EP1060291B1 - Method for producing a corrosion protective coating and a coating system for substrates made of light metal - Google Patents

Description

The invention relates to a method for producing a corrosion-protecting Coating for a substrate made of a light metal or Light metal alloy.

Light metals, especially aluminum, find their low specific gravity in more and more technologies. Disadvantageous is that they are very electrochemically base in character are susceptible to corrosion. They are therefore covered with anti-corrosion layers of all kinds. A known method of this type exists in metal layers without current or galvanically on the light metal to separate. This is particularly interesting if there are additional high ones decorative demands are placed on the surface.

A practical example of this are alloy wheels or actually Alloy rims. Due to the high decorative demands, especially at for example this product it would be desirable if it were chrome plated could. Known chromed rims of this type initially suffice for the high decorative standards, but are very susceptible to damage and then quickly lose attractiveness.

DE 196 21 881 A1 therefore proposes using a method for Chromium-plating car rims from an aluminum alloy first one Apply a primer coat of powder or wet paint, then the rim dry, apply a layer of plastic wet varnish, dry again and finally to carry out galvanic chrome plating. This different process steps are quite complex and require multiple relocation of the intermediate products to other devices. in addition comes the time it takes to dry

A method known from DE 195 39 645 A1 works in a similar manner. Even there a light alloy rim for motor vehicle wheels is coated, namely This rim is initially given a full paint job. Beyond that Intermediate coating as powder coating or as bright nickel plating trained to level the surface structure. This will make it smooth Basis for an electrodeposable, finally deposited decorative gloss metallization created.

For the electroplating of aluminum, the manual of electroplating, edited by Heinz W. Dettner and Johannes Elze (1964), Volume 1, part 2, chapter 15, page 1034, initially an intermediate metal layer to apply with good adhesive strength. alternatively there is also a porous oxide film mentioned. The subsequent metallic layers are each galvanically upset. This is possible because both the metallic intermediate layer and the porous oxide layer are also conductive. In the same essay is already found that this makes the substrate easily vulnerable. So manufactured Coatings are therefore not protective against corrosion, on the contrary.

The methods in the state of the art provide concrete and practical experience Production of decorative layers with good corrosion protection, for example Aluminum looks something like this: On an aluminum substrate, one is de-energized thin layer of zinc applied with a zincate stain. Then there is a galvanic direct copper plating and then a galvanic application of one Duplex or tri-nickel layer with the aim of leveling and Corrosion protection. Then a thin one is electroplated Gloss chrome layer applied.

This layer system offers sufficient corrosion protection for as long as the aluminum substrate as there is no mechanical in the layer There is damage that affects the metal substrate.

If there is such deep damage to the layer or Layer system, so creates a so-called galvanic element in which the outer layer acts as a cathode and the substrate as an anode, which is oxidized.

Although chromium is a chemically very base metal, the formation of a thin oxide layer on the surface (called passivation) gives it a very positive potential. Oxygen is then reduced on this surface, which is very large compared to the aluminum exposed by the damage. The oxidation process is the conversion of metallic aluminum to Al ³⁺ . Due to the very large cathode surface of the chromium oxide, the corrosion of the aluminum at this damaged point is dramatic. One speaks here of a catastrophic failure of the corrosion protection layer.

The object of the present invention is to provide an alternative method for Manufacture of a corrosion protective coating for a substrate to propose a light metal and a corresponding layer system that is less sensitive to such damage.

This object is achieved by a method for producing a Corrosion protection coating for a substrate made of a light metal or a light metal alloy, in which a first on the substrate electrically non-conductive first layer is applied, the non-conductive first layer generated by anodic oxidation of the substrate later, a densification of the non-conductive by anodic Oxidation occurs first layer, then on the not conductive first layer, a metallized layer is applied without current and a third layer is later applied to the metallic second layer.

This task is also solved by a layer system comprising a Substrate made of light metal or a light metal alloy, but not one conductive first layer, which consists of an oxide of the substrate material, thereon a currentless applied second layer of one or more metals, a third layer.

Preference is given to smoothing and leveling between those applied without current second layer and the third layer a smoothing metallic Intermediate layer applied. The third layer is particularly preferably one decorative third layer.

With such a method and such a layer system Problems solvable. The invention makes use of the knowledge that the A prerequisite for the catastrophic failure of the known layer systems the electrical conductivity between anode and cathode at Oxidation process after the damage is.

According to the invention, the electrical conductivity is now at precisely this point reliably prevented. The electrode flow is not electrically conductive layer between the substrate on the one hand and the outer layers otherwise provided. These outer layers can be both previous corrosion protection properties continue to be good Have functioned with undamaged shift systems, and they on the other hand, the decorative effects like a glossy chrome layer own and / or be wear-resistant and / or low-friction.

The electrically non-conductive layer can by physical methods. for example PVD (physical vapor deposition) or plasma CVD (chemical vapor deposition), through simple polymer layers, i.e. lacquers, or through electrochemical processes are generated.

It is particularly preferred if the non-conductive layer is replaced by anodic Oxidation of the substrate is generated.

If the substrate is, as is preferred, aluminum, the is not used for the production conductive layer uses an anodizing process. It just becomes that Metal substrate switched as an anode and by applying a voltage Oxidized surface. This oxide layer is chemically relatively inert and forms an ideal electrical one, especially after appropriate post-treatments Barrier.

This non-conductive first layer, here the oxide layer, is preferred then a metal layer is preferably made using an electroless method Nickel, copper or another metal that can be deposited without current, upset.

Copper can then be applied to this metal layer using galvanic processes Flattening of the still rough surface for mechanical Equalization of tension or also applied as a shine, also nickel similar purposes and in particular for additional corrosion protection conceivable.

The decorative layer can then also be applied to this layer in the prior art lying layer, in particular chrome, are applied.

In the prior art, there was previously a belief that it was possible. Electrolessly metallize plastics in which the non-conductive Plastic surface roughened and activated accordingly. With ceramics Up until now this was thought to be possible only to a very limited extent. Are oxide layers Ceramics and the activation and adhesive metallization encountered problems. To achieve the very good adhesive strength of electrolessly applied Metal layers, especially on plastics, have so far been mechanical Considering the two surfaces being clamped together, the so-called push button effect. This is only the case with oxidic surfaces conditionally possible.

According to the invention, a very successful and advantageous method is preferably used here. This is because it is the layer created by anodic oxidation, in the case of aluminum it is the anodized layer. post-compressed. This is because the process of oxidation creates pores that should be reduced in size to prevent the non-conductive layer from being destroyed and possibly creating conductive bridges. This post-compression can be done using various methods, one of which is the so-called hot water compression. By immersing it in boiling water, the resulting anhydrous Al ₂ O _{3 is converted} into a boehmite type Al ₂ O ₃ x H ₂ O. This leads to an increase in the volume of the material around the pores, so that the pores shrink themselves.

This effect is now used in addition to simultaneously with this Compaction step to activate the surface. A Activation in the sense of a metallization of non-conductive surfaces is in in this case by applying conductive nuclei possible. Preference is given to a noble metal seed as the crystallization seed used, especially conductive palladium seeds.

These palladium nuclei or other crystallization nuclei are during the Compaction applied to the surface and penetrate into the pores during their downsizing.

This now enables these crystallization nuclei to be metallized in the next process step not just as applying another layer cause the non-conductive first layer, but that this metallization also takes place in the now reduced pores. The conductive metallic second layer into the pores, taking it too Undercuts and a very good interlocking and adhesion of the ensures non-conductive first layer with the conductive second layer.

After the second layer is applied, it is easily possible then, for example, galvanically further desired layers and finally also to deposit a decorative, in particular chrome layer. Further preferred features are characterized in the subclaims.

Figur 1

einen schematischen Schnitt durch ein erfindungsgemäßes Schichtsystem; und

Figur 2

eine vergrößerte schematische Schnittdarstellung durch einen vergrößerten Ausschnitt aus Figur 1.

The invention is described below using an exemplary embodiment with reference to the drawings. Show it:

Figure 1

a schematic section through an inventive layer system; and

Figure 2

an enlarged schematic sectional view through an enlarged section of Figure 1.

FIG. 1 shows a layer system in a very schematic form. A substrate 5 consists of a light metal or a light metal alloy, in particular aluminum. For example, it can be a light alloy rim for a motor vehicle.

An electrically non-conductive first layer 10 is closed on the substrate 5 recognize, in particular an oxide from the material of the substrate 5 can, for example alumina. The aluminum oxide can by means of a Anodizing process have been generated.

There is a conductive, on the non-conductive first layer 10, metallic second layer 20. This is de-energized on layer 10 deposited.

Another metallic intermediate layer follows the second layer 20 25, which are particularly rough in order to level the usually relatively rough Surface of electrolessly deposited layers 20 is used.

The intermediate layer 25 is in particular electrodeposited. this leads to to slight material differences between the second layer 20 and the Intermediate layer 25, even if both e.g. should consist of nickel, because chemically deposited electroless nickel Phosphorus or Contains boron components but does not contain galvanically deposited nickel. For the functionality of the layer system does not matter.

Finally, a layer 30 follows the intermediate layer 25, For example, a glossy chrome layer that the decorative the outside and / or low-friction and / or wear-resistant properties of the finished Product. Are the decorative properties of the finished Product especially in the foreground, for example in the case of motor vehicle rims, a bright chrome layer is applied. Should the layer be special wear-resistant, hard chrome would be considered. for low-friction exterior decorative layers of nickel teflon or lead.

In FIG. 2 , the boundary area between layers 10 and 20 is greatly enlarged during the manufacturing process, but is again shown schematically.

The non-conductive and in particular by anodic oxidation of the substrate 5 generated first layer 10 has a surface 12. This surface 12 is however not completely flat, but has a large number of pores 13; this is, in particular, the production-related result of carrying out a Anodizing process.

These pores 13 are now reduced or the layer 10 is "compressed" in the in a so-called hot water compaction, the substrate 5 with the Surface 12 is immersed in boiling water. Is preferred together with the boiling water also activating the surface 12 through the Application of conductive nuclei 18, in particular Palladium germs causes. This is because these nuclei 18 arrive due to the initially still large pores 13 into them and remain there also after the compression process when the pores 13 become smaller are.

After removing the boiling water, the palladium or Crystallization nuclei 18 on the surface 12 and in particular in the pores 13. Now then the metallization takes place through the Crystallization nuclei 18 through the now electrolessly applied materials second layer 20 instead, in particular of copper and / or nickel. This As a result, materials reach into the pores or form precisely there particularly intensive contacts with the material of layer 10. This does the formation of undercuts for firm adhesion of the in FIG. 2 Layer 20 not yet shown on layer 10.

Reference list

5

Substrate

10th

non-conductive first layer

12th

Surface of the non-conductive layer

13

Pores

18th

Crystallization nuclei

20th

metallic second layer

25th

Intermediate layer

30th

decorative third layer

Claims (18)

1. A method of producing a corrosion protective coating for a substrate made of a light metal or a light metal alloy in which

   an electrically non-conductive first layer (10) is initially formed on the substrate (5) whereby the non-conductive first layer (10) is produced by anodic oxidisation of the substrate (5),

   the non-conductive first layer (10) produced by anodic oxidisation is then sealed,

   whereafter a metallized layer (20) is formed on the non-conductive first layer (10) in currentless manner

   and a third layer (30) is then formed on the metallized second layer (20).
2. A method in accordance with Claim 1,
   characterised in that
   aluminium or magnesium or an alloy of at least one of these two light metals is utilised to form the substrate (5).
3. A method in accordance with Claim 2,
   characterised in that
   aluminium is utilised to form the substrate (5) and an anodising process is utilised to produce the non-conductive first layer (10).
4. A method in accordance with any of the preceding Claims,
   characterised in that
   an activating process is effected at the same time as the sealing process by depositing conductive nucleating agents (18) onto the upper surface (12) of the first layer (10) or into the pores (13) in the upper surface (12) of the first layer (10) which result from the anodic oxidisation process.
5. A method in accordance with Claim 4,
   characterised in that
   noble metal crystallisation nuclei, especially palladium nuclei, are utilised as the conductive nucleating agents (18).
6. A method in accordance with any of the preceding Claims,
   characterised in that
   the second metallic layer (20) is produced by a currentless metallisation process using copper and/or nickel.
7. A method in accordance with any of the preceding Claims,
   characterised in that
   a smoothing metallic intermediary layer (25) is formed between the metallic second layer (20) and the third layer (30).
8. A method in accordance with any of the preceding Claims,
   characterised in that
   a decorative third layer is applied to form the third layer (30).
9. A method in accordance with Claim 8,
   characterised in that
   chromium is deposited, especially by utilisation of an electroplating process, to form the decorative third layer (30).
10. A method in accordance with any of the preceding Claims,
    characterised in that
    a material having low friction and/or wear resistant properties is utilised for the third layer (30).
11. A system of layers produced by a method in accordance with any of the preceding Claims.
12. A system of layers comprising

    a substrate (5) of light metal or a light metal alloy,

    a non-conductive first layer (10) thereon consisting of an oxide of the substrate material,

    a second layer (20) consisting of one or more metals formed on the first layer by means of a currentless process,

    a third layer (30).
13. A system of layers in accordance with Claim 12 comprising an additional, smoothing metallic intermediary layer (25) between the second layer (20) and the third layer (30).
14. Asystem of layers in accordance with Claim 12 or 13,
    characterised in that
    the substrate (5) consists of aluminium or magnesium or an aluminium or magnesium alloy.
15. A system of layers in accordance with any of Claims 12 to 14,
    characterised in that
    the thickness of the non-conductive first layer (10) lies between 1 µm and 200 µm.
16. A system of layers in accordance with any of Claims 12 to 15,
    characterised in that
    the thickness of the second layer (20) that was formed by means of a currentless process lies between 0.5 µm and 20 µm.
17. A system of layers in accordance with any of Claims 12 to 16,
    characterised in that
    the layers of the metallic intermediary layer (25) between 2 µm and 20 µm.
18. Wheel rims or wheel trims of light metal, especially for motor vehicles, coated in accordance with any of the methods of Claims 1 to 10 or provided with a system of layers in accordance with any of Claims 11 to 17.

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