Processes to reduce interfacial enrichment of alloying elements under anodic oxide films and improve anodized appearance of heat treatable alloys

Patent metadata

Field	Value
Publication number	US-9359686-B1
Application number	US-201514593845-A
Country	US
Kind code	B1
Filing date	Jan 9, 2015
Priority date	Jan 9, 2015
Publication date	Jun 7, 2016
Grant date	Jun 7, 2016

Abstract

Anodic oxide coatings and methods for forming anodic oxide coatings on metal alloy substrates are disclosed. Methods involve post-anodizing processes that improve the appearance of the anodic oxide coating or increase the strength of the underlying metal alloy substrates. In some embodiments, a diffusion promoting process is used to promote diffusion of one or more types of alloying elements enriched at an interface between the anodic oxide coating and the metal alloy substrate away from the interface. The diffusion promoting process can increase an adhesion strength of the anodic oxide film to the metal alloy substrate and reduce an amount of discoloration due to the enriched alloying elements. In some embodiments, a post-anodizing age hardening process is used to increase the strength of the metal alloy substrate and to improve cosmetics of the anodic oxide coatings.

First claim

What is claimed is:

1. A method of treating a part comprising a metal alloy substrate, the method comprising:
forming an anodic oxide film on the metal alloy substrate by anodizing the metal alloy substrate, wherein alloying elements from the metal alloy substrate are enriched at an interface between the metal alloy substrate and the anodic oxide film, wherein the alloying elements enriched at the interface are associated with an amount of discoloration of the anodic oxide film;
exposing the part to a diffusion promoting process causing at least some of the alloying elements enriched at the interface to diffuse away from the interface toward one or both of the metal alloy substrate and the anodic oxide film; and
measuring a color of the anodic oxide film to determine whether the amount of discoloration is reduced to at least a predetermined amount of discoloration.

2. The method of claim 1 , wherein the alloying elements enriched at the interface are associated with reducing an adhesion strength between the anodic oxide film and the metal alloy substrate, wherein the adhesion strength is increased after exposing the part to the diffusion promoting process.

3. The method of claim 1 , wherein the alloying elements enriched at the interface are associated with galvanic corrosion of the metal alloy substrate, wherein exposing the part to the diffusion promoting process substantially prevents the galvanic corrosion of the metal alloy substrate.

4. The method of claim 1 , wherein exposing the part to a diffusion promoting process comprises:
heating the part to a predetermined temperature.

5. The method of claim 4 , wherein the predetermined temperature is about 150 degrees C. or higher.

6. The method of claim 4 , wherein the predetermined temperature is between about 200 degrees C. and about 300 degrees C.

7. The method of claim 4 , where the predetermined temperature is sufficiently low to substantially prevent cracking of the anodic oxide film.

8. The method of claim 1 , wherein a surface of the part corresponds to an exposed surface of the anodic oxide film, wherein exposing the part to a diffusion promoting process comprises:
exposing the surface of the part to light.

9. The method of claim 8 , wherein the part is positioned on a support that cools a portion of the metal alloy substrate during the exposure of the surface to light.

10. The method of claim 1 , wherein exposing the part to a diffusion promoting process comprises:
exposing the part to a heated liquid, gas or a combination thereof.

11. The method of claim 10 , wherein the heated liquid, gas or a combination thereof is substantially free of water.

12. The method of claim 10 , wherein the heated liquid, gas or a combination thereof comprises water such that pores of the anodic oxide film become sealed while the alloying elements diffuse away from the interface.

13. The method of claim 10 , wherein the heated liquid, gas or a combination thereof is heated to a temperature of about 150 degrees C. or higher.

14. A method of treating a part comprising a metal alloy substrate, the method comprising:
converting a portion of the metal alloy substrate to an anodic oxide film, wherein alloying elements from the metal alloy substrate become enriched within an enrichment layer at an interface between the metal alloy substrate and the anodic oxide film, wherein the alloying elements enriched within enrichment layer are associated with an amount of discoloration of the part;
removing at least a portion of the alloying elements from the enrichment layer so as to reduce the amount of discoloration; and
measuring a color of the part to determine whether the amount of discoloration is reduced to at least a predetermined amount of discoloration.

15. The method of claim 14 , wherein removing at least the portion of the alloying elements from the enrichment layer comprises removing substantially all the discoloration.

16. The method of claim 14 , wherein measuring the color of the part includes measuring the part for amounts of yellow, blue, green or magenta color yellow, blue, green or magenta color.

17. The method of claim 14 , wherein measuring the color of the part includes measuring an L* (brightness) value of the part.

18. The method of claim 14 , wherein the alloying elements enriched within the enrichment layer is associated with a reduced adhesion strength of the anodic oxide film to the metal alloy substrate, wherein removing at least the portion of the alloying elements from the enrichment layer comprises increasing the adhesion strength.

19. The method of claim 14 , wherein removing at least the portion of the alloying elements from the enrichment layer comprises:
heating at least a portion of the part to a predetermined temperature.

20. The method of claim 14 , wherein the alloying elements include at least one of zinc, copper, manganese, iron and lead.

Assignees

• Apple Inc

Inventors

• Curran James A
• Counts William A
• Hamann Eric W

Classifications

• C25D11/18 Primary

  After-treatment, e.g. pore-sealing · CPC title

• C25D11/04 Primary

  of aluminium or alloys based thereon · CPC title

• C25D11/24

  Chemical after-treatment · CPC title

• C22F1/047

  of alloys with magnesium as the next major constituent · CPC title

• C22F1/053

  of alloys with zinc as the next major constituent · CPC title