Method for surface treatment of a protectively coated substrate

Abstract

A method is shown for surface-treating a protectively coated substrate ( 1 ), more particularly steel strip, for the purpose of enhancing the strength of adhesion with an adhesive ( 10 ), where the at least partly multi-phase protective coat ( 2 ) comprises at least zinc and magnesium. In order to provide a particular suitability for adhesive bonding, it is proposed that the protective coat ( 2 ) be subjected to a pickling treatment, directed substantially at at least one intermetallic Zn—Mg phase ( 4 ) of the protective coat ( 2 ), with acidic pickle, more particularly acid.

1 . Method for surface treatment of a protectively coated substrate ( 1 ), particularly steel strip, for improvement of the adhesion strength, with an adhesive ( 10 ), wherein the at least partly multi-phase protective coating ( 2 ) comprises at least zinc and magnesium, wherein the protective coating ( 2 ) is subjected to a pickling treatment, which is essentially directed at at least one intermetallic Zn—Mg phase ( 4 ) of the protective coating ( 2 ), with acidic pickle, particularly acid. 
     
     
         2 . Method according to  claim 1 , wherein in the pickling step for selective pickling of the protective coating ( 2 ), an oxide layer ( 9 ) of the protective coating ( 2 ) is also removed by pickling. 
     
     
         3 . Method according to  claim 1 , wherein the protective coating ( 2 ) is subjected to a pickling treatment essentially directed at MgZn 2 . 
     
     
         4 . Method according to  claim 1 , wherein the protective coating ( 2 ), which additionally comprises aluminum, is subjected to a pickling treatment essentially directed at a particularly ternary eutectic ( 7 ). 
     
     
         5 . Method according to  claim 1 , wherein an acid having a pK s  value less than 0 is used as an acidic pickle. 
     
     
         6 . Method according to  claim 5 , wherein a non-oxidizing acid, particularly H 2 SO 4 , is used as an acidic pickle. 
     
     
         7 . Method according to  claim 1 , wherein the protective coating ( 2 ) is subjected to a pickling duration of 0.5 to 20 seconds, with an acid at a concentration of 1 to 20 volume-%. 
     
     
         8 . Method according to  claim 1 , wherein the protective coating ( 2 ) is subjected to a pickling duration of 1 to 15 seconds, with an acid at a concentration of 2 to 10 volume-%. 
     
     
         9 . Method according to  claim 1 , wherein the product resulting from the pickling duration in seconds and the concentration in volume-% lies in the range of 1 to 100. 
     
     
         10 . Method according to  claim 1 , wherein the product resulting from the pickling duration in seconds and the concentration in volume-% lies in the range of 6 to 75. 
     
     
         11 . Use of an acid having a pk s  value less than 0 for surface treatment of an object corrosion-protected with a multi-phase protective coating ( 2 ) comprising zinc and magnesium, particularly a steel strip ( 1 ), for improvement of the adhesion strength, with an adhesive ( 10 ). 
     
     
         12 . Use according to  claim 11 , wherein the acid is used for a pickling treatment essentially directed at the protective coating ( 2 ), which additionally comprises aluminum, particularly at its ternary eutectic ( 7 ). 
     
     
         13 . Object, particularly a steel strip ( 1 ), having a multi-phase protective coating ( 2 ) comprising zinc and magnesium, wherein the protective coating ( 2 ) has a microstructure reduced by the proportion of intermetallic Zn—Mg phase ( 4 ), produced by means of a method for surface treatment according to  claim 1 . 
     
     
         14 . Object according to  claim 13 , wherein the protective coating ( 2 ) has a microstructure reduced by the MgZn 2  component. 
     
     
         15 . Object according to  claim 13 , wherein the protective coating ( 2 ) that additionally comprises aluminum has a microstructure reduced by the proportion of, in particular, ternary eutectic ( 7 ).