Passivating layer for metal-containing substrates

Abstract

The present invention relates to a method for sequential manufacture of metal-containing substrates which on at least part of their surface have a conversion layer. The invention further relates to a metallic substrate treated by the method of the invention. The invention additionally relates to a passivating conversion layer produced by the method of the invention.

Description

[0001] Passivation layer for metal-containing substrates

[0002] The present invention relates to a method for the sequential production of metal-containing substrates having a conversion layer on at least part of their surface. The invention further relates to a metallic substrate treated by the method according to the invention. The invention also relates to a passivating conversion layer produced by the method according to the invention.

[0003] BACKGROUND OF THE INVENTION

[0004] To protect metallic material surfaces from corrosive environmental influences, they are passivated, among other things. Passivation, also known as conversion treatment, increases the corrosion resistance of the unpainted metal surface and prepares the surface for a final coating, such as painting. A conversion layer is a very thin layer created on and with the surface of metals through a chemical or electrochemical reaction. During conversion, either metal ions from the surface react with the solution used for treatment, or inorganic layers are deposited on the metal. These are then firmly bonded to the underlying metal. The conversion layer serves to increase corrosion protection even without further treatment or coating.The formation of the conversion layer can also be an important step in surface pretreatment, ensuring good adhesion of a subsequent coating and at the same time guaranteeing good corrosion protection of the coated surface.

[0005] Good corrosion resistance is achieved with passivations based on hexavalent chromium. However, hexavalent chromium has a negative

[0006] Impact on health and the environment, as it is highly toxic and known to cause cancer. Hexavalent chromium has therefore been replaced by chromium(III) compounds for several years, as these are considered harmless.

[0007] WO 2018 / 146292 describes a process for the electrolytic passivation of an outer chromium or outer chromium alloy layer. A trivalent chromium electrolyte is generated by reducing hexavalent chromium ions in the presence of phosphoric acid and at least one reducing agent.

[0008] EP 3 456 865 describes an aqueous conversion solution for zinc and zinc alloys, which essentially contains chain-like colloidal silicon nanoparticles in addition to trivalent chromium and zirconium compounds. The molar ratio of chromium ions to zirconium ions is 0.1 to 4.

[0009] EP 3 045 563 describes a method for applying a trivalent chromium conversion layer, which additionally contains a titanium compound (titanium lactate) and is applied to zinc or zinc alloys.

[0010] WO 2017 / 194187 describes a method for improving the corrosion protection of metallic, particularly zinc-containing, surfaces. The reaction solution contains chromium(III), zirconium, and titanium ions, silicon oxide nanoparticles, and fluoride ions. The aqueous treatment solution contains Cr(III) ions in a concentration of 0.1 g / L to 8.0 g / L, zirconium and / or titanium anions in a concentration of 0.1 g / L to 15 g / L, organosilane-modified silicon oxide nanoparticles in a concentration of 0.1 g / L to 50 g / L, and fluoride ions in a concentration of 0.5 g / L to 10 g / L. It is further described that a weight fraction of Zr / Cr < 1 and only in combination with silicon oxide nanoparticles achieves particularly good corrosion protection. A mass ratio of Cr:Zr > 0.7 in the conversation layer is not described.

[0011] WO 2018 / 178390 discloses a method for increasing the corrosion protection of electrodeposited chromium layers by contacting them with an electrolyte containing Cr(II) ions, at least one conductive salt and at least one reducing agent and subjecting them to reverse pulse plating, whereby a trivalent chromium oxide layer is formed on the substrate.

[0012] WO 02 / 055758A2 describes a process for depositing corrosion-resistant films on aluminum surfaces using aqueous acidic media containing chromium(III) and zirconium. In addition to the chromium and zirconium salts, thickeners and surfactants are also used.

[0013] WO 2004 / 065642 describes a process for treating aluminum and aluminum alloys with aqueous acidic solutions containing trivalent chromium salts and alkali metal hexafluorozirconate salts. The treatment solution also contains zinc compounds, alkali metal fluorine compounds, and effective amounts of water-soluble thickeners, surfactants, or wetting agents.

[0014] WO 2006 / 088519 discloses a process for producing chromium-zirconium coatings on aluminum, its alloys, anodized aluminum, and iron alloys. The coating solution contains trivalent chromium salts, fluorozirconate and zinc compounds, surfactants, and organic carboxyl compounds.

[0015] WO 2020 / 061427 describes solution-based corrosion inhibitors (containing chromium and zirconium sources) for aluminum-based coatings. Chromium sulfate is used at a concentration of 25 g / 1000 mL, and hexafluorozirconate at a concentration of 20 g / 1000 mL. Among other things, it describes how the inhibition solution can be maintained functional by measuring the ion concentrations and pH and, if necessary, by adding chromium ions and zirconium ions, as well as a common acid or base.

[0016] US 2004 / 024487 relates to a method for treating metal surfaces, wherein the treatment agent contains a zirconium-containing and a fluorine-containing compound. The treatment is carried out by cathodic electrolysis. The weight ratio of zirconium metal to fluorine is 0.2 to 1.0. The concentration of zirconium and fluorine can be adjusted and is determined by atomic absorption analysis.

[0017] US 3,162,207 relates to chromate conversion coatings from liquid media and a method for automatically controlling the effectiveness of the conversion coating bath. At low conductivity, an additional liquid chromating concentrate was added to the bath in an amount sufficient to restore the original conductivity.

[0018] In summary, the prior art presents several methods for producing conversion coatings on metal surfaces. However, the corrosion protection achieved with the coatings described in the prior art is in need of improvement. Therefore, there is still a need for conversion coatings / passivation coatings that offer improved corrosion protection, particularly those that increase corrosion protection without further treatment or coating.

[0019] The present invention is therefore based on the object of providing a method for producing a conversion layer which has better corrosion protection.

[0020] It has now surprisingly been found that this object is achieved by the process according to the invention for the sequential production of metal-containing substrates which have a conversion layer on at least part of their surface, the metal treated by the process according to the invention and the conversion layer according to the invention.

[0021] The process according to the invention and the conversion layer obtained by the process have the following advantages:

[0022] - The process according to the invention makes it possible to achieve a higher chromium content in the conversion layer than with prior art processes. This is associated with improved corrosion protection, as demonstrated in the salt spray test according to DIN EN ISO 9227:2017-07.

[0023] - With the method according to the invention, the desired Cr:Zr mass ratio can be specifically monitored and, if necessary, adjusted. It is possible to regulate / control at least one of the following parameters during the production of the passivating conversion layer: a) Cr:Zr mass ratio in the conversion layer, b) Cr:Zr mass ratio in the electrolyte solution, c) Cr concentration in the electrolyte solution, d) Zr concentration in the electrolyte solution.

[0024] - The process enables a single-step and currentless dipping process for producing the conversion layer.

[0025] - The process is free from harmful substances, especially hexavalent chromium compounds.

[0026] - The relatively higher proportion of Cr(lll) in the layer leads to a slightly stronger coloration due to the body color that Cr(lll) compounds bring with them, which improves visual recognition and enables easy qualitative quality control

[0027] SUMMARY OF THE INVENTION

[0028] A first subject matter of the invention is a process for the sequential production of metal-containing substrates which have a conversion layer comprising chromium and zirconium on at least part of their surface, in which process metal-containing substrates are brought into contact with at least part of their surface to form the conversion layer with an electrolyte solution which comprises at least one trivalent chromium compound and at least one tetravalent zirconium compound, wherein fresh trivalent chromium and tetravalent zirconium compounds are added to the electrolyte solution to compensate for the chromium and zirconium deposited in the conversion layer, and the Cr:Zr mass ratio in the electrolyte solution and / or the addition of trivalent chromium compounds and tetravalent zirconium compounds to the electrolyte solution is controlled or regulated such that the Cr:Zr mass ratio in the conversion layer, based on the sum of the metals Zr and Cr, is > 0.7.

[0029] Another object of the invention is a treated metal produced by the process according to the invention, as defined above and below.

[0030] A further subject of the invention is a passivating conversion layer produced by the process according to the invention, as defined above and below.

[0031] DESCRIPTION OF THE INVENTION

[0032] In the context of the invention, "metal-containing substrates" is understood to mean a component that contains at least one metal, preferably selected from copper, copper alloys, nickel, nickel alloys, aluminum, aluminum alloys, steels, tin alloys, zinc, and zinc alloys. Metal-containing substrates preferably contain or consist of aluminum or aluminum alloys. It may happen that the aluminum has an oxide layer. Aluminum forms an oxide layer when stored in air or upon contact with water. The oxide layer thickness in this case is 0.01-0.05 pm. Furthermore, an oxide layer can be formed on the metal by electrolytic oxidation (anodizing process) of aluminum. The oxide layer thickness is between 3-25 pm. In any case, a possible oxide layer on the aluminum has no negative influence on the process according to the invention. Aluminum alloys, in particular, have an aluminum content of >60%.

[0033] According to the invention, the conversion layer is produced by bringing metal-containing substrates into contact with an electrolyte solution which comprises at least one trivalent chromium compound and at least one tetravalent zirconium compound, wherein fresh trivalent chromium and tetravalent zirconium compounds are added to the electrolyte solution to compensate for the chromium and zirconium deposited in the conversion layer, and the Cr:Zr mass ratio in the electrolyte solution and / or the addition of trivalent chromium compounds and tetravalent zirconium compounds to the electrolyte solution is controlled or regulated such that the Cr:Zr mass ratio in the conversion layer, based on the sum of the metals Cr and Zr, is > 0.7.

[0034] The method according to the invention is advantageously suitable for the sequential passivation of metal-containing substrates. This means that, according to the passivation method according to the invention, a single substrate or several substrates simultaneously are subjected to the same passivation process in a sequence that is, in principle, unlimited. The method for measuring, controlling or regulating according to the invention ensures that the electrolyte solution used always has an optimal mass ratio of Cr:Zr. For this purpose, at least one of the aforementioned measurement, control or regulated variables can be determined continuously or at regular intervals, e.g. after completion of each coating sequence or a certain number of coating sequences, and the content of Cr and / or Zr in the electrolyte solution can be supplemented according to this. In the case of continuous passivation, e.g.a strip treatment, the passivated strip can be measured and, if necessary, the content of Cr and / or Zr in the electrolyte solution can be adjusted.

[0035] Conveniently, contact is achieved by immersion, i.e., the metal-containing substrate is partially or completely immersed in the electrolyte solution contained in a container. For this purpose, the metal-containing substrate can, for example, be held on racks and immersed in the reaction solution with the racks, or it can be placed in a drum, a centrifuge, or on a tray, and immersed in the reaction solution with the drum or tray.

[0036] In an alternative procedure, the metal-containing substrate is brought into contact with the electrolyte solution by spray dipping.

[0037] In another alternative procedure, the metal-containing substrate is brought into contact with the electrolyte solution by spraying.

[0038] In another alternative procedure, the metal-containing substrate can also be brought into contact with the electrolyte solution by flooding. Unlike immersion, flooding involves placing the substrate(s) in a container, which is then filled with the electrolyte solution. The electrolyte solution is then removed from the container after treatment.

[0039] Furthermore, the metal-containing substrate can also be sprayed with the electrolyte solution, for example, using a nozzle from which a jet of electrolyte solution emerges. Another treatment method involves applying the electrolyte solution to the substrate surfaces by brushing, rolling, pad coating, or another application technique. The treatment can take place in conventional systems where the metal-containing substrates are treated in batches, or in continuous systems through which the substrates are continuously fed and treated.

[0040] In a preferred embodiment of the invention, the electrolyte solution has a bath temperature of approximately 10 to 100°C, more preferably 15 to 80°C, even more preferably 20 to 60°C, especially 25 to 45°C. If the metal-containing substrates are brought into contact with the electrolyte solution by immersion, the immersion time is preferably 5 to 900 seconds, even more preferably 15 to 600 seconds, and especially 30 to 300 seconds. Depending on the technique used to bring the metal-containing substrates into contact with the electrolyte solution, longer or shorter treatment times can also be used.

[0041] Before contacting the electrolyte solution, the metal-containing substrates to be treated are cleaned if necessary. This can be done, for example, by mechanically treating the substrate and / or bringing it into contact with a suitable cleaning solution.

[0042] It may also be advantageous for the metal-containing substrate to undergo a surface pretreatment. Suitable surface pretreatment methods include degreasing, pickling, brightening, pickling, anodizing, and combinations thereof. Pretreatment methods are known to those skilled in the art.

[0043] After completion of the process according to the invention, the metal-containing substrates are preferably dried, for example, with warm air. Additionally, the substrates can also be rinsed before drying to remove excess electrolyte solution from the surface.

[0044] In a preferred embodiment of the invention, the process is a single-stage process. However, it is also conceivable for the treated metal-containing substrate to be treated with an additional electrolyte solution, for example, a sealing solution, before and / or after the application of the conversion layer. The additional electrolyte solution can be based, for example, on polymers, silane compounds, other metal salt solutions, and / or inhibitors.

[0045] Furthermore, the method according to the invention makes it possible to monitor, control, and / or regulate the Cr:Zr mass ratio. Preferably,

[0046] - a target value for the mass ratio of Cr : Zr, based on the sum of the masses of the metals Zr and Cr, in the conversion layer,

[0047] - the actual value for the mass ratio of Cr : Zr, based on the sum of the masses of the metals Zr and Cr, in the conversion layer is determined,

[0048] - an actuator is provided to influence a parameter to be controlled,

[0049] - after reaching a limit value for the deviation of the actual value from the setpoint, the value of the control variable of the actuator (control value) is changed in order to influence the parameter to be controlled.

[0050] By definition, "control" or "open-loop control" refers to a process in which a variable, the controlled variable (actual value), is continuously recorded, compared with another variable, the reference variable (setpoint), and influenced to achieve an adjustment to the reference variable. The control deviation, as the difference between the actual value and the setpoint, is fed to the controller, which then generates a manipulated variable. The manipulated variable is the output variable (the position) of the actuator used, which is used to specifically intervene in the control system. The actuator can be part of the controller, but in many cases it represents a separate device. By setting or adjusting the actuator, the process is controlled, e.g., by changing a mass or energy flow. The controlled variable in the method according to the invention is the Cr:Zr mass ratio in the conversion layer. Examples of actuators include valves, switches, etc.An example of a manipulated variable is the opening state of a valve. Its manipulated variable is, for example, the position of the handwheel used to operate the valve.

[0051] In closed-loop control, the process described above occurs automatically in a control loop consisting of continuous measurement and control, i.e., the target value is compared with the actual value permanently or at regular intervals. In open-loop control, the effect path is open, i.e., an actuator is controlled from the actual value and a target value stored in the control system; however, no feedback is then provided to the control system as to whether the output state corresponds to the target value. In the simplest case, control can be manual. In the event of a control deviation, a specific amount of Cr and / or Zr is defined as the manipulated variable, which is added to the electrolyte.

[0052] It has now been found that conversion coatings on metal-containing substrates offer improved corrosion protection compared to the state of the art if the Cr:Zr mass ratio in the conversion coating, based on the sum of the metals Zr and Cr, is > 0.7. Furthermore, it has been found that a conversion coating improved compared to the state of the art can be produced if the Cr:Zr mass ratio in the conversion coating is used as a control variable.

[0053] In a preferred embodiment of the method according to the invention, in addition to the mass ratio Cr:Zr in the conversion layer, at least one further control and / or regulating variable is determined, selected from the mass ratio Cr:Zr in the electrolyte solution, the concentration of Cr in the electrolyte solution, the concentration of Zr in the electrolyte solution, a target value is set for each further control and / or regulating variable, the actual value for each further control and / or regulating variable in the electrolyte solution is determined, after reaching a lower limit value for the deviation of the actual value from the target value of the electrolyte solution, the amount of trivalent chromium compound and / or tertavalent zirconium compound is added which is required to compensate for the loss of the electrolyte solution due to deposited chromium and zirconium.

[0054] The Cr:Zr mass ratio in the conversion layer can be determined either offline or online. The Cr:Zr mass ratio in the conversion layer can be determined using conventional methods known to those skilled in the art. Preferably, the Cr:Zr mass ratio in the conversion layer is determined / monitored using X-ray fluorescence analysis.

[0055] The Cr:Zr mass ratio in the electrolyte solution can be determined either offline or online. The Cr:Zr mass ratio in the electrolyte solution can be determined using conventional methods known to those skilled in the art. The Cr:Zr mass ratio in the electrolyte solution is preferably determined / monitored using sensory methods, e.g., colorimetric methods, spectroscopic methods, e.g., atomic absorption spectrometry (AAS) or inductively coupled plasma mass spectrometry (ICP), or by titration.

[0056] The concentration of Cr and / or Zr in the electrolyte solution can also be determined either offline or online. The concentration in the electrolyte solution can be determined using conventional methods known to those skilled in the art. Preferably, the concentration of Cr and / or Zr in the electrolyte solution is determined / monitored using sensory methods, e.g., colorimetric methods, spectroscopic methods, e.g., atomic absorption spectrometry (AAS) or inductively coupled plasma mass spectrometry (ICP), or by titration.

[0057] The concentration of Cr and / or Zr can be determined simultaneously or sequentially.

[0058] According to the invention, the target value for the mass ratio Cr:Zr in the conversion layer is > 0.7, preferably > 2.5.

[0059] The limit value for the Cr : Zr mass ratio in the conversion layer is preferably < 0.7.

[0060] Preferably, the target value for the mass ratio Cr : Zr in the electrolyte solution is > 0.58, in particular > 0.60.

[0061] Preferably, the limit value for the mass ratio Cr : Zr in the electrolyte solution is < 0.55, in particular 0.58.

[0062] Preferably, the target value for the Cr concentration in the electrolyte solution is from 0.02 to 2 g / L, in particular, the target value for the Cr concentration in the electrolyte solution is from 0.02 to 0.8 g / L. The minimum Cr concentration in the electrolyte solution is preferably 0.02 g / L.

[0063] Preferably, the limit value for the concentration of Cr in the electrolyte solution is < 0.02 g / l and > 2 g / L.

[0064] Preferably, the target value for the Zr concentration in the electrolyte solution is 0.03 to 2.8 g / L. In particular, the target value for the Zr concentration in the electrolyte solution is 0.03 to 1.3 g / L. The minimum Zr concentration in the electrolyte solution is preferably 0.03 g / L.

[0065] Preferably, the limit value for the concentration of Zr in the electrolyte solution is < 0.03 g / L and > 1.3 g / L.

[0066] In a preferred embodiment, it is a method in which a1 ) a conversion layer comprising chromium and zirconium is deposited on at least part of the surface of a metal-containing substrate, b1 ) the actual value for the mass ratio Cr : Zr in the conversion layer is determined, c1 ) if the actual value is 0.7 or less, at least one of the following parameters is determined, selected from the mass ratio Cr : Zr in the electrolyte solution, the concentration of Cr in the electrolyte solution, the concentration of Zr in the electrolyte solution, d1 ) a target value is set for each further selected parameter and the actual value in the electrolyte solution is determined, e1 ) the amount of trivalent chromium compound and / or tetravalent zirconium compound required to compensate for the loss of the electrolyte solution due to deposited chromium and zirconium is added to the electrolyte solution, wherein steps b1 ) to e1 ) can be carried out once or several times.

[0067] Preferably, in the method according to the invention a2) a conversion layer comprising chromium and zirconium is deposited on at least part of the surface of a metal-containing substrate, c2) at least one of the following parameters is determined, selected from the mass ratio Cr:Zr in the electrolyte solution, the concentration of Cr in the electrolyte solution, the concentration of Zr in the electrolyte solution, d2) a target value is set for each further selected parameter and the actual value in the electrolyte solution is determined, e2) the amount of trivalent chromium compound and / or tetravalent zirconium compound is added to the electrolyte solution which is required to compensate for the loss of the electrolyte solution due to deposited chromium and zirconium, wherein steps c2) to e2) can be carried out once or several times.

[0068] In particular, the invention relates to a method for producing a passivating conversion layer having a Cr : Zr mass ratio of > 0.7, in which a) providing an electrolyte solution comprising trivalent chromium compounds and tetravalent zirconium compounds, wherein the Cr : Zr mass ratio in the electrolyte solution is > 0.6, b) bringing the electrolyte solution from a) or a recycled electrolyte solution into contact with a metallic substrate, c) forming a passivating conversion layer.

[0069] Specifically, the invention relates to a process for producing a passivating conversion layer having a Cr:Zr mass ratio of > 0.7, in which a) an electrolyte solution is provided which comprises trivalent chromium compounds and tetravalent zirconium compounds, wherein the Cr:Zr mass ratio in the electrolyte solution is > 0.6, b) a metal-containing substrate is brought into contact with at least part of its surface with the electrolyte solution from a) or a recycled electrolyte solution, c) formation of a passivating conversion layer, wherein the Cr:Zr mass ratio in the electrolyte solution is determined in the passivating conversion layer and the amount of the chromium source and / or zirconium source is controlled or regulated as a function of the Cr:Zr mass ratio.

[0070] A further preferred embodiment is a method for monitoring, controlling and / or regulating a method for producing a passivating conversion layer which has a Cr:Zr mass ratio of > 0.7, in which a) an electrolyte solution is provided which comprises trivalent chromium compounds and tetravalent zirconium compounds, wherein the Cr:Zr mass ratio in the electrolyte solution is > 0.6, b) the electrolyte solution from a) is brought into contact with a metallic substrate; c) a passivating conversion layer is formed, wherein the Cr:Zr mass ratio in the electrolyte solution a) or in the passivating conversion layer is determined and the amount of the chromium source and / or zirconium source is controlled as a function of the Cr:Zr mass ratio.

[0071] In the process according to the invention, the addition of trivalent chromium compounds and tetravalent zirconium compounds to the electrolyte solution is preferably controlled or regulated independently of one another. In a first embodiment, the Cr:Zr mass ratio according to the invention is adjusted by adding further trivalent chromium compounds. The Cr:Zr mass ratio according to the invention can also be adjusted by adding further tetravalent zirconium compounds. It is also possible to adjust the Cr:Zr mass ratio according to the invention by adding further trivalent chromium compounds and tetravalent zirconium compounds.

[0072] The electrolyte solution is preferably an acidic, aqueous solution comprising at least one trivalent chromium compound and at least one tetravalent zirconium compound. The preferred pH of the electrolyte solution is in the range of 2 to 5, especially in the range of 3 to 4.

[0073] Preferred trivalent chromium compounds are those selected from Cr2(SO4)s, (NH4)Cr(SO4)2, Cr(NO5) 9H2O, KCr(SO4)2, Cr(OH)SO4, Cr2O3, and mixtures thereof. In particular, the chromium compound is Cr2(SO4)s.

[0074] Tetravalent zirconium compounds selected from salts of H2ZrF6 are preferred.

[0075] Alkali hydroxides, carbonates, ammonia, amines or mixtures thereof are suitable for adjusting the pH value.

[0076] To achieve a uniform and particularly adhesive conversion layer on the metallic substrate, inhibitors are preferably added to the electrolyte solution according to the invention. Suitable inhibitors are selected from triazoles, thiazoles, oxazoles, and mixtures thereof. In particular, inhibitors are selected from benzotriazole, 3-mercapto-1,2,4-triazole, 2-aminothiazole, 2-mercaptobenoxazole, and mixtures thereof. The inhibitors are preferably present in the electrolyte in a concentration range of 0.001–2.0 g / L, in particular 0.02–1.0 g / L.

[0077] It may also be advantageous to add surfactants to the electrolyte solution according to the invention. Suitable surfactants are selected from nonionic surfactants, anionic surfactants, and cationic surfactants. The surfactants are preferably present in the electrolyte in a concentration range of 0-10.0 g / L, in particular 0.05-8.0 g / L.

[0078] In order to achieve improved resistance to filiform corrosion compared to the prior art, it is advantageous if the electrolyte solution according to the invention is free of zinc compounds, zinc ions or zinc-containing compounds.

[0079] For the purposes of the invention, filiform corrosion refers to a thread-like corrosion phenomenon. It is a specific form of anodic infiltration, particularly in coatings on aluminum-containing substrates. Any zinc present is usually incorporated into the conversion layer. The presence of zinc-containing compounds promotes filiform corrosion. Furthermore, the presence of zinc-containing compounds can have a negative impact on any subsequent coating, such as paint.

[0080] Therefore, the electrolyte solution according to the invention is preferably free of zinc compounds, zinc ions or zinc-containing compounds, or contains these compounds in the range from 0 to 0.01 wt.%, based on the total weight of the electrolyte solution.

[0081] It is also preferred that the electrolyte solution according to the invention is free from organosilane-modified silicon oxide nanoparticles, in particular free from silicon oxide nanoparticles, or comprises organosilane-modified silicon oxide nanoparticles, in particular silicon oxide nanoparticles in the range from 0 to 0.01 wt.%, based on the total weight of the electrolyte solution.

[0082] In organosilane-modified silicon oxide nanoparticles or

[0083] In silicon oxide nanoparticles, the silicon oxide is preferably present in the form of a nanoscale agglomerate. The agglomerate of the organosilane-modified

[0084] Silicon oxide nanoparticles can be viewed as a core whose surface is silane-modified, i.e., on whose surface organic silane compounds are arranged. Organosilane modification is understood in particular to mean that oxygen atoms, at least on the surface of the silicon oxide nanoparticles, are covalently bonded to silicon atoms of an organic silicon compound. The organic silicon compound is preferably an epoxy, amido, ureido, amino, ester, mercapto, and / or isocyanate silane.

[0085] Nanoparticles generally have a size (average particle diameter) of 1 to 100 nm.

[0086] Furthermore, the electrolyte solution according to the invention is preferably free of thickeners. The use of thickeners is disadvantageous because it increases electrolyte consumption due to carryover. In other words, the electrolyte adheres more strongly to the substrates / components to be coated and is carried away.

[0087] Thickeners according to the invention are selected from cellulose, methylcellulose, polyurethane compounds and mixtures thereof.

[0088] The electrolyte solution according to the invention preferably contains thickeners in the range of 0 to 0.1 wt.%, based on the total weight of the electrolyte solution.

[0089] Another object of the invention is a treated metallic substrate produced by the process according to the invention as defined above.

[0090] A further subject of the invention is a passivating conversion layer produced by the process according to the invention, as defined above.

[0091] The conversion layer may also contain other elements selected from Ni, Ti, Hf, Al, Fe, Co, Cd, Mn and rare earths, for example from the treated surface.

[0092] The thickness of the conversion layer can vary, for example, depending on the desired corrosion protection properties. For most applications, it has proven advantageous to set the conversion layer to a thickness of 10 nm to 1000 nm, preferably 20 nm to 600 nm, and especially 50 nm to 300 nm. The layer thickness can be determined by measuring a fracture under a scanning electron microscope.

[0093] The passivating conversion layer according to the invention preferably has a layer weight of 30 to 500 mg / m 2 , especially from 50 to 400 mg / m 2 on.

[0094] The passivating conversion layer according to the invention preferably has a chromium content of the surface in the range of 3 to 15 cps, with the calibration factor being 8.5406. The passivating conversion layer according to the invention preferably has a chromium content of the surface in the range of 25 to 130 mg / m 2, especially in the range of 35 to 100 mg / m 2 , especially in the range of 40 to 85 mg / m 2 .

[0095] The passivating conversion layer preferably has a surface zirconium content in the range of 1.5 to 7.5 cps, with the calibration factor being 23.258. The passivating conversion layer according to the invention preferably has a surface zirconium content in the range of 35 to 175 mg / m 2 , especially in the range of 45 to 140 mg / m 2 , especially in the range of 60 to 115 mg / m 2 .

[0096] Counts per second (cps) is a unit of measurement for the counting rate (the average repetition rate of measurement signals counted as individual, time-separated events).

[0097] As mentioned above, the conversion layer according to the invention already provides the treated metallic substrate with excellent corrosion protection.

[0098] Therefore, it is not necessary to provide it with an additional layer, such as a sealing layer. Nevertheless, the conversion layer according to the invention is excellently suited as a base for further inorganic and / or organic layers. Objects or articles comprising a conversion layer according to the invention can thus be permanently and thus particularly advantageously protected against corrosion. Objects or articles comprising a conversion layer according to the invention are also subject of the present invention.

[0099] The invention will be explained with reference to the following examples, without, however, being limited to the specifically described embodiments.

[0100] DESCRIPTION OF THE CHARACTERS

[0101] Figure 1 : shows the mass ratio Cr : Zr in the deposited conversion layer depending on the different concentrations of chromium and zirconium in the electrolyte solution.

[0102] The concentration of chromium and zirconium on the surface of an EN AW 2024 T3 aluminum sheet was measured by X-ray fluorescence analysis (Fischerscope X-Ray XDV, Helmut Fischer), the measured value CPS (counts per second) was calibrated using test surfaces with known Cr or Zr concentrations.

[0103] Figure 2: shows the result of a neutral salt spray test according to DIN EN ISO 9227:2017-07 and 336 h, carried out on EN AW 2024 T3 aluminum test panels; with increasing Cr / Zr ratio on the surface of the test panels, the corrosion points (CP) that occur after 336 h of corrosion exposure decrease.

[0104] Figure 3: shows the result of a neutral salt spray test according to DIN EN ISO 9227:2017-07 carried out on an aluminum alloy 2024 T6.

[0105] EXAMPLES

[0106] Example 1 :

[0107] An EN AW 2024 T3 aluminum test panel was degreased with a mild alkaline cleaner and immersion surfactant (5 vol%, 0.5 vol%) and then rinsed with distilled water. This was followed by pickling with caustic soda and complexing agent (5 vol%) and subsequent rinsing with distilled water. The test panel was then subjected to pickling with nitric acid and iron(III) compounds (20 vol%) and rinsed again with distilled water. Passivation was carried out for 5 minutes in an electrolyte solution with a pH of 3.8 and a temperature of 30 °C. The zirconium and chromium concentrations are given in Table 1. After passivation, the test panel was rinsed with distilled water and dried in an oven at 60 °C for 20 minutes.

[0108] Table 1 :

[0109] The round measurement points in Figure 1 indicate the mass ratio of chromium and zirconium on the surface of the aluminum test sheets treated as described above, as measured by X-ray fluorescence (Fischerscope X-Ray XDV, Helmut Fischer). It can be seen that with increasing Cr:Zr ratio in the electrolyte, more chromium is deposited on the aluminum surface, which leads to an increase in the Cr:Zr ratio on the surface of the aluminum sheets.

[0110] Example 2:

[0111] An EN AW 2024 T3 aluminum test panel was treated as in Example 1 (degreased, pickled, decapitated, and passivated) and subsequently subjected to a neutral salt spray test according to DIN EN ISO 9227:2017-07 for 336 hours. The results are shown in Figure 2. It can be seen that with increasing Cr:Zr ratio on the surface of the test panels (ad), fewer corrosion points (KP) appear. This is considered evidence of improved corrosion protection.

[0112] Example 3:

[0113] Alloys listed in Table 2 were treated as in Example 1 (degreased, pickled, decapitated, and passivated). The corrosion protection results are also shown in Table 2.

[0114] Table 2:

[0115]

[0116] Example 4:

[0117] An aluminum sheet alloy 2024T6 was treated as in Example 1 and subsequently subjected to a neutral salt spray test according to DIN EN ISO 9227:2017-07. The compositions of the electrolyte solution and parameters are listed in Table 3.

[0118] Table 3:

[0119]

[0120] The results are shown in Figure 3. It can be seen that the inventive examples exhibit significantly better corrosion protection compared to the prior art, despite longer salt spray treatment.

Claims

Claims: A process for the sequential production of metal-containing substrates having a conversion layer comprising chromium and zirconium on at least a part of their surface, wherein metal-containing substrates with at least a part of their surface are brought into contact with an electrolyte solution comprising at least one trivalent chromium compound and at least one tetravalent zirconium compound to form the conversion layer, wherein fresh trivalent chromium and tetravalent zirconium compounds are added to the electrolyte solution to compensate for the chromium and zirconium deposited in the conversion layer, and wherein the mass ratio Cr : Zr in the electrolyte solution and / or the addition of trivalent chromium compounds and tetravalent zirconium compounds to the electrolyte solution is controlled or regulated such that the mass ratio Cr : Zr in the conversion layer, based on the sum of the metals Zr and Cr, is > 0.7.The method according to claim 1, wherein, in addition to the mass ratio Cr : Zr in the conversion layer, at least one further control variable is determined, selected from the mass ratio Cr : Zr in the electrolyte solution, the concentration of Cr in the electrolyte solution, the concentration of Zr in the electrolyte solution, a setpoint is set for each further control variable, the actual value for each further control variable in the electrolyte solution is determined, and after reaching a lower limit value for the deviation of the actual value from the setpoint of the electrolyte solution, the amount of trivalent chromium compound and / or tetravalent zirconium compound is added. required to compensate for the loss of electrolyte solution due to deposited chromium and zirconium. A method according to claim 2, wherein the target value for the mass ratio Cr : Zr in the electrolyte solution, based on the sum of the metals Zr and Cr, is > 0.58, preferably > 0.

6. A method according to claim 1, wherein the limit value for the mass ratio Cr : Zr in the conversion layer, based on the sum of the metals Zr and Cr, is < 0.

7. A method according to claim 2 or 3, wherein the limit value for the mass ratio Cr : Zr in the electrolyte solution, based on the sum of the metals Zr and Cr, is < 0.

55. A method according to claim 2, wherein the target value for the concentration of Cr in the electrolyte solution is 0.02 to 2 g / L. A method according to claim 2 or 6, wherein the limit value for the concentration of Cr in the electrolyte solution is < 0.02 and > 2 g / L.A method according to claim 2, wherein the target value for the concentration of Zr in the electrolyte solution is 0.03 to 2.8 g / L. A method according to claim 2 or 8, wherein the limit value for the concentration of Zr in the electrolyte solution is < 0.03 and > 2.8 g / L. A method according to any one of claims 1 to 9, wherein... a1) deposits a conversion layer comprising chromium and zirconium on at least a part of the surface of a metal-containing substrate, b1) determines the actual value for the mass ratio Cr : Zr in the conversion layer, c1) if the actual value is 0.7 or less, determines at least one of the following parameters, selected from the mass ratio Cr : Zr in the electrolyte solution, the concentration of Cr in the electrolyte solution, the concentration of Zr in the electrolyte solution, d1) sets a target value for each further selected parameter and determines the actual value in the electrolyte solution, e1) adds to the electrolyte solution the amount of trivalent chromium compound and / or tetravalent zirconium compound required to compensate for the loss of electrolyte solution due to deposited chromium and zirconium, whereby steps b1) to e1) may be carried out once or more.Method according to any one of claims 1 to 9, wherein a2) a conversion layer comprising chromium and zirconium is deposited on at least a part of the surface of a metal-containing substrate, c2) at least one of the following parameters is determined, selected from the mass ratio Cr : Zr in the electrolyte solution, the concentration of Cr in the electrolyte solution, the concentration of Zr in the electrolyte solution. d2) sets a target value for each further selected parameter and determines the actual value in the electrolyte solution, e2) adds to the electrolyte solution the amount of trivalent chromium compound and / or tetravalent zirconium compound required to compensate for the loss of electrolyte solution due to deposited chromium and zirconium, wherein steps c2) to e2) may be performed once or more frequently. A method according to any of the preceding claims, wherein the metal-containing substrate is or contains aluminum. A treated metallic substrate produced according to the method of claims 1 to 12. A passivating conversion layer produced according to the method of claims 1 to 12.

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