DE102011115802A1 - Process for the corrosion protection treatment of a workpiece made of an aluminum material, in particular of an aluminum wrought alloy - Google Patents

Abstract

The invention relates to a method for anticorrosive treatment of a workpiece made of an aluminum material, in particular of an aluminum wrought alloy.
According to the invention, the workpiece, which has a surface into which the size of the pores and / or cavities is smaller than 20 μm, is subjected in a first method step to a removal pretreatment with a solution containing sodium hydroxide, that in a next method step With a dilute nitric acid, the workpiece is dekapiert that small recesses are produced in a further process step in the surface of the workpiece, and then that a pre-layer and then a chemical nickel layer is applied.

Description

The invention relates to a method for anticorrosive treatment of a workpiece made of an aluminum material, in particular of an aluminum wrought alloy.

Made of aluminum workpieces are due to the low specific weight of aluminum and their sufficient mechanical stability multiple use when it comes to particularly heavy loads, especially in the military field. Plugs designed for military use are made from aluminum materials that are used in and on the clothing of soldiers and at interfaces to vehicle and weapon systems. However, due to the base nature of aluminum alloys, corrosion protection is required to meet the military required corrosion resistance of 96 hours Neutral Salt Spray Test (NSS). The workpieces produced from an aluminum material must be degreased, deoxidized and activated before they can be coated with a galvanic corrosion protection layer. For this purpose, the fat and oil residues adhering to the aluminum material are removed in a degreasing bath containing solvents and emulsifying components. Subsequently, in a heating bath containing sodium hydroxide solution, the oxide layers present on the aluminum material are removed so that the corrosion-protective layer to be applied by electroplating or the corrosion-protective layers to be applied by electroplating can adhere to the aluminum material. In addition, the pickling solution can fulfill an erosive function. The workpieces made from the aluminum material are then deboned in dilute nitric acid to remove residues and clean their surface. To remove silicon and other sparingly soluble alloying constituents, the workpieces are previously pickled in a fluoride-containing solution prior to pickling by the above-mentioned nitric acid treatment. Thereafter, the workpieces are subjected to zincate activation in a known process, wherein a thin layer of zinc is applied. On top of that, a thin chemico-nickel base layer with a thickness of 0.5 to 2.0 .mu.m is applied from a robust chemical nickel process, before the actual corrosion-protecting chemical nickel layer in a thickness of at least 20 .mu.m is applied.

Chemically-nickel layers are suitable for this because they can be used to form a uniformly thick layer even on complicated surface geometries of the workpieces. It is therefore particularly suitable for the coating of electrical low, medium or high frequency connectors. It is essential in the coating of the workpiece with a chemical nickel layer that this layer or these layers are closed continuously and contain no defects, so that the aluminum material is wrapped closed. Otherwise, a corrosion stress which would affect the solution applied to the chemical-nickel-coated workpiece by this defect, the aluminum immediately. For example, a solution containing only 5 percent NaCl would attack the workpiece within 24 hours due to this defect, thereby significantly removing aluminum and thus destroying the workpiece as corrosion progresses.

Aluminum wrought alloys have a fine, uniform structure, but also contain pores and voids, which are not eliminated by extrusion, but only stretched in the longitudinal direction, resulting in a stretched, rigid structure. The aluminum wrought alloys are pressed into bars and from these bars a variety of workpieces, especially connector components and parts for the assembly of connector systems, rotated on CNC machines. These rods not only contain pores and voids, but may also contain smudges on the surface if no suitable turning tools are used or the tools are worn. In addition, defects such as burrs, chips, breakouts, etc. can occur due to defective tools or machining errors on the workpieces.

On the thus protected against corrosion workpieces are additionally applied layers that meet functional and / or decorative requirements, such. B. certain electrical properties, eg. B. the realization of a certain contact resistance, or a certain color of the thus treated workpiece to ensure as many or few reflections.

It is an object of the present invention to develop a method for anticorrosion treatment of a workpiece consisting of an aluminum material or coated with an aluminum material, by which an improved corrosion protection of this workpiece is achieved. The inventive method should be particularly suitable for Aluminiumknetlegierungen.

This object is achieved in that the workpiece having a surface into which the size of the pores and / or cavities is less than 20 microns, in a first process step of a removing pretreatment with a sodium hydroxide-containing solution is subjected to that in one next process step the workpiece with a dilute nitric acid is dekapiert that in a further process step in the surface of the workpiece small recesses are generated, and that subsequently a pre-layer and then a chemical nickel layer is applied.

The inventive measures a method for corrosion protection treatment of manufactured from an aluminum material workpieces is created in an advantageous manner, which allows in a simple manner to coat such workpieces with a corrosion protection layer that meets high requirements. The inventive method is particularly for made of an aluminum wrought alloy workpieces such. B. Stanal 32 or Stanal 40A suitable.

An advantageous development of the invention provides that the pre-layer applied before the application of the chemical nickel layer is formed by a pre-nickel layer.

A further advantageous embodiment of the invention provides that a brass layer is deposited as a pre-layer.

A further advantageous development of the invention provides that a thin copper layer of cyanide-containing copper electrolytes is deposited as a pre-layer.

A further advantageous development of the invention provides that a further layer which brings about functional and / or decorative properties is deposited on the chemical nickel layer.

Further advantageous developments of the invention are the subject of the dependent claims.

Further details and advantages of the invention will be apparent from the embodiment which will be described below. Show it:

to : enlarged representations of a surface area of the workpiece after different process steps.

The method described assumes that the workpiece formed from an aluminum material or coated with such an aluminum material, ie made from an aluminum material, has a surface in which the size of the pores and / or cavities is less than 20 .mu.m, preferably less than 10 microns, since otherwise the applied to the workpiece chemical nickel layer is not able to coat the aluminum material closed. In addition, the corresponding workpieces may have no or only insignificant defects such as burrs, chips and damage, as such defects can lead to the fact that the chemical nickel layer is not able to securely enclose the workpiece and to close its surface.

The workpieces are first - if not sufficiently fat-free - subjected to a removing pretreatment with a solution containing sodium hydroxide. Preferably, this solution contains 0.5 to 20 g / l of sodium hydroxide, preferably 9 to 11 g / l of sodium hydroxide. The treatment time is between 1 and 30 minutes, preferably 10 minutes. The erosive pretreatment of the above-described sodium hydroxide solution is carried out at a temperature between 4 and 80 ° C, preferably at 20 ° C. The pretreatment solution further contains as residual degreasing salt a mixture of disodium ascorbate, sodium carbonate, sodium dodecylbenzenesulfonate in an amount of 1 to 20 kg / 100 l of liquid, it being preferred that the proportion of this degreasing salt in the pretreatment solution is between 9 to 11 kg / 100 l liquid is lying.

By pre-treating the workpiece with the above-described solution containing sodium hydroxide, the smears present on the surface of the workpiece are dissolved and removed as far as possible. The effect of this pretreatment is by comparing the . and seen. The pictures and show - in greatly enlarged representation - surface areas of the workpiece. You can clearly see the smudges on it. In the a surface area of the same workpiece is shown after pretreatment. One recognizes from the in that the surface is clearly leveled.

In a subsequent process step, the workpieces to be treated are dekapiert with a dilute nitric acid to those on the workpiece - like apparent - to remove remaining residues and to produce an even cleaner surface for the next treatment step. The nitric acid used in this process step has a concentration of 5 to 75%, with a concentration of 50% being preferred. The treatment of the workpieces is carried out at a temperature of 4 to 40 ° C, preferably in the range between 18 and 22 ° C and in particular at 20 ° C, with a time duration between 0.5 and 5 minutes, preferably with a time duration between 0.5 and 2 minutes, and more preferably 1 minute.

Thereafter, the workpieces are treated with a fluoride pickling, whereby the surface of the same is further leveled and further alloying components of the aluminum alloy are removed from the workpiece. The fluoride-containing pickle used here per 100 l of liquid 1-30 kg, preferably 12 kg Ammoniumhydrogendifluorid, 1-50 l, preferably 25 l of sulfuric acid chemically pure, 1-60 l, preferably 50 l of nitric acid chemically pure, and the remainder water. The treatment time of the workpieces in this fluoride-containing pickling is between 1 to 20 minutes, preferably between 3 and 7 minutes and more preferably about 5 minutes, at a temperature of 4 to 40 ° C, preferably at a temperature of 18 to 22 ° C and more preferably at a temperature of 20 ° C. In this further Dekapierungsschritt - as in the above-described process step - the treatment with nitric acid - the surface of the workpieces further cleaned of impurities. The and now show pictures of surface areas of the thus treated workpiece; It can be seen that its surface is flat and largely planar, but has small depressions. These depressions advantageously allow the chemico-nickel layer to be anchored on the surface pretreated in this way, in the manner of a "pushbutton effect". This effect can only be achieved if the material - as already mentioned - has hardly any pores or pores smaller than 20 μm, preferably smaller than 10 μm. If the pores contained in the surface of the aluminum workpiece are widened too large, this causes a pre-layer applied before application of the chemical nickel layer, in particular a pre-nickel layer, which as a rule has a thin nickel-phosphorus layer. Layer is formed on the surface treated as described can not adhere, so that caused by the described method corrosion protection layer does not or not completely encloses the material of the workpiece.

In order to coat the aluminum workpiece with a pre-layer and at least one chemical nickel layer, a well-known and therefore only briefly described two-stage zincate treatment is carried out. The solution used contains 2.5 to 25 g / l zinc, preferably 10 to 15 g / l zinc and in particular 13 g / l zinc. The treatment time of the first stage of the two-stage zincate treatment is about 0.5 to 2 minutes, preferably 0.8 to 1.2 minutes, in particular 1 minute and is at a temperature between 10 and 40 ° C, preferably between 18 and 22 ° C and especially at 20 ° C performed. The second stage of the described zincate treatment again uses the same solution and the treatment time is 0.25 to 0.75 minutes, preferably 0.5 minutes. The now shows the aluminum workpiece after this zincate treatment. It can be seen that the surface of the workpiece hardly visually differs from that of the and differs, but has a 0.5 to 5 microns thick zinc layer.

• 1. 345 g/l Natriumhydroxid, 87 g/l Zinkcarbonat, 23 g/l Eisen(II)-chlorid, 23 g/l Zinkoxid, 100 g/l Kaliumnatriumtartrat.
• 2. 60 g/l Natriumhydroxid, 10 g/l Zinkoxid, 7 g/l Natriumglukonat, 4 g/l Salicylsäure
• 3. 335 g/l Natriumhydroxid, 63 g/l Zinkoxid
• 4. 10 g/l Natriumhydroxid, 5 g/l Zinkoxid, 500 g/l Natriumhydroxid, 2 g/l Eisen(II)chlorid, 20 g/l Zinkoxid, 50 g/l Kaliumnatriumtartrat
• 5. 120 g/l Natriumhydroxid, 2 g/l Eisen(II)-chlorid, 20 g/l Zinkoxid, 50 g/l Kaliumnatriumtartrat.

The Zinkatbeizen typically used for this purpose can have the following composition:

• 1. 345 g / l sodium hydroxide, 87 g / l zinc carbonate, 23 g / l ferrous chloride, 23 g / l zinc oxide, 100 g / l potassium sodium tartrate.
• 2. 60 g / l sodium hydroxide, 10 g / l zinc oxide, 7 g / l sodium gluconate, 4 g / l salicylic acid
• 3. 335 g / l sodium hydroxide, 63 g / l zinc oxide
• 4. 10 g / l sodium hydroxide, 5 g / l zinc oxide, 500 g / l sodium hydroxide, 2 g / l ferrous chloride, 20 g / l zinc oxide, 50 g / l potassium sodium tartrate
• 5. 120 g / l sodium hydroxide, 2 g / l ferrous chloride, 20 g / l zinc oxide, 50 g / l potassium sodium tartrate.

The preferred zincate pickle used for the application described here is the composition of number 1 with the application parameters described above.

This zinc layer forms the prerequisite for an autocatalytic deposition of a thin nickel-phosphorus layer, that is to say the pre-nickel layer already mentioned above. To prepare this nickel-nickel layer, the workpiece treated as above is placed in a nickel bath containing nickel, preferably in the form of nickel acetate, with 2 to 10 g / l nickel, preferably 4 to 8 g / l nickel at a pH of 10.5 to 11.5, wherein the temperature is 15 to 40 ° C, preferably 18 to 22 ° C and in particular 20 ° C. The deposition time is 1 to 20 minutes, preferably 8 to 12 minutes and especially 10 minutes, wherein a nickel-phosphorus layer of 1 to 3 microns thickness is deposited. The now shows the surface of the workpiece after the deposition of the pre-nickel layer. It can be seen that the structure of the surface is essentially that of the and Although this is now a thin zinc layer and a Vornickel layer were applied to this.

As an alternative to nickel plating, it is also possible to deposit as a pre-layer a brass layer which fulfills the same function and also forms the basis for the subsequent chemical-nickel layer. Such a brass electrolyte has the following composition: 20 g / l copper cyanide, 20 g / l zinc cyanide, 40 g / l sodium cyanide, 15 g / l sodium carbonate, 1.5 m / l ammonia. The deposition of the brass layer is carried out at a current density of 0.1-0.6 A / dm ^2, preferably 0.3 A / dm ² at a temperature of 10-40 ° C, preferably 25 ° C. The deposition time is 2-7 min., Preferably 5 min. To achieve a layer thickness of 1-3 microns.

As a further alternative to nickel plating to form the pre-layer, a thin copper layer of cyanide-containing copper electrolytes may be deposited which operate at higher or lower current densities. An electrolyte operating at higher current levels of 2-6 A / dm ² contains potassium sodium tartrate and has the following composition: 45 g / l copper (I) cyanide, 57 g / l sodium cyanide, 30 g / l sodium carbonate, 45-60 g / l potassium sodium tartrate preferably 50 g / l. The deposition takes place with a current density of 2-6 A / dm ^2, preferably 4 A / dm ² at a temperature of 50 to 80 ° C, preferably at 65 ° C.

Another useful in the described method cyanide electrolyte operates at lower current densities, it contains 25 g / l copper (I) cyanide, 30 g / l sodium cyanide, 3 g / l sodium hydrogen sulfite, 6 g / l sodium carbonate. The deposition takes place at a current density of 0.1 to 1 A / dm ² at a temperature of 20-40 ° C, preferably at 25 ° C.

In the next step, a chemical nickel layer is applied to the pre-layer, in particular the pre-nickel, Vormessing- or Vorkupfer layer described above, which is between 15 and 30 .mu.m, preferably between 18 and 25 .mu.m and more preferably 20 .mu.m is thick. The deposition process is in turn basically known, so that it is only briefly outlined here: The chemical nickel layer is formed here by depositing a nickel-phosphorus layer, which is preferably deposited by means of a high-phosphorus chemical nickel process, wherein the proportion of phosphorus is between 5 and 15% by weight, preferably between 9 and 14% by weight. The process contains 4 to 8 g / l nickel, preferably 5.5 to 6.5 g / l nickel and in particular 6 g / l nickel. As a reducing agent Natriumhypophosfit for electroless deposition of the nickel-phosphorus layer is preferably used with at least 10.5 wt .-% phosphorus. The deposition takes place at a temperature between 85 and 90 ° C, preferably at 88 ° C at a deposition rate of 9.5 to 11 microns / hour. The now shows the surface of the deposited nickel-phosphorus layer with a phosphorus content of greater than 10.5%. A comparison of with the and shows that the surface of the coated workpiece is flattened, there are no more pores to recognize, only a slightly streaky structure, which results from the turning of the starting workpiece, can be seen. In this case, the nickel-phosphorus layer should be amorphous, otherwise there is a risk of layer corrosion at nickel-phosphorus weak points.

The now shows the back side of a coating of a pre-nickel layer and a chemical nickel layer after it has been peeled off from the workpiece treated as described above. It can be seen that this coating has protruding "pushbuttons" which cause a good adhesion of this coating on the surface of the workpiece pretreated as described above, by bringing these "pushbuttons" into the process caused by the pretreatment process in the surface of the aluminum workpiece. " Depressions "intervene.

The thus treated workpiece then has a corrosion resistance of 96 hours NSS. On the basis of this pretreatment and coating with the anticorrosion layer as described above, it is additionally possible to apply decorative and / or functional surface layers, preferably noble metal layers, but also non-noble metal layers in order to bring about certain mechanical, optical or electrical properties.

For this purpose, the nickel-phosphorus layer usually has to be reactivated because it passivates very quickly when it comes into contact with air and / or moisture, thereby forming a nickel oxide or nickel hydroxide layer on the surface of the workpiece. No precious metal layer can be deposited on such a surface without activation. To activate the nickel-phosphorus layer, it is envisaged that depending on the functional layer to be applied, either Au pre-electroplating, Ni pre-electroplating, PdNi pre-plating or fluoride activation or gold or palladium coating will be performed.

Pre-galvanization with gold is preferably carried out at a temperature between 20 and 50 ° C, preferably at a temperature between 30 and 40 ° C, preferably at 35 ° C, the current density between 2 and 10 A / dm ² , preferably between 4 and 6 A / dm ² and especially 5 A / dm ² and is carried out for a period of 2 to 10 minutes. The solution used has 2 to 6 g / l Au, preferably 4 g / l Au and the process is carried out at a very acidic pH.

In nickel pre-electroplating, the solution used has 40 to 60 g / l nickel and 120 to 170 g / l chloride, preferably 48 g / l nickel and 150 g / l chloride. It is envisaged that this Vorgalvanisierung takes place at a temperature between 20 and 30 ° C, preferably at 25 ° C. The current density is between 2 and 10 A / dm ² , preferably between 4 and 6 A / dm ² and in particular 5 A / dm ² . The treatment lasts for 2 to 20 minutes, preferably 4 to 6 minutes and especially 5 minutes, and is carried out in a very acidic pH environment.

The PdNi pre-plating is carried out at a temperature of 30 to 60 ° C, preferably at a temperature between 38 and 45 ° C and in particular at 42 ° C. The treatment time is between 0.15 and 5 minutes, with a treatment time of 0.5 minutes being preferred. The current density in this case is 0.25 to 1.5 A / dm ² , preferably 0.5 to 1 A / dm ² and in particular 0.8 A / dm ² . The solution contains 60 to 80 wt .-% palladium and 40 to 20 wt .-% nickel, in particular 3 to 4 g / l palladium and 2 to 3 g / l nickel and is carried out at a neutral pH.

In a fluoride activation, a solution is provided which contains 1 to 3% fluoro-hydrazoic acid, 1 to 5% hexafluorosilicic acid and 20 to 25% methanesulfonic acid and 5 kg of ammonium hydrogendifluoride per 100 l of water. The fluoride activation is carried out in a very acidic pH environment, the temperature is 22 to 40 ° C, preferably 23 to 27 ° C and especially at 35 ° C and lasts 2 to 10 minutes, with a period of 2 minutes is preferred ,

In a gold deposition, a solution is used which uses 4 g / l Au and the process in a very acidic pH environment at a temperature between 30 and 70 ° C, preferably between 40 and 50 ° C and especially at 45 ° C. and takes 0.5 to 5 minutes, preferably 4 minutes. The current density is 0.5 to 5 A / dm ² , preferably 1 to 2 A / dm ² and in particular 1.5 A / dm ² .

The palladium deposition is carried out in a solution containing 4 to 8 g / l of palladium, in particular 6 g / l of palladium. The process is carried out at a neutral pH and at a temperature between 30 and 70 ° C, in particular at 40 ° C. It lasts 0.15 to 5 minutes, in particular 1 minute, and the current density is 0.15 to 3 A / dm ² , preferably 0.5 to 1.5 A / dm ² and in particular 1 A / dm ² .

Preferably, the applicant hereby for activating the nickel-phosphorus layer, the PdNi pre-electroplating to then apply adherent noble metal layers.

On the thus activated surface can then z. Example, a black-ruthenium layer, a black-palladium layer, a black-rhodium layer are applied to give the workpiece surface targeted coloration and low reflection. It is also possible that a yellow gold layer, a red gold layer or white layers of platinum, palladium or ruthenium are applied.

For the functional properties, in particular to witness electrical contact properties, gold layers, silver layers, palladium layers and, to ensure a high chemical resistance, fine gold layers are suitable.

The preferred process for decorative properties such as low reflectance dark color is black ruthenium coating. For this purpose, a commercially available black ruthenium process is used with 4.5 to 6 g / l Ru preferably 5 g / l Ru. It is deposited at 50 ° C to 90 ° C, preferably at 65 ° C with 0.8 to 1.5 A / dm ^2, preferably 1 A / dm ^second The blackness addition is 30 to 38 ml / l, preferably 35 ml / l. The coating time is 7 to 10 minutes, preferably 8 minutes, to deposit a layer thickness of 0.2 to 0.6 μm Ru.

This applied black ruthenium layer is preferably finally subjected to a passivation with chromic acid to complete the coating process. The solution preferably used here contains 1 g / l chromic acid. The passivation process is preferably carried out at a temperature between 50 and 70 ° C, preferably at 60 ° C. The treatment time is 5 to 15 minutes, preferably about 10 minutes.

Alternative to noble metal layers to achieve a dark color with low reflection, non-precious metal coatings are also possible, such as black-chrome layers or black-nickel layers. Layer constructions with these final layers show even after a passivation consistently poorer corrosion resistance than in noble metal layers and therefore the noble metal layers are preferably used.

These passivations are beneficial for all dark layers to ensure corrosion protection.

Claims (12)

Method for corrosion protection treatment of a workpiece made of an aluminum material, in particular of an aluminum wrought alloy, characterized in that the workpiece having a surface into which the size of the pores and / or cavities is smaller than 20 microns, in a first step of an eroding pretreatment with a sodium hydroxide-containing solution is subjected, that in a next step, the workpiece is dekapiert with a dilute nitric acid, that in a further process step in the surface of the workpiece small recesses are generated, and that Subsequently, a pre-layer and then a chemical nickel layer is applied. A method according to claim 1, characterized in that as a pre-layer, a nickel layer, a brass layer or a copper layer of cyanide-containing copper electrolyte is deposited. Method according to one of the preceding claims, characterized in that the chemical nickel layer is formed by depositing a nickel-phosphorus layer. Method according to one of the preceding claims, characterized in that prior to the application of a pre-layer, a two-stage zincate treatment to form a zinc layer is performed. Method according to one of the preceding claims, characterized in that for the preparation of the pre-nickel layer, the workpiece to be treated is introduced into a nickel bath, which nickel, preferably in the form of nickel acetate, with 2 to 10 g / l nickel, preferably 4 to 8 g / l nickel contains a pH of 10.5 to 11.5. Method according to one of the preceding claims, characterized in that after the pickling with the dilute nitric acid and the application of the pre-layer, the workpiece is treated with a fluoride-containing pickling. A method according to claim 6, characterized in that the fluoride-containing pickle per 100 l of liquid 1 to 30 kg, preferably 12 kg of ammonium hydrogendifluoride, 1 to 50 l, preferably 25 l of sulfuric acid chemically pure, 1 to 60 l, preferably 50 l of nitric acid chemically pure and as the rest contains water. Method according to one of claims 6 or 7, characterized in that the treatment time of the workpiece in this fluoride-containing pickle is between 1 to 20 minutes, preferably between 3 and 7 minutes, and more preferably about 5 minutes, the temperature between 4 and 40 ° C, preferably between 18 and 22 ° C and more preferably 20 ° C. Method according to one of the preceding claims, characterized in that at least one decorative and / or functional surface layer is applied to the chemical nickel layer. A method according to claim 8, characterized in that the chemico-nickel layer is activated prior to applying the decorative and / or functional surface layer. Method according to one of the preceding claims, characterized in that for the coloring of the workpiece on this a black ruthenium layer, a black palladium layer, a black rhodium layer, a yellow-gold layer, a red-gold Layer or a white layer of platinum, palladium or ruthenium is applied. A method according to claim 11, characterized in that the layer applied as above is subjected to a passivation, preferably with chromic acid.

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