Non-chromium conversion coatings for ferrous alloys

Abstract

Composition and process for coating ferrous alloys to improve the corrosion resistance and adhesive bonding strength of the alloys. The process comprises using the composition for treating the ferrous alloys such as steel with an acidic aqueous solution comprising, per liter of solution, from about 0.1 to 22 grams of hexafluorozirconates, effective amounts of at least one water soluble divalent zinc compound, and 0.0 to 10 grams of water soluble thickeners and/or water soluble surfactants.

1 . Composition for preparing conversion coatings for ferrous alloys to improve the corrosion resistance and adhesive bonding strength of the alloys 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, and from about 0.1 gram up to the solubility limit of a divalent zinc compound, from 0.0 to about 10 grams of at least one water soluble thickener and from 0.0 to about 10 grams of at least one water soluble surfactant.  
   
   
       2 . The composition of  claim 1  wherein the pH of the aqueous solution ranges from about 3.7 to 4.0 and the ferrous alloy is steel.  
   
   
       3 . The composition of  claim 1  wherein the hexafluorozirconate is an alkali metal salt 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.  
   
   
       4 . The composition of  claim 3  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.  
   
   
       5 . Process for preparing conversion coatings on ferrous alloys to improve the corrosion resistance and adhesive bonding of the alloys which comprises treating said alloys with an acidic aqueous solution having a pH ranging from about 3.7 to 4.0 at temperatures ranging from about ambient to 200° F.; said acidic aqueous solution comprising, per liter of solution, from about 0.1 to 22 grams of a hexafluorozirconate, and from about 0.1 gram up to the solubility limits of a divalent zinc compound, from 0.0 to about 10 grams of at least one water soluble thickener and from 0.0 to about 10 grams of at least one water soluble surfactant.  
   
   
       6 . The process of  claim 5  wherein the alloy is steel.  
   
   
       7 . The process of  claim 6  wherein the thickener is a cellulose compound.  
   
   
       8 . The process of  claim 6  wherein the zinc compound is zinc sulfate.  
   
   
       9 . The process of  claim 6  wherein the zirconate is an alkali metal hexafluorozirconate.  
   
   
       10 . The process of  claim 6  wherein the hexafluorozirconate ranges from about 1.0 to 12 grams, and the zinc compound ranges from about 1.0 to 6.0 grams per liter of solution.  
   
   
       11 . The process of  claim 6  wherein the zinc compound is zinc acetate.  
   
   
       12 . The process of  claim 7  wherein the thickener is a water soluble alkyl cellulose.  
   
   
       13 . The process of  claim 5  wherein the divalent zinc compound is zinc sulfate and the zirconate is potassium hexafluorozirconate.  
   
   
       14 . The process of  claim 5  wherein the surfactant is a water soluble non-ionic, surfactant.  
   
   
       15 . The process of  claim 14  wherein the zinc compound is present in the aqueous solution in an amount ranging from about 1.0 to 6.0 grams per liter of solution.  
   
   
       16 . The process of  claim 15  wherein the zinc compound is divalent zinc acetate and the surfactant is a non-ionic surfactant.  
   
   
       17 . The process of  claim 15  wherein the zinc compound is divalent zinc sulfate present in the aqueous solution in an amount ranging from about 1.0 to 6.0 grams.  
   
   
       18 . Coated ferrous alloy obtained by the process of  claim 5 .  
   
   
       19 . Coated steel obtained by the process of  claim 6 .  
   
   
       20 . Coated steel obtained by the process of  claim 10.