EP4251792A1

EP4251792A1 - Ruthenium alloy layer and its layer combinations

Info

Publication number: EP4251792A1
Application number: EP21820188.7A
Authority: EP
Inventors: Sascha Berger; Klaus Bronder; Uwe Manz; Martin Pohl; Martin Stegmaier; Matthias Wahl
Original assignee: Umicore Galvanotechnik GmbH
Current assignee: Umicore Galvanotechnik GmbH
Priority date: 2020-11-26
Filing date: 2021-11-25
Publication date: 2023-10-04
Also published as: JP2023550807A; CN116157557A; WO2022112379A1; KR20230113355A; DE102020131371B4; US20240018679A1; DE102020131371A1

Abstract

Aqueous electrolyte for deposition of a ruthenium alloy layer on metal surfaces, in particular base metal surfaces, its use and a corresponding electrolytic process, and a correspondingly produced layer sequence.

Description

Ruthenium alloy layer and their layer combinations

description

The present invention is directed to an aqueous electrolyte for depositing a ruthenium alloy layer onto metallic surfaces, particularly base metallic surfaces. Another subject of the present invention is the use of the electrolyte according to the invention for the production of ruthenium alloy layers on corresponding surfaces by an electrolytic process, which is also a subject of the invention. Finally, the invention also encompasses layer sequences which have a ruthenium alloy layer deposited in this way.

Consumer goods and technical items, pieces of jewelry and decorative items are finished with thin, oxidation-resistant metal layers to protect against corrosion and/or to enhance their appearance. These layers must be mechanically stable and should not show any tarnishing or signs of wear even after prolonged use. A tried and tested means of producing such layers are galvanic processes, with which a large number of metal and alloy layers can be obtained in high-quality form. Well-known examples from everyday life are galvanic bronze and brass layers on door handles or buttons, chrome coatings on vehicle parts, galvanized tools or gold coatings on watch straps.

In this context, galvanic deposits of palladium and its alloys have also been known for a long time. Because of its light color, outstanding electrical properties, hardness, contact resistance and corrosion resistance as well as its stability, palladium is often used as a coating for, for example, electrical connectors, printed circuit boards, decorative applications and many other industrial and commercial uses. As a substitute material for gold and platinum, palladium represents an economical, more cost-effective alternative, since palladium also has a wide range of possible uses. Alloys of palladium with base metals such as nickel or cobalt are less expensive than pure precious metals, so such alloys have been and are used for a long time. Coatings of such palladium alloys are often produced by electrodeposition from Palladiumle alloy electrolytes. Nowadays, the price of palladium has skyrocketed, so that cheaper alternatives are being sought, with which the use of palladium can be avoided with otherwise the same properties. Here, the view of the person skilled in the art is directed, among other things, to the use of much cheaper ruthenium.

The ruthenium baths and processes described in the prior art often relate to the deposition of black ruthenium and ruthenium alloy layers and may contain toxicologically questionable compounds such as thio compounds as blackening additives (e.g. DE102011105207B4 and the literature cited there). Due to their acidic character, these baths often only allow deposition on metals that are relatively noble in character (e.g. DE1959907A1).

According to US4082625, light-colored ruthenium deposits can also be obtained in the basic range. A process for the deposition of ruthenium is described, which works in a pH range of 9-10. In this pH range, the ruthenium is kept in solution by complexing anions (EDTA, NTA, CDTA). Stable and bright deposits of ruthenium are obtained.

A nitridochloro complex of ruthenium can be used in an aqueous, non-acidic bath for the electrodeposition of ruthenium. Such a method is described in US4297178. It also contains oxalic acid or an oxalate anion. According to this, only pure ruthenium deposits are generated, which, however, cannot replace palladium and palladium alloy deposits in this form without disadvantages.

Ruthenium deposits are mentioned, inter alia, in US3692641 or GB2101633. In the former, deposits of ruthenium with other precious metals, among others, are propagated. In the latter, ruthenium alloy deposits in an acidic environment are addressed.

WO18142430A1 describes the production of differently colored ruthenium or ruthenium alloy deposits, inter alia, with metals such as Ni, Co, Cu, Sn, etc. It is mentioned that deposits on base metallic substrates are possible. However, only strongly acidic electrolytes are presented here, which is why direct deposition on these substrates is certainly not possible. A possibility is also being sought of successfully avoiding palladium-containing layers in electrolytic deposition practice. For this, the replacing layers should have properties that are as similar as possible to layers containing palladium. This should apply in particular with regard to, inter alia, appearance, corrosion resistance, abrasion resistance and cracking characteristics. It should also be possible to deposit corresponding layers on base metal surfaces in order to be able to replace the Pd strike depositions that are frequently used for this purpose. In addition, replacing the palladium should of course result in cost savings.

These and other tasks to be solved by those skilled in the art are solved by specifying an electrolyte according to present claim 1. Claims 2 to 7 are directed to preferred configurations of the electrolyte according to the invention. Claims 8, 12 and 15, respectively, are directed with the corresponding subclaims to the use of the electrolyte, a method for electrolytic deposition from the electrolyte and a layer sequence obtainable therewith.

By using an aqueous electrolyte for the deposition of ruthenium alloys on base metal surfaces in particular, comprising: a) ruthenium as a binuclear, anionic ruthenium nitrido complex of the formula [RU ₂ N(H ₂ 0) ₂ X ₈ ] ³ , where X is one or more simple or multiply negatively charged counterions, such as halide ions, hydroxide ions or other anionic ligands (eg sulfate, phosphate, oxalate, citrate), in a concentration of 0.5-20 g/l based on ruthenium as the metal; b) one or more alloying metals dissolved in ionic form, selected from the group consisting of: Cu, W, Fe, Co, Ni, In, Zn, Sn, Pd, Pt in a concentration of 0.5 - 10 g/l each related to the metal; c) one or more anions of a di-, tri- or tetracarboxylic acid in a concentration of 0.05-2 moles per liter; d) one or more anionic surfactants in a concentration of 0.1 - 500 mg/l; where the electrolyte indicates a pH of 5 to 10, one surprisingly achieves the solution to the problems presented above. With the electrolyte presented here, layers of ruthenium alloys that are similar in color to the palladium deposits can be deposited, which have high corrosion resistance, low cracking tendency and high hardness and thus high abrasion resistance. Ruthenium is preferably used in the form of a water-soluble compound known to those skilled in the art as a binuclear, anionic nitridohalogeno complex compound of the formula [RU ₂ N(H ₂ O) ₂ X ₈ ] ³ , where X is a halide ion. The chloro complex [Ru ₂ N(H ₂ O) ₂ Cl ₈ ] ³ is particularly preferred in this context. The amount of the complex compound in the electrolyte according to the invention can preferably be chosen such that the concentration of ruthenium after complete dissolution of the compound is between 1 and 20 grams per liter of electrolyte, calculated as ruthenium metal. The finished electrolyte particularly preferably contains 1 to 10 grams of ruthenium per liter of electrolyte, very particularly preferably 3 to 7 grams of ruthenium per liter of electrolyte.

The electrolyte contains certain organic compounds that have one or more carboxylic acid groups. In particular, these are di-, tri-, or tetracarboxylic acids. These are well known to those skilled in the art and can be found, for example, in literature (Beyer-Walter, Textbook of Organic Chemistry, 22nd edition, S. Hirzel-Verlag, p. 324 ff). be removed. In this context, particular preference is given to acids selected from the group consisting of oxalic acid, citric acid, tartaric acid, succinic acid, maleic acid, glutaric acid, adipic acid, malonic acid and malic acid. Oxalic acid is particularly preferred in this connection. The acids are naturally present in their anionic form in the electrolyte at the pH value to be set. The carboxylic acids mentioned here are added to the electrolyte in a concentration of 0.05-2 moles per liter, preferably 0.1-1 mole per liter and very particularly preferably between 0.2-0.5 mole per liter. This applies in particular to the use of oxalic acid, which is believed to also serve as a conducting salt in the electrolyte.

In the electrolyte according to the invention, anionic surfactants are used as wetting agents. These are, for example, those selected from the group consisting of fatty alcohol sulfates, alkyl sulfates, alkyl sulfonates, aryl sulfonates, alkylaryl sulfonates, heteroaryl sulfates and their salts and in particular their alkoxylated derivatives (see also: Kanani, N: Galvanotechnik; Hanser Verlag, Munich Vienna, 2000; page 84 ff). Ethoxylated sodium fatty alcohol (C12-C14) ether sulfate or sodium fatty alcohol sulfate (C12-C14) are particularly preferred.

The pH of the electrolyte is preferably in the only slightly acidic to slightly alkaline range. According to the invention, the pH is adjusted to a range between 5 and 10. More preferably, the pH of the electrolyte in use is between 6 and 9, most preferably between 7 and 8 pH adjusted to approx. 7.5. The pH value is kept constant during the electrolysis by adding buffer substances. These are well known to those skilled in the art (Handbook of Chemistry and Physics, CRC Press, 66th Edition, D-144 ff). Preferred buffer systems are borate, phosphate and carbonate buffers. Compounds for producing these buffer systems can be selected from the group consisting of boric acid, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, potassium hydrogen carbonate or dipotassium carbonate. The buffer system comes in a concentration of 0.08-1.15 moles per liter, preferably 0.15-0.65 moles per liter and very particularly preferably 0.2-0.4 moles per liter (based on the anion) for use.

Naturally, further substances that are advantageous for the deposition can be added to the electrolyte discussed here. These are well known to those skilled in the art. Preference is given to those selected from the group consisting of conductive salts and brightening additives, etc. (Praktische Galvanotechnik, 5th edition, Eugen G. Leuze Verlag, Bad Saulgau, p. 39 et seq.). Preferred conductive salts are those selected from the group consisting of alkali metal sulfates, ammonium sulfate, ammonium chloride and ammonium oxalate.

In addition to the ruthenium, other dissolved metals are also present in the electrolyte. These are electrolytically deposited together with the ruthenium as a ruthenium alloy layer. There are those selected from the group consisting of: Cu, W, Fe, Co, Ni, In, Zn, Sn, Pd, Pt in question. These are usually dissolved as salts, in particular as sulfates in the electrolyte. In this context, it is particularly preferred if the alloying metal is selected from the group consisting of Ni, Sn, Zn, Co and Pd. It is extremely preferred to use Ni. The alloying metals are present in the electrolyte in a concentration of 0.1 - 10 g/l each. The concentration of the alloying metal is preferably 1-6 g/l and very particularly preferably 2-5 g/l. It has been found that the addition of the alloying metal to the electrolyte according to the invention in the specified concentration ranges helps in particular to improve the corrosion resistance and the tendency for the ruthenium layer to form cracks. Ni in particular has shown good results here.

The present electrolyte can contain sulphur-containing compounds, such as the wetting agents or surfactants mentioned above. However, it is advantageous if the electrolyte does not contain any sulfur-containing compounds in which the sulfur is present in an oxidation state of <+4. In particular, blackening additives based on sulfur compounds are not present in the electrolyte according to the invention. The present electrolyte does not produce a black or dark anthracite-colored deposit, but rather a greyish, metallic-looking deposit. It is thus even similar in appearance to the Pd and Pd alloy deposits to be replaced. The a* value is preferably between -3 and +3 and the b* value between -7 and +7 according to the Cielab color system (EN ISO 11664-4 - latest version on the filing date).

The present invention also relates to the use of the electrolyte just described for the production of articles with an electrolytically deposited alloy metal layer, in particular on base metal surfaces, containing the metals ruthenium and one or more of the alloy metals dissolved in ionic form, selected from the group consisting of: Cu, W, Fe, Co, Ni, In, Zn, Sn, Pd, Pt, where the alloy metal layer has a corrosion resistance similar to that of the corresponding palladium containing layers. The alloying of the listed metals also means that the tendency to form cracks during electrolytic deposition is significantly reduced compared to pure ruthenium deposits. The tendency to form cracks is preferably determined by optical assessment in a light microscope at 20x magnification. Noble metal underlayers upon which the ruthenium alloy layer can be deposited are known to those skilled in the art. According to the invention, base metal surfaces include those which are unstable in an acidic or more basic environment and tend to dissolve. Preferred base metal sub-layers for the ruthenium alloy layer are those selected from the group consisting of copper, copper alloys, nickel or nickel alloys.

The ruthenium alloy layer that can be obtained by using the electrolyte according to the invention can have a specific thickness as determined by a person skilled in the art. Preferably, the thickness of the alloy metal layer is 0.05 - 5 µm, more preferably 0.05 - 2 µm, and most preferably 0.05 - 1 µm. Furthermore, the alloy metal layer is preferably used as a sub-layer for a further metal layer to be electrolytically deposited, just as is the case, for example, for Pd or Pd-Ni layers. The metal layer deposited on the ruthenium alloy layer can consist, for example, of noble metals such as Ag, Au, Pt, Rh or their alloys and generally has a thickness of 0.03-10 μm, preferably 0.05-3 μm and very preferably 0 ,1 - 1 p.m. It has been found that the metal deposits discussed here (for the ruthenium alloy layer itself and for the layer sequence) have a very high abrasion resistance, which is particularly advantageous both for jewelry and for technical applications (e.g. as a contact material). In the so-called Bosch-Weinmann test (Bosch-Weinmann, AM Erichsen GmbH, publication 317 / D - V / 63, or Weinmann K., Farb und Lack 65 (1959), pp 647-651), the metal deposits of the ruthenium alloy also achieve values below 0.25 μm/1000 strokes with the electrolyte according to the invention. Further advantageous are even less than 0.1 μm/1000 strokes and very advantageously less than 0.08 μm/1000 strokes in the realm of feasibility. For such abrasion-resistant metal deposits, the composition of the ruthenium alloy layer is very preferably 95:5 to 80:20, most preferably 90:10 to 80:20, based on the weight ratio of ruthenium to the other metal(s).

The subject matter of the present invention is also a method for depositing an alloy metal layer on, in particular, base metal surfaces, in which: a) the metal surface as the cathode is contacted with an aqueous electrolyte as just described; b) contacting an anode with the electrolyte; c) and established a sufficient current flow between cathode and anode.

It should be mentioned that the embodiments described as preferred for the electrolyte and its use also apply, mutatis mutandis, to the process addressed here. The current density established during the deposition process in the electrolyte between the cathode and the anode can be chosen by those skilled in the art based on the efficiency and quality of the deposition. The current density in the electrolyte is advantageously set to 0.1 to 50 A/dm ² depending on the application and the type of coating system. If necessary, the current densities can be increased or decreased by adjusting the system parameters such as the structure of the coating cell, flow rates, anode and cathode conditions, etc. A current density of 0.2-25 A/dm ² , preferably 0.25-15 A/dm ² and very particularly preferably 0.25-10 A/dm ² is typically advantageous. Most preferably, the current density is 0.25-5 A/dm ² . The selected current density value is also determined by the type of coating process. In a drum coating process lies the preferred current density between 0.25 to 5 A/dm2. In rack coating processes, a current density of 0.5 to 10 A/dm2 gives better results.

Typically, thin layer thicknesses in the range from 0.1 to 0.3 μm are produced in rack operation. Here, low current densities in the range from 0.25 to 5 A/dm ² are advantageously used. Another application of low current densities is in drum or vibration technology, for example when coating contact pins. Here, approx. 0.25 to 0.5 μm thick layers are applied in the current density range from 0.25 to 0.75 A/dm ² . Layer thicknesses in the range from 0.1 to 1.0 μm are typically deposited in rack operation, primarily for decorative applications with current densities in the range from 0.25 to 5 A/dm ² .

Pulsed direct current can also be used instead of direct current. The current flow is interrupted for a certain period of time (pulse plating). With reverse pulse plating, the polarity of the electrodes is reversed so that the coating is partially anodicly detached. In this way, the layer structure is controlled in constant alternation with cathodic pulses. The use of simple pulse conditions such as 1 s current flow (t _on ) and 0.5 s pulse pause ( ) with medium current densities leads to more homogeneous coatings (pulse plating, J.-C. Puippe, F. Leaman, Eugen G. Leu- zeverlag, Bad Saulgau, 1990).

When using the electrolyte according to the invention, insoluble anodes can preferably be used. The insoluble anodes used are preferably those made from a material selected from the group consisting of platinized titanium, graphite, mixed metal oxides, glassy carbon anodes and special carbon material (“diamond-like carbon” DLC) or combinations of these anodes. Insoluble anodes made of platinized titanium or titanium coated with mixed metal oxides are advantageous, the mixed metal oxides preferably being selected from iridium oxide, ruthenium oxide, tantalum oxide and mixtures thereof. Iridium transition metal oxide mixed oxide anodes, particularly preferably mixed oxide anodes made from iridium-ruthenium mixed oxide, iridium-ruthenium-titanium mixed oxide or iridium-tantalum mixed oxide, are also used advantageously for carrying out the invention. More can be found at Cobley, AJ et al. (The use of insoluble anodes in Acid Sulphate Copper Electrodeposition Solutions, Trans IMF, 2001, 79(3), p. 113 and 114). The deposition of the ruthenium alloy layers on, in particular, base metallic objects according to the present invention can be carried out as follows, taking into account the above:

For the galvanic application of the ruthenium alloy layer, the pieces of jewelry, decorative goods, consumer goods or technical objects to be coated are immersed in the electrolytes according to the invention (collectively referred to as substrates). These form the cathode. An anode made of, for example, platinized titanium (product information PLATINODE ^® from Umicore Galvanotechnik GmbH) is also immersed in the electrolyte. A corresponding current flow is then ensured between the anode and the cathode. A maximum current density of 10 amperes per square decimeter [A/dm ² ] has proven advantageous in order to obtain adherent, uniform layers.

The temperature which the electrolyte has during the deposition can be adjusted accordingly by a person skilled in the art. The temperature range to be set is advantageously a range of 20-80.degree. A temperature of 50° to 75° C. and particularly preferably 60° to 70° C. is preferably set. It can be advantageous if the electrolyte under consideration is stirred during the deposition.

Suitable substrate materials that are advantageously used here are copper-based materials such as pure copper, brass or bronze, ferrous materials such as iron or stainless steel, nickel, gold and silver. The substrate materials can also be multi-layer systems that have been coated galvanically or with another coating technique. This applies, for example, to circuit board base material or iron materials that have been nickel- or copper-plated and then optionally gold-plated or coated with pre-silver. Another substrate material is, for example, a wax core that has been pre-coated with conductive silver lacquer (so-called electroforming).

A further object of the present invention is a metallic layer sequence comprising a substrate equipped with a base metal surface in particular, an alloy metal layer electrolytically applied thereto produced by the method according to the invention with a thickness as described above and a metal layer of noble metals such as e.g. Ag, Au, Pt or Rh and their alloys with a thickness also as previously described. The thicknesses of the layers can be in the ranges given above preferred areas vary. The preferred embodiments described for the electrolyte, its use and the method according to the invention are also used mutatis mutandis for the layer sequence described here.

The ruthenium alloy layer described here represents an adequate replacement for the expensive Pd or Pd alloy layers, in particular Pd-Ni layers. Wherever the latter are used advantageously, the ruthenium alloy layer described here can represent a more cost-effective alternative. A precious metal layer can be applied as a finish to the ruthenium alloy layer according to the invention, particularly in the case of items of jewelry. Rhodium, platinum, gold and silver are particularly suitable as noble metals. The person skilled in the art knows how to carry out such a finish.

However, the ruthenium alloy layer can also be established as a Pd or Pd-Ni substitute in electronic articles. Here form rhodium. Rhodium alloys e.g. RhRu), platinum, platinum alloys (PtRh, PtRu) or gold preferred top layers. Thin palladium or palladium-nickel layers can also be applied as top layers. The top layer to be applied and its layer thickness depends on the application and is known to the person skilled in the art.

The present invention can be preferably used in barrel and rack coating processes. With the electrolyte described here, it is possible to achieve particularly crack-free, corrosion-resistant and abrasion-resistant deposits of ruthenium alloys on a corresponding substrate that are similar to Pd deposits. Furthermore, it is possible to work with the electrolyte in the neutral range, which for the first time allows the deposition of ruthenium alloy coatings on base metals without having to provide them with a noble intermediate layer beforehand. Against the background of the known state of the art, this was by no means obvious. Examples:

1 liter of the electrolyte specified in the respective exemplary embodiment is heated to the temperature specified in the exemplary embodiment using a magnetic stirrer while stirring with a 60 mm long cylindrical magnetic stirring rod at at least 200 rpm. This agitation and temperature is also maintained during coating.

After the desired temperature has been reached, the pH of the electrolyte is adjusted to the value specified in the exemplary embodiment using a KOH solution (c=0.5 g/ml) and sulfuric acid (c=25%). Expanded metal sections made of platinized titanium serve as anodes.

A mechanically polished brass sheet with a surface area of at least 0.2 dm ² is used as the cathode. This can be coated beforehand with at least 5 μm of nickel from an electrolyte, which produces high-gloss layers. A gold layer approximately 0.1 μm thick can also be deposited on the nickel layer. Before being introduced into the electrolyte, these cathodes are cleaned with the aid of electrolytic degreasing (5-7 V) and desmutting containing sulfuric acid (c= 5% sulfuric acid). Between each cleaning step and before entering the electrolyte, the cathode is rinsed with deionized water.

The cathode is positioned in the electrolyte between the anodes and moved parallel to them at at least 5 cm/second. The distance between anode and cathode should not change.

In the electrolyte, the cathode is coated by applying an electrical direct current between the anode and cathode. The amperage is chosen so that at least 0.5 A/dm ² is reached on the surface. Higher current densities can be selected if the electrolyte mentioned in the application example is intended to be used to produce layers that can be used for technical and decorative purposes.

The duration of the current flow is chosen so that at least a layer thickness of 0.5 to 1 μm is achieved on average over the area. Higher layer thicknesses can be produced if the electrolyte mentioned in the application example is intended to produce layers with a quality that can be used for technical and decorative purposes. After coating, the cathode is removed from the electrolyte and rinsed with deionized water.

The cathodes can be dried by compressed air, hot air or centrifugation. The area of the cathode, the level and duration of the applied current and the weight of the cathode before and after coating are documented and used to calculate the average coating thickness and the efficiency of the deposition determine.

Deposition of ruthenium alloy layers

Claims

patent claims

1. Aqueous electrolyte for the deposition of ruthenium alloys on base metal surfaces in particular, comprising: a) ruthenium as a binuclear, anionic ruthenium nitrido complex of the formula [Ru ₂ N(H ₂ 0) ₂ X ₈ ] ³ , where X is one or more singly or multiply negatively charged Counterions are in a concentration of 0.5 - 20 g/l based on ruthenium as the metal; b) one or more alloying metals dissolved in ionic form selected from the group consisting of: Cu, W, Fe, Co, Ni, In, Zn, Sn, Pd, Pt, in a concentration of 0.1 - 10 g each /l related to the metal; c) one or more anions of a di-, tri- or tetracarboxylic acid in a concentration of 0.05-2 moles per liter; d) one or more anionic surfactants in a concentration of 0.1 - 500 mg/l; wherein the electrolyte has a pH of 5.0 to 10.0.

2. Electrolyte according to claim 1, characterized in that the carboxylic acid is selected from the group consisting of oxalic acid, citric acid, tartaric acid, succinic acid, maleic acid, glutaric acid, adipic acid, malonic acid, malic acid.

3. Electrolyte according to one of the preceding claims, characterized in that the surfactant is selected from the group consisting of fatty alcohol sulfates, alkyl sulfates, alkyl sulfonates, aryl sulfonates, alkylaryl sulfonates, heteroaryl sulfates, salts of the same and their alkoxylated derivatives.

4. Electrolyte according to one of the preceding claims, characterized in that the pH of the electrolyte is in a range of 7-8.

5. Electrolyte according to one of the preceding claims, characterized in that the electrolyte has a buffer system selected from the group consisting of borate, phosphate and carbonate buffers.

6. Electrolyte according to one of the preceding claims, characterized in that the alloying metal is selected from the group Ni, Pd, Pt, Sn, Zn, Co.

7. Electrolyte according to one of the preceding claims, characterized in that it contains no sulfur-containing compounds in which the sulfur is present in an oxidation state of <+4.

8. Use of an aqueous electrolyte according to any one of claims 1-7 for the production of articles with an electrolytically deposited alloy metal layer on in particular base metal surfaces comprising the metals ruthenium and one or more of the alloy metals dissolved in ionic form selected from the group consisting of: Cu , W, Fe, Co, Ni, , In, Zn, Sn, Pd, Pt.

9. Use according to claim 7, characterized in that the alloy metal layer has a thickness of 0.05-5 μm

10. Use according to one of claims 8 - 9, characterized in that the alloy metal layer serves as a sub-layer for a further electrolytically deposited metal layer made of precious metals or their alloys, the latter having a thickness of 0.05 - 5 μm.

11. Use according to one of Claims 8-10, characterized in that the metal layer/metal layers produced has an abrasion resistance of less than 0.25 μm/1000 strokes (in the Bosch-Weinmann test).

12. A process for the electrolytic deposition of an alloy metal layer on, in particular, base metal surfaces, in which: a) the metal surface as cathode is contacted with an aqueous electrolyte according to one of claims 1-7; b) contacting an anode with the electrolyte; and c) establishing a sufficient current flow between cathode and anode.

13. The method according to claim 12, characterized in that the current density in the electrolyte is 0.1-50.0 A/dm ² .

14. The method according to any one of claims 12 or 13, characterized in that the temperature during the electrolysis is between 20°C and 80°C.

15. Metallic layer sequence comprising a substrate equipped with an in particular base metal surface, an alloy metal layer electrolytically applied thereto and produced according to a method of claims 12-14.