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
  • C23C22/78—Pretreatment of the material to be coated
• • 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
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
  • C23F11/08—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids
  • C23F11/18—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids using inorganic inhibitors
  • C23F11/187—Mixtures of inorganic inhibitors
  • C23F11/188—Mixtures of inorganic inhibitors containing phosphates
• • 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
• • 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
  • C23C22/73—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

Definitions

• the present invention relates to a process for the layer-forming zinc phosphating of components comprising surfaces of steel with high tolerance to dissolved in the zinc phosphating aluminum, in which the precipitation of sparingly soluble aluminum salts can be largely avoided.
• activation of the zinc surfaces by means of dispersions containing particulate hopeite, phosphophyllite, scholzite and / or hureaulite is resorted to, wherein the proportion of particulate phosphates must be adjusted in the activation of the amount of free fluoride and dissolved aluminum in the zinc phosphating.
• Zinc phosphating has been used for decades and has been excellently studied for the formation of crystalline anticorrosive coatings on metallic surfaces, in particular on materials of the metals iron, zinc and aluminum.
• the Zinkphosphat ist takes place in a layer thickness of a few micrometers and is based on a corrosive stain of the metallic material in an acidic aqueous composition containing zinc ions and phosphates, which precipitate as sparingly soluble crystallites in an alkaline diffusion layer directly to the metallic surface phase boundary and there on grow up.
• water-soluble compounds are often added, which are a source of fluoride ions.
• the Zinkphosphat ist is always initiated with an activation of the metallic surfaces of the component to be phosphated.
• the wet-chemical activation is carried out conventionally by contacting with colloidal dispersions of phosphates, which in this respect immobilized on the metal surface, in the subsequent phosphating serve as a growth nucleus for the formation of a crystalline coating.
• Suitable dispersions are colloidal, mostly alkaline aqueous compositions Basis of phosphate crystallites, which have in their crystal structure only small crystallographic deviations from the nature of the deposited zinc phosphate layer.
• water-insoluble bi-and trivalent phosphates are also suitable as starting materials for providing a colloidal solution suitable for activating a metal surface for zinc phosphating. That's how it teaches WO 98/39498 A1 in this context, in particular bi- and trivalent phosphates of the metals Zn, Fe, Mn, Ni, Co, Ca and Al, wherein technically preferred phosphates of the metal zinc are used for activation for a subsequent zinc phosphating.
• Each type of layer-forming phosphating as a process of activation and zinc phosphating, has its peculiarity, which is particularly important in the treatment of components composed of a mix of different metallic materials or in the treatment of novel materials.
• a homogeneous layer formation on the surfaces of the material iron in the presence of aluminum ions does not succeed and makes a masking with fluoride ions required.
• the masking of the aluminum ions reaches its limits where high levels of aluminum enter the zinc phosphating bath and, in turn, equilibrium aluminum ions interfere with the formation of defect-free coatings on the steel surfaces.
• the aluminum dissolved in the zinc phosphating is at least partially removed from the zinc phosphating bath.
• cryolite or Elpasolith precipitation is technically complicated to control and requires on the one hand to avoid the formation of encrustations removal of the mud from the bath and on the other hand to avoid defects in the dip coating an intensive sink after Zinkphosphatierung to finest deposition of Kryolith- or Elpasolite crystallites are removed from the phosphated surfaces.
• the WO 2004/007799 A2 proposes, therefore, to carry out a phosphating at the lowest possible levels of sodium and / or potassium ions, so that a separate precipitation range for aluminum ions does not have to be provided, with dissolved aluminum contents above 0.1 g / L as not However, a preferred range of 0.01-0.4 g / L for dissolved aluminum for the Phosphating of at least partially made of aluminum components is specified.
• EP 1 988 189 A1 describe in each case a method for wet-chemical surface treatment of a series of metallic components comprising at least partially Fe surfaces, wherein activation takes place before zinc phosphating.
• the activation is carried out with an alkaline aqueous dispersion which has a D50 value of less than 3 ⁇ m and whose inorganic particulate constituent comprises phosphates, the entirety of these phosphates being composed at least partially of hopeite, phosphophyllite and / or scholzite.
• the zinc phosphating is carried out with acidic aqueous compositions containing phosphate ions, zinc ions and at least one source of fluoride ions.
• the object is to find suitable conditions for a process for zinc phosphating of metallic components which tolerates high proportions of dissolved aluminum, for which zinc phosphate coatings largely defect-free on the steel surfaces result, so that an overall excellent paint adhesion results.
• a method is to be provided in which metallic components in the phosphating can be treated layer-forming, the surfaces of which are formed both of metallic materials of the element iron and metallic materials of the element aluminum.
• the care needs of Zinkphosphatierbades should be as low as possible and ideally be adjusted by pickling and pickling stationary equilibrium concentration in the treatment of a series of components unproblematic for the Phosphatieraff on the steel surfaces of the components.
• This object is surprisingly achieved in that the proportion of contributing to the activation of particulate phosphates on the amount of free fluoride and dissolved in water aluminum ions in the zinc phosphating is to be adjusted.
• the treated according to the present invention components can be any arbitrarily shaped and designed spatial structures, which originate from a fabrication process, in particular also semi-finished products such as strips, sheets, rods, tubes, etc. and composite structures assembled from the aforementioned semi-finished products, wherein the semi-finished products preferably by gluing, welding and / or flanging to the composite structure are connected together.
• a component is metallic if its geometric surface is formed by at least 10% of metallic surfaces.
• galvanized steel grades according to the invention form surfaces of zinc, whereas at the cutting edges and fürschliffstellen example, an automobile body, which is made solely of galvanized steel, according to the invention surfaces of iron can be exposed.
• the components of the series which have at least partially surfaces of iron, preferably at least 5% with respect to the component surface surfaces of iron.
• Steel grades such as hot-formed steel may also be provided with a metallic coating of aluminum and silicon several microns thick to prevent scaling and forming.
• An anti-corrosive treatment of the components in series is when a plurality of components is brought into contact with in the respective treatment steps provided and usually held in system tanks treatment solution, wherein the bringing into contact of the individual components sequentially and thus separated in time he follows.
• the system tank is the container in which the pre-treatment solution is in series for the purpose of anti-corrosive treatment.
• the treatment steps of activation and zinc phosphating are carried out for a component of the anticorrosive treatment in series then "successively", unless they are interrupted by any other than the respectively provided subsequent wet chemical treatment.
• Wet-chemical treatment steps in the context of the present invention are treatment steps which take place by bringing the metallic component into contact with a composition consisting essentially of water and which do not constitute rinsing steps.
• a rinsing step serves only the complete or partial Removal of soluble residues, particles and active components, which are adhered to the component from a previous wet-chemical treatment step, from the component to be treated, without the active component itself containing active components based on metallic or semi-metallic elements, which are already Contacting the metallic surfaces of the component with the flushing liquid consume. So the flushing liquid can only be city water.
• the concentration of aluminum ion dissolved in the acidic aqueous zinc-phosphating composition is determined in the filtrate by membrane filtration of the acidic aqueous composition made using a membrane having a nominal pore size of 0.2 ⁇ m by atomic emission spectrometry (ICP-OES) , Similarly, in the context of the present invention, the concentrations of other ions of metallic or semimetallic elements in the acidic aqueous composition of the zinc phosphating are to be determined in dissolved form.
• the "pH" as used in the present invention corresponds to the negative decadic logarithm of the hydronium ion activity at 20 ° C and can be determined by means of pH-sensitive glass electrodes. Accordingly, a composition is acidic if its pH is below 7, and alkaline if its pH is above 7.
• the preferred pH of the acidic aqueous composition of zinc phosphating in the process according to the invention is above 2.5, more preferably above 2.7, but preferably below 3.5, most preferably below 3.3.
• the concentration of aluminum ions in dissolved form in the acidic aqueous composition of the zinc phosphating is therefore greater than 30 mmol / kg.
• the amount of particulates containing phosphates necessary for sufficient activation of the iron surfaces is so high that the process becomes economically unattractive.
• the concentration of aluminum ions in dissolved form in the acidic aqueous composition of the zinc phosphating is less than 100 mmol / kg, particularly preferably less than 60 mmol / kg, and particularly preferably less than 45 mmol / kg.
• the particulate constituent of the alkaline aqueous dispersion is that solid fraction which, after drying the retentate, remains an ultrafiltration of a defined partial volume of the alkaline aqueous dispersion with a nominal cutoff limit of 10 kD (NMWC, Nominal Molecular Weight Cut Off).
• the ultrafiltration is carried out with the addition of deionized water ( ⁇ ⁇ 1 ⁇ Scm -1 ) until a conductivity below 10 ⁇ Scm -1 is measured in the filtrate.
• the inorganic particulate component of the alkaline aqueous dispersion is, in turn, the one remaining when the particulate component obtained from the drying of the ultrafiltration retentate remains in a reaction furnace at 900 ° C.
• the phosphates contained in the inorganic particulate ingredient are determined after acid digestion thereof with aqueous 10 wt .-% HNO 3 solution at 25 ° C for 15 min as phosphorus content by atomic emission spectrometry (ICP-OES) directly from the acid digestion.
• ICP-OES atomic emission spectrometry
• the alkaline aqueous dispersion has a D50 value of less than 3 microns, since otherwise only very high and thus non-economic proportions of particulate components sufficient occupancy of the metal surfaces with particles, the crystallization nuclei for zinc phosphating, can be done.
• dispersions whose particles are on average larger tend to sedimentation.
• the D50 value of the alkaline aqueous dispersion of the activation is therefore less than 2 .mu.m, more preferably less than 1 .mu.m, the D90 value being preferably less than 5 .mu.m, so that at least 90 vol. -% of the particulate components contained in the alkaline aqueous composition fall below this value.
• the D50 value in this context refers to the volume-average particle diameter of the 50% by volume of that in the alkaline aqueous composition do not exceed containing particulate ingredients.
• the active components of the alkaline dispersion which effectively promote the formation of a closed zinc phosphate coating on the iron surfaces of the component in the subsequent phosphating and in this sense activate the iron surfaces, are composed primarily of phosphates, which in turn are at least partially hopeite, phosphophyllite, scholzite and / or hureauxite include.
• phosphates which in turn are at least partially hopeite, phosphophyllite, scholzite and / or hureauxite include.
• such activation is preferred in which the phosphate fraction of the inorganic particulate constituents of the alkaline aqueous dispersion of the activation is calculated at at least 30% by weight, more preferably at least 35% by weight, particularly preferably at least 40% by weight PO 4 and based on the inorganic particulate component of the dispersion.
• Activation in the context of the present invention is thus essentially based on the phosphates according to the invention in particulate form, wherein the phosphates are preferably at least partially composed of hopeite, phosphophyllite and / or scholzite, particularly preferably hopeite and / or phosphophyllite and particularly preferably hopite are.
• the phosphites hopeite, phosphophyllite, scholzite and / or hureaulite may be dispersed into an aqueous solution to provide the alkaline aqueous dispersion as finely ground powders or as a powder paste triturated with a stabilizer.
• Hopeite without consideration of water of crystallization, comprise stoichiometrically Zn 3 (PO 4 ) 2 as well as the nickel- and manganese-containing variants Zn 2 Mn (PO 4 ) 3 , Zn 2 Ni (PO 4 ) 3 , whereas phosphophyllite comprises Zn 2 Fe (PO 4 ) 3 , Scholzite consists of Zn 2 Ca (PO 4 ) 3 and Hureaulith consists of Mn 3 (PO 4 ) 2 .
• the existence of the crystalline phases hopeite, phosphophyllite, scholzite and / or hureaulite in the alkaline aqueous dispersion may, after separation of the particulate component by ultrafiltration with a nominal cutoff limit of 10 kD (NMWC) as described above and drying of the retentate to Constant mass at 105 ° C using X-ray diffractometric methods (XRD) are detected.
• NMWC 10 kD
• the alkaline aqueous dispersion of activation is at least 20% by weight, preferably at least 30% Wt .-%, particularly preferably at least 40 wt .-% of zinc in the inorganic particulate component of the alkaline aqueous dispersion based on the phosphate content of the inorganic particulate Bestanteils, calculated as PO 4 contains.
• activation in the sense of the present invention is not intended to be achieved by means of colloidal solutions of titanium phosphates, since otherwise the layer-forming zinc phosphating on surfaces of iron, especially steel, does not succeed reliably and the advantage of thin effectively corrosion-protective phosphate coatings on aluminum is not realized.
• the proportion of titanium in the inorganic particulate component of the alkaline aqueous dispersion of the activation is preferably less than 5 wt .-%, more preferably less than 1 wt .-% based on the inorganic particulate component of the dispersion ,
• the alkaline aqueous dispersion of the activation contains a total of less than 10 mg / kg, more preferably less than 1 mg / kg of titanium.
• the proportion of the inorganic particulate components comprising phosphates should be adjusted accordingly.
• the proportion of phosphates in the inorganic particulate constituent based on the alkaline aqueous dispersion of the activation is at least 40 mg / kg, preferably at least 80 mg / kg, more preferably at least 150 mg / kg calculated as PO 4 is.
• the proportion of the phosphates in the inorganic particulate constituent based on the alkaline aqueous dispersion of the activation is less than 0.8 g / kg, more preferably less than 0.6 g / kg, particularly preferably less than 0.4 g / kg calculated as PO 4 .
• the metal surfaces are only slightly stained during activation.
• the inorganic particulate constituents in particular the insoluble phosphates, should undergo only a slight degree of corrosion. Accordingly, it is preferred in the process according to the invention if the pH of the alkaline aqueous dispersion in the activation is greater than 8, more preferably greater than 9, but preferably less than 12, more preferably less than 11.
• the second zinc phosphating treatment step is followed by activation with or without intermediate rinsing step, immediately, so that each component of the series successively undergoes activation followed by zinc phosphating without intervening wet chemical treatment step.
• neither a rinsing nor a drying step takes place between the activation and the zinc phosphating for the components of the series.
• a drying step in the context of the present invention refers to a process in which the surfaces of the metallic component having a wet film are to be dried with the aid of technical measures, for example by supplying thermal energy or passing an air stream.
• the amount of phosphate ions comprises the orthophosphoric acid and the anions of the salts of orthophosphoric acid dissolved in water, calculated as PO 4 .
• the proportion of the free acid in points in the acidic aqueous composition of the zinc phosphating is preferably at least 0.4, but preferably not more than 3, more preferably not more than 2.
• the proportion of free acid in points is determined by adding 10 ml sample volume of the diluted acidic aqueous composition to 50 ml and titrated with 0.1 N sodium hydroxide solution to a pH of 3.6. The consumption of ml of sodium hydroxide gives the score of free acid.
• the acidic aqueous composition of the zinc phosphating additionally comprises cations of the metals manganese, calcium, iron, magnesium and / or aluminum.
• the customary addition of zinc phosphating can also be carried out in an analogous manner according to the invention so that the acidic aqueous composition can contain the conventional accelerators such as hydrogen peroxide, nitrite, hydroxylamine, nitroguanidine and / or N-methylmorpholine-N-oxide.
• the conventional accelerators such as hydrogen peroxide, nitrite, hydroxylamine, nitroguanidine and / or N-methylmorpholine-N-oxide.
• a source of free fluoride ions is essential for the process of layer-forming zinc phosphating on all metallic surfaces of the component, insofar as these are selected from surfaces of iron, aluminum and / or zinc. If all surfaces of these metallic materials are to be provided with a phosphate coating as constituents of the components which are treated in the series, then the amount of the particulate constituents in the activation must be adapted to the amount of free fluoride required for layer formation in the zinc phosphating. For a closed and defect-free phosphate coating on the surfaces of iron, especially steel, is preferred in the process according to the invention if the amount of free fluoride in the acidic aqueous composition of the zinc phosphating is at least 0.5 mmol / kg.
• the amount of free fluoride in the acidic aqueous composition is at least 2 mmol / kg.
• concentration of free fluoride in the acidic aqueous composition of zinc phosphating is below 50 mmol / kg, more preferably below 40 mmol / kg, especially preferably below 30 mmol / kg.
• the concentration of free fluoride does not exceed values above which the phosphate coatings have loose adhesions of phosphates which are easily wipeable because they can not be avoided even by increasing the amount of particulate phosphates in the alkaline aqueous dispersion of activation. Therefore, it is preferred for such devices that in the process of the present invention, the concentration of free fluoride in the acidic aqueous composition of zinc phosphating is below 8 mmol / kg.
• the amount of free fluoride is determined potentiometrically after calibration with fluoride-containing buffer solutions without pH buffering by means of a fluoride-sensitive measuring electrode at 20 ° C in the respective acidic aqueous composition.
• Suitable sources of free fluoride are hydrofluoric acid and its water-soluble salts, such as ammonium bifluoride and sodium fluoride, as well as complex fluorides of the elements Zr, Ti and / or Si, in particular complex fluorides of the element Si.
• the source of free fluoride is therefore selected from hydrofluoric acid and its water-soluble salts and / or complex fluorides of the elements Zr, Ti and / or Si.
• Salts of hydrofluoric acid are water-soluble for the purposes of the present invention, if their solubility in deionized water ( ⁇ ⁇ 1 ⁇ Scm -1 ) at 60 ° C is at least 1 g / L calculated as F.
• the acidic aqueous composition of zinc phosphating contains only limited amounts of sodium and / or potassium ions.
• a further advantage of the method according to the invention consists in the fact that thin closed zinc phosphate coatings are also formed on surfaces of aluminum during its course. Consequently, the series of components to be treated in the method according to the invention preferably also includes the treatment of components which have at least one surface of aluminum. It is irrelevant whether the surfaces of zinc and aluminum are realized in a component composed of corresponding materials or in different components of the series. In the method according to the invention, therefore, within the series preferably also those components are treated which have surfaces of aluminum, wherein the components of the series preferably also have surfaces of aluminum in addition to the surfaces of iron.
• the pickling rate of aluminum exceeds the above zinc phosphating carry-over, it is advantageous to deplete and refresh aluminum ions in the zinc phosphating bath when the zinc phosphating continuously or intermittently extracts a partial volume of the acidic aqueous composition and the zinc phosphating continuously or discontinuously an equal partial volume is supplied by means of one or more such aqueous compositions, each based on the partial volume in comparison to the concentration of the corresponding ions in the withdrawn partial volume higher concentration with respect to the phosphate ions, zinc ions and / or the source of fluoride ions, but with respect to the aluminum ions in dissolved form have a lower concentration than in the withdrawn partial volume.
• a good lacquer adhesion base for a subsequent dip coating in the course of which a substantially organic cover layer is applied, is realized.
• Aluminum (AA6014) and steel sheets (CRS) were treated in zinc phosphating baths with different levels of free fluoride and dissolved aluminum after previous activation with dispersions of particulate zinc phosphate and the appearance of the coatings evaluated immediately after zinc phosphating.
• Table 1 gives an overview of the activation and zinc phosphating compositions and the results of the evaluation of the quality of the coatings. The sheets went through the following steps in the order given: A1) Dipping and degreasing at 55 ° C for 180 seconds 15 g / L BONDERITE® C-AK 11566 (Henkel AG & Co. KGaA) 1.1 g / L BONDERITE® M-AD ZN-2 (from Henkel AG & Co.

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