Sealing anodized aluminum using a low-temperature nickel-free process
The inventive two-step process operates at low temperature, without any toxic heavy metals, to provide excellent sealing on anodized aluminum substrates, especially those aluminum substrates comprising silicon. The first step of the process seals the anodized surface and the second step passivates the anodized surface. The process allows for corrosion resistance in anodized aluminum and anodized aluminum alloys to be achieved that is comparable to traditional nickel based sealants, without the toxicity of nickel. The process additionally does not require any excessive temperatures, as required by hot water sealing processes. The composition used for the sealing step comprises soluble lithium ions, fluoride ions, and preferably, a complexing agent comprising phosphines, phosphonates and/or polymers of acrylic acid. The composition used for the passivation step comprises metal ions and preferably a complexing agent comprising phosphines, phosphonates and/or polymers of acrylic acid.
1. A method for sealing an anodized aluminum or anodized aluminum alloy surface comprising:
(i) contacting the anodized surface with a sealing composition comprising a source of lithium ions, a source of fluoride ions, and a complexing agent, followed by;
(ii) contacting the anodized surface with a passivation composition wherein the passivation composition comprises a source of metal ions and a complexing agent;
wherein the surface of the anodized aluminum or anodized aluminum alloy becomes corrosion resistant, and
wherein the temperature of the passivation composition is less than 80° C.
2. The method according to claim 1 , wherein the complexing agent in the sealing composition is selected from the group consisting of phosphines, phosphonates, acrylic acid polymers, and mixtures thereof.
3. The method according to claim 2 , wherein the complexing agent is in the sealing composition in a concentration from 50 ppm to 500 ppm.
4. The method according to claim 1 , wherein the complexing agent in the passivation composition is selected from the group consisting of phosphines, phosphonates, acrylic acid polymers, and mixtures thereof.
5. The method according to claim 4 , wherein the complexing agent is in the passivation composition in a concentration from 50 ppm to 500 ppm.
6. The method according to claim 2 , wherein the complexing agent in the sealing composition is selected from the group consisting of phosphino-carboxylic acid polymers, phosphono-carboxylic acid polymers and mixtures thereof.
7. The method according to claim 2 , wherein the complexing agent is 2-phosphonobutane-1,2,4-tricarboxylic acid.
8. The method according to claim 4 , wherein the complexing agent in the passivation composition is selected from the group consisting of phosphino-carboxylic acid polymers, phosphono-carboxylic acid polymers and mixtures thereof.
9. The method according to claim 4 , wherein the complexing agent in the passivation composition is nitrilotrimethylene phosphonic acid.
10. The method according to claim 1 , wherein the aluminum alloy comprises at least 1% silicon.
11. The method according to claim 10 , wherein the aluminum alloy comprises at least 5% silicon.
12. The method according to claim 11 , wherein the aluminum alloy comprises at least 7% silicon.
13. The method according to claim 1 , wherein the metal ions in the passivation composition are selected from the group consisting of tungsten, titanium, molybdenum, vanadium, zirconium, and mixtures thereof.
14. The method according to claim 13 , wherein the metal ions are in the passivation composition at a concentration of between 100 ppm and 3000 ppm.
15. The method according to claim 13 , wherein the metal ions in the passivation composition are tungsten.
16. The method according to claim 13 , wherein the metal ions are provided by a metal salt selected from the group consisting of ammonium metatungstate, ammonium molybdate, ammonium tungstate, ammonium vanadate, zirconium acetate, titanium oxalate and mixtures thereof.
17. The method according to claim 16 , wherein the metal salt providing the metal ions is ammonium metatungstate.
18. The method according to claim 1 , wherein the lithium ions are in the sealing composition at a concentration between 300 ppm and 800 ppm.
19. The method according to claim 1 , wherein the fluoride ions are in the sealing composition at a concentration between 150 ppm and 800 ppm.
20. The method according to claim 1 , wherein the temperature of the sealing composition is between 20° C. and 60° C.
21. The method according to claim 1 , wherein the temperature of the passivation composition is between 40° C. and 65° C.
22. The method according to claim 1 , wherein a duration for contacting the anodized surface with the sealing composition is between 0.75 min and 1.25 min per micron of anodized coating on the aluminum alloy surface.
23. The method according to claim 1 , wherein the pH of the passivation composition is between 5.5 and 7.0.
24. The method according to claim 1 , wherein the anodized surface comprises greater than 1% Silicon.
25. The method according to claim 1 , wherein the temperature of the passivation composition is between 55° C. and 65° C.