EP1451392A2

EP1451392A2 - Pretreatment process for coating of aluminium materials

Info

Publication number: EP1451392A2
Application number: EP02785370A
Authority: EP
Inventors: Rudolf Linde; Wolfgang Stuckert
Original assignee: Federal Mogul Burscheid GmbH
Current assignee: Federal Mogul Burscheid GmbH
Priority date: 2001-12-06
Filing date: 2002-11-07
Publication date: 2004-09-01
Anticipated expiration: 2022-11-07
Also published as: EP1451392B1; DE10159890B4; DE50207452D1; ATE332401T1; PL368710A1; DE10159890A1; WO2003048427A3; PL204301B1; JP2005511898A; BR0212923A; US20050067296A1; WO2003048427A2; CN1599809A; ES2264735T3; AU2002350675A1

Abstract

The invention relates to a method for applying electro-deposited metal coatings (3) upon aluminium or aluminium alloy components (1). According to said method, the surface (4) of the component is cleaned in an appropriate solution, in particular a solution of oils, fats, emulsions, pigments, etc. Said surface (4 ) is then etched in an appropriate solution, such that a certain quantity of material or near-surface alloy constituents is dissolved. After cleaning and dissolution, water rinsing is carried out. Immediately after the dissolution of the near-surface regions, the surface (4) of said component (1) is activated in a solution, containing iron ions, with a sulphate base by the anodic coupling of said component (1). The functional layer (3) is then applied by the cathodic coupling of said component (1), without intermediate rinsing, in the same electrolyte or in a similar or equivalent electrolyte, said functional layer (3) being made of iron (5).

Description

Neat treatment process for coating aluminum materials

description

Process for applying electrodeposited metal coatings to components made of aluminum or an aluminum alloy, in which the surface of the component is cleaned in a suitable solution, in particular oils, greases, emulsions, pigments, etc., and that the surface is then etched in a suitable solution is so that a certain amount of the material or the near-surface alloy components are dissolved and that after cleaning and after dissolving, rinsing with water takes place.

In order to protect components that are subject to high stress and / or wear, these components can be subjected to various measures. Measures to increase wear resistance include alloying, tempering and coating. Coating in particular plays an important role in aluminum materials and their alloys, because this enables the positive properties of these materials to be combined with those of the coating.

In engines, and in particular in the tribological system of pistons and cylinder liners, it has long been standard to manufacture these two elements from aluminum, since the engine manufacturers' endeavor is to reduce the weight of the elements. If the piston and cylinder liner were made of aluminum or aluminum alloys, the tribological system would fail and the contact surfaces would show signs of seizure. In order to avoid these feeding phenomena and to increase the wear resistance of the friction partners, it has been part of the state of the art for many years to coat aluminum pistons.

One problem that arises with the coating of aluminum is the chemically very stable and naturally forming oxide layer on the surface of the aluminum. To improve the adhesion of coatings to the aluminum or only to enable the oxide layer must be broken up and removed. So that the oxide layer does not form again after removal and before a further coating, it is common practice to apply an intermediate layer to the surface of the aluminum, which then enables the deposition of so-called functional layers. A functional layer can consist of iron, for example, and is used for wear resistance, among other things.

DE 19 15 762 discloses a method for applying electrodeposited metal coatings on aluminum and aluminum alloys. The surface of the material is cleaned, then activated and provided with an adhesive intermediate layer and then plated with a coating material, in this case the coating would be the functional layer. The intermediate layers used here can consist of zinc, nickel, tin or copper. The parts to be metallized are immersed in a solution consisting of hydrochloric acid, copper (II) chloride and a metallic copper powder after the cleaning and activation process until an intermediate layer of monovalent copper has formed on the surface of the aluminum in this immersion bath.

A disadvantage of this method is the high aggressiveness of the chloride electrolyte, so that the use of this method is expensive and with great effort, for. B. is related to occupational safety.

The development of an intermediate layer based on zinc is described in the article: Advances in zincate treatment of aluminum, from the magazine JOT, year 04/2001, by Peter Volk and Dr. Karl Brunn. The article describes the zincate treatment of aluminum as an essential step in the pretreatment of the coating of aluminum with metals or metal alloys. The article points out that processes for direct copper plating, nickel plating and chrome plating have a very narrow process window and cannot be used as stable processes in industrial series production. Rather, it is recommended to generally carry out a pretreatment on the aluminum surface in which the surface is activated and the natural oxide layer of the Aluminum is removed. A thin, conductive intermediate layer is then deposited, which prevents the reoxidation of the surface during the introduction into the coating bath and causes good adhesion to the coating (functional layer). The further development of the process is aimed at replacing cyanide zincate stains with cyanide-free ones. This is done by using organic complexing agents instead of cyanide and iron instead of nickel and copper. A special complexing agent system was developed for the cyanide-free zincate stain. The metal ions are complexed exactly so that there is a uniform and controlled deposition with excellent adhesion. At the same time, the complexing agent enables rapid ion exchange and thus ensures rapid layer build-up. The article does not provide any indication that an intermediate layer can be completely dispensed with for the deposition of a functional layer, described below using the example of a nickel layer. The article also does not show that it is possible to directly deposit iron layers on the aluminum surface.

It is therefore an object of the invention to develop a method for coating an aluminum-based material, an aluminum alloy or an aluminum-based composite material which, using a sulfate-based solution, on a metallic or oxidic intermediate layer on the surface of the aluminum, as the basis for depositing a functional layer, dispensed with and thus significantly accelerated the coating process and at the same time minimized the production costs.

The idea according to the invention achieves the object in that the surface of the component is activated immediately after the dissolving of the areas near the surface in a solution containing iron ions based on sulfate by anodic switching of the component and that without intermediate rinsing in the same, in the same or in an equivalent electrolyte by cathodic switching of the Component the functional layer is applied and that the functional layer consists of iron.

It is achieved by the method according to the invention and the process sequence used in this way that the number of process steps known to date and previously necessary can be significantly minimized.

Until now, it was common practice to remove the natural oxide layer on the aluminum and to deposit a reoxidation layer on the aluminum, but now this intermediate step or the intermediate layer that is formed can be completely dispensed with.

The components are cleaned and freed from troublesome fats, oils, emulsions, pigments and similar impurities in the manufacturing process. After cleaning, rinse thoroughly with water. The surface of the components is then etched in a suitable solution, i. H. a certain amount of aluminum or alloy components close to the surface is dissolved. Then the component is again thoroughly rinsed with water.

According to the invention, the deposition of an intermediate layer does not follow, but the component is introduced directly into a sulfate-based electrolyte. The electrolytes usually used work on the basis of chloride, fluoroborate or ammonium sulfate. As described above, chloride electrolytes have a high level of aggressiveness, the fluoroborates have a high level of aggressiveness and toxicity, and the ammonium sulfate electrolytes have poor wastewater compatibility.

The invention is advantageously based on a sulfate-based electrolyte which is neither aggressive, nor toxic, nor harmful to waste water. According to the invention, the surface in the electrolyte is first activated by anodic switching of the component. The activation takes place, for example, in a solution with the following

Process parameters: in a solution with 300 g / 1 iron II sulfate heptahydrate (FeSO4 * 7H2O), at a temperature of 70 ° C, with a pH of 2, an activation current density of 2 A / dm ² and a treatment time of 20 seconds.

Then, according to the invention, the component without intermediate rinsing by cathodic switching of the component, using an iron electrolyte based on sulfate

Functional layer applied. This can be done in the same, but also in an equivalent electrolyte.

The invention is to be described below on the basis of further exemplary embodiments.

In Example 1, hard materials with a size of 0.5 to 2.0 μm are added to the electrolyte. As hard materials z. B. aluminum oxide, silicon nitride,

Chromium nitride, titanium carbide, cubic boron nitride as well as diamond particles can be used. The invention relates not only to these hard materials, but also includes all solids made from oxides or oxide ceramics, carbides and

Nitrides with a. These hard materials are mainly used individually, but can also be used as a mixture or mixtures.

Under the conditions according to the invention, an iron layer is formed, which contains about 15% by weight of the hard materials in finely divided form. The most secluded

Functional layer had excellent wear properties and had a hardness of approx. 400 HV 0.05.

In a further example 2, solid lubricants were added to the electrolyte, which were approximately 0.2 to 2.0 μm in size. Solid lubricants here include hexagonal boron nitride, carbon fluoride, graphite, molybdenum sulfide, Teflon, steel particles or microcapsules filled with oil. These solid lubricants can be used separately but also as a mixture or mixtures. The tests have shown that the solid lubricants have an extremely positive influence on the tribological system and that the friction coefficients were more favorable. A functional layer formed in which the solid lubricants were finely divided and were present with a share of approximately 20% by volume. In a further embodiment of the invention, given here as example 3, it is of course also possible that solid lubricants and hard substances can be contained together in the electrolyte, so that the positive properties of these two substances can be combined.

Under these conditions, an iron layer or functional layer separates, in which the two substances are finely divided and dispersive. The hardness of this layer was 350 HV 0.05.

In the series of experiments on Example 4, a sulfate-based electrolyte according to the invention containing 300 g / 1 iron II sulfate heptahydrate was used in a proportion of 5 ml / 1 of a hypophosphorous acid, e.g. B. H3PO2 added. The functional layer formed by the method according to the invention then had a hardness of 700 HV 0.05. With the help of proportions of phosphorus in the electrolyte, it is thus possible to influence the hardness of the layer in a targeted manner.

In Example 5, a hard material according to Example 1 was added to the phosphorus-containing electrolyte from Example 4. The hardness of the layer produced was 750 HV 0.05, which means that the hardness could be increased even further. The wear tests showed values similar to those in Example 1.

In a further embodiment example 6 of the idea according to the invention, a solid lubricant according to example 2 was added to the phosphorus-containing electrolyte from example 4. Under these conditions, a functional layer separated out as an iron layer, in which about 20% by volume of solid lubricants were contained in finely divided form.

The hardness of this layer was 650 HV 0.05. The results of the friction coefficient tests were better than those of the layers without phosphorus components. However, the results of the wear tests were comparable.

In the test series for Example 7, mixtures of solid lubricants and hard materials were added to the phosphorus-containing electrolyte. After that one forms Functional layer, which contains these substance mixtures in finely divided form. The hardness of this layer was 700 HV 0.05. The friction and wear values were comparable to those from example 4.

The applied functional layers were characterized by an excellent bond to the base material of the component. A functional layer applied according to the examples of the invention, as an iron layer, showed in an adhesion test under extreme conditions, e.g. B. thermal shock test, glass bead test and scratch test, an excellent bond to the base material and was comparable to the functional layers, which were applied with an adhesion-promoting intermediate layer based on zinc and copper and even superior in some areas.

The functional layer has an excellent bond to the base material and at the same time serves as the basis for one or more layers. The coating materials are named in the subclaims, but they can only be seen as examples. Since the functional layer is primarily formed from iron, any layer material that has an affinity for iron can be applied to the component or to the functional layer. In particular, these are all metallic materials, but also plastics and ceramics.

Also in the choice of the coating method, only examples can be mentioned in the subclaims. In principle, any method is suitable with which iron materials can also be coated. Electrochemical, with the u. a. Tin, copper, etc. can be deposited, thermal, with which u. a. Molybdenum, etc., and reactive processes. To be called u. a. high-speed flame spraying, plasma spraying, the PVD and CVD processes as well as screen printing processes or sprayed-on organic coatings.

With the method according to the invention and the resulting process sequence, it is now possible to significantly minimize the number of conventionally required process steps, to improve the quality of the products to be coated, to reduce manufacturing costs and to conserve environmental resources. These advantages make it possible to coat products with a range of uses even in market segments that could not previously be served due to cost reasons.

The method according to the invention is illustrated below using an exemplary embodiment and is explained in more detail below. It shows:

1 shows the cross section through the surface of a component coated according to Example 3 of the description.

FIG. 1 shows the cross section through a component 1 coated according to the invention. The figure shows the base material 2 and the functional layer 3 applied thereon. In the activation phase, the natural oxide layer on the base material 2 was removed and the components near the surface were dissolved, so that a clean surface 4 was available for coating. The functional layer 3 was directly deposited on this pure surface 4 by means of an electrolyte without an intermediate layer. According to Example 3, the functional layer 3 consists primarily of iron 5, in which hard materials 6 and solid lubricants 7 are finely distributed.

Claims

claims

1. A method for applying electrodeposited metal coatings (3) to components (1) made of aluminum or an aluminum alloy, in which the surface (4) of the component is cleaned in a suitable solution, in particular of oils, fats, emulsions, pigments, etc. , and that the surface (4) is then etched in a suitable solution, so that a certain amount of the material or the near-surface alloy components are dissolved and that after cleaning and after dissolving there is a rinsing with water, characterized in that the The surface (4) of the component (1) is activated immediately after the dissolving of the areas close to the surface in a sulfate-based solution containing iron ions by anodic switching of the component (1) and that without intermediate rinsing in the same, in an identical or in an equivalent Electrolyte by cathodic circuit of the component (1) on the functional layer (3) is brought and that the function layer (3) consists of iron (5).

2. The method according to claim 1, characterized in that the activation is carried out in a sulfate-based solution with 50-500 g / 1 iron II sulfate heptahydrate.

3. The method according to one of claims 1 and 2, characterized in that the activation of the component (1) in the solution is carried out with an exposure time between 5 seconds and 5 minutes.

4. The method according to any one of claims 1 to 3, characterized in that the activation of the surface (4) and the application of the functional layer is carried out with a direct current density of 2 to 20 A / dm ² .

5. The method according to any one of claims 1 to 4, characterized in that the activation is carried out in a solution with a pH between 0.5 and 2.5.

6. The method according to any one of claims 1 to 5, characterized in that the activation is carried out in a solution in a temperature range between 20 and 95 ° C.

7. The method according to any one of claims 1 to 6, characterized in that at least one hard material (6) is added to the electrolyte and that the hard material particles have a size between about 0.2 to 5 microns, wherein as hard material (6) aluminum oxide, silicon nitride , Chromium nitride, titanium carbide, cubic boron nitride as well as diamond particles is provided.

8. The method according to any one of claims 1 to 6, characterized in that at least one solid lubricant (7) is added to the electrolyte and wherein hexagonal boron nitride, carbon fluoride, graphite, molybdenum disulfide, Teflon or also oil-filled microcapsules are provided as the solid lubricant (7) and that the solid lubricant articles have a size between approximately 0.2 to 5 μm.

9. The method according to any one of claims 1 to 8, characterized in that at least one hard material (6) and at least one solid lubricant (7) is added to the electrolyte.

10. The method according to any one of claims 1 to 6, characterized in that in the electrolyte a hypophosphorous acid with 0.25 to 5 ml / 1, for. B. as H3PO2, preferably as 50% H3PO2 acid, is added.

11. The method according to any one of claims 1 to 6 and 10, characterized in that at least one hard material (6) is added to the electrolyte and that Hard material particles have a size between approximately 0.2 to 5.0 μm, aluminum oxide, silicon nitride, chromium nitride, titanium carbide, cubic boron nitride and diamond particles being provided as hard material (6).

12. The method according to any one of claims 1 to 6 and 10, characterized in that at least one solid lubricant (7) is added to the electrolyte and provided as the solid lubricant (7) hexagonal boron nitride, carbon fluoride, graphite, molybdenum disulfide, Teflon or also oil-filled microcapsules are and that the solid lubricant particles have a size between about 0.2 to 5.0 microns.

13. The method according to any one of claims 1 to 6 and 10, 11 and 12, characterized in that at least one hard material (6) and at least one solid lubricant (7) is added to the electrolyte.

14. The method according to any one of claims 1 to 13, characterized in that at least one further layer is applied to the functional layer (3).

15. The method according to any one of claims 1 to 14, characterized in that at least one further layer is applied to the functional layer (3) and that the layer made of at least one of the materials tin, copper, nickel, chromium made of ceramic or metal-ceramic materials, and all materials and alloys that have an affinity for iron (5) and form layers.

16. The method according to any one of claims 1 to 15, characterized in that at least one further layer is applied to the functional layer (3) and that the layer made of at least one of the materials tin, copper, nickel, chromium made of ceramic or metal-ceramic materials, and all materials that have an affinity for iron (5) and form layers, is formed and that the Layer is applied electrochemically, thermally or by means of a reactive process, in particular PVD or CVD.

17. The method according to any one of claims 1 to 16, characterized in that the component (1) contains at least one silicon alloy content of between 3 and 22% by weight.

18. Piston for an internal combustion engine, manufactured according to one of claims 1 to 17, characterized in that the functional layer (3) is applied directly to the surface (4) of the component (1).

19. Cylinder liner for an internal combustion engine, manufactured according to one of claims 1 to 17, characterized in that the functional layer (3) is applied directly to the surface (4) of the component (1)