Non-chromium post-treatment for aluminum coated steel

Abstract

Compositions and process for post-treating aluminum and aluminum alloy coated steel substrates to improve the corrosion resistance and adhesive bonding strength of the aluminum coated substrates. The composition comprises treating the aluminum or aluminum alloy coated steel substrates with an acidic aqueous solution comprising, per liter of solution, from about 0.1 to 22 grams of a hexafluorozirconate, from about 0.1 gram up to the solubility limit of a water soluble cationic zinc compound and, optionally, effective amounts of water soluble thickeners and/or surfactants.

1 . Process for improving the adhesion bonding and corrosion resistance of aluminum and aluminum alloys coated on steel substrates which comprises treating the coated steel substrates with effective amounts of an acidic aqueous solution having a pH ranging from about 2.5 to 5.5 at solution temperatures ranging from ambient to about 200° F.; said acidic aqueous solution comprising, per liter of solution, from about 0.1 to 22 grams of at least one hexafluorozirconate, from about 0.1 gram up to the solubility limit of at least one cationic zinc compound, from 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.  
   
   
       2 . The process of  claim 1  wherein the pH of the acidic solution ranges from about 3.7 to 4.0 and the temperature of the solution ranges from about room temperature to 120° F.  
   
   
       3 . The process of  claim 2  wherein the hexafluorozirconate is an alkali metal hexafluorozirconate.  
   
   
       4 . The process of  claim 3  wherein the alkali metal hexafluorozirconate is sodium hexafluorozirconate.  
   
   
       5 . The process of  claim 4  wherein the zinc compound is zinc sulfate.  
   
   
       6 . The process of  claim 1  wherein the steel substrate is coated with an aluminum alloy.  
   
   
       7 . The process of  claim 5  wherein the aqueous solution contains from about 0.5 to 10 grams of a cellulose thickener.  
   
   
       8 . The process of  claim 7  wherein the aqueous solution contains from about 0.5 to 10 grams of a non-ionic surfactant.  
   
   
       9 . The process of  claim 8  wherein the hexafluorozirconate is present in the aqueous solution in an amount ranging from about 1.0 to 12 grams.  
   
   
       10 . Process for post-treating aluminum and aluminum alloy coated steel to improve the corrosion resistance and adhesive bonding which comprises treating the aluminum coated steel with an acidic aqueous solution having a pH ranging from about 3.7 to 4.0 at temperatures ranging from room temperature to about 120° F.; said acidic aqueous solution comprising, per liter of solution, from about 1.0 to 12 grams of an alkali metal hexafluorozirconate, from about 0.1 to 12 grams of at least one divalent zinc compound, from 0.5 to about 1.5 grams of a water soluble thickener and from 0.5 to about 1.5 grams of a water soluble surfactant.  
   
   
       11 . The process of  claim 10  wherein the thickener is a cellulose and the surfactant is a non-ionic surfactant.  
   
   
       12 . The process of  claim 10  wherein the coated steel is an aluminum alloy coated steel.  
   
   
       13 . The process of  claim 11  wherein the thickener is methyl cellulose.  
   
   
       14 . The process of  claim 13  wherein the zinc compound is zinc sulfate.  
   
   
       15 . The process of  claim 14  wherein the alkali metal zirconate is potassium hexafluorozirconate.  
   
   
       16 . The process of  claim 15  wherein the hexafluorozirconate ranges from about 1.0 to 12 grams and the zinc sulfate ranges from about 1.0 to 6.0 grams per liter.  
   
   
       17 . The process of  claim 10  wherein the thickener is a water soluble alkyl cellulose and the surfactant is non-ionic.  
   
   
       18 . The process of  claim 10  wherein the zinc compound is zinc sulfate.  
   
   
       19 . The process of  claim 10  wherein the zinc compound is zinc acetate.  
   
   
       20 . The process of  claim 17  wherein the zinc compound is zinc sulfate present in the aqueous solution in an amount ranging from about 1.0 to 6.0 grams.  
   
   
       21 . The post-treated aluminum coated steel substrate obtained by the process of  claim 1 .  
   
   
       22 . The post-treated aluminum alloy coated steel substrate obtained by the process of  claim 10   
   
   
       23 . Composition for improving the adhesion bonding and corrosion resistance of aluminum and aluminum alloy coated steel substrates which comprises 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 hexafluorozirconates, from about 0.1 gram 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 about 10 grams of at least one water soluble surfactant.  
   
   
       24 . The composition of  claim 23  wherein the pH of the aqueous solution ranges from about 3.7 to 4.0 grams.  
   
   
       25 . The composition of  claim 24  wherein the hexafluorozirconate is an alkali metal 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.  
   
   
       26 . The composition of  claim 25  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.