Corrosion resistant aluminum alloy substrates and methods of producing the same

Abstract

Aluminum alloy products comprising an aluminum alloy base and a sulfate-phosphate oxide zone integral therewith are disclosed. Methods of making the same are also disclosed.

1 . A method comprising:
 producing a sulfate-phosphate oxide zone having a thickness of at least about 5 microns in an aluminum alloy base, wherein the producing step comprises electrochemically oxidizing a surface of the aluminum alloy base via an electrolyte comprising both phosphoric acid and sulfuric acid; and   forming a silicon-containing polymer zone integral with at least a portion of the sulfate-phosphate oxide zone, wherein the aluminum alloy base, the sulfate-phosphate oxide zone and the silicon-containing polymer zone at least partially define a corrosion resistant aluminum alloy substrate.   
   
   
       2 . The method of  claim 1 , wherein the corrosion resistant aluminum alloy substrate is capable of passing a copper-accelerated acetic acid salt spray test, as defined by ASTM B368-97 (2003)e1. 
   
   
       3 . The method of  claim 1 , wherein the electrochemically oxidizing step comprises applying current to the aluminum alloy base at a current density of at least about 12 amps per square foot. 
   
   
       4 . The method of  claim 1 , wherein the electrochemically oxidizing step comprises applying current to the aluminum alloy base at a current density of at least about 18 amps per square foot. 
   
   
       5 . The method of  claim 1 , wherein the electrolyte comprises at least about 0.1 wt % phosphoric acid. 
   
   
       6 . The method of  claim 7 , wherein the electrolyte comprises not greater than about 5 wt % phosphoric acid. 
   
   
       7 . The method of  claim 1 , wherein the electrochemically oxidizing step comprising heating the electrolyte to a temperature of at least about 75° F. 
   
   
       8 . The method of  claim 1 , wherein the electrochemically oxidizing step comprising heating the electrolyte to a temperature of at least about 90° F. 
   
   
       9 . The method of  claim 1 , further comprising:
 prior to the forming a sulfate-phosphate oxide zone step, pretreating a surface of the aluminum alloy base with a pretreating agent.   
   
   
       10 . The method of  claim 9 , wherein the pretreating agent comprises a chemical brightening composition that includes at least one of nitric acid, phosphoric acid and sulfuric acid. 
   
   
       11 . The method of  claim 9 , wherein the pretreating agent comprises an alkaline cleaner. 
   
   
       12 . The method of  claim 9 , further comprising:
 prior to the forming a silicon-containing polymer zone step, applying at least one of a dye and a nickel acetate solution to at least a portion of the sulfate-phosphate oxide zone.   
   
   
       13 . The method of  claim 1 , wherein the silicon-containing polymer zone comprises at least one of polysiloxane and polysilazane. 
   
   
       14 . The method of  claim 13 , wherein the forming a silicon-containing polymer zone step comprises:
 depositing a colloid on at least a portion of the sulfate-phosphate oxide zone; and   curing the colloid to form a gel comprising the silicon-containing polymer coating on the surface of the aluminum alloy base.   
   
   
       15 . The method of  claim 14 , wherein the depositing step comprises:
 applying a sufficient amount of the sol to both (a) fill pores of the sulfate-phosphate oxide zone and (b) form a coating comprising the silicon-containing polymer coating.   
   
   
       16 . The method of  claim 1 , wherein the electrolyte consists of essentially of sulfuric acid and phosphoric acid. 
   
   
       17 . The method of  claim 1 , wherein the producing step comprises:
 generating pores within the sulfate-phosphate oxide zone; and   wherein the forming step comprises:
 flowing at least some of a silicon-containing polymer into the pores of the sulfate-phosphate oxide zone. 
   
   
   
       16 . The method of  claim 17 , wherein the pores have an average pore size of from about 10 to about 15 nanometers.