Method for sequentially constructing a conversion layer on components comprising steel surfaces

Abstract

The invention relates to a method for the anti-corrosion pre-treatment of a plurality of components in series, in which the components of the series are at least partially formed of iron and/or steel, and in which the components of the series each initially undergo a first conversion stage, followed by a rinsing stage and a subsequent second conversion stage, wherein, in the conversion stages, respective acidic aqueous conversion solutions based on compounds of the elements Zr and/or Ti dissolved in water are brought into contact with the components, and, additionally, copper ions are contained in the conversion solution for the second stage.

1 . A method for anti-corrosion pre-treatment of a plurality of components in series, in which the components of the series are at least partially formed of iron and/or steel, and in which the components of the series each undergo successive method steps i)-iii) and at least surfaces of the iron and/or steel of the components are successively brought into contact with respectively provided aqueous solutions (I)-(III):
 i) a first conversion stage providing an aqueous conversion solution (I) having a pH in a range of 2.5 to 5.0, comprising free fluoride and at least 0.10 mmol/kg of compounds of the elements Zr and/or Ti dissolved in water;   ii) a rinsing stage providing an aqueous rinsing solution (II) having a pH in a range of 5.0 to 10.0, containing less than 0.25 mmol/kg of free fluoride and a concentration of compounds of the elements Zr and/or Ti dissolved in water that is reduced by at least a factor of 5 compared to the aqueous conversion solution (I);   iii) a second conversion stage providing an aqueous conversion solution (III) having a pH in a range of 2.5 to 5.0, comprising at least 0.10 mmol/kg of compounds of the elements Zr and/or Ti dissolved in water and at least 15 μmol/kg of copper ions dissolved in water.   
     
     
         2 . The method according to  claim 1 , wherein the contacting with the conversion solution (I) in the first conversion stage in method step (i) takes place at least for a period of time during which a coating of at least 20 mg/m 2  is produced on the surfaces of steel and/or iron, but not for so long that the coating is more than 150 mg/m 2 , in each case based on the elements Zr and/or Ti results. 
     
     
         3 . The method according to  claim 2 , wherein the contacting with the conversion solution (III) in the second conversion stage in method step (iii) does not continue until there is an increase of more than 15 mg/m2 on the surfaces of steel and/or iron, but at least for such a period of time that the coating on said surfaces is increased by at least 2 mg/m2, in each case based on the elements Zr and/or Ti. 
     
     
         4 . The method according to  claim 1 , wherein in the conversion solution (I) of the first conversion stage in method step i), the compounds of the elements Zr and/or Ti dissolved in water are present in an amount of at least 0.15 mmol/kg. 
     
     
         5 . The method according to  claim 1 , wherein in the conversion solution (I) of the first conversion stage in method step i), the free fluoride is present in an amount of at least 0.5 mmol/kg, but less than 8.0 mmol/kg of free fluoride. 
     
     
         6 . The method according to  claim 1 , wherein the quotient λ in the conversion solution (I) of the first conversion stage in method step i) is according to the Formula (1) 
       
         
           
             
               
                 
                   
                     
                       λ 
                       = 
                       
                         
                           F 
                           / 
                           mM 
                         
                         
                           
                             Me 
                             / 
                             mM 
                           
                         
                       
                     
                     , 
                   
                 
                 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
       where F/mM and Me/mM are the free fluoride (F) or reduced zirconium and/or titanium concentration (Me) reduced by the unit of the concentration in mmol/kg, and the quotient λ is greater than 0.80. 
     
     
         7 . The method according to  claim 1 , wherein in the conversion solution (III) of the second conversion stage in method step iii), the compounds of the elements Zr and/or Ti dissolved in water are present in an amount of less than 1.00 mmol/kg. 
     
     
         8 . The method according to  claim 1 , wherein in the conversion solution (III) of the second conversion stage in method step iii), further comprises free fluoride present in an amount of at least 0.1 mmol/kg, and less than 3.00 mmol/kg. 
     
     
         9 . The method according to  claim 1 , wherein the conversion solution (III) of the second conversion stage in method step iii), comprises copper ions dissolved in water in an amount of more than 40 μmol/kg. 
     
     
         10 . The method according to  claim 1 , wherein the compounds of the elements Zr and/or Ti dissolved in water in the conversion solutions (I) and (III) of the respective conversion stages of method steps i) and iii) are selected from fluoro complexes of the elements Zr and/or Ti. 
     
     
         11 . The method according to  claim 1 , wherein the aqueous rinsing solution (II) of the rinsing stage in method step (ii) additionally contains at least 0.1 mmol/kg, but no more than 10 mmol/kg of a depolarizer selected from nitrate ions, nitrite ions, nitroguanidine, N-methylmorpholine N-oxide, hydrogen peroxide in free or bound form, hydroxylamine in free or bound form, reducing sugars and combinations thereof. 
     
     
         12 . The method according to  claim 1 , wherein the aqueous conversion solutions of the conversion stages in method steps (i) and (iii) each have a pH above 3.0 but below 4.5. 
     
     
         13 . The method according to  claim 1 , wherein in the rinsing stage of method step (ii), the contacting with the provided rinsing solution is carried out by dipping and/or spraying. 
     
     
         14 . The method according to  claim 1 , wherein after the method step (iii), with an intermediate rinsing step, further coating of the components is carried out using a paint system comprising an electrodeposition coating. 
     
     
         15 . The method according to  claim 1 , wherein the components of the series also have surfaces of zinc and/or aluminum in addition to the surfaces of steel and/or iron. 
     
     
         16 . The method according to  claim 1 , wherein in the conversion solution (I) of the first conversion stage in method step i), the compounds of the elements Zr and/or Ti dissolved in water are present in an amount of at least at least 0.30 mmol/kg; the free fluoride is present in an amount of at least 1.5 mmol/kg, but less than 6.0 mmol/kg; and the contacting of the surfaces of steel and/or iron takes place for a period of time during which the coating produced is not more than more than 80 mg/m2, in each case based on the elements Zr and/or Ti. 
     
     
         17 . The method according to  claim 16 , wherein wherein the aqueous rinsing solution (II) of the rinsing stage in method step (ii) contains a total of less than 50 μmol/kg of metal ions of the elements copper, nickel and cobalt that are dissolved in water. 
     
     
         18 . The method according to  claim 16 , wherein the conversion solution (III) of the second conversion stage in method step iii), comprises the compounds of the elements Zr and/or Ti dissolved in water present in an amount of less than 0.70 mmol/kg; and the free fluoride is present in an amount of less than 2.50 mmol/kg but at least 0.1 mmol/kg. 
     
     
         19 . The method according to  claim 1 , wherein the conversion solution (III) of the second conversion stage in method step iii), comprises copper ions dissolved in water in an amount of more than 50 μmol/kg, but no more than 300 μmol/kg. 
     
     
         20 . The method according to  claim 6 , wherein the quotient λ is greater than 1.60.