Method for surface treating aluminum products

• US 6,440,290 B1
• Filed: 12/04/2000
• Issued: 08/27/2002
• Est. Priority Date: 08/28/1998
• Status: Expired due to Term

• Current Assignee: Howmet Aerospace, Inc.
• Original Assignee: Alcoa Incorporated (Howmet Aerospace, Inc.)
• Inventors: Vega, Luis F., Grassi, John R., Robare, Kevin M., Dando, Neal R., Holtz, Mark A.
• Primary Examiner(s): Wong, Edna
• Application Number:
  US09/729,567
• Time in Patent Office: 631 Days
• Field of Search: 205/172, 205/201, 205/213, 205/229
• US Class Current: 205/201
• CPC Class Codes: C25D 11/16 Pretreatment , e.g. desmutting
• CPC Class Codes: C25D 11/24 Chemical after-treatment

Abstract

There is disclosed a method for surface treating aluminum products, especially vehicle wheels, to improve their brightness. The method comprises: (a) applying a chemical brightening composition to these products; (b) deoxidizing the surface of these wheel products in a nitric acid-based bath; (c) forming a porous oxide on that with an electrolytic bath containing phosphoric acid; and (d) applying, preferably spraying, a siloxane-based film to that porous oxide. In many instances, intermediate rinsing substeps are performed between these respective main steps.

Claims

1. A method for surface treating an aluminum wheel product to improve its brightness, said method comprising the main steps of:

(a) applying a chemical brightening composition to the product;

(b) deoxidizing the product surface in a nitric acid-based bath;

(c) electrochemically forming a porous oxide/phosphate on said product surface by contacting with an electrolytic bath containing phosphoric acid, said oxide/phosphate being less than about 500 angstroms thick; and

(d) chemically bonding a siloxane-based outer layer to the porous oxide/phosphate.

2. The method of claim 1 wherein said aluminum wheel product is made from a 5000 or 6000 Series aluminum alloy (Aluminum Association designation).

3. The method of claim 2 wherein said aluminum alloy is a 5000 Series alloy selected from the group consisting of:

5454, 5182 and 5052 aluminum.

4. The method of claim 2 wherein said aluminum alloy is a 6000 Series alloy selected from the group consisting of:

6061, 6063 and 6005 aluminum.

5. The method of claim 4 wherein said alloy contains less than about 0.35 wt. % iron.

6. The method of claim 5 wherein said alloy contains less than about 0.15 wt. % iron.

7. The method of claim 1 wherein said aluminum wheel product is forged or cast.

8. The method of claim 1 wherein said aluminum product is subjected to cleaning and rinsing prior to step (a).

9. The method of claim 8 wherein said pre-step (a) cleaning is alkaline-based.

10. The method of claim 8 wherein said pre-step (a) cleaning is acid-based.

11. The method of claim 1 wherein said aluminum wheel product is subjected to a rinsing substep after one or more of steps (a), (b) or (c).

12. The method of claim 1 wherein the chemical brightening composition of step (a) includes:

about 2.7 wt % or less nitric acid, about 70-90 wt % phosphoric acid, the balance water and impurities.

13. The method of claim 12 wherein said chemical brightening composition contains about 1.2-2.2 wt % nitric acid.

14. The method of claim 1 wherein said oxide/phosphate forming step (c) includes contacting the product with an electrolytic bath containing about 2 to 15 vol % phosphoric acid.

15. The method of claim 1 wherein said oxide/phosphate is between about 75 and 200 angstroms thick.

16. The method of claim 1 wherein said siloxane-based outer layer is applied by spray coating.

17. The method of claim 1 wherein said aluminum wheel product is subjected to air drying after step (d).

18. The method of claim 17 wherein said siloxane-based film is thermally cured after air drying.

19. A method for surface treating aluminum wheel products to improve their brightness and abrasion resistance, said method comprising the steps of:

(a) applying a chemical brightening composition to said wheel products;

(b) deoxidizing the surface of said wheel products in a nitric acid-based bath;

(c) electrochemically forming a porous oxide/phosphate on said surface by contacting with an electrolytic bath containing phosphoric acid, said oxide/phosphate being less than about 500 angstroms thick;

(d) chemically bonding a siloxane-based film to the porous oxide/phosphate; and

(e) thermally curing the siloxane-based film on said surface.

20. The method of claim 19 wherein said wheel products are made from a 5000 or 6000 Series aluminum alloy (Aluminum Association designation).

21. The method of claim 19 wherein said aluminum alloy is a 5000 Series alloy selected from the group consisting of:

5454, 5182 and 5052 aluminum.

22. The method of claim 21 wherein said oxide/phosphate forming step (c) includes contacting said wheel products with an electrolyte containing about 2 to 15 vol % phosphoric acid.

23. The method of claim 20 wherein said aluminum alloy is a 6000 Series alloy selected from the group consisting of:

6061, 6063 and 6005 aluminum.

24. The method of claim 20 wherein said aluminum alloy contains less than about 0.35 wt. % iron.

25. The method of claim 24 wherein said aluminum alloy contains less than about 0.15 wt. % iron.

26. The method of claim 19 wherein said wheel products are subjected to cleaning and rinsing prior to step (a).

27. The method of claim 26 wherein said pre-step (a) cleaning is alkaline-based.

28. The method of claim 26 wherein said pre-step (a) cleaning is acid-based.

29. The method of claim 19 wherein said wheel products are subjected to a rinsing substep after one or more of steps (a), (b) or (c).

30. The method of claim 19 wherein the chemical brightening composition of step (a) includes:

about 2.7 wt % or less nitric acid, about 70-90 wt % phosphoric acid, the balance water and impurities.

31. The method of claim 30 wherein said chemical brightening composition contains about 1.2-2.2 wt % nitric acid.

32. The method of claim 19 wherein said oxide/phosphate is between about 75 and 200 angstroms thick.

33. The method of claim 19 wherein said siloxane-based film is applied by spray coating.

34. A method for surface treating cleaned and rinsed, 6000 Series aluminum wheel products to improve their brightness, soil and abrasion resistance, said method comprising the steps of:

(a) chemically brightening said wheel products with a composition that includes phosphoric acid and nitric acid;

(b) rinsing said wheel products;

(c) deoxidizing the surface of said wheel products in a nitric acid-based bath;

(d) rinsing said wheel products;

(e) electrochemically forming a porous oxide/phosphate on said surface by contacting with an electrolytic bath containing phosphoric acid, said oxide/phosphate being less than about 500 angstroms thick;

(f) rinsing said wheel products;

(g) chemically bonding a siloxane-based film to said oxide/phosphate; and

(h) thermally curing the siloxane-based film on said wheel products.

35. The method of claim 34 wherein said 6000 Series aluminum is selected from the group consisting of:

6061, 6063 and 6005 alloys.

36. The method of claim 35 wherein said alloy contains less than about 0.35 wt. % iron.

37. The method of claim 36 wherein said alloy contains less than about 0.15 wt. % iron.

38. The method of claim 35 wherein said oxide/phosphate forming step (e) includes contacting said wheel products with an electrolytic bath containing about 2 to 15 vol % phosphoric acid.

39. The method of claim 34 wherein the composition of step (a) includes:

about 2.7 wt % or less nitric acid, about 70-90 wt % phosphoric acid, the balance water and impurities.

40. The method of claim 39 wherein said chemical brightening composition contains about 1.2-2.2 wt % nitric acid.

41. The method of claim 34 wherein said oxide/phosphate is between about 75 and 200 angstroms thick.

42. The method of claim 34 wherein said wheel products are air dried after step (g).