Rare earth coating process for aluminum alloys

• US 5,362,335 A
• Filed: 03/25/1993
• Issued: 11/08/1994
• Est. Priority Date: 03/25/1993
• Status: Expired due to Term

• Current Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Rungta, Ravi
• Primary Examiner(s): Silverberg, Sam
• Application Number:
  US08/037,142
• Time in Patent Office: 593 Days
• Field of Search: 148/273, 148/272, 148/275
• US Class Current: 148/272
• CPC Class Codes: C23C 22/56 Treatment of aluminium or alloys based thereon

Abstract

A method is provided by which a corrosion-resistant barrier layer composed of a rare earth oxide coating incorporated in an oxide film is developed on the surface of a metal for the purpose of improving the corrosion resistance of the metal. The method is particularly suitable for forming a corrosion-resistant barrier on an aluminum alloy, in which the corrosion-resistant barrier layer is composed of a cerium oxide coating incorporated with a uniform aluminum oxide film which has been formed on the aluminum alloy. The corrosion-resistant barrier layer exhibits a broader passivation range as compared to chromium conversion coatings typically used in the art. Simultaneously, the method of this invention avoids the environmental hazards associated with chromium conversion processes, making the method more suitable for manufacturing operations. Furthermore, the method of this invention does not employ hazardous compounds, making the process suitable for a manufacturing environment.

Claims

1. A process for enhancing the corrosion resistance of an aluminum alloy, the process comprising the steps of:

exposing a surface of the aluminum alloy to a hygroscopic solution so as to form a bohmite film on the aluminum alloy;

exposing the aluminum alloy to an aqueous solution consisting essentially of cerous chloride and water at a temperature of about 100°

F. to about 200°

F. and for a duration of about 10 to about 20 minutes so as to form cerium oxide on the aluminum alloy, such that the cerium oxide is incorporated in the bohmite film, the aqueous solution of cerous chloride comprising about 8000 to about 12,000 ppm cerous chloride and having a pH of about 3 to about 5;

rinsing the aluminum alloy in water; and

drying the aluminum alloy at an elevated temperature of about 200°

F. to about 320°

F. and for a duration of about 10 to about 30 minutes, so as to form a mixed barrier layer of the cerium oxide in the bohmite film which significantly extends the passivity range of the aluminum alloy.

2. A process as recited in claim 1 wherein the hygroscopic solution is an aqueous solution of triethanolamine.

3. A process as recited in claim 2 wherein the aqueous solution of triethanolamine comprises about 0.1 to 10 volume percent triethanolamine in water.

4. A process as recited in claim 1 wherein the temperature of the hygroscopic solution is about 160°

F. to about 210°

F.

5. A process as recited in claim 1 wherein the aluminum alloy is exposed to the hygroscopic solution for a duration of about 1 to about 8 minutes.

6. A process as recited in claim 1 further comprising the step of cleaning the surface of the aluminum alloy prior to the step of exposing the surface of the aluminum alloy to the hygroscopic solution so as to facilitate the formation of the aluminum oxide film.

7. A process as recited in claim 1 further comprising the step of painting the surface of the aluminum alloy after drying the aluminum alloy.

8. A process for enhancing the corrosion resistance of an aluminum alloy, the process comprising the steps of:

cleaning a surface of the aluminum alloy;

exposing a surface of the aluminum alloy to triethanolamine in deionized water at a temperature of about 160°

F. to about 210°

F. and for a duration of about 1 to about 8 minutes so as to form a bohmite film on the aluminum alloy;

rinsing the aluminum alloy with water;

exposing the aluminum alloy to an aqueous solution consisting essentially of cerous chloride and water at a temperature of about 100°

F. to about 200°

F. and for a duration of about 10 to about 20 minutes so as to form cerium oxide on the aluminum alloy, the aqueous solution of cerous chloride comprising about 8000 to about 12,000 ppm cerous chloride and having a pH of about 3 to about 5;

rinsing the aluminum alloy in water; and

drying the aluminum alloy at a temperature of about 200°

F. to about 320°

F. and for a duration of about 10 to about 30 minutes;

whereby the incorporation of the cerium oxide in the bohmite film significantly extends the passivity range of the aluminum alloy.