Method for passivating a metallic surface

• US 10,351,959 B2
• Filed: 03/21/2015
• Issued: 07/16/2019
• Est. Priority Date: 04/11/2014
• Status: Active Grant

• Current Assignee: Audi AG (Volkswagen AG)
• Original Assignee: Audi AG (Volkswagen AG)
• Inventors: Grabowski, Michael, Blucher, Daniel, Korte, Michael, Brettmann, Matthias, Virtanen, Sannakaisa
• Primary Examiner(s): Zheng, Lois L
• Application Number:
  US15/303,376
• Publication Number:
  US 20170037517A1
• Time in Patent Office: 1,578 Days
• CPC Class Codes: C23C 22/22 containing alkaline earth metal cations
• CPC Class Codes: C23C 22/68 using aqueous solutions with pH between 6 and 8
• CPC Class Codes: C25D 13/20 Pretreatment
• CPC Class Codes: C25D 13/22 Servicing or operating apparatus or multistep processes

Abstract

A method for passivating a metal surface of a light-weight metal part is disclosed, wherein a conversion layer is applied to the surface of the light-weight metal part in a passivation step. A passivation step is carried out wherein an aqueous passivation solution is used to create a calcium phosphate-containing conversion layer (5) on the metal surface of the part, said conversion layer comprising oxides and hydroxides from the material of the part and from the passivation solution and containing amino acids.

Claims

1. A method for passivating a metallic surface of a lightweight metal component, said method comprising:

in a passivating step applying an aqueous passivation solution on the metallic surface of the lightweight metal component, thereby generating on the metallic component surface a conversion layer which contains calcium phosphate, amino acids, and further contains oxides and hydroxides of the lightweight metal component; and

in a first coating step forming a lightweight metal KTL (cathodic dip painting) layer as an organic protective layer in a dip bath as paint particles dissolved in the dip bath are attracted by the lightweight metal component and adhere to the lightweight metal component.

2. The method of claim 1, further comprising at least one further coating step in which at least one further layer is applied.

3. The method of claim 2, wherein the at least one further layer is applied in a powder coating process with applied direct voltage.

4. The method of claim 1, wherein at least the metallic surface of the component is formed by a lightweight metal.

5. The method of claim 4, wherein the lightweight metal is magnesium, aluminum or alloys thereof.

6. The method of claim 1, wherein the passivation solution contains at least one of the following components as activators for activating the metal surface of the components:

NaCl at a concentration between 5000 and 8000, and

KCl with a concentration between 300 and 500.

7. The method of claim 1, wherein the passivation solution contains as a catalyst and layer former D-Ca-pantothenate at a concentration between 2 and 30 mg/l.

8. The method of claim 1, wherein the passivation solution contains L-Isoleucine as a layer adhesion agent at a concentration between 90 and 150 mg/l.

9. The method of claim 1, wherein the passivation solution contains at least one of the following components, which are integrated into the conversion layer as fragments for supporting formation of the conversion layer:

NaH₂PO₄ at a concentration between 100 and 170 mg/l;

CaCl₂) at a concentration between 170 and 300 mg/l.

10. The method of claim 1, wherein the conversion layer contains carbonate containing components for supporting formation of the conversion layer, and wherein the passivation solution contains NaHCO₃ for providing the carbonate containing components.

11. The method of claim 1, wherein the passivation solution contains Na-pyruvate at a concentration between 90-170 mg/l for supporting formation of the conversion layer.

12. The method of claim 1, wherein a pH value of the passivation solution is in a neutral to acid range.

13. The method of claim 1, wherein the passivation solution contains further the following components whose concentration is modeled according to their respective concentrations in human blood:

NaCl at 6400 mg/l,

KCl at 400 mg/l,

NaH₂PO₄ at 124 mg/l,

CaCl₂ at 200 mg/l,

NaHCO₃ at 3700 mg/,l

Na-Pyruvate at 110 mg/l,

D-Ca-pantothenate at 4 mg/l,

Myo-Inositol at 7.2 mg/l,

L-Isoleucine at 105 mg/l.

14. The method of claim 1, wherein the passivation solution contains at least one of the following components for increasing coating properties:

L-Arginine at 50 to 120 mg/l,

L-Cysteine with 30 to 80,

L-Histidine.HCl.H₂O at 25 to 65 mg/l,

L-Leucine at 70 to 140 mg/l,

L-Lysin.HCl at 110 to 170 mg/l,

L-Methionine at 20 to 50 mg/l,

L-Penthylalanine at 40 to 80 mg/l,

L-Threonine at 60 to 120 mg/l,

L-Tryptophan at 13 to 20 mg/l,

L-Tyrosine at 40 to 90 mg/l,

L-Valine at 60 to 120 mg/l,

L-Serine at 20 to 60 mg/l,

Colin chloride at 2 to 10 mg/l,

Folic acid at 2 to 10 mg/l,

Nicotine amide at 2 to 10 mg/l,

Pyridoxale.HCl at 2 to 10 mg/l,

Riboflavine at 0.2 to 1 mg/l,

Thiamine-HCl at 2 to 10 mg/l.

15. The method of claim 1, wherein the conversion layer of the component is at least partially covered with a layer in a subsequent coating step.

16. The method of claim 1, wherein the conversion layer has a floe-like layer morphology with crack structures, said layer morphology ensuring in the first coating step a sufficient residual conductivity between the dip bath and the lightweight metal component and/or increasing an adhesive connection between the conversion layer and the lightweight metal KTL layer by entering of a liquid starting component of the lightweight metal KTL layer into the cracks.

17. The method of claim 1, wherein the cathodic dip painting includes a dip method with applied direct voltage.