Methods and compositions for coating aluminum substrates
The present invention relates to methods and compositions for coating aluminum substrates. In an embodiment, the invention includes a method of applying a coating on an aluminum substrate including contacting the aluminum substrate with a first solution. The first solution can include a zinc metal salt, a sugar acid or alkali metal salt thereof, and an alkali metal hydroxide. The method can also include contacting the aluminum substrate with a second solution. The second solution can include a molybdate salt, an alkanolamine, and a fluorine acid. Other embodiments are also included herein.
1. A method of applying a coating on an aluminum substrate comprising:
contacting the aluminum substrate with a first solution, the first solution comprising
a zinc metal salt,
gluconic acid, glucoheptonic acid, or an alkali metal salt thereof, and
an alkali metal hydroxide, and
contacting the aluminum substrate with a second solution to create the coating, the coating exhibiting black color stability for a period of 60 days without a separate passivating treatment, the second solution comprising
a molybdate salt,
an alkanolamine, and
a fluorine acid.
2. The method of claim 1 , the zinc metal salt comprising zinc (II) oxide.
3. The method of claim 1 , the alkali metal hydroxide selected from the group consisting of sodium hydroxide, potassium hydroxide, and lithium hydroxide.
4. The method of claim 1 , the molybdate salt comprising ammonium heptamolybdate.
5. The method of claim 1 , the alkanolamine selected from the group consisting of monoethanolamine, triethanolamine, and 2-amino-2-methyl-1-propanol.
6. The method of claim 1 , the alkanolamine comprising 2-amino-2-methyl-1-propanol.
7. The method of claim 1 , the fluorine acid selected from the group consisting of fluoroboric acid and fluorosilicic acid.
8. The method of claim 1 , the second solution comprising:
at least about 20 grams per liter of the molybdate salt,
at least about 10 grams per liter of the alkanolamine, and
at least about 2 grams per liter of the fluorine acid.
9. The method of claim 1 , the first solution further comprising:
an iron metal salt,
a carboxylic acid or alkali metal salt thereof, and
an oxidizing agent.
10. The method of claim 9 , the iron metal salt comprising an iron (III) salt.
11. The method of claim 10 , the iron (III) salt comprising FeCl 3 .
12. The method of claim 9 , the carboxylic acid selected from the group consisting of glycolic acid, malic acid, tartaric acid, and citric acid.
13. The method of claim 9 , the carboxylic acid or alkali metal salt thereof comprising one or more of sodium tartrate, potassium tartrate, and sodium-potassium tartrate.
14. The method of claim 9 , the oxidizing agent comprising an alkali metal nitrate.
15. The method of claim 9 , the first solution comprising:
at least about 2 grams per liter of the zinc metal salt,
at least about 0.5 grams per liter of the iron metal salt,
at least about 2 grams per liter of the carboxylic acid or alkali metal salt thereof,
at least about 2 grams per liter of gluconic acid, glucoheptonic acid, or an alkali metal salt thereof,
at least about 20 grams per liter of the alkali metal hydroxide, and
at least about 1 gram per liter of the alkali metal nitrate.