphating solution with the following composition:

Zn: 1.5 g / l Mn: 1.0 g / l Neither: 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 acid free

Starting from this solution, the ions were varied of SiF6 and Na, as well as the part of free fluoride in other Preparations

3. Practical realization

They were poured into a 0.5 l plastic container of the phosphating solution described above and the possibly higher silicofluoride content with a solution of H 2 SiF 6 {24} at 24%, the content being corrected in free acid with an addition of NaOH. The content was adjusted in Na by NaNO 3, the corresponding fluoride content free by a dilute solution of ammonium bifluoride. I know 20 mg / l of aluminum was added to the bath by a solution of aluminum nitrate After 0, 15, 30 and 60 minutes, the free fluoride, and a sample of the solution was extracted for Determine the aluminum.

To prevent further precipitation of Aluminum in the extracted sample, proceeded as follows: they added 5 ml of the filtered sample with membrane filter to a concentrated solution of hydrochloric acid and deionized water and se He took up to 50 ml with deionized water. It was investigated in this solution the aluminum content by ICP.

The results are represented in Table 1.

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In trial 1, none were observed Aluminum precipitation during the 5 day period. In the trials 4, 8 and 15 a drastic reduction of content was observed in aluminum, even in 15 minutes. Quantities are preferred high alkalines in relation to high fluoride contents free. SiF6 was added because of the stability of the solution phosphating and for use for a mixture of different metal surfaces, in particular to prevent the formation of chopped on zinc-plated or zinc-containing surfaces.

After the evaluation of the values found In Example 1, the following calculations are made by way of example:

4. Calculation by way of example of flows or reaction vessel

Bathroom of phosphating 200 m 3 Partial current for precipitation in a precipitation vessel 100 m 3 Al feeding per hour 10 ppm

This feed corresponds approximately to 40 bodies per hour with a surface proportion of 50% aluminum and pickling attack of approximately 1 g / m2 3 during the contact time.

Calculation formula for concentration stationary aluminum in phosphating solution:

Al (ppm) = (((200 m 3 - partial current) \ Al concentration in ppm after 1 h + (partial current \ remainder of Al in ppm after  precipitation)) / 200) + Al in ppm from feed by attack of pickling / h.

From this it was deduced that it is necessary that the flow to be treated is at least 0.0 volumes of container per hour, to be able to detect a proportion what high enough in dissolved aluminum. This gives a time of average residence of 30 min a reaction vessel volume of 50 m 3. A residual aluminum content at the exit of the treatment vessel of approximately 5 ppm gives as result a theoretical stationary content in aluminum in the bathroom of treatment of approximately 25 ppm. Since there are also to be counted in the treatment bath (see, for example, Test 3 of Table 1) with a partial precipitation of aluminum, the  actual content in dissolved aluminum at a lower value: approximately 20% of all precipitates appear in the bath of phosphating and provide approximately 20 ppm of the content in Al in the bath phosphating solution in the state stationary. Approximately 80% of total precipitates are they precipitated in the precipitation vessel.

Claims (13)

1. Procedure for the treatment or pretreatment of parts, profiles, strips or wires with aluminum surfaces or alloys containing aluminum - possibly in the presence of surfaces of other metals or alloys - with an acidic aqueous solution containing fluoride and phosphate, characterized in that the fluoride is found, at least in part, as free fluoride in the solution and because the contents in the phosphate solution bath that are maintained in free fluoride in the concentration range is 6 to 120 mg / l of F_ { free} and in the aluminum in the concentration range is less than or equal to 100 mg / l of Al ions (including Al bound to the
complex), lowering the increasing contents in aluminum, in a precipitation vessel outside the bathroom phosphation, through the circulation of the phosphating solution from the phosphating bath to the precipitation and return container, up to contents less than or equal to 100 mg of Al ions in the bath. 2. Method according to claim 1, characterized in that the increasing aluminum contents in the phosphating solution are lowered in a separate area of the phosphating bath to contents less than or equal to 100 mg / l of Al ions. 3. Method according to claim 1 or 2, characterized in that in the precipitation container or in the separate area of the bath, aluminum is precipitated from the phosphating solution by the addition of alkali ions, fluoride complexes and / or fluoride ions, in particularly with Na or K ions, or with at least one easily dissociating fluoride such as p. ex. NaF, NH4F, NaHF3 or KF. Method according to one of the preceding claims, characterized in that the content of alkali metal ions in the bath that is maintained in a concentration range is from 1 to 20 g / l. 5. Method according to one of the preceding claims, characterized in that the concentration of free fluoride in the precipitation vessel or in the separate zone of precipitation is 5 to 500 mg / l of fluoride
free. Method according to one of the preceding claims, characterized in that the residence time of the phosphating solution in the precipitation vessel is 5 to 500 mg / l of free fluoride. 7. Method according to one of the preceding claims, characterized in that the parts, profiles, strips and / or wires to be treated or pretreated are cleaned, washed and eventually separated from the washing and cleaning stages, are brought into contact with an activation solution, e.g. ex. based on colloidally dispersed titanium phosphate. Method according to one of the preceding claims, characterized in that the parts, profiles, strips and / or wires to be treated or pretreated are washed and / or passivated, after pickling / phosphating, in particular with a passivating solution to base of a compound containing chromate, titanium fluoride, zirconium fluoride, silane, self-organizing molecules, e.g. ex. based on phosphonate, soluble polymer and / or solvent dispersible, soluble rare earth compound - in particular compound containing cerium, including the concept of rare earth element also scandium, yttrium and lanthanum. Method according to one of the preceding claims, characterized in that the parts, profiles, strips and / or wires treated or pretreated and / or passivated are dried after pickling / phosphating or after passivation. Method according to one of the preceding claims, characterized in that the precipitation of the aluminum is carried out at normal pressure and at a temperature in the range from room temperature to 70 ° C. Method according to one of the preceding claims, characterized in that the formation of the conversion or passivation layer is carried out at normal pressure and at a temperature in the range from room temperature to 70 ° C. 12. Method according to one of the preceding claims, characterized in that the parts, profiles, strips and / or wires treated or pretreated and / or passivated are coated with a varnish, with an organic coating of another type, with a sheet and / or with a layer of adhesive, eventually printed and eventually molded, the metal parts coated in this way being able to additionally glue, weld and / or bond with each other. 13. Use of products prepared according to process according to claims 1 to 12 in the industry of the automobile, in the aviation industry, in manufacturing of apparatus and machines, in the furniture industry, in the construction, for household appliances, electrical appliances, measuring devices, control devices, test devices, construction elements, housings, coatings, shelves, supports, racks, dividers, separation walls, plasters, lighting equipment, protectors, body elements heaters or fences, as well as small parts, in particular for body parts or bodies.