Two-stage pretreatment of aluminum, in particular aluminum casting alloys, comprising pickle and conversion treatment

Patent metadata

Field	Value
Publication number	US-11499237-B2
Application number	US-202016817044-A
Country	US
Kind code	B2
Filing date	Mar 12, 2020
Priority date	Sep 18, 2017
Publication date	Nov 15, 2022
Grant date	Nov 15, 2022

Abstract

The present invention relates to a method for the anti-corrosion treatment of components produced from aluminum, in particular casting parts such as vehicle rims, comprising a pretreatment stage and subsequent coating, wherein the pretreatment stage in turn includes a pickle on the basis of sulfuric acid aqueous solutions containing water-soluble compounds of the element Ti and at least one α-hydroxycarboxylic acid which is carried out upstream of an acidic conversion treatment on the basis of an acidic aqueous solution containing water-soluble compounds of the elements Zr and/or Ti.

First claim

What is claimed is:

1. A method for an anti-corrosion treatment of components produced from aluminum, comprising a pre-treatment stage and subsequent coating, wherein the pre-treatment stage comprises steps of: a) contacting an aluminum or aluminum alloy component with an aqueous phosphate-free sulfuric acid pickling solution which has a pH of from 1 to 2.5, a free acid content of at least 5 points and contains at least one water-soluble compound of the element Ti, a source of fluoride ions and at least one polybasic α-hydroxycarboxylic acid present in the pickling solution in an amount of at least 0.1 g/kg but does not exceed 4 g/kg; and subsequently b) contacting the aluminum or aluminum alloy component pickled in a) with an aqueous conversion treatment solution which has a pH of from 1 to 3.5 and contains at least one water-soluble compound of the elements Zr and/or Ti.

2. The method according to claim 1 , wherein the at least one polybasic α-hydroxycarboxylic acid in the pickling solution is selected from citric acid and/or tartaric acid.

3. The method according to claim 2 , wherein the at least one polybasic α-hydroxycarboxylic acid in the pickling solution is tartaric acid.

4. The method according to claim 1 , wherein the water-soluble compounds of the element Ti are present in the pickling solution in an amount of at least 0.04 g/kg, but not exceeding 0.6 g/kg, in each case based on the element Ti.

5. The method according to claim 4 , wherein the at least one water-soluble compound of the element Ti is present in the pickling solution in an amount of no more than 0.3 g/kg based on the amount of Ti.

6. The method according to claim 5 , wherein the at least one water-soluble compound of the element Ti is present in the pickling solution in an amount of at least 0.1 g/kg based on the element Ti.

7. The method according to claim 6 , wherein the ratio of Zr and Ti to total fluoride content in the conversion treatment solution is at least 0.4.

8. The method according to claim 1 , wherein the pickling solution has a pH of less than 2.

9. The method according to claim 1 , wherein the pickling solution has a free acid content of at least 6 points, but no more than 10.

10. The method according to claim 1 , wherein the pickling solution has a total acid content of at least 12 points, but no more than 18 points.

11. The method according to claim 1 , wherein the at least one water-soluble compound of the elements Zr and/or Ti in the conversion treatment solution is present in an amount of at least 0.1 mmol/kg, and does not exceed 5 mmol/kg, in each case calculated as corresponding amounts of the elements Zr and/or Ti.

12. The method according to claim 1 , wherein the water-soluble compounds of the elements Zr and/or Ti are selected from water-soluble compounds of the element Zr, which are in turn selected from hexafluorozirconic acid and the salts thereof.

13. The method according to claim 1 , wherein the aluminum or aluminum alloy component is brought into contact with the pickling solution for long enough to pickle at least 2 mg of aluminum per square meter from contacted surfaces of the component and to optionally produce a layer of at least 4 mg titanium per square meter on the contacted surfaces of the component.

14. The method according to claim 1 , wherein before contacting with the pickling solution, the component undergoes alkaline degreasing, by contacting the component with an alkaline aqueous composition which has a pH of greater than 9 but less than 12 and a free alkalinity of at least 3 points but less than 6 points and which optionally contains surface-active compounds which are selected from non-ionic surfactants.

15. The method according to claim 14 , wherein after the alkaline degreasing and before contact with the pickling solution, the aluminum or aluminum alloy component is subjected to a rinsing step, but not a drying step.

16. The method according to claim 1 , wherein after contact with the pickling solution and before contact with the conversion treatment solution, the aluminum or aluminum alloy component is subjected to a rinsing step, but not a drying step.

17. The method according to claim 1 , wherein after contact with the conversion treatment solution and before the subsequent coating, a rinsing step takes place, and immediately before the subsequent coating, a drying step also takes place.

18. The method according to claim 1 , wherein the component is coated with a powder coating during the subsequent coating.

19. The method according to claim 1 , wherein a ratio of Zr and Ti to total fluoride content in the conversion treatment solution is at least 0.1.

20. The method according to claim 1 , wherein the at least at least one polybasic α-hydroxycarboxylic acid is present in the pickling solution in an amount of at least 0.5 g/kg but does not exceed 2 g/kg.

Assignees

• Henkel Ag & Co Kgaa

Inventors

• Geick Volker
• Schaeuble Kathrin

Classifications

• C23C24/00

  Coating starting from inorganic powder (spraying of the coating material in molten state C23C4/00; solid state diffusion C23C8/00 - C23C12/00) · CPC title

• C23G1/22

  Light metals · CPC title

• C23C22/34 Primary

  containing fluorides or complex fluorides · CPC title

• C23G1/125 Primary

  aluminium · CPC title

• C23C22/80

  with solutions containing titanium or zirconium compounds · CPC title