Composition and process for the treatment of metal surfaces

Abstract

A method of forming a conversion layer on a metallic surface and a composition usable in the method are provided. The composition is an aqueous solution comprising a source of tungstate ions and a soluble material comprising zirconium. The method provides a conversion coating on a surface that can then be painted or otherwise treated. The conversion coatings of the present invention are minimally affected by heating and/or baking, unlike chromate conversion coatings of the prior art.

What is claimed is:  
     
         1 . A method of forming a conversion layer on a metallic surface comprising the steps of: 
 treating the metallic surface with an aqueous treating solution comprising: 
 (a) a source of tungstate ions; and  
 (b) a soluble material comprising zirconium; and  
   thereafter drying and/or baking the treated metal surface.    
     
     
         2 . A method according to  claim 1 , wherein the aqueous treating solution further comprises ammonium hydroxide.  
     
     
         3 . A method according to  claim 1 , wherein the source of tungstate ions is selected from the group consisting of ortho-tungstates, meta-tungstates and para-tungstates, polytungstates, heteropolytungstates, isopolytungstates, peroxytungstates, and combinations thereof.  
     
     
         4 . A method according to  claim 3 , wherein the source of tungstate ions is meta-tunstate or para-tungstate.  
     
     
         5 . A method according to  claim 3 , wherein the source of tungstate ions is selected from the group consisting of sodium, potassium, lithium, calcium, cerium, barium, magnesium, strontium, hydrogen and ammonium tungstate salts.  
     
     
         6 . A method according to  claim 3 , wherein the source of tungstate ions is tangstic acid, hexaamonium salt.  
     
     
         7 . A method according to  claim 1 , wherein the concentration of tungstate ions, measured as tungsten, in treating solution is about 0.01 g/l to about 10.0 g/l.  
     
     
         8 . A method according to  claim 7 , wherein the concentration of tungstate ions, measured as tungsten, in the treating solution is about 0.1 g/l to about 1.5 g/l.  
     
     
         9 . A method according to  claim 8 , wherein the concentration of tungstate ions, measured as tungsten, in the treating solution is 1.0 g/l.  
     
     
         10 . A method according to  claim 1 , wherein the soluble material comprising zirconium is selected from the group consisting of zirconium ammonium fluoride, dihydrogen hexafluorozirconate, potassium hexafluorozirconate, zirconium sulfate, zirconium carbonate, zirconium nitrate, and zirconium phosphate.  
     
     
         11 . A method according to  claim 10 , wherein the soluble material comprising zirconium is dihydrogen hexafluorozirconate.  
     
     
         12 . A method according to  claim 1 , wherein the concentration of the soluble material comprising zirconium in the treating solution is about 0.01 g/l to about 2.0 g/l.  
     
     
         13 . A method according to  claim 12 , wherein the concentration of the soluble material comprising zirconium in the treating solution is about 0.05 g/l to about 0.5 g/l.  
     
     
         14 . A method according to  claim 1 , wherein the aqueous treating solution further comprises a soluble aluminum salt.  
     
     
         15 . A method according to  claim 14 , wherein the concentration of the soluble aluminum salt is between 5 and 500 parts per million as aluminum.  
     
     
         16 . A method according to  claim 1 , wherein the temperature of the treating solution is within the range of about 55° F. to about 180° F.  
     
     
         17 . A method according to  claim 16 , wherein the temperature of the treating solution is about 70° F. to about 120° F.  
     
     
         18 . A method according to  claim 1 , wherein the pH of the treating solution is maintained from about 2.8 to about 7.0.  
     
     
         19 . A method according to  claim 1 , wherein the parts are cleaned prior to treating the metallic surface with the treating solution.  
     
     
         20 . A method according to  claim 19 , wherein the metallic surface is deoxidized after cleaning and prior to treating with the treating solution.  
     
     
         21 . A method according to  claim 1 , wherein the treating solution is free of chromium.  
     
     
         22 . A method according to  claim 1 , wherein the treating solution is applied by immersion or by spraying.  
     
     
         23 . A method according to  claim 1 , wherein the treating solution further comprises at least one of a surfactant, an accelerator, a dye, an organic polymer, a buffering agent, and a pH adjusting agent.  
     
     
         24 . An aqueous conversion coating composition comprising a source of tungstate ions and a soluble material comprising zirconium.  
     
     
         25 . A composition according to  claim 24 , wherein the aqueous treating solution further comprises ammonium hydroxide.  
     
     
         26 . A composition according to  claim 24 , wherein the source of tungstate ions is selected from the group consisting of ortho-tungstates, meta-tungstates and para-tungstates, polytungstates, heteropolytungstates, isopolytungstates, peroxytungstates, and combinations thereof.  
     
     
         27 . A composition according to  claim 26 , wherein the source of tungstate ions is meta-tungstate or para-tungstate.  
     
     
         28 . A composition according to  claim 26 , wherein the source of tungstate ions is selected from the group consisting of sodium, potassium, lithium, calcium, cerium, barium, magnesium, strontium, hydrogen and ammonium tungstate salts.  
     
     
         29 . A composition according to  claim 26 , wherein the source of tungstate ions is tungstic acid, hexaamonium salt.  
     
     
         30 . A composition according to  claim 24 , wherein the concentration of tungstate ions, measured as tungsten, in treating solution is about 0.01 g/l to about 10.0 g/l.  
     
     
         31 . A composition according to  claim 30 , wherein the concentration of tungstate ions, measured as tungsten, in the treating solution is about 0.1 g/l to about 1.5 g/l.  
     
     
         32 . A composition according to  claim 31 , wherein the concentration of tungstate ions, measured as tungsten, in the treating solution is 1.0 g/l.  
     
     
         33 . A composition according to  claim 24 , wherein the soluble material comprising zirconium is selected from the group consisting of zirconium ammonium fluoride, dihydrogen hexafluorozirconate, potassium hexafluorozirconate, zirconium sulfate, zirconium carbonate, zirconium nitrate, and zirconium phosphate.  
     
     
         34 . A composition according to  claim 33 , wherein the soluble material comprising zirconium is dihydrogen hexafluorozirconate.  
     
     
         35 . A composition according to  claim 24 , wherein the concentration of the soluble material comprising zirconium in the treating solution is about 0.01 g/l to about 2.0 g/l.  
     
     
         36 . A composition according to  claim 35 , wherein the concentration of the soluble material comprising zirconium in the treating solution is about 0.05 g/l to about 0.5 g/l.  
     
     
         37 . A composition according to  claim 24 , wherein the aqueous treating solution further comprises a soluble aluminum salt.  
     
     
         38 . A composition according to  claim 37 , wherein the concentration of the soluble aluminum salt is between 5 and 500 parts per million as aluminum.  
     
     
         39 . A composition according to  claim 24 , wherein the temperature of the treating solution is within the range of about 55° F. to about 180° F.  
     
     
         40 . A composition according to  claim 39 , wherein the temperature of the treating solution is about 70° F. to about 120° F.  
     
     
         41 . A composition according to  claim 24 , wherein the pH of the treating solution is maintained from about 2.8 to about 7.0.  
     
     
         42 . A composition according to  claim 24 , wherein the treating solution is free of chromium.  
     
     
         43 . A composition according to  claim 24 , wherein the treating solution further comprises at least one of a surfactant, an accelerator, a dye, an organic polymer, a buffering agent, and a pH adjusting agent.