WO2005035835A2

WO2005035835A2 - Workpieces coated with an aluminum/magnesium alloy

Info

Publication number: WO2005035835A2
Application number: PCT/EP2004/052097
Authority: WO
Inventors: Hans De Vries; Matthias HÄRTEL; Jörg HELLER
Original assignee: Aluminal Oberflächentechnik Gmbh & Co. Kg
Priority date: 2003-10-18
Filing date: 2004-09-09
Publication date: 2005-04-21
Also published as: CN1871375A; US20070212563A1; EP1675974A2; RU2353714C2; EP1524336A1; KR20060097016A; WO2005035835A3; RU2006117025A; JP2007509233A

Abstract

The invention relates to a coated workpiece comprising a substrate, a metallic intermediate layer applied to said substrate, and a layer containing an aluminum/magnesium alloy applied to the intermediate layer. The invention also relates to a method for producing this coated workpiece.

Description

Workpieces coated with an aluminum / magnesium alloy

The present invention is directed to workpieces coated with an aluminum / magnesium alloy, and to a process for their production.

[0002] The deposition of aluminum, magnesium or aluminum / magnesium alloys on workpieces which consist of base metal is a tried and tested means of protecting these workpieces from corrosion. At the same time, they are provided with a decorative coating. The protective metal layer is mainly electrodeposited on the workpiece. The deposited metal layer significantly improves the corrosion resistance of the workpiece. It turns out, however, that the corrosion resistance of the workpiece depends on the adhesion of the protective layer applied to the workpiece. If the protective layer does not adhere sufficiently to the workpiece, the protective layer is easily removed, e.g. B. at

1. Screwing a screw provided with a surface layer of aluminum, magnesium or an aluminum / magnesium alloy as a workpiece into a second workpiece. As a result, corrosion, particularly contact corrosion, occurs at these points. This corrosion inevitably leads to the destruction of the workpiece. Long-term prevention of corrosion is therefore not guaranteed.

20 achieves.

[0003] Various attempts have been made in the prior art to solve this problem.

DE 31 12 919 A1 proposes to provide metal-coated iron workpieces with an adhesion-promoting intermediate layer made of cobalt, cobalt alloys or nickel-containing cobalt and to galvanically apply an aluminum layer thereon. The intermediate layer serving as an adhesion promoter is applied galvanically from an aqueous medium. Optionally, after opening bring the galvano-aluminum layer on the bonding layer, the galvano-aluminum layer are chromated. This further improves the corrosion resistance.

[0005] DE 38 04 303 proposes a method for improving the adhesion of galvanic aluminum layers to metal workpieces by applying an adhesion-promoting layer. A non-aqueous electrolyte is used to apply the adhesive layer made of iron, iron and nickel, nickel, cobalt, copper and alloys of the above-mentioned metals or tin-nickel alloys. After the intermediate layer has been applied as an adhesion-promoting layer to a metal workpiece, a galvano-aluminum layer is applied to the intermediate layer. In this case, the application of the intermediate layer from a non-aqueous electrolyte is essential, since otherwise, when using an aqueous electrolyte, the metal workpiece becomes embrittled due to the hydrogen generated during the electrolysis. As a result, the often used low-alloy high-strength steels are adversely affected. Embrittlement of the workpieces is avoided by using a non-aqueous electrolyte to apply the metallic intermediate layer.

[0006] Both DE 31 21 919 A1 and DE 38 04 303 A1 apply pure galvano-aluminum layers to the workpieces provided with an intermediate layer. Both documents do not describe the application of aluminum / magnesium alloys to workpieces.

[0007] EP 1 141 447 B1 describes electrolytes for coating

Workpieces with layers of an aluminum / magnesium alloy are disclosed. Such a coating is particularly necessary if connections with magnesium parts are to be created because the corrosion products of the magnesium metal are alkaline and attack the aluminum surface coatings. The use of aluminum / magnesium alloys prevents contact corrosion and ensures long-term durability of the coating. It It is proposed to coat steel fastening elements for contact with magnesium components, especially in the automotive industry with aluminum / magnesium alloys. EP 1 141 447 B1 does not disclose any metallic intermediate layers which are arranged between the workpiece and the corrosion-reducing layer made of an aluminum / magnesium alloy.

The aluminum / magnesium applied to a workpiece

Prior art layers are very hard and brittle. Are fasteners that are provided with an aluminum / magnesium layer, such as. B. screws, used to fasten components, there is a risk that the screws roughen the components by the aluminum / magnesium layer applied to the fastener and destroy them in the worst case. This risk is particularly so when the components are made of relatively soft or brittle materials, such as. B. made of magnesium. Due to the superficial destruction of the component, this can in turn be exposed to increased corrosion, which can lead to the destruction of the component.

However, there is also a risk that the aluminum / magnesium layer, which is applied to the fastener, breaks off and thus the base material of the fastener, such as. B. iron or steel is exposed. The result of such exposure of the base material, which is susceptible to corrosion, is in turn increased corrosion of the fastening means by contact corrosion.

[0010] Basically, the above-described corrosion occurs increasingly at high pH values, so that in both of the aforementioned cases of destruction of the surface layer of the fastening means or of the component, the rate of corrosion increases at high pH values.

[0011] The technical object of the present invention is to provide coated workpieces which have improved corrosion resistance, have in particular in the alkaline range and, in combination with other materials, show reduced corrosion, in particular if the coated workpieces are used as fastening means for fastening components.

The technical object of the present invention is achieved by a coated workpiece comprising a substrate, a metallic intermediate layer applied to the substrate and a layer applied to the intermediate layer containing an aluminum / magnesium alloy.

[0013] In a preferred embodiment, the surface of the substrate is electrically conductive. This can preferably be done by coating the substrate with graphite.

[0014] The substrate preferably contains a metal and / or a metal

Alloy. Alternatively, the substrate can be a metallized substrate, wherein the substrate can be metallized over the entire surface or over part of the surface. Preferred substrates contain plastics.

[0015] The substrate can furthermore be selected from the ingredients

Group iron, steel, iron alloy, non-ferrous metals, zinc die casting, aluminum die casting, titanium, titanium as an alloy, magnesium, magnesium die casting or mixtures thereof, wherein the aforementioned metals are preferably present as an alloy component in the substrate ,

The metallic intermediate layer preferably contains iron, iron and nickel, tin and nickel, nickel, cobalt, copper, chromium, molybdenum, vanadium or alloys of the above-mentioned metals.

The metallic intermediate layer preferably has a layer thickness of 0.1 μm to 30 μm. In a further preferred embodiment, the Layer thickness of the metallic intermediate layer 0.5 μm to 20 μm, more preferably 1 μm to 10 μm and most preferably 1.5 μm to 8 μm

The applied to the metallic intermediate layer containing an aluminum / magnesium alloy preferably contains 0.5 to 70 5 wt.% Magnesium. In a further preferred embodiment, 1 to 50% by weight, more preferably 2 to 40% by weight, in a further preferred embodiment 3 to 30% by weight, preferably 4 to 25% by weight and most preferably 5 to 20% by weight. % Magnesium contained in the aluminum / magnesium alloy.

[0019] The layer containing an aluminum / magnesium alloy preferably has a layer thickness of 0.1 μm to 100 μm. In a further preferred embodiment, the layer thickness is 0.5 μm to 70 μm, more preferably 1 μm to 50 μm, preferably 2 μm to 40 μm, more preferably 3 μm to 30 μm, more preferably 4 μm to 28 μm and most preferred 5 μm to

15 25 μm.

The layer containing the aluminum / magnesium alloy is preferably the surface layer of the coated workpiece. Alternatively, at least one layer can also be applied to the layer containing the aluminum / magnesium alloy, which is preferably a passivation ₂ o.

The coated workpiece is preferably a rack, bulk goods or a continuous product, wherein the coated workpiece is preferably a wire, a sheet, a screw, a nut, a concrete anchor, a fastener or a machine component. The coated workpiece is preferably used in the automotive industry in the transmission, engine and body area. It can be an oil pan or a transmission oil pan. Another object of the present invention is to provide a method for producing a coated workpiece, comprising the steps of: a) applying a metallic intermediate layer to a substrate and b) applying a layer containing an aluminum / magnesium alloy to the metallic intermediate layer ,

Preferably, in step a) the metallic intermediate layer is deposited from an aqueous solution or a non-aqueous solution.

[0024] In a preferred embodiment, the metallic intermediate layer is chemically deposited.

Alternatively, in step a) the metallic intermediate layer can be electrodeposited from an aqueous electrolyte. Possible electrolytes are solutions of the metal salts of iron, cobalt, nickel, copper or tin. These can be in the form of halides, sulfates, sulfonates or fluoroborates. The electrolytes can contain further additives, such as, for example. B. complexing substances.

Alternatively, it is also possible in step a) to electrodeposit the metallic intermediate layer from a non-aqueous electrolyte. Possible electrolytes contain compounds of molybdenum or vanadium or all other aforementioned metals, which the intermediate layer can contain. The metals are preferably in the form of halides which can be complexed or reacted with ether, in particular diethyl ether and / or acetylacetonate (acac), to give corresponding metal acetylacetonates. In step b), the layer containing an aluminum / magnesium alloy is preferably deposited from an anhydrous electrolyte. In a further preferred embodiment, the layer containing an aluminum / magnesium alloy is electrodeposited from a water-free electrolyte in step b). Any electrolyte which is known to the person skilled in the art can be used as the electrolyte. In particular, the electrolyte contains organoaluminum compounds of the general formulas (I) and (II)

M [(R ¹ ) 3AI- (H-AI (R ² ) ₂ ) _n -R ³ ] (I) AI (R ⁴ ) ₃ (II)

where n is 0 or 1, M is sodium or potassium and R ¹ , R ² , R ³ , R ^{4 may be the} same or different, where R ¹ , R ² , R ³ , R ^{4 is} a Ci to C Al- are alkyl group and a halogen-free, aprotic solvent is used as the solvent for the electrolyte.

A mixture of the complexes K [AIEt ₄ ], Na [AlEtJ and AIEt ₃ can be used as the electrolyte. The molar ratio of the complexes to AIEt ₃ is preferably 1: 0.5 to 1: 3 and more preferably 1: 2.

[0029] The electrolytic deposition of the layer containing an aluminum / magnesium alloy on the workpiece is carried out using a soluble aluminum and a likewise soluble magnesium anode or using an anode made of an aluminum / magnesium alloy.

The electrolytic coating is preferably carried out at a temperature of 80 to 105 ° C. A temperature of the electroplating bath of 91 to 100 ° C. is preferred

In a preferred embodiment, a layer that conducts the electrical current is applied to the substrate before the metallic intermediate layer is applied in step a). The layer which conducts the electrical current can be applied to the substrate by any method which is known to the person skilled in the art. The layer that conducts the electrical current is preferably applied to the substrate by metallization.

When the coated workpiece of the present invention as

If fasteners are used, unexpectedly no impairment of the coated workpiece occurs. Although a surface layer made of an aluminum / magnesium alloy is very hard, brittle and not very ductile, it still adheres very firmly to the coated workpiece after and during use as a fastener. Furthermore, the coating used, consisting of the intermediate layer and the surface layer, is so elastic that it has not adversely changed after use as a fastening means. If the coated workpiece e.g. screwed into a component as a screw, the surface treatment of the workpiece yields unexpectedly. This then leads to a further reduction in the stress on the coated workpiece. Since the metallic intermediate layer and the surface layer containing an aluminum / magnesium alloy are not destroyed, the coated workpiece is reliably protected against corrosion, in particular against contact corrosion, even after and during its use.

These advantages mentioned do not have the prior art workpieces provided with an aluminum / magnesium coating. Either the surface layer consisting of an aluminum / magnesium layer is destroyed, so that corrosion of the workpiece then occurs, or else the very hard and brittle layer of aluminum / magnesium alloy of the prior art workpieces destroys the surface of the components to be fastened in such a way that that they are subsequently exposed to increased corrosion.

The present invention is illustrated by the following examples, but without being restricted to these: Examples:

example 1

A sheet of size 100 x 25 x 1 mm made of St37 steel is provided with a nickel intermediate layer with a thickness of approx. 1 μm. The nickel layer is electrodeposited from an aqueous nickel sulfamate electrolyte. A layer of an aluminum / magnesium alloy with a magnesium content of 20% by weight and a layer thickness of 12 μm is subsequently deposited on the nickel layer by electrodeposition from a non-aqueous electrolyte. The coated sheet is bent lengthwise through an angle of 180 °, the applied metal layers remaining intact in the area of the bending edge.

Comparative Example 1:

A sheet of size 100 x 25 x 1 mm made of St37 steel is provided with a layer of an aluminum / magnesium alloy with a magnesium content of 20% by weight and a layer thickness of 12 μm by electrodeposition from a non-aqueous electrolyte. The sheet coated in this way is bent lengthwise through an angle of 180 °, parts of the coating tearing open at the bending edge and flaking off in the form of the finest needles.

Example 2

Five M6 x 55 screws are provided with an aluminum / magnesium alloy with a magnesium content of 15% by weight and a layer thickness of 16 μm by electrodeposition from a non-aqueous electrolyte. Five additional M6 x 55 screws are covered with a nickel layer with a layer thickness of approx. 1 μm. The nickel layer is electrodeposited from an aqueous nickel sulfamate electrolyte. An aluminum / magnesium alloy with a magnesium content of 15% by weight and a layer thickness of 16 μm is subsequently applied to the nickel layer by electrodeposition from a non-aqueous electrolyte.

All screws are screwed up to half in a nut of the appropriate size and then out again. The screws treated in this way are then hung in a salt spray chamber and their corrosion behavior is examined. It turns out that it takes a long time for the screws that have been provided with an intermediate nickel layer before the screws start to show corrosion.

Example 3

M5 x 5 screws are electroplated in a drum with an aluminum / magnesium alloy with a magnesium content of 10% by weight and an average layer thickness of 14 μm from a non-aqueous electrolyte.

Additional screws are provided with an intermediate nickel layer with a layer thickness of approx. 1-2 μm nickel. The nickel layer is electroplated from an aqueous nickel sulfamate electrolyte. Subsequently, a layer of an aluminum / magnesium alloy with a magnesium content of 10% by weight and an average layer thickness of 15 μm from a non-aqueous electrolyte is applied galvanically to the nickel layer in a drum.

Three screws with the same coating are inserted as far as possible into a housing made of an aluminum / magnesium alloy with a screw screwed in suitable diameter nut. The corrosion behavior in a salt spray chamber is examined below. It can be seen that the housings into which the screws were screwed with an intermediate layer of nickel only corrode significantly later. The housing with the screws without an intermediate nickel layer shows the first signs of corrosion at an earlier point in time.

In summary, it can be determined from the examples mentioned above that the metallic intermediate layer causes a significant improvement in the corrosion resistance. Coated workpieces comprising a substrate, a metallic intermediate layer applied to the substrate and a layer containing an aluminum / magnesium alloy applied to the intermediate layer show a superior property profile which the prior art workpieces do not have.

Claims

claims

1. A coated workpiece comprising a substrate, a metallic intermediate layer applied to the substrate and a layer applied to the intermediate layer containing an aluminum / magnesium alloy.

5 2. The coated workpiece according to claim 1, characterized in that the surface of the substrate is electrically conductive.

3. The coated workpiece according to claim 1 or 2, characterized in that the substrate contains a metal and / or a metal alloy and / or is a metallized substrate. O

4. The coated workpiece according to one or more of the preceding claims, characterized in that the substrate ingredients selected from the group iron, steel, iron alloy, non-ferrous metals, zinc die casting, aluminum die casting, titanium, titanium as an alloy, Contains magnesium, magnesium die casting or mixtures thereof, the aforementioned metals preferably being present in the substrate as an alloy component.

5. The coated workpiece according to one or more of the preceding claims, characterized in that the intermediate layer contains iron, iron and nickel, tin and nickel, nickel, cobalt, copper, chromium, molybdenum, vanadium or alloys of the aforementioned metals. 0

6. The coated workpiece according to one or more of the preceding claims, characterized in that the intermediate layer has a layer thickness of 0.1 μm to 30 μm.

7. The coated workpiece according to one or more of the preceding claims, characterized in that the applied on the intermediate layer brought layer containing an aluminum / magnesium alloy containing 0.5 to 70 weight percent magnesium.

8. The coated workpiece according to one or more of the preceding claims, characterized in that the layer applied to the intermediate layer containing an aluminum / magnesium alloy has a layer thickness of 0.1 μm to 100 μm.

9. The coated workpiece according to one or more of the preceding claims, characterized in that the coated workpiece is a rack, bulk goods or an endless product, wherein the coated workpiece is preferably a wire, a sheet, a screw, a nut, a Is concrete anchoring or a machine component.

10. A method for producing a coated workpiece comprising the steps: a) applying a metallic intermediate layer to a substrate and b) applying a layer containing an aluminum / magnesium alloy to the metallic intermediate layer.

11. A method for producing a coated workpiece according to claim 10, characterized in that in step a) the metallic intermediate layer is deposited from an aqueous solution or a non-aqueous solution.

12. A method for producing a coated workpiece according to claim 10 or 11, characterized in that in step a) the metallic intermediate layer is electrodeposited from an aqueous electrolyte.

13. A method for producing a coated workpiece according to claim 10, characterized in that in step b) the layer containing an A- aluminum / magnesium alloy is deposited from an anhydrous electrolyte.

14. A method for producing a coated workpiece according to claim 13, characterized in that in step b) the layer containing an aluminum / magnesium alloy is electrodeposited from the anhydrous electrolyte.

15. A method for producing a coated workpiece according to one or more of claims 10 to 14, characterized in that a layer which conducts the electrical current is applied to the substrate before the metallic intermediate layer is applied in step a).

16 Method for producing a coated workpiece according to claim 15, characterized in that the layer conducting the electrical current is applied by metallizing the substrate.