Corrosion resistant cr(III) coating

Abstract

The present invention relates to an electroplated article comprising a substrate and a coating, which includes a hard chromium layer produced from a Cr(III) compound, characterized in that the coating additionally comprises zinc. The electroplated article is characterized by high corrosion resistance. The present invention further relates to a method for producing the electroplated article, comprising the step of producing an electroplated coating on a surface of a substrate, wherein this production includes the electroplating of a Cr(III) compound from an electroplating bath and, during the process, the additional electroplating of zinc ions.

Description

[0001] The present invention relates to a corrosion-resistant, electroplated article with a chromium layer made of a chromium(III) compound, and to a method for its production.

[0002] Coating objects with a layer of chromium is a process that has been carried out for many years. A distinction is made between so-called bright chrome coatings, up to about 2 µm thick, which primarily serve decorative purposes, and so-called hard chrome coatings with greater thicknesses. Hard chrome coatings give an object technical functionality and are used, for example, in the manufacture of tempering rollers or straightening rollers in the steel industry, or conveyor rollers for fibrous products.

[0003] EP-0 565 070 B1 and EP-0 722 515 B1 describe a process for electroplating surfaces, in which a chromium coating is electroplated onto the surface of a substrate under specific current conditions. This process is now established in the market as the TOPOCROM® process. With the TOPOCROM® process, a chromium coating can be easily applied in various configurations without the need for mechanical or chemical pre- or post-treatment of the surface. In particular, it eliminates the need for shot blasting or sandblasting of the surface to be coated, which results in a surface texture ("orange peel") that is unfavorable for processing carbon fibers.

[0004] In the current state of the art, hard chrome plating is commercially deposited from chromium electrolytes containing hexavalent chromium. However, in recent years the use of Cr(VI) electrolytes has been increasingly restricted by regulations, as Cr(VI) compounds are classified as highly hazardous to health and the environment.

[0005] One possible alternative is the use of Cr(III) electrolytes in electroplating processes. Cr(III) electrolytes are already used in decorative chrome plating processes to achieve layer thicknesses in the range of 200 nm to 1000 nm. However, for hard chrome plating with its considerably greater required layer thicknesses, there is currently no industrially viable process that can produce chromium layers with the necessary properties using Cr(III) electrolytes with a layer thickness of ≥ 3 µm.

[0006] In patent application EP23217110.8, the applicant describes a device and a method for the electroplating of a hard chrome layer made of a chromium(III) compound onto the surface of a substrate. The device comprises an anode and an electroplating bath into which the substrate, acting as a cathode, can be introduced, wherein the electroplating bath contains a Cr(III) compound and a carboxyl compound of the formula R-COOH or a salt thereof, where RH is a C1-10 alkyl group, characterized in that the anode is separated from the electroplating bath by a cation-selective membrane.

[0007] It has been shown that although the deposition of a hard chrome layer from a chromium(III) compound can be achieved very well in this way, the hard chrome layer obtained in this way is disadvantageous in terms of its corrosion resistance compared to conventional hard chrome layers made from Cr(VI) compounds.

[0008] The object of the present invention was therefore to provide an electroplated article with a chromium layer, preferably a hard chromium layer, made from a chromium(III) compound, and a method for its production, which has improved corrosion resistance.

[0009] This problem is solved by the present invention.

[0010] In detail, the present invention relates to an electroplated article comprising a substrate and a coating which includes a chromium layer produced from a Cr(III) compound, preferably a hard chromium layer, characterized in that the chromium layer, preferably a hard chromium layer, additionally comprises zinc.

[0011] It was found according to the invention that the presence of zinc provides an unexpectedly high level of corrosion protection for a chromium layer, preferably a hard chromium layer, produced from a Cr(III) compound.

[0012] According to the invention, corrosion resistance is determined in a neutral salt spray test according to DIN EN ISO 9227.

[0013] According to the invention, a "coating" is understood to be a system consisting of one or more layers which are electroplated onto a substrate surface.

[0014] Chromium coatings deposited in electroplating baths using a Cr(III) compound as the Cr source showed no corrosion protection whatsoever in this salt spray test. Distinct red rust stains were observable after only a few minutes / hours. Attempts to improve corrosion resistance through measures such as the application of a nickel layer (suitable for coatings produced from a Cr(VI) compound) between the substrate surface and the trivalent chromium layer did not yield sufficient improvement.

[0015] Without committing to a specific theory, the invention hypothesizes that the corrosion of trivalent chromium layers is not caused by external factors, but rather by irregularities in the substrate surface (e.g., induced by defects or liquid residues) that promote the formation of cracks in the applied chromium layer, which in the worst case can extend through the entire applied chromium layer. In this case, the cracks can rupture through the surface of the applied chromium layer. Corrosion can then occur very rapidly, in the worst case even without external influences (such as the salt spray test).

[0016] It is suspected that the high susceptibility to corrosion of chromium layers electroplated from Cr(III) compounds is due to the fact that the layer build-up takes place at an angle of about 90° to the substrate surface, which could promote the formation of the cracks described above through the entire chromium layer.

[0017] According to the invention, it has been found that, in contrast to other metals such as nickel or copper, whose presence in such a coating does not sufficiently improve corrosion resistance, a proportion of zinc in the chromium layer, preferably a hard chromium layer, leads to a surprisingly high corrosion resistance of a chromium layer electroplated from Cr(III) compounds in a neutral salt spray test according to DIN EN ISO 9227 of at least 72 h, preferably at least 120 h, more preferably at least 300 h and particularly preferably at least 500 h.

[0018] The corrosion resistance of a material or its corrosion protection coating can be determined using a salt spray test according to DIN EN ISO 9227 (NSS test). During the test, the specimens are placed in a chamber where a 5% sodium chloride solution with a controlled pH value is continuously atomized at a temperature of 35 °C. The mist settles on the specimens, coating them with a corrosive salt water film. The test duration depends on the expected corrosion resistance of the material system being tested. After the salt spray test, the specimens are rinsed with deionized water to remove any loosely adhering corrosion products. The corrosion attack on the tested material system is then assessed visually or using electrical and microscopic methods.

[0019] According to the present invention, it has been shown that high corrosion resistance can be achieved when zinc is provided within the chromium layer, preferably a hard chromium layer.

[0020] According to the invention, the zinc in the chromium layer, preferably a hard chromium layer, is preferably contained in an amount of 0.1 to 10 wt.% Zn, preferably 1 to 5 wt.% Zn. This can be achieved according to the invention by adding zinc ions to the electroplating bath containing a Cr(III) compound and electroplating them together with the chromium to obtain a zinc-containing chromium layer, preferably a hard chromium layer. Preferably, the zinc ions are added in the form of a zinc compound such as Zn formate, a Zn salt of a carboxylic acid, ZnCl₂, or ZnSO₄.

[0021] It is preferred that the electroplating bath containing a Cr(III) compound has a proportion of zinc ions in the range of 1 to 800 ppm, preferably 50 to 600 ppm, particularly preferably 100 to 500 ppm.

[0022] Investigations have shown that the chromium layer, preferably a hard chromium layer, deposited from such an electroplating bath has a semi-shell structure with zinc layers arranged between the semi-shells. The semi-shells can be, for example, CrZn semi-shells or a semi-shell structure with zinc inclusions.

[0023] In this embodiment, the formation of cracks as described above, which extend from the surface of the substrate to the surface of the chromium layer, preferably hard chromium layer, was not observed.

[0024] According to the invention, the electroplating of such a zinc-containing chromium layer, preferably a hard chromium layer, is preferably carried out under conditions (current density, temperature, type of substrate) as described below for the production of a pure hard chromium layer.

[0025] According to the invention, the electroplated article comprises a chromium layer, preferably a hard chromium layer, in its coating.

[0026] As described in the applicant's patent application EP23217110.8, for the large-scale deposition of hard chrome layers, the oxidation of carboxylate ions to CO₂ at the anode must be prevented or at least significantly limited. This can be achieved by separating the anode from the electroplating bath using an ion-selective membrane. This allows for stable process control over a longer period, as it prevents a rapid and significant increase in pH. In this way, the high layer thicknesses required for hard chrome plating can be deposited stably.

[0027] During electroplating from a bath containing Cr(III) ions, oxidation of Cr(III) ions to Cr(VI) ions can occur. This is generally undesirable and can completely prevent successful hard chrome plating. Therefore, the anode is preferably made of a material in which oxidation of Cr(III) ions to Cr(VI) ions does not occur. In principle, the hard chrome layer can be produced with any anode material suitable for electroplating from a chromium-containing electroplating bath. A mixed metal oxide (MMO) electrode is preferred.

[0028] Mixed metal oxide (MMO) electrodes are well known and commercially available. To manufacture these MMO electrodes, a substrate (e.g., a titanium plate or a titanium grid) is coated with a thin layer of other metals (for example, selected from the group consisting of ruthenium, iridium, and tantalum) or compounds thereof, such as their oxides, to give the anodes specific properties.

[0029] If electroplating is carried out using a metal mixed oxide (MMO) electrode as the anode, unwanted oxidation of Cr(III) ions to Cr(VI) ions can be avoided.

[0030] The anode is separated from the electroplating bath by a cation-selective membrane. Cation-selective membranes are well-known and commercially available. Perfluorinated cation exchange membranes are one example. Cation-selective membranes can be penetrated by cations, but not by anions.

[0031] In principle, the anode can be separated from the electroplating bath in any way by means of a cation-selective membrane. For example, the electroplating bath can be divided into two sections, preferably two halves, by placing a cation-selective membrane at a desired position within the electroplating bath.

[0032] It is preferred that the anode and the cation-selective membrane are arranged in a container, preferably a plastic container, wherein the container comprises an inlet and an interior space, the anode being located in the interior space, and a medium entering through the inlet can only reach the interior space by passing through the cation-selective membrane. The shape of the container is freely selectable and can, for example, be in the form of a cube, cuboid, or cylinder.

[0033] For example, it could be a cuboid or cube-shaped container with one open side. This open side can be closed with a plate that has openings allowing the electrolyte solution to pass into the container. The openings must be sized to allow the molecules and ions contained in the electrolyte solution to pass through.

[0034] Behind the plate, a cation-selective membrane is arranged in such a way that the molecules and ions passing through the plate must pass through the cation-selective membrane in order to reach the interior of the container and thus the anode located in this interior.

[0035] The container is preferably dimensioned such that it has enough space to accommodate a conventional anode, but occupies as little volume as possible of the electroplating bath.

[0036] The anode, located inside the container, is connected to a power source, such as a battery, via an electrical connection like a power cable. This electrical connection is routed through a surface, preferably the top surface, of the container in such a way that no molecules or ions of the electrolyte solution can enter the container at the point of penetration.

[0037] The device for electroplating according to the invention comprises an electroplating bath. Depending on the type of electroplating desired (zinc-containing chromium layer, preferably hard chromium layer, pure chromium layer, preferably hard chromium layer), the electroplating bath has a different composition as described above.

[0038] The electroplating bath is provided in a container of the type commonly used in electroplating. In addition to the electroplating bath (i.e., the electrolyte solution), the container also contains the anode described above, the cation-selective membrane (in the case of deposition of a chromium layer, preferably a hard chromium layer), and a substrate to be coated. During electroplating, the substrate acts as the cathode.

[0039] In principle, any electrically conductive material suitable for electroplating can be used as a substrate. According to the invention, the substrate is preferably made of a metal such as iron or steel.

[0040] While not required, it can be advantageous in certain cases to subject the substrate to conventional pretreatment, such as applying a nickel layer, to make it suitable for electroplating. This eliminates the need for shot blasting or sandblasting, or for additional complex chemical and / or electrochemical pretreatment steps of the surface to be coated, which can lead to an undesirable surface texture ("orange peel"). According to the invention, a pure chromium layer from a Cr(III) electrolyte or a zinc-containing chromium layer from a Cr(III) electrolyte containing zinc ions can be applied directly to the substrate. As mentioned, however, such pretreatment may be advantageous or appropriate under certain circumstances.

[0041] Preferably, a layer of a polyhydroxy compound such as glycerin can be applied to the substrate before electroplating, in particular the electroplating of a chromium layer, preferably a hard chromium layer, as described in EP-3 000 918 A1.

[0042] The anode and the substrate acting as the cathode are connected to a power source by means of electrical conductors, for example, power cables. The power source, together with the anode and the substrate acting as the cathode, forms a circuit in which direct current flows during operation. Conventional direct current sources can be used. Preferably, the device can include a temperature control unit to enable electroplating at a temperature preferred according to the invention in the range of 35 to 75°C, preferably 40 to 60°C. Such temperature control units, for example, external heating elements, are well known.

[0043] For the deposition of a coating with several chromium layers, preferably hard chromium layers (pure or zinc-containing), a device and a process are preferred as described in EP-3 000 918 A1, in which the process stages are not realized by heating or cooling a single electrolyte contained in the reactor, but rather an electrolyte solution with a temperature T1 is replaced for the next process stage by an electrolyte solution with a temperature T2 ≠ T1.

[0044] According to the present invention, the electroplating bath, i.e., the electrolyte solution, used for depositing a chromium layer, preferably a hard chromium layer (pure or zinc-containing), contains at least one Cr(III) compound in an aqueous solution for the electroplating of chromium onto the substrate acting as the cathode. Any Cr(III) compound used in the prior art for electroplating processes can be used. According to the invention, Cr(III) sulfate (Cr₂(SO₄)₃) is preferred.

[0045] Preferably, the electroplating bath used for depositing a chromium layer, preferably a hard chromium layer (pure or zinc-containing), i.e., the electrolyte solution, contains at least one carboxylate compound of the formula R-COOH, where RH is a C1-10 alkyl group, preferably H or a C1-4 alkyl group. The alkyl group may be linear or branched but does not have any further functional group. Formic acid or acetic acid are examples. A salt of the aforementioned carboxylate compound may also be used. Alkali metal salts, alkaline earth metal salts, or ammonium salts of the corresponding carboxylate compound are preferred. A preferred salt is ammonium formate as a formic acid salt.

[0046] According to a particularly preferred embodiment of the present invention, the electroplating bath used for depositing a chromium layer, preferably a hard chromium layer (pure or zinc-containing), contains no added foreign ions such as lead, copper, iron, or nickel ions, apart from any zinc ions that may be present. Such foreign ions can interfere with or influence the electroplating of chromium from a Cr(III) electrolyte. According to a preferred embodiment of the present invention, the electroplating bath used for depositing a chromium layer, preferably a hard chromium layer (pure or zinc-containing), consists of the Cr(III) compound and the carboxylate compound described above, and optionally a zinc compound.

[0047] According to the invention, the electroplating bath used for the deposition of a chromium layer, preferably a hard chromium layer (pure or zinc-containing), preferably has a concentration of Cr(III) ions in the range of 0.5 mol / l to 2.0 mol / l, preferably 0.6 mol / l to 1.5 mol / l.

[0048] According to the invention, the electroplating bath used for the deposition of a chromium layer, preferably a hard chromium layer (pure or zinc-containing), preferably has a concentration of carboxylate ions such that the molar ratio of Cr(III) ions to carboxylate ions is in the range of 0.1-0.9, preferably 0.12 to 0.7 and particularly preferably 0.13 to 0.5.

[0049] According to the invention, the electroplating bath used for the deposition of a chromium layer, preferably a hard chromium layer (pure or zinc-containing), preferably has a pH value in the range of 4.5 to 6.5, preferably 5.0 to 5.5.

[0050] The present invention further relates to a method for producing an electroplated article according to one of the preceding claims, comprising the step of producing an electroplated coating on a surface of a substrate, wherein this production comprises the electroplating of a Cr(III) compound from an electroplating bath, characterized in that zinc ions are added to the electroplating bath containing a Cr(III) compound and are electroplated together with the chromium to obtain a zinc-containing chromium layer, preferably a hard chromium layer.

[0051] According to the inventive method, the zinc ions are added to the electroplating bath containing a Cr(III) compound and electroplated together with the chromium to obtain a zinc-containing chromium layer, preferably a hard chromium layer. In this embodiment, the electroplating bath containing a Cr(III) compound preferably has a zinc ion content in the range of 1 to 800 ppm, preferably 50 to 600 ppm, and particularly preferably 100 to 500 ppm.

[0052] The chromium(III) compound chromium(III) sulfate used for depositing the chromium layer, preferably a hard chromium layer, is preferred. The electroplating bath containing the Cr(III) compound is particularly preferably supplemented with a carboxyl compound of the formula R-COOH or a salt thereof, where RH is a C1-10 alkyl group. The zinc compound ZnCl₂ or ZnSO₄ used for depositing the chromium layer, preferably a hard chromium layer, is also preferred.

[0053] The electroplating of the chromium layer, preferably a hard chromium layer, on a substrate surface according to the invention is preferably carried out in a device described above and comprises the following steps: a) Inserting the substrate into the appropriate electroplating bath of the device, b) Applying a direct current to the anode of the device and the substrate acting as the cathode.

[0054] As described above, during the electroplating of a chromium layer, preferably a hard chromium layer (pure or zinc-containing), the separation of the anode or the anode compartment from the electroplating bath by means of a cation-selective membrane essentially prevents undesirable oxidation of the carboxyl compound contained in the electroplating bath at the anode. This has the advantage, among others, that this electroplating process can be carried out at a pH value in the range of 4.5 to 6.5, preferably 5.0 to 5.5, without a rapid, significant increase in pH value during the electroplating process. Furthermore, the carboxyl compound contained in the electroplating bath is thus protected from decomposition.

[0055] According to the invention, the electroplating of a chromium layer, preferably a hard chromium layer (pure or zinc-containing), is preferably carried out at a temperature in the range of 35 to 75°C, preferably 40 to 60°C, when a single layer is to be deposited.

[0056] In the case of the deposition of multiple chromium layers, as described in EP-0 565 070 B1 and EP-0 722 515 B1 and established on the market as the TOPOCROM® process, the deposition preferably takes place in several process stages at different or, optionally, the same temperatures. In a first process stage, a base layer of chromium can be deposited with an electrolyte having a temperature in the range of 40 to 60°C, preferably 45 to 55°C. In a second process stage, a structural chromium layer can be deposited with an electrolyte having a temperature in the range of 25 to 39°C, preferably 30 to 38°C, or alternatively in the range of 40 to 60°C, preferably 45 to 55°C. Finally, in a third process stage, a top chromium layer can be deposited with an electrolyte which again has a higher temperature in the range of 40 to 60°C, preferably 45 to 55°C.

[0057] According to the invention, at least one chromium layer of the aforementioned multilayer structure shall contain zinc, which can be introduced as described above. Preferably, the base layer described above contains zinc in the amounts described above. However, it is also possible to introduce the zinc alternatively or additionally into one of the other chromium layers of the multilayer structure.

[0058] According to another embodiment, the deposition of a base layer described above can be dispensed with, so that only one or two chromium layers (structural and optionally top layer) need to be deposited as described above (which may optionally contain zinc as described above).

[0059] It is further preferred that the electroplating of a layer (zinc-containing layer or chromium layer, preferably hard chromium layer (pure or zinc-containing)) is carried out with a current density in the range of 10 to 300 A / dm², preferably 25 to 200 A / dm² and particularly preferably 30 to 120 A / dm².

[0060] The chromium layers obtained according to the invention can be applied to untreated substrates as described above.

[0061] The coatings obtained according to the invention exhibit exceptionally high corrosion resistance. In a neutral salt spray test according to DIN EN ISO 9227, the coatings according to the invention show no corrosion whatsoever over a period of 500 hours and more. Long-term tests also show no corrosion of the coatings according to the invention even after a significantly longer test period.

[0062] It is still possible to deposit another chromium layer from a Cr(III) electrolyte solution onto an existing chromium layer (pure or zinc-containing). In this way, greater layer thicknesses or multilayer chromium coatings with sublayers exhibiting different properties can be obtained.

[0063] For example, as described in EP-0 722 515 B1 and EP-4 012 074 A1, a multilayer chromium coating system can be produced using the TOPOCROM® process. First, a DC base layer can be applied to a substrate, followed by a structural layer. In certain applications, an additional chromium layer (so-called finished chromium layer or topcoat) can be applied to the structural layer. This creates a structural layer with dome-shaped (hemispherical) protrusions, allowing for precise adjustment of the desired surface roughness and density (topography). This surface is completely free of sharp edges.

[0064] As described above, one or more of these layers may contain zinc.

[0065] Preferably, the base layer has a thickness of preferably 1 to 500 pm, preferably 10 to 250 pm. According to the invention, the thickness of the structural layer is roughness-dependent. An exemplary roughness value (average roughness Ra according to DIN EN ISO 4287:2010, i.e., the calculated mean value of all deviations of the roughness profile from the mean line along the reference section) of a structural layer according to the invention is 0.1–15 pm, preferably 0.4–12 pm. The finished chromium layer for protecting the structural layer preferably has a thickness of preferably 2 to 20 pm, particularly preferably 3 to 15 pm, and especially 4 to 10 pm.

[0066] To produce a chromium base layer, current densities in the range of 30 to 50 A / dm² are preferably applied, preferably 35 to 45 A / dm² for a period of 5 to 360 min, preferably 5 to 60 min, preferably 30 to 50 min.

[0067] The so-called structural layer is then applied to this base layer. For example, in the TOPOCROM® process, the structural chromium layer formed comprises hemispherical domes. Preferably, the structural layer is produced using a direct current deposition process, wherein at least one initial pulse of electrical voltage and / or electrical current is applied to the surface to be coated to initiate nucleation of the deposit material, and subsequently, at least one follow-up pulse is applied to promote the growth of the deposit material nuclei through the deposition of further deposit material, with the electrical voltage and / or electrical current being increased or decreased in several stages during the nucleation phase.

[0068] Alternatively, as described in EP-4 012 074 A1, a surface coating can be applied, comprising a base layer and a structural layer applied thereto, wherein the base layer comprises at least two sub-layers in which the deposited chromium is contained in different amounts.

[0069] According to the invention, one of these sublayers, or alternatively both sublayers, can contain zinc, which can be introduced as described above.

[0070] According to another embodiment, the deposition of a base layer described above can be dispensed with, so that only one or two chromium layers (structural and optionally top layer, optionally containing zinc as described above) need to be deposited as described above.

[0071] The present invention is explained in more detail with reference to non-limiting figures and examples. These show: Fig. 1 a microscopic (SEM) image of a hard chrome layer electroplated from Cr(III) Fig. 2 a microscopic (SEM) image of a hard chrome layer electroplated from Cr(III) according to Example 1, which contains additional zinc Fig. 3 a microscopic (SEM) image of a cross section through the electroplated article produced in Example 1. Example 1

[0072] An iron rod (coating length 100 mm, diameter 6 mm) was placed in an electroplating bath (with a volume of 800 ml) containing chromium(III) sulfate (corresponding to an amount of 20–25 g / l Cr(II) ions in the bath), ammonium formate (in an amount corresponding to a molar ratio of Cr(III) ions to carboxylates in the range of 0.2 to 0.5), and 350 to 400 ppm zinc sulfate. The electroplating bath had a pH of 5 and a temperature in the range of 55–60°C.

[0073] Electroplating was carried out for 50 min at 55°C under conditions of 10⁻¹² A, 10⁻¹² V and a current density of 50–60 A / dm². Halfway through the plating time, additional chromium sulfate (corresponding to an amount of 5 g / l Cr(III) ions in the bath) was added. A layer with a thickness of 50 pm was produced.

[0074] As a comparison of Figures 1 and 2 It is evident that a hard chrome layer electroplated from a Cr(III) compound in the absence of Zn ions has visible openings of cracks in its surface and is therefore not corrosion-resistant.

[0075] The hard chrome layer produced in Example 1 contains approximately 3% zinc, based on the total amount of the deposited layer. The surface structure of the layer according to Example 1 is, as shown from Fig. 2 evidently, clearly different from the surface structure of the pure hard chrome layer according to Fig. 1 .

[0076] In Fig. 3A microscopic (SEM) image of a cross-section of the article is shown, which was electroplated as described in Example 1. The substrate (iron) is visible at the bottom. The deposited hard chrome layer is located on top of it. A hemispherical structure of the chrome layer is clearly visible. Zinc layers (stained yellow) are arranged between some of the hemispherical sections.

[0077] In a neutral salt spray test according to DIN EN ISO 9227, the article produced in Example 1 showed no corrosion even after 500 h.

Claims

1. Electroplated article comprising a substrate and a coating comprising a chromium layer produced from a Cr(III) compound, preferably a hard chromium layer, characterized by the fact that the chrome layer, preferably a hard chrome layer, additionally contains zinc.

2. Electroplated article according to claim 1, characterized by the fact that the zinc in the chromium layer, preferably hard chromium layer, is contained in an amount of 0.1 to 10 wt.% Zn, preferably 1 to 5 wt.% Zn.

3. Electroplated article according to claim 1 or 2, characterized by the fact that The chrome layer, preferably a hard chrome layer, has a semi-shell structure with zinc layers arranged between the semi-shells.

4. Electroplated article according to any one of the preceding claims, characterized by the fact that The substrate is selected from the group consisting of iron and steel.

5. Electroplated article according to any one of the preceding claims, characterized by the fact that on the zinc-containing chromium layer, preferably hard chromium layer, one or more further chromium layers, preferably hard chromium layers, are electroplated from a Cr(III) compound.

6. A method for producing an electroplated article according to one of the preceding claims, comprising the step of producing an electroplated coating on a surface of a substrate, wherein this production comprises the electroplating of a Cr(III) compound from an electroplating bath, characterized by the fact that Zinc ions are added to the electroplating bath containing a Cr(III) compound and electroplated together with the chromium to obtain a zinc-containing chromium layer, preferably a hard chromium layer.

7. Method according to claim 6, characterized by the fact thatthe electroplating bath containing a Cr(III) compound has a proportion of zinc ions in the range of 1 to 800 ppm, preferably 50 to 60 ppm, particularly preferably 100 to 500 ppm.

8. Method according to one of claims 6 to 7, characterized by the fact that the chromium(III) compound is chromium(III) sulfate and the electroplating bath containing the Cr(III) compound additionally contains a carboxyl compound of the formula R-COOH or a salt thereof, where RH is a C1-10 alkyl group.

9. Method according to any one of claims 6 to 8, characterized by the fact that The zinc ions are added in the form of a zinc compound such as Zn formate, a Zn salt of a carboxylic acid, ZnCl2 or ZnSO4.

10. Method according to any one of claims 6 to 9, characterized by the fact that the process with a current density in the range of 10 to 300 A / dm² 2 , preferably 25 to 200 A / dm² 2 and especially preferably 30 to 120 A / dm² 2 is carried out.

11. Method according to any one of claims 6 to 10, characterized by the fact that For electroplating, a metal mixed oxide (MMO) electrode is used as the anode.

12. Method according to any one of claims 6 to 11, characterized by the fact that For electroplating, the anode is separated from the electroplating bath by means of a cation-selective membrane.

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