Steel Pre-Paint Treatment Composition

Abstract

An aqueous conversion coating composition for treating steel substrates to provide a conversion coating thereon. The conversion coating composition comprises a) a source of aluminum ions; b) hexafluorozirconic acid or its salts; c) at least one pH adjuster; and d) optionally, a surfactant. The conversion coating composition provides a corrosion resistant coating on the metal surface and improves the adhesion of subsequently applied layers.

1 . An aqueous conversion coating composition comprising:
 a) from 0 g/l to 300 g/l of aluminum ions;   b) hexafluorozirconic acid or salts thereof;   c) at least one pH adjuster;   d) optionally, a surfactant.   
     
     
         2 . The aqueous conversion coating composition according to  claim 1 , wherein the conversion coating composition does not contain chromium or sequestering agents for zinc. 
     
     
         3 . The aqueous conversion coating composition according to  claim 1 , wherein the pH adjuster comprises ammonium hydroxide. 
     
     
         4 . The aqueous conversion coating composition according to  claim 1  wherein the aluminum ions are from a source comprising aluminum hydroxide. 
     
     
         5 . The aqueous conversion coating composition according to  claim 1  wherein the concentration of aluminum ions is from 1 g/l to 50 g/l. 
     
     
         6 . A method of treating a steel substrate to form a conversion coating thereon, the method comprising the steps of
 a) contacting the steel substrate with a composition comprising:
 i) from 0 g/l to 300 g/l of aluminum ions; 
 ii) hexafluorozirconic acid or its salts; 
 iii) at least one pH adjuster; 
 iv) optionally, a surfactant; and 
   b) thereafter drying the treated steel surface.   
     
     
         7 . The method according to  claim 6 , wherein the conversion coating composition does not contain chromium or sequestering agents for zinc. 
     
     
         8 . The method according to  claim 6 , wherein the pH adjuster comprises aluminum hydroxide. 
     
     
         9 . The method according to  claim 6 , wherein the aluminum ions are from a source comprising aluminum hydroxide. 
     
     
         10 . The method according to  claim 6 , wherein the concentration of aluminum ions is from 1 g/l to 50 g/l.