Supplementary corrosion protection for components made of organically precoated metal sheets

Abstract

The invention relates to a corrosion protection method for application in connection with the production of finished metallic components from organically precoated metal sheets. In the course of such production, areas of uncoated metal which inevitably come about in the course of cutting, forming and joining the precoated metal sheets are provided with a chromium-free corrosion protection coat that is not a zinc phosphate coating, which serves at the same time as a tie coat for the subsequent finish. The treatment solution preferably contains fluoro complexes of Ti, Zr and/or Si and also organic polymers. The invention also embraces a metallic component treated accordingly.

1 . A method of producing a finished component comprising metal parts made of galvanized steel, said method comprising 
 a) cutting and/or punching and/or forming sheets of galvanized steel which carry a coating based on organic polymers, and joining the resultant metal parts to produce a joined component, thereby giving rise to areas of the joined component that comprise metal surfaces of the galvanized steel that are not covered by the coating based on organic polymers;    b) cleaning the joined component,    c) contacting the cleaned joined component with a chromium-free acidic aqueous treatment solution, which on the areas of the metal surface formed in substep a) that are not covered by the coating based on organic polymers produces a passivating coat which is not a zinc phosphate coat,    d) optionally, subjecting the component treated in substep c) to one or more rinses with water, and    e) coating the component of substep c) or d) with a finish coat,    wherein all metal parts of the component during the implementation of substeps b) to e) are composed exclusively of the sheets of galvanized steel which carry a coating based on organic polymers, and    wherein substep c) is the only treatment step after substep a) which produces a passivating coat on the areas of the joined component that comprise metal surfaces formed in substep a) that are not covered by the coating based on organic polymers.    
     
     
         2 . The method as claimed in  claim 1 , wherein the metallic component comprises a vehicle body, a domestic appliance, a piece of furniture or a part of each thereof.  
     
     
         3 . The method as claimed in  claim 1 , wherein the coating based on organic polymers comprises electrically conductive particles.  
     
     
         4 . The method as claimed in  claim 1 , wherein the acidic aqueous treatment solution in substep c) has a pH of at least 2 and not more than 5.  
     
     
         5 . The method as claimed in  claim 1 , wherein the acidic aqueous treatment solution contains in total at least 0.01 g/l Ti and/or Zr and/or Si ions and also contains at least an amount of fluoride such that the atomic ratio of Ti to F and/or of Zr to F and/or of Si to F is in the range from 1:1 to 1:6, and wherein the treatment solution additionally contains at least 0.005 g/l organic polymers.  
     
     
         6 . The method as claimed in  claim 5 , wherein the organic polymers are selected from homopolymers and copolymers of vinylpyrrolidone.  
     
     
         7 . The method as claimed in  claim 4 , wherein the acidic aqueous treatment solution is contacted at a temperature in the range from 20 to 45° C. for a time in the range from 1 to 5 minutes with the cleaned joined component.  
     
     
         8 . The method as claimed in  claim 1 , wherein the acidic aqueous treatment solution contains no transition-group metals other than metals from transition group four of the Periodic Table.  
     
     
         9 . The method as claimed in  claim 1 , wherein the metallic component is coated in substep e) with a finish material selected from a dip-coating material, an electrodeposition coating material or a powder coating material.  
     
     
         10 . A finished component comprising galvanized-steel parts which is made according to the method as claimed in  claim 1 .  
     
     
         11 . A method of producing a passivated component comprising metal parts made of galvanized steel, said method comprising 
 a) cutting and/or punching and/or forming sheets of galvanized steel which carry a coating based on organic polymers, and joining the resultant metal parts to produce a joined component, thereby giving rise to areas of the joined component that comprise metal surfaces of the galvanized steel that are not covered by the coating based on organic polymers;    b) cleaning the joined component,    c) contacting the cleaned joined component with a chromium-free acidic aqueous treatment solution, which on the areas of the metal surface formed in substep a) that are not covered by the coating based on organic polymers produces a passivating coat which is not a zinc phosphate coat, wherein the treatment solution comprises in total at least 0.01 g/l Ti and/or Zr and/or Si ions and also contains at least an amount of fluoride such that the atomic ratio of Ti to F and/or of Zr to F and/or of Si to F is in the range from 1:1 to 1:6, and wherein the treatment solution additionally contains at least 0.005 g/l organic polymers,    d) optionally, subjecting the component treated in substep c) to one or more rinses with water, and    e) optionally, coating the component of substep c) or d) with a finish coat,    wherein all metal parts of the component during the implementation of substeps b) to e) are composed exclusively of the sheets of galvanized steel which carry a coating based on organic polymers, and    wherein substep c) is the only treatment step after substep a) which produces a passivating coat on the areas of the joined component that comprise metal surfaces formed in substep a) that are not covered by the coating based on organic polymers.    
     
     
         12 . The method as claimed in  claim 11 , wherein the metallic component comprises a vehicle body, a domestic appliance, a piece of furniture or a part of each thereof.  
     
     
         13 . The method as claimed in  claim 11 , wherein the coating based on organic polymers comprises electrically conductive particles and has a thickness in the range from 1 to 10 μm.  
     
     
         14 . The method as claimed in  claim 11 , wherein the acidic aqueous treatment solution in substep c) has a pH of at least 2 and not more than 5.  
     
     
         15 . The method as claimed in  claim 11 , wherein the acidic aqueous treatment solution contains in total at least 0.025 g/l and up to 10 g/l Ti and/or Zr and/or Si ions and also contains at least an amount of fluoride such that the atomic ratio of Ti to F and/or of Zr to F and/or of Si to F is in the range from 1:1 to 1:6, and wherein the treatment solution additionally contains at least 0.01 g/l and up to 20 g/l organic polymers.  
     
     
         16 . The method as claimed in  claim 15 , wherein the organic polymers are selected from homopolymers and copolymers of vinylpyrrolidone.  
     
     
         17 . The method as claimed in  claim 16 , wherein the organic polymers are selected from copolymers of vinylpyrrolidone with monomers containing caprolactam groups or imidazole.  
     
     
         18 . The method as claimed in  claim 11 , wherein the acidic aqueous treatment solution contains no transition-group metals (transition metals) other than metals from transition group four of the Periodic Table.  
     
     
         19 . The method as claimed in  claim 11 , wherein the acidic aqueous treatment solution contains at least one fluoroacid of Ti and/or Zr.  
     
     
         20 . A finished component comprising galvanized-steel parts which is made according to the method as claimed in  claim 11.