Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
  • C23C22/36—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also phosphates
  • C23C22/362—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also phosphates containing also zinc cations
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  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
  • C23C22/36—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also phosphates
  • C23C22/364—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also phosphates containing also manganese cations
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
  • C23C22/36—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also phosphates
  • C23C22/364—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also phosphates containing also manganese cations
  • C23C22/365—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also phosphates containing also manganese cations containing also zinc and nickel cations
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/40—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing molybdates, tungstates or vanadates
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/73—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/78—Pretreatment of the material to be coated
  • C23C22/80—Pretreatment of the material to be coated with solutions containing titanium or zirconium compounds
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/82—After-treatment
  • C23C22/83—Chemical after-treatment
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/40—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing molybdates, tungstates or vanadates
  • C23C22/44—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing molybdates, tungstates or vanadates containing also fluorides or complex fluorides
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2222/00—Aspects relating to chemical surface treatment of metallic material by reaction of the surface with a reactive medium
  • C23C2222/20—Use of solutions containing silanes

Definitions

• the present invention relates to the anticorrosive treatment of composite metal constructions comprising metallic surfaces of aluminum, zinc and optionally iron in a multistage method.
• the method of the invention enables the selective zinc phosphation of the zinc and iron surfaces of the composite metal construction without deposition of significant amounts of zinc phosphate on the aluminum surfaces.
• the aluminum surface is available, in a subsequent method step, for passivation with, for example, conventional acidic and optionally silane-containing passivation compositions that generate a homogeneous, thin passive layer that provides protection from corrosion.
• firstly the formation of phosphate crystal clusters on the aluminum surfaces and secondly the formation of specks on zinc surfaces are prevented.
• cryolite precipitation on the surface of the composite metal constructions, especially on the aluminum parts thereof, and preferably the poisoning of the phosphation bath by titanium, zirconium and hafnium are reduced.
• the present invention also relates to a zinc phosphation composition
• a zinc phosphation composition comprising water-soluble inorganic compounds of boron in an amount sufficient to suppress the formation of specks, but not exceeding values for which the zinc phosphation loses its selectivity for the zinc and iron surfaces of the composite metal construction.
• German published specification DE 19735314 proposes a two-stage method in which there is firstly a selective phosphation of the steel surfaces and galvanized steel surfaces of a chassis likewise having aluminum surfaces, followed by a treatment of the chassis with a passivation solution for anticorrosive treatment of the aluminum parts of the chassis.
• the selective phosphation is achieved by lowering the pickling action of the phosphation solution.
• DE 19735314 teaches phosphation solutions having a free fluoride content of less than 100 ppm, where the source of the free fluoride is formed exclusively by water-soluble complex fluorides, especially of hexafluorosilicates in a concentration of 1 to 6 g/l.
• the prior art discloses other two-stage pretreatment methods that likewise follow the concept of depositing a crystalline phosphate layer on the steel surfaces and any galvanized and alloy-galvanized steel surfaces in the first step and passivating the aluminum surfaces in a further subsequent step.
• These methods are disclosed in documents WO 1999/012661 and WO 2002/066702.
• the methods disclosed therein are performed in such a way that, in a first step, the steel surfaces or galvanized steel surfaces are phosphated selectively, and the phosphation is also maintained in the subsequent passivation in a second method step, while no phosphate crystals are formed on the aluminum surfaces.
• the selective phosphation of the steel surfaces and galvanized steel surfaces is possible by a temperature-dependent restriction of the proportion of free fluoride ions in the phosphation solutions, the free acid contents of which are set within a range from 0 to 2.5 points.
• European application EP 2588646 discloses a method of selective phosphation of steel and galvanized steel in metallic components that also have aluminum surfaces. By means of this method, moreover, the formation of phosphate crystal clusters on the aluminum surfaces and of specks on the galvanized steel surfaces are prevented. For this purpose, silicon is added to the zinc phosphation composition in the form of water-soluble inorganic compounds.
• the aim is to further develop the selective phosphation of steel and galvanized steel in the anticorrosive treatment of metallic components in hybrid composition, i.e. composite metal constructions that have aluminum surfaces, to the effect that an improvement in process economics during the phosphation is achieved by specific control of the bath parameters that control selectivity.
• this includes not only the avoidance of the formation of phosphate crystal clusters on the aluminum surfaces and of specks on the galvanized steel surfaces, but especially also the reduction of cryolite precipitation on the surface of the metallic components, especially on the aluminum surfaces, and preferably the poisoning of the phosphation bath by titanium, zirconium and/or hafnium.
• Phosphate crystal clusters are understood by the person skilled in the art to mean the individualized and locally limited deposition of phosphate crystals on metal surfaces (here: aluminum surfaces). Such “crystal clusters” are enclosed by a subsequent paint primer and constitute in-homogeneities in the coating that can both distort the uniform visual impression of the painted surfaces and cause spot damage to paintwork.
• Speck formation is understood by the person skilled in the art to mean the phenomenon in phosphation of the local deposition of amorphous white zinc phosphate in an otherwise crystalline phosphate layer on the treated zinc surfaces or on the treated galvanized or alloy-galvanized steel surfaces. Speck formation is caused by a locally elevated pickling rate of the substrate. Such point defects in phosphation may be a starting point for the corrosive loss of adhesion of subsequently applied organic paint systems, and so the formation of specks should be largely avoided in practice.
• the sodium ions in the phosphation composition originally from additions such as, in particular, additives and/or accelerators.
• Additives that should be particularly mentioned here are sodium fluoride, sodium nitrate, sodium phosphate and sodium hydroxide, and an accelerator that should be particularly mentioned is sodium nitrite.
• an accelerator that should be particularly mentioned is sodium nitrite.
• potassium ions are added to the bath according to the situation and the existing bath parameters.
• the aluminum ions by contrast, were removed from the aluminum parts of the composite metal constructions by pickling in the acidic medium of the phosphation bath composition.
• a particular minimum amount of free fluoride (fluoride ions) in the phosphation bath is necessary to assure adequate deposition kinetics for the zinc phosphate layer on the surfaces of iron and zinc of the composite metal construction, since the simultaneous treatment of the aluminum surfaces of the composite metal construction especially causes aluminum ions to get into the zinc phosphation composition (see above), and these in turn, in uncomplexed form, disrupt or even prevent the formation of a uniform, homogeneous zinc phosphate layer on the iron and zinc parts of the composite construction.
• the free fluoride here may also come from fluoro complexes from which it is released in equilibrium reactions.
• the cause of the poisoning of the phosphate bath by titanium, zirconium and/or hafnium may lie, in particular, in encrusted conveying systems for the composite metal constructions or in pre-passivated aluminum parts of the constructions.
• the crusts (e.g. phosphate crusts or unbaked paint layers) on the conveying systems comprise titanium, zirconium and/or hafnium.
• the latter come from the passivation (cf. step (II)) with titanium-, zirconium- and/or hafnium-comprising water-soluble compounds that follows the phosphation (cf. step (I)) of the composite metal constructions, and they are absorbed by the crusts owing to their porosity. Since the conveying systems run in a cycle, the crusts that have been in contact with titanium, zirconium and/or hafnium in the passivation bath are exposed again to the acidic phosphation composition in the phosphation bath. Titanium, zirconium and/or hafnium are partly redissolved therein.
• the aluminum portions of composite metal constructions are often pre-passivated, meaning that they have already been provided with a passivation layer comprising titanium, zirconium and/or hafnium that has already been applied to the aluminum portions by the suppliers thereof.
• a “composite metal construction” in the context of the present invention is a metallic component in hybrid composition, especially a chassis.
• the composite metal construction may, as well as surfaces of zinc, surfaces of aluminum and optionally surfaces of iron, also have surfaces of other metals and/or surfaces of nonmetals, especially of plastics.
• the material “aluminum” is also understood to mean alloys thereof.
• the material comprises zinc, according to the invention, and also comprises zinc alloys, for example zinc-magnesium alloys, and also galvanized steel and alloy-galvanized steel, while the mention of iron also includes iron alloys, especially steel. Alloys of the aforementioned materials have an extraneous atom content of less than 50% by weight.
• an “aqueous composition” is understood to mean a solution or dispersion comprising water as solvent or dispersion medium to a predominant extent, i.e. to an extent of more than 50% by weight, preferably to an extent of more than 70% by weight, more preferably to an extent of more than 90% by weight (based on the entirety of the solvents and dispersion media present).
• the aqueous composition may thus also comprise dispersed constituents as well as dissolved constituents. However, it is preferably a solution, i.e. a composition that comprises only small amounts of dispersed constituents, preferably no dispersed constituents at all, but rather comprises solely or almost solely dissolved constituents.
• a “passive layer” in the context of the present invention is a passivating, i.e. anticorrosive, inorganic or mixed inorganic-organic thin-film coating that does not have a continuous crystalline phosphate layer.
• passive layers may consist, for example, of oxidic compounds of titanium, zirconium and/or hafnium.
• water-soluble compounds means either one water-soluble compound or two or more water-soluble compounds.
• zinc phosphate layers having an area-based coat weight of preferably at least 1.0 g/m 2 , more preferably of at least 2.0 g/m 2 , but preferably not more than 4.0 g/m 2 , are deposited on these surfaces of the composite metal construction in step (I) of the method according to the invention.
• the zinc phosphate coat weight is determined with the aid of gravimetric difference weighing on test sheets of the individual metallic materials of the respective composite metal construction. This is done by contacting steel sheets, directly after a step (I), with an aqueous solution of 9% by weight of EDTA, 8.7% by weight of NaOH and 0.4% by weight of triethanolamine at a temperature of 70° C. for 5 minutes and in this way freeing them of the zinc phosphate layer.
• a corresponding test sheet immediately after a step (I), is contacted with an aqueous solution of 20 g/l of (NH 4 ) 2 Cr 2 O 7 and 27.5% by weight of NH 3 at a temperature of 25° C. for 4 minutes and in this way freed of the zinc phosphate layer.
• Aluminum sheets by contrast, immediately after a step (I), are contacted with an aqueous 65% by weight HNO 3 solution at a temperature of 25° C. for 15 minutes and correspondingly freed of zinc phosphate components.
• the difference in the weight of the dry metal sheets after this respective treatment from the weight of the same dry untreated metal sheet immediately prior to step (I) corresponds to the coat weight of zinc phosphate according to this invention.
• step (II) The requirement of the invention that, in step (II), not more than 50% of the crystalline zinc phosphate layer on the steel and galvanized steel and/or alloy-galvanized steel surfaces is dissolved can likewise be appreciated using test sheets of the individual metallic materials of the respective composite metal construction.
• step (II) of the process of the invention is then contacted in step (II) of the process of the invention with the acidic passivation composition, then rinsed with deionized water, blown dry with compressed air and then weighed again.
• the zinc phosphation of the same test sheet is then removed completely with an aqueous solution of 9% by weight of EDTA, 8.7% by weight of NaOH and 0.4% by weight of triethanolamine or with an aqueous solution of 20 g/l of (NH 4 ) 2 Cr 2 O 7 and 27.5% by weight of NH 3 , as described above, and the dry test sheet is weighed once more.
• the percentage loss of phosphate layer in step (II) of the process of the invention is then determined from the weighing differences of the test sheet.
• the free acid with added KCl (FA, KCl) of the zinc phosphation composition in points in step (I) of the process of the invention is determined as follows (see: W. Rausch “Die Phosphat réelle von Metallen” [The Phosphation of Metals], Eugen G. Leuze Verlag, 3rd edition, 2005, chapter 8.1, p. 333-334):
• a suitable vessel for example a 300 mL Erlenmeyer flask.
• a suitable vessel for example a 300 mL Erlenmeyer flask.
• an additional 6-8 g of potassium chloride is added to the sample. Titration then takes place, using a pH meter and an electrode, with 0.1 M NaOH to a pH of 4.0. The quantity of 0.1 M NaOH consumed in this titration, in ml per 10 ml of the phosphation composition, gives the free acid value with added KCl (FA, KCl) in points.
• the zinc phosphation composition in step (I) preferably has a temperature in the range from 30 to 60° C., more preferably from 35 to 55° C.
• the concentration of free fluoride in the zinc phosphation composition is determined in the process of the invention by means of a potentiometric method. This is done by taking a sample volume of the zinc phosphation composition and determining the activity of the free fluoride ions with any desired commercial fluoride-selective potentiometric combination electrode after calibration of the combination electrode by means of fluoride-containing standard solutions without pH buffering. Both the calibration of the combination electrode and the measurement of free fluoride are undertaken at a temperature of 20° C.
• the zinc phosphation composition therefore has a free fluoride content of at least 5 mg/l but not greater than 200 mg/l, preferably at least 10 mg/l but not greater than 200 mg/l, further preferably at least 20 mg/l but not greater than 175 mg/l, further preferably at least 20 mg/l but not greater than 150 mg/l, further preferably at least 20 mg/l but not greater than 135 mg/l, further preferably at least 20 mg/l but not greater than 120 mg/l, especially preferably at least 50 mg/l but not greater than 120 mg/l and very especially preferably at least 70 mg/l but not greater than 120 mg/l.
• the total fluoride content (F tot. ) of the zinc phosphation composition is preferably in the range from 0.01 to 0.3 mol/I, more preferably from 0.02 to 0.2 mol/I.
• the total fluoride content is the content of fluoride (F ⁇ ) in total and is composed of complex-bound fluoride and simple fluoride.
• Complex-bound fluoride is fluoride bound to Si and B, but also to Al and in further complexes.
• Simple fluoride by contrast, is the fluoride not bound in complexes and is composed of the free fluoride determinable by means of a combination electrode, i.e. the unbound fluoride, and the fluoride bound as HF.
• step (I) of the process of the invention the higher the content of sodium and/or potassium ions, aluminum ions and free fluoride in the zinc phosphation composition in step (I) of the process of the invention, the more significant the precipitation of cryolite on the surface of the composite metal constructions, especially on the aluminum portions.
• the content of sodium and/or potassium ions (calculated as sodium) is in the range from 1 to 4 g/l, especially from 2 to 3 g/l, and the free fluoride content is in the range from 50 to 150 mg/l, especially from 70 to 120 mg/l, it is possible in the presence of aluminum ions to particularly effectively reduce the precipitation of cryolite by the presence of boron in the form of water-soluble inorganic compounds, especially in the form of fluoroborates such as HBF 4 .
• the zinc phosphation composition preferably has a concentration of boron in the form of water-soluble inorganic compounds calculated as BF 4 in the range from 0.08 to 2.5 g/l, further preferably from 0.08 to 2 g/l, further preferably from 0.25 to 2 g/l, especially preferably from 0.5 to 1.5 g/l and very especially preferably from 0.8 to 1.2 g/l.
• the inventive addition of water-soluble inorganic compounds comprising boron additionally results in the suppression of speck formation on the zinc surfaces.
• the upper limit of 3.2 g/l calculated as BF 4 results firstly from the economic viability of the process and secondly from the fact that the process is made more difficult to control by such high concentrations of water-soluble inorganic compounds comprising boron since the formation of phosphate crystal clusters on the aluminum surfaces can be suppressed only to a minor degree via an increase in the free acid content.
• the crystal clusters on completion of paint application, result in point elevations that have to be sanded for visually homogeneous painting of the composite metal construction, for example an automobile chassis, as desired by the customer.
• the boron concentration in the form of water-soluble inorganic compounds calculated as BF 4 is a critical parameter crucial to the success of the process of the invention. If a concentration of 2.0 g/l is exceeded, there is already formation at least of individual zinc phosphate crystal clusters on the aluminum surfaces.
• step (I) of the process of the invention zinc phosphation compositions in which the concentration of boron in the form of water-soluble inorganic compounds does not exceed a value of 3.2 g/l, more preferably a value of 2.0 g/l each calculated as BF 4 are used.
• the inventive proportion of boron in the form of water-soluble inorganic compounds is sufficient for prevention of speck formation on the zinc portions treated in accordance with the invention.
• Water-soluble inorganic compounds comprising boron that are preferred in the method of the invention are fluoroborates, more preferably HBF 4 , (NH 4 )BF 4 , LiBF 4 and/or NaBF 4 .
• the water-soluble fluoroborates are additionally suitable as a source of free fluoride and therefore serve to complex trivalent aluminum cations introduced into the bath solution, such that phosphation on the surfaces of steel and galvanized and/or alloy-galvanized steel is still assured.
• the zinc phosphation composition in step (I) includes, as well as water-soluble inorganic compounds comprising boron, also a certain content of water-soluble inorganic compounds comprising silicon.
• the latter may have been introduced into the phosphation composition for example, from preceding process steps or in the case of a high silicon content of the aluminum portions also originate from the composite metal constructions.
• a content of inorganic compounds comprising silicon is firstly undesirable in the context of the present invention since this increases cryolite precipitation on the surface of the composite metal constructions, especially on the aluminum portions thereof, which can be explained as follows:
• a content of inorganic compounds comprising silicon is also secondly undesirable since it has now been found that, surprisingly, a zinc phosphation bath composition having a free fluoride content that includes silicon in the form of water-soluble inorganic compounds is capable of much more significant leaching of titanium, zirconium and/or hafnium out of the encrusted conveying systems for the composite metal constructions and/or the pre-passivated aluminum portions of the constructions, and hence can lead to significantly greater poisoning of the phosphation bath by titanium, zirconium and/or hafnium than one including boron in the form of water-soluble inorganic compounds.
• fluoride is released from fluoride complexes and can then complex titanium, zirconium and hafnium. As a result, these remain soluble and can accumulate in the bath.
• fluorosilicates such as hexafluorosilicate
• fluoroborates such as tetrafluoroborate release fluoride ions less readily, which means that less free fluoride is available for the complexation of titanium, zirconium and hafnium.
• the concentration of free fluoride can be better controlled.
• a content of inorganic compounds comprising silicon is thirdly undesirable since sparingly soluble precipitates form in the presence of potassium ions especially in the case of fluorosilicates such as H 2 SiF 6 .
• the formation of such precipitates is just as undesirable as the precipitation of cryolite.
• Potassium ions are advantageous compared to sodium ions as cations in salts for adjustment of the bath parameters, for example in phosphates, hydroxides and fluorides, since K 3 AlF 6 is of better solubility than Na 3 AlF 6 and hence less cryolite is precipitated.
• ammonium ions that may be present in the zinc phosphation composition also have this advantage (good solubility of (NH 4 ) 3 AlF 6 ), they are however more environmentally harmful in the wastewater than potassium ions.
• the formation of sparingly soluble, potassium-containing precipitates has not been found for corresponding boron-comprising compounds especially in the case of fluoroborates such as HBF 4 .
• the content of inorganic compounds comprising silicon is therefore preferably below 25 mg/l, further preferably below 15 mg/l, more preferably below 5 mg/l and most preferably below 1 mg/l.
• the zinc phosphation composition in step (I) preferably has a points number of free acid with added KCl in the range from 0.6 to 3.0 points, preferably from 0.8 to 3.0 points, more preferably from 1.0 to 3.0 points and most preferably from 1.0 to 2.5 points. Observance of the preferred ranges for free acid firstly ensures adequate deposition kinetics of the phosphate layer on the selected metal surfaces and secondly prevents unnecessary pickling removal of metal ions, which in turn entails intensive monitoring or workup of the phosphation bath for avoidance of precipitation of sludges or for disposal thereof in continuous operation of the method of the invention.
• total acid (TA) in the phosphation composition in step (I) of the method of the invention should be in the range from 10 to 50, further preferably from 15 to 40 and especially preferably from 20 to 35 points.
• Fischer total acid should be in the range from 10 to 30, further preferably from 12 to 25 and more preferably from 15 to 20 points, while the A value should be in the range from 0.04 to 0.20, further preferably from 0.05 to 0.15 and especially preferably from 0.06 to 0.12.
• cryolite precipitation at the surface of the composite metal constructions and the poisoning of the phosphation bath by titanium, zirconium and/or hafnium can be reduced particularly effectively when, for the zinc phosphation composition in step (I), the dimensionless quotient
• T represents the temperature/° C.
• F tot. represents the total fluoride content/(mol/l)
• [B] represents the concentration of the element boron/(mol/l).
• FTA Free acid (diluted) (FA (dil.)
• FAA Fischer total acid
• FTA total acid
• a suitable vessel such as a 300 ml Erlenmeyer flask.
• 150 ml of fully demineralized water is then added.
• titration takes place with 0.1 M NaOH to a pH of 4.7.
• the diluted phosphation composition Following determination of free acid (diluted), the diluted phosphation composition, following addition of potassium oxalate solution, is titrated, using a pH meter and an electrode, with 0.1 M NaOH to a pH of 8.9. The consumption of 0.1 M NaOH in this procedure, in ml per 10 ml of the diluted phosphation composition, gives Fischer total acid (FTA) in points.
• FFA Fischer total acid
• Total acid is the sum of the divalent cations present and also free and bonded phosphoric acids (the latter being phosphates). It is determined by the consumption of 0.1 M NaOH, using a pH meter and an electrode. For this purpose, 10 ml of the phosphation composition is pipetted into a suitable vessel, such as a 300 ml Erlenmeyer flask, and diluted with 25 ml of fully demineralized water. This is followed by titration with 0.1 M NaOH to a pH of 9. The consumption during this procedure, in ml per 10 ml of the diluted phosphation composition, corresponds to the points number of the total acid (TA).
• a value is the ratio of free acid with added KCl to Fischer total acid, i.e. (FA, KCl):FTA, and is found by division of the value for free acid with added KCl (FA, KCl) by the Fischer total acid value (FTA).
• the phosphation composition in step (I) preferably has a pH in the range from 2.5 to 3.5.
• zinc phosphation compositions in step (I) of the process of the invention that comprise a total of not more than 20 ppm, preferably not more than 15 ppm, further preferably not more than 10 ppm, more preferably not more than 5 ppm and most preferably a total of not more than 1 ppm of water-soluble compounds of zirconium, titanium and/or hafnium, based on the elements zirconium, titanium and/or hafnium, and especially preferably do not comprise any water-soluble compounds of zirconium, titanium and/or hafnium.
• step (I) of the process of the invention is dispensed with entirely.
• Mapping is understood by the person skilled in the art of dip coating of metallic components to mean a spotty visual impression of the paint coating owing to an inhomogeneous paint layer thickness after the baking of the dip paint.
• the cause of poisoning of the phosphate bath by titanium, zirconium and/or hafnium may as already described above lie, in particular, in encrusted conveying systems for the composite metal constructions or in pre-passivated aluminum parts of the constructions.
• the boron content of the zinc phosphation composition in the form of water-soluble inorganic compounds especially via fluoroborates such as tetrafluoroborate in particular, to reduce the poisoning of the phosphation bath by titanium, zirconium and/or hafnium.
• the zinc phosphation composition therefore has a free fluoride content of at least 5 mg/l but not greater than 200 mg/l, preferably at least 10 mg/l but not greater than 200 mg/l, further preferably at least 20 mg/l but not greater than 175 mg/l, further preferably at least 20 mg/l but not greater than 150 mg/l, further preferably at least 20 mg/l but not greater than 135 mg/l, further preferably at least 20 mg/l but not greater than 120 mg/l, especially preferably at least 50 mg/l but not greater than 120 mg/l and very especially preferably at least 70 mg/l but not greater than 120 mg/l.
• the conveying systems for the composite metal constructions have crusts that comprise titanium, zirconium and/or hafnium and preferably originate from the passivation of the composite metal constructions with titanium, zirconium- and/or hafnium-comprising water-soluble compounds in step (II) that follows the phosphation in step (I).
• the conveying systems preferably run in a cycle, such that the crusts that have come into contact with titanium, zirconium and/or hafnium in step (II) are exposed again to the acidic phosphation composition in step (I).
• the aluminum portions of the composite metal constructions have been pre-passivated, i.e. they have already been provided with a passivation layer comprising titanium, zirconium and/or hafnium.
• the conveying systems for the composite metal constructions have crusts that comprise titanium and/or zirconium and preferably originate from the passivation of the composite metal constructions with titanium-, zirconium- and/or hafnium-comprising water-soluble compounds in step (II) that follows the phosphation in step (I).
• the conveying systems preferably run in a cycle, such that the crusts generated in step (II) are exposed again to the acidic phosphation composition in step (I).
• the aluminum portions of the composite metal constructions have been pre-passivated, i.e. they have already been provided with a passivation layer comprising titanium, zirconium and/or hafnium.
• the zinc phosphation composition in step (I) of the process of the invention preferably comprises at least 0.3 g/l, more preferably at least 0.8 g/l, but preferably not more than 3 g/l, more preferably not more than 2 g/l, of zinc ions.
• the content of phosphate ions in the phosphation solution is preferably in the range from 5 to 50 g/l, further preferably from 8 to 25 g/l and more preferably from 10 to 20 g/l in each case calculated as P 2 O 5 .
• the zinc phosphation composition of the process of the invention may, as well as the aforementioned zinc ions and phosphate ions, additionally comprise at least one of the following accelerators:
• Such accelerators are familiar in the art as components of phosphation baths and fulfill the function of “hydrogen scavengers” in that they directly oxidize hydrogen formed by the acidic attack on the metallic surface and in so doing are themselves reduced.
• the forming of a homogeneous crystalline zinc phosphate layer is significantly facilitated by the accelerator that prevents the formation of gaseous hydrogen at the metal surface.
• the zinc phosphation composition of the process of the invention may, as well as the aforementioned zinc ions and phosphate ions, additionally comprise at least one of the following anions:
• the proportion of up to 5 g/l, preferably up to 3 g/l, of nitrate which is customary in nickel-containing phosphation facilitates the formation of a crystalline homogeneous and continuous phosphate layer on steel and on galvanized and alloy-galvanized steel surfaces.
• nickel-free phosphation In the case of nickel-free phosphation, however, the acceleration of the layer formation reaction by nitrate is critical. Such a nickel-free phosphation leads to lower coat weights and in particular to reduced incorporation of manganese into the crystal. Since the phosphate coating has a zero nickel content, however, too low a manganese content of the phosphate coating is at the expense of its alkali resistance.
• the alkali resistance in turn plays a critical part during subsequent cathodic electrocoat deposition.
• electrolytic dissociation of water occurs at the substrate surface: hydroxide ions are formed.
• the pH at the substrate interface goes up. This makes agglomeration and deposition of the electrocoat possible in the first place; but the elevated pH can also damage the crystalline phosphate layer.
• iron(III) cations result in improved corrosion protection on steel and on zinc and zinc alloys.
• iron(III) cations lead to improved stability of the corresponding phosphation bath.
• the addition of iron(III) cations can additionally generate a more easily filterable sludge floc, such that cryolite can be more easily removed from the bath.
• Aqueous compositions for conversion treatment that comprise not only zinc ions but also both manganese and nickel ions, as tricationic phosphation solutions, are known to the person skilled in the art in the field of phosphation and are also of good suitability in the context of the present invention.
• the phosphation solutions in step (I) of the process of the invention optionally also comprise ammonium ions that pass into the phosphation solution for adjustment of the free acid content.
• step (I) The water rinse operation between step (I) and step (II) is obligatory since the phosphate ions and metal cations present in the phosphation composition would otherwise be entrained into the passivation bath. This would lead to a change in the bath parameters that would be difficult to control and to precipitation of titanium, zirconium and/or hafnium as sparingly soluble phosphates.
• the water rinse operation may be one water rinse or else a totality of at least two water rinses.
• Each water rinse may be conducted with fully demineralized water or tap water. There may also be at least one surfactant present in each case.
• step (I) After the workup of the rinse water enriched with the components of the phosphation bath in step (I), selective recycling of the components into the phosphation bath may be undertaken.
• step (I) The composite metal construction treated and rinsed in step (I) and is contacted in step (II) with the acidic passivation composition by dipping or by spray application of the solution.
• step (II) of the method by virtue of the contacting of the composite metal construction with the acidic passivation composition, in accordance with the invention, a passivation layer is formed on the aluminum surfaces, with dissolution of the zinc phosphate layer on the steel surfaces or galvanized and/or alloy-galvanized steel surfaces during the contacting with the passivation composition to an extent of not more than 50%, preferably to an extent of not more than 20%, more preferably to an extent of not more than 10%.
• passive layers of aluminum are considered to be passivating inorganic or mixed inorganic-organic thin-film coatings that do not form continuous crystalline phosphate layers.
• the pH of the acidic passivation composition in the range from 2.0 to 5.5, preferably from 2.5 to 5.5, more preferably from 3.0 to 5.5 and most preferably from 3.5 to 5.5 essentially ensures that not more than 50% of the zinc phosphate layer on the steel surfaces or galvanized and/or alloy-galvanized steel surfaces is dissolved, the corresponding passive layers on the aluminum surfaces of the composite metal construction are typically generated by chromium-free acidic passivation compositions.
• the passivation composition comprises at least one water-soluble compound selected from the water-soluble compounds of the metal ions of Mo, Cu, Ag, Au, Ti, Zr, Hf, Pd, Sn, Sb, Li, V and Ce.
• the water-soluble compounds are respectively present in a concentration in the following preferred, particularly preferred and very particularly preferred ranges (each calculated as the corresponding metal):
• the metal ions present in the water-soluble compounds are deposited either in the form of a salt which comprises the corresponding metal cation (e.g. molybdenum or tin) preferably in at least two oxidation stages more particularly in the form of an oxyhydroxide, a hydroxide, a spinel or a defect spinel or in elemental form on the surface that is to be treated (e.g. copper, silver, gold or palladium).
• a salt which comprises the corresponding metal cation (e.g. molybdenum or tin) preferably in at least two oxidation stages more particularly in the form of an oxyhydroxide, a hydroxide, a spinel or a defect spinel or in elemental form on the surface that is to be treated (e.g. copper, silver, gold or palladium).
• the passivation composition comprises molybdenum ions and optionally further metal ions each in the form of water-soluble compounds. They are added to the passivation composition preferably in the form of molybdate, further preferably of ammonium heptamolybdate and especially preferably of ammonium heptamolybdate ⁇ 7H 2 O.
• the molybdenum ions may also be added in the form of sodium molybdate.
• Molybdenum ions may alternatively be added to the passivation composition, for example, in the form of at least one salt comprising molybdenum cations, such as molybdenum chloride, and then oxidized to molybdate by a suitable oxidizing agent, examples being the accelerators described earlier on above.
• a suitable oxidizing agent examples being the accelerators described earlier on above.
• the passivation composition itself comprises a corresponding oxidizing agent.
• the passivation composition comprises molybdenum ions in combination with copper ions, tin ions or zirconium ions.
• molybdenum ions in combination with zirconium ions and also, optionally, comprises a polymer or copolymer selected more particularly from the group consisting of the polymer classes of the polyamines, polyethyleneamines, polyanilines, polyimines, polyethyleneimines, polythiophenes and polypyrroles and also mixtures thereof and copolymers thereof and polyacrylic acid.
• the content of molybdenum ions here is preferably in the range from 20 to 225 mg/l, more preferably from 50 to 225 mg/l and very preferably from 100 to 225 mg/l (calculated as Mo), and the content of zirconium ions is preferably in the range from 50 to 300 mg/l, more preferably from 50 to 150 mg/l (calculated as Zr).
• the passivation composition comprises copper ions, especially copper(II) ions, and optionally other metal ions each in the form of water-soluble compounds.
• the passivation composition in that case comprises a content of copper ions in the range from 100 to 500 mg/l, more preferably from 150 to 225 mg/l.
• the passivation composition comprises Ti, Zr and/or Hf in complexed form, preferably in a concentration in the range from 20 to 500 mg/l, further preferably from 50 to 300 mg/l and more preferably from 50 to 150 mg/l (calculated as Ti, Zr and/or Hf), and optionally further metal ions in the form of water-soluble compounds.
• the complexes in question are preferably fluoro complexes, more preferably hexafluoro complexes.
• the passivation composition comprises preferably 10 to 500 mg/l, further preferably 15 to 100 mg/l and especially preferably 15 to 50 mg/l of free fluoride.
• the passivation composition comprises, as well as Ti, Zr and/or Hf in complex form, especially as fluoro complexes, and additionally at least one water-soluble compound selected from the water-soluble compounds of the metal ions of molybdenum, copper, especially copper(II), silver, gold, palladium, tin and antimony, and also lithium, preferably of molybdenum and copper, especially copper(II).
• the water-soluble compounds are respectively present in a concentration in the following preferred ranges (each calculated as the corresponding metal):
• the passivation composition comprises, as well as Ti, Zr and/or Hf in complex form, especially as fluoro complexes, additionally at least one organosilane and/or at least one hydrolysis product thereof, i.e. an organosilanol, and/or at least one condensation product thereof, i.e. an organosiloxane/polyorganosiloxane, preferably in a concentration in the range from 5 to 200 mg/l, further preferably from 10 to 100 mg/l and especially preferably from 20 to 80 mg/l (calculated as Si).
• the at least one organosilane preferably has at least one amino group. Particular preference is given to one that can be hydrolyzed to an aminopropylsilanol and/or to 2-aminoethyl-3-aminopropylsilanol and/or is a bis(trimethoxysilylpropyl)amine.
• the passivation composition comprises, as well as Ti, Zr and/or Hf in complex form, especially as fluoro complexes, additionally at least one water-soluble compound selected from the water-soluble compounds of the metal ions of molybdenum, copper, especially copper(II), silver, gold, palladium, tin and antimony, and also lithium, preferably of molybdenum and copper, especially copper(II), and at least one organosilane and/or at least one hydrolysis product thereof, i.e. an organosilanol, and/or at least one condensation product thereof, i.e.
• an organosiloxane/polyorganosiloxane preferably in a concentration in the range from 5 to 200 mg/l, further preferably from 10 to 100 mg/l and especially preferably from 20 to 80 mg/l (calculated as Si).
• the water-soluble compounds are respectively present in a concentration in the following preferred ranges (each calculated as the corresponding metal):
• the process of the invention for anticorrosive treatment of composite metal constructions assembled from metallic materials that also have aluminum surfaces at least to some degree, after cleaning and activation of the metallic surfaces, is effected firstly by contacting the surfaces with the zinc phosphation composition of step (I), for example by a spraying or dipping method, at temperatures in the range of 20-65° C. and for a period of time matched to the mode of application.
• step (I) of the process of the invention is suitable especially also for those phosphation plants that work by the principle of the dipping method, since speck formation in the method of the invention is suppressed.
• step (I) It is advantageous first to clean and especially to degrease the composite metal construction prior to the treatment with the zinc phosphation composition in step (I).
• an acidic, neutral, alkaline or strongly alkaline cleaning composition it is especially possible to use an acidic, neutral, alkaline or strongly alkaline cleaning composition, but optionally also additionally an acidic or neutral pickling composition.
• An alkaline or strongly alkaline cleaning composition has been found here to be especially advantageous.
• the aqueous cleaning composition may, as well as at least one surfactant, optionally also comprise a detergent builder and/or other additions, for example complexing agents. It is also possible to use an activating detergent.
• the composite metal construction is then advantageously at least rinsed with water, in which case the water may optionally have been admixed as well with a water-dissolved additive such as a nitrite or surfactant, for example.
• a water-dissolved additive such as a nitrite or surfactant
• the activating composition Prior to the treatment of the composite metal construction with the zinc phosphation composition in step (I), it is advantageous to treat the composite metal construction with an activation composition.
• the purpose of the activating composition is to deposit a multitude of ultrafine phosphate particles as seed crystals on the surface of the portions made of zinc and iron. These crystals help to form an in particular crystalline phosphate layer having an extremely high number of densely disposed, fine phosphate crystals, or a largely continuous phosphate layer on the portions made of zinc and iron, in the subsequent method step, in contact with the phosphation composition—preferably without rinsing in-between.
• compositions contemplated in this case include, in particular, acidic or alkaline compositions based on titanium phosphate or zinc phosphate.
• activating agents especially titanium phosphate or zinc phosphate, in the cleaning composition—in other words, to carry out cleaning and activation in one step.
• the composite metal construction may be provided with a primer coat, preferably with an organic dip coat, especially an electrocoat preferably without prior oven drying of the component treated in accordance with the invention.
• a top coat which may be a powder coat or a wet coat.
• the present invention additionally relates to a zinc phosphation composition for selective phosphation of steel, galvanized steel and/or alloy-galvanized steel surfaces in a metallic composite construction comprising a portion made of aluminum, wherein the zinc phosphation composition has a points number of free acid with added KCl of at least 0.6 points and a pH preferably in the range from 2.5 to 3.5, and
• zinc phosphation composition additionally comprises a content of sodium and/or potassium ions and of aluminum ions.
• the free fluoride content is in the range from 10 to 200 mg/l, further preferably from 20 to 175 mg/l, further preferably from 20 to 150 mg/l, further preferably from 20 to 135 mg/l, further preferably from 20 to 120 mg/l, especially preferably from 50 to 120 mg/l and very especially preferably from 70 to 120 mg/l.
• cryolite precipitation at the surface of the composite metal constructions and the poisoning of the phosphation bath by titanium, zirconium and/or hafnium can be reduced particularly effectively when, for the zinc phosphation composition, the dimensionless quotient
• T represents the temperature/° C.
• F tot. represents the total fluoride content/(mol/l)
• [B] represents the concentration of the element boron/(mol/l).
• the zinc phosphation composition of the invention comprises a total of not more than 20 ppm, preferably not more than 15 ppm, further preferably not more than 10 ppm, more preferably not more than 5 ppm and most preferably not more than 1 ppm in total of water-soluble compounds of zirconium, titanium and/or hafnium, based on the elements zirconium, titanium and/or hafnium, and especially no water-soluble compounds of zirconium, titanium and/or hafnium.
• the present invention also relates to a concentrate from which the zinc phosphation composition of the invention can be obtained by diluting with a suitable solvent and/or dispersion medium, preferably with water, and optionally adjusting the pH.
• the dilution factor here is preferably between 2 and 100, preferably between 5 and 50.
• the present invention finally relates to a corrosion-protected composite metal construction which comprises at least a portion of aluminum and at least a portion of zinc and optionally a further portion of iron, and is obtainable by the method of the invention.
• the composite metal constructions protected against corrosion by the method of the invention correspondingly find use in the automotive supplier industry, in bodywork construction in automobile manufacture, in agricultural machine construction, in shipbuilding, in the construction sector or for the production of white goods.
• Aqueous zinc phosphation solutions were made up, each of which had a points number of free acid with added KCl of 1.1 points, a Fischer total acid of 19.5 points, an A value of 0.056 and a pH in the range from 2.5 to 3.5.
• Said phosphation solutions were nickel-free and each comprised 15 g/l of phosphate ions calculated as P 2 O 5 , 0.8 g/l of zinc ions, 1.0 g/l of manganese ions, different amounts of free fluoride (see tab. 1), 1.0 g/l of boron in the form of and calculated as BF 4 , and 34 mg/l of the hydrogen peroxide accelerator.
• the phosphation solutions were brought to a temperature of 45° C.
• Cleaned test sheets of aluminum (AA 6016) were each sprayed uniformly with one phosphation solution, rinsed and dipped at room temperature into an acidic aqueous passivation composition comprising 150 mg/l of H 2 ZrF 6 calculated as Zr for 30 s. Without prior oven drying, the sheets were provided with an electrocoat and finally with a wet coat (standard automobile paint structure).
• test sheets were subjected to a 144-hour CASS test to DIN EN ISO 9227, 2017-07 and to a 1008-hour filiform test to DIN EN 3665, 1997-08.
• the applicant took samples over a period of 2.2 years from a customers operating zinc phosphation bath with varying free fluoride content and determined the content of free fluoride (F free ) and of zirconium (Zr). For this purpose, a fluoride-selective potentiometric combination electrode was used, or an ICP (inductively coupled plasma) analysis was performed.
• F free free fluoride
• Zr zirconium
• Aqueous zinc phosphation solutions (ZPS No. 1-8) were made up, each of which had a points number of free acid with added KCl of 1.5 points.
• Said phosphation solutions were nickel-free and each comprised 15 g/l of phosphate ions calculated as P 2 O 5 , 0.8 g/l of zinc ions, 1.0 g/l of manganese ions, 100 mg/l of free fluoride and different amounts of sodium and potassium ions, and also either tetrafluoroborate or hexafluorosilicate.
• the phosphation solutions were brought to a temperature of 45° C. and stirred in a beaker by means of a stir bar at moderate speed.
• the dissolved concentrations of aluminum, silicon and boron were determined at the start (0 h) and after 24 h. When the concentration of dissolved aluminum fell, this was attributable to precipitation in the form of cryolite. If, by contrast, there was a decrease in the concentration of dissolved silicone, this was based on precipitation in the form of K 2 SiF 6 .

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