Method for zinc phosphating metal components in series so as to form layers
11486044 · 2022-11-01
Assignee
Inventors
- Jan-Willem Brouwer (Willich, DE)
- Frank-Oliver Pilarek (Bergheim, DE)
- Fernando Jose Resano Artalejo (Duesseldorf, DE)
- Jens Kroemer (Neuss, DE)
- Matthias Hamacher (Huerth, DE)
- Thibault Leseur (Bruehl, DE)
- Marc Balzer (Duesseldorf, DE)
Cpc classification
International classification
C23C22/00
CHEMISTRY; METALLURGY
Abstract
The invention relates to a method for zinc phosphating components comprising surfaces made of zinc in order to suppress the formation of insoluble phosphation constituents removably adhered to the zinc surfaces and thus further improve the adhesion of dip-paint coatings applied later. In the method, a process is used of activating the zinc surfaces by means of dispersions containing particulate hopeite, phosphophyllite, scholzite, and/or hureaulite, wherein the proportion of particulate phosphates in the activation process must be adapted to the quantity of free fluoride and dissolved silicon in the zinc phosphation.
Claims
1. A method for an anti-corrosion treatment of a series of metal components comprising metal components that have, at least in part, zinc surfaces, in which method the metal components of the series successively undergo the following wet-chemical treatment steps: (I) activation by contacting the metal components with an alkaline aqueous dispersion that has a D50 value of less than 3 μm and an inorganic particulate constituent of which comprises phosphates composed at least in part of hopeite, phosphophyllite, scholzite and/or hureaulite; the phosphates from the inorganic particulate constituent in the alkaline aqueous dispersion are present in an amount less than 0.8 g/kg calculated as PO.sub.4 and based on the dispersion; (II) zinc phosphating by contacting the metal components from step (I) with an acidic aqueous composition containing: (a) 5-50 g/kg of phosphate ions, (b) 0.3-3 g/kg of zinc ions, and (c) at least one source of free fluoride, wherein the concentration of free fluoride in the acidic aqueous composition is at least 0.5 mmol/kg, wherein the quotient of the concentration of the phosphates in the inorganic particulate constituent of the alkaline aqueous dispersion of step (I) in mmol/kg with respect to the sum of the concentration of free fluoride and the concentration of silicon in each case in the acidic aqueous composition of step (II), in each case in mmol/kg, is greater than 0.5.
2. The method according to claim 1, wherein the proportion of phosphates, based on the inorganic particulate constituents of the alkaline aqueous dispersion of step (I), is at least 30 wt. %, calculated as PO.sub.4.
3. The method according to claim 1, wherein the proportion of zinc in the inorganic particulate constituent of the alkaline aqueous dispersion of step (I) is at least 20 wt. %.
4. The method according to claim 1, wherein the proportion of titanium in the inorganic particulate constituent of the alkaline aqueous dispersion of step (I) is less than 5 wt. %.
5. The method according to claim 1, wherein the amount of phosphates from the inorganic particulate constituent of the alkaline aqueous dispersion of step (I) is at least 40 mg/kg, calculated as PO.sub.4 and based on the dispersion.
6. The method according to claim 1, wherein the pH of the alkaline aqueous dispersion of step (I) is greater than 8, but less than 12.
7. The method according to claim 1, wherein, as the source of free fluoride, complex fluorides of the element silicon are contained in the acidic aqueous composition of step (II).
8. The method according to claim 7, wherein the concentration of silicon in water-dissolved form in the acidic aqueous composition of step (II) is at least 0.5 mmol/kg.
9. The method according to claim 1, wherein free acid in the acidic aqueous composition of step (II) is at least 0.4 points.
10. The method according to claim 1, wherein the concentration of free fluoride in the acidic aqueous composition of step (II) is less than 8 mmol/kg.
11. The method according to claim 1 wherein neither a rinsing nor a drying step takes place between the activation step (I) and the zinc phosphating step (II).
12. The method according to claim 1 wherein, in the series of components, components that have at least one aluminum surface are also treated.
13. The method according to claim 1 wherein the zinc phosphating step (II), with or without an intermediate rinsing and/or drying step between step (I) and step (II), is followed by dip coating.
14. The method according to claim 1, wherein (I) in step (I), the alkaline aqueous dispersion comprises an amount of phosphates from the inorganic particulate constituent of at least 150 mg/kg, calculated as PO.sub.4 and based on the dispersion; and (II) in the acidic aqueous composition of step (II), the source of free fluoride comprises complex fluorides of the element silicon, with the concentration of silicon in water-dissolved form being at least 1 mmol/kg, but less than 6 mmol/kg.
15. The method according to claim 14, wherein (I) in step (I), the alkaline aqueous dispersion has a pH of greater than 9, but less than 11; has a proportion of phosphates, based on the inorganic particulate constituent of at least 40 wt. %, calculated as PO.sub.4; a proportion of zinc in the inorganic particulate constituent of at least 40 wt. %; and a proportion of titanium in the inorganic particulate constituent of less than 1 wt. %; and (II) in step (II), the acidic aqueous composition of step (II) has a concentration of free fluoride of at least 2 mmol/kg, but less than 8 mmol/kg and free acid is at least 0.4 points, but not more than 2 points.
16. The method according to claim 14, wherein after step (II), the metal components are subjected to a rinsing step and no drying step, followed by electrocoating.
17. The method according to claim 1, wherein the amount of phosphates from the inorganic particulate constituent in the alkaline aqueous dispersion is less than 0.4 g/kg calculated as PO.sub.4 based on the dispersion.
18. The method according to claim 1, wherein a concentration of silicon in water-dissolved form in the acidic aqueous composition is at least 0.5 mmol/kg.
Description
EXAMPLES
(1) Galvanized steel sheets (HDG) were treated in zinc phosphating baths with different levels of free fluoride after prior activation with dispersions of particulate zinc phosphate, and the appearance of the coatings was evaluated immediately after the zinc phosphating. Table 1 contains an overview of the activation and zinc phosphating compositions and the results of the evaluation of the quality of the coatings. The sheets underwent the following method steps in the sequence indicated: A) Cleaning and degreasing by spraying at 60° C. for 90 seconds 25 g/L BONDERITE® C-AK 1565 (Henkel AG & Co. KGaA) 2 g/L BONDERITE® C-AD 1270 (Henkel AG & Co. KGaA) Preparing with deionized water (κ<1 μmScm.sup.−1); adjusting the pH to 11.8 with potassium hydroxide solution. B) Rinsing with deionized water (κ<1 μmScm.sup.−1) at 20° C. for 60 seconds C) Dip activation at 20° C. for 60 seconds 0.5-3 g/kg contains 8.4 wt. % of zinc in the form of Zn.sub.3(PO.sub.4).sub.2*4H.sub.2O 200 mg/kg K.sub.4P.sub.2O.sub.7 PREPALENE® X (Nihon Parkerizing Co., Ltd.) Preparing with deionized water (κ<1μScm.sup.−1); adjusting the pH to 10.0 with H.sub.3PO.sub.4. The D50 value of the dispersion for activation was 0.25 μm at 20° C., determined on the basis of the static scattered light analysis according to the Mie theory in accordance with ISO 13320:2009 by means of particle analyzer HORIBA LA-950 (Horiba Ltd.) assuming a refractive index of the scattering particles of n=1.52−i.Math.0.1. D) Zinc phosphating by immersion at 50° C. for 180 seconds
(2) TABLE-US-00001 1.1 g/kg zinc 1.0 g/kg manganese 1.0 g/kg nickel 15.7 g/kg phosphate 2 g/kg nitrate An amount of a source of fluoride was added in accordance with Table 1. Preparing with demineralized water (κ<1 μScμm.sup.−1); adjusting the free acid with 10% NaOH free acid: 1.0 point The free acid is determined from 10 ml sample volume diluted to 50 ml with deionized water and subsequent titration with 0.1 N NaOH to pH 3.6, where the consumption of sodium hydroxide solution in milliliters corresponds to the amount of free acid in points. Total acid content: 20 points The total acid content is determined from 10 ml sample volume diluted to 50 ml with deionized water and subsequent titration with 0.1 N NaOH to pH 8.5, where the consumption of sodium hydroxide solution in milliliters corresponds to the total amount of acid in points. Sodium nitrite: 2.0 gas points measured in the azotometer after addition of sulfamic acid E) Rinsing with deionized water (κ<1 μScμm.sup.−1) at 20° C. for 60 seconds F) Drying in ambient air It can be seen from Table 1 that satisfactory phosphate coatings, which thus have no loose adhesions on the galvanized steel, can be achieved by adapting the amount of particulate zinc phosphate in the activation to the amount of free fluoride and the hexafluorosilicic acid in the zinc phosphating. If the amount of particulate zinc phosphate in the activation falls below the value defined by the free fluoride amount and the concentration of silicon, coatings that appear partially dusty (A1-Si-300, A3-Si-600 and A1-F-90) are formed which are completely unsuitable for subsequent dip coating.
(3) TABLE-US-00002 TABLE 1 Example* Activation PO.sub.4/mmolkg.sup.−1 Zinc phosphating Free fluoride.sup.#/ Layer mmolkg.sup.−1 Source weight/gm.sup.−2