Non-chromium coatings for aluminum

Abstract

Composition and process for treating aluminum, aluminum alloys and anodized aluminum substrates to improve the corrosion resistance and adhesive bonding strength of the aluminum substrates. The process comprises pre- or post-treating said aluminum with an acidic aqueous solution comprising, per liter of solution, from about 0.1 to 22 grams of at least one fluorometallate, about 0.1 gram up to the solubility limit of a water soluble cationic or divalent zinc compound and, optionally, effective amounts of water soluble thickeners and/or surfactants.

1 . Process for preparing coatings on aluminum to improve the adhesive bonding and corrosion resistance which comprises treating the aluminum with an acidic aqueous solution having a pH ranging from about 2.5 to 5.5 at temperatures ranging from ambient up to about 212° F.; said acidic aqueous solution comprising, per liter of solution, from about 0.1 to 22 grams of at least one fluorometallate selected from the group consisting of hexafluorozirconates, tetrafluoroborates, hexafluorosilicates, hexafluorotitanates, and heptafluorotantalates, from about 0.1 up to the solubility limit of at least one cationic zinc compound, from about 0.0 to 10 grams of a water soluble thickener, and 0.0 to 10 grams of a water soluble surfactant.  
   
   
       2 . The process of  claim 1  wherein the aluminum is an alloy of aluminum.  
   
   
       3 . The process of  claim 1  wherein the aluminum is anodized aluminum.  
   
   
       4 . The process of  claim 1  wherein the aluminum is an anodized aluminum alloy.  
   
   
       5 . The process of  claim 1  wherein the pH of the acidic aqueous solution ranges from about 3.7 to 4.0.  
   
   
       6 . The process of  claim 5  wherein the fluorometallate is a hexafluorozirconate.  
   
   
       7 . The process of  claim 6  wherein the zinc compound is zinc sulfate and the hexafluorozirconate is an alkali metal zirconate.  
   
   
       8 . The process of  claim 7  wherein the aqueous solution contains from about 0.5 to 10 grams of a cellulose thickener.  
   
   
       9 . The process of  claim 8  wherein the aqueous solution contains from about 0.5 to 10 grams of a non-ionic surfactant.  
   
   
       10 . Process for preparing coatings on aluminum to improve the adhesive bonding and corrosion resistance of the aluminum which comprises treating the aluminum with an acidic aqueous solution having a pH ranging from about 3.7 to 4.0 at temperatures ranging from ambient up to about 160° F.; said acidic aqueous solution comprising, per liter of solution, from about 1.0 to 12 grams of an alkali metal fluorometallate, from about 0.1 up to the solubility limits of at least one cationic zinc salt, from 0.5 to 1.5 grams of a water soluble thickener and from 0.5 to 1.5 grams of a water soluble surfactant.  
   
   
       11 . The process of  claim 10  wherein the thickener is a cellulose compound and the surfactant is a non-ionic surfactant.  
   
   
       12 . The process of  claim 11  wherein the cellulose compound is methyl cellulose.  
   
   
       13 . The process of  claim 10  wherein the zinc salt is zinc sulfate and the fluorometallate is a hexafluorozirconate.  
   
   
       14 . The process of  claim 13  wherein the zirconate is potassium hexafluorozirconate.  
   
   
       15 . The process of  claim 14  wherein the potassium hexafluorozirconate ranges from about 1.0 to 12 grams and the zinc salt ranges from about 0.1 to 12 grams.  
   
   
       16 . The process of  claim 14  wherein the zinc salt is zinc acetate.  
   
   
       17 . The coated aluminum obtained by the process of  claim 1 .  
   
   
       18 . Compositions for improving the adhesion bonding and corrosion resistance of aluminum, aluminum alloy, and anodized aluminum which comprise an acidic aqueous solution having a pH ranging from about 2.5 to 5.5, and per liter of solution, from about 0.1 to 22 grams of at least one fluorometallate selected from the group consisting of hexafluorozirconates, tetrafluoroborates, hexafluorosilicates, hexafluorotitanates, and heptafluorotantalates, from about 0.1 up to the solubility limit of a cationic zinc compound, from about 0.0 to 10 grams of at least one water soluble thickener and from 0.0 to 10 grams of at least one water soluble surfactant.  
   
   
       19 . The composition of  claim 18  wherein the pH of the aqueous solution ranges from about 3.7 to 4.0.  
   
   
       20 . The composition of  claim 19  wherein the fluorometallate is a hexafluorozirconate ranging from about 1.0 to 12 grams and the zinc compound is a divalent zinc salt ranging from about 0.1 to 12 grams per liter of solution.  
   
   
       21 . The composition of  claim 20  wherein the thickener is a cellulose compound ranging from about 0.5 to 10 grams and the surfactant is a non-ionic surfactant ranging from about 0.5 to 10 grams per liter of solution.