Method of improving anti-corrosion characteristics of anodized aluminum

Abstract

The invention relates to an improved anodizing process that by modifying the reagents used in a sealing step of the anodizing process may be used to provide for improved anti-corrosion properties of the finished anodized part.

1 . A method of providing an anodized aluminum part, the method including the steps of: 
 a) Anodizing the aluminum part,    b) Sealing the anodized part using a sealing solution, and    wherein the sealing solution includes aqueous silica.    
     
     
         2 . The method as claimed in  claim 1  wherein the sealing solution includes at least 1% silica.  
     
     
         3 . The method as claimed in  claim 1  wherein the sealing solution includes silica in the range 3-8% and preferably 5%.  
     
     
         4 . The method as claimed in  claim 1  wherein the sealing solution is a hot seal, the sealing being conducted at a temperature greater than 65 degrees centigrade and optimally at a temperature in the range 85 to 95 degrees centigrade.  
     
     
         5 . The method as claimed in  claim 1  wherein the silica is provided as an aqueous silicate solution, optimally in the form includes of a metal silicate.  
     
     
         6 . The method as claimed in  claim 1  when used in the preparation of automotive parts.  
     
     
         7 . An aluminum part treated in accordance with  claim 1 , the part being fully sealed and having silica on its surface.  
     
     
         8 . The part as claimed in  claim 8  wherein pores on the surface are not greater than 5 microns in diameter.  
     
     
         9 . The part as claimed in  claim 7  or  8  wherein when the part is exposed to a corrosive caustic solution having a pH greater than 12.5 for a time period greater than 10 minutes, the part shows no visible impact or discoloration of the surface  
     
     
         10 . Use of silica in a sealing process for anodized aluminum in the preparation of parts for the automotive industry.