Method of forming a corrosion-resistant protective coating on aluminum substrate

A method of forming a corrosion-resistant protective coating on an aluminum substrate which comprises:

• (a) forming on said aluminum substrate an aluminum oxide layer having a minimum thickness of at least about 0.1 micrometers (1000 Angstroms);
• and
• (b) contacting said aluminum oxide layer on said aluminum substrate with one or more fluorine-containing gases at a concentration of from 5 to 100 volume %, a pressure of from 1 Torr to about atmospheric pressure, and at a temperature of from about 375.degree. C. to about 500.degree. C. for a period of from about 30 to 120 minutes;
• whereby a protective layer having from 3 to 18 wt.% fluorine will be formed on said aluminum substrate.

A method of forming on an aluminum substrate a corrosion-resistant protective coating containing less than about 3 wt.% of elements other than aluminum, hydrogen, oxygen, and fluorine which comprises:

• (a) forming an aluminum oxide layer having a purity of at least about 97 wt.% and having a minimum thickness of at least about 0.1 micrometers (1000 Angstroms) on the surface of an aluminum substrate having a purity of at least about 97 wt.%;
• and
• (b) contacting said aluminum oxide layer on said aluminum substrate with one or more fluorine-containing gases containing less than 100 ppm of impurities (other than carrier gases) at a concentration of from 5 to 100 volume % fluorine-containing gases, a pressure of from 1 Torr to about atmospheric pressure, and at a temperature of from about 375.degree. C. to about 500.degree. C. for a period of from about 30 to 120 minutes;
• whereby a high purity protective layer having from 3 to 18 wt.% fluorine, and containing less than about 3 wt.% of elements other than aluminum, oxygen, hydrogen, and fluorine will be formed on said aluminum substrate.