Methods for producing a pre-lacquered metal sheet having zn-al-mg coatings and corresponding metal sheet

Abstract

A method is provided. The method includes providing a steel substrate having two faces coated by dipping the substrate in a bath, altering layers of magnesium oxide or magnesium hydroxide formed on the outer surfaces of the metal coatings by applying an acid solution, optionally a conversion solution with a pH between 1 and 2, and/or mechanical forces, and painting the outer surfaces of the metal coatings. Additional methods and a metal sheet are also provided.

What is claimed is: 
     
         1 - 23 . (canceled) 
     
     
         24 . A method for producing a metal sheet, the method comprising the following series of steps:
 providing a steel substrate having two faces each coated with a metal coating obtained by dipping the substrate in a bath and cooling, each metal coating comprising zinc, between 0.1 and 20 wt % of aluminum, and between 0.1 and 10 wt % of magnesium, the substrate thus coated having been subjected to a skin-pass step;   degreasing the outer surfaces of the metal coatings;   rinsing and drying the outer surfaces of the metal coatings;   altering layers of magnesium oxide or magnesium hydroxide formed on the outer surfaces of the metal coatings, the altering step comprising the application of an acid solution on the outer surfaces of the metal coatings;   further rinsing the outer surfaces of the metal coatings;   applying a conversion solution on the outer surfaces of the metal coatings;   drying the outer surfaces of the metal coatings;   painting the outer surfaces of the metal coatings to cover each of the outer surfaces with a paint film comprising at least one polymer chosen from the group consisting of melamine-cross-linking polyesters, isocyanate-cross-linking polyesters, polyurethanes and halogenated derivatives of vinyl polymers, excluding cataphoretic paints.   
     
     
         25 . The method according to  claim 24 , wherein the degreasing step includes applying an alkaline solution on the outer surfaces of the metal coatings. 
     
     
         26 . The method according to  claim 24 , wherein the acid solution is applied during a duration between 0.2 s and 30 s on the outer surfaces of the metal coatings. 
     
     
         27 . The method according to  claim 24 , wherein the acid solution has a pH between 1 and 4. 
     
     
         28 . The method according to  claim 24 , wherein after the step of further rinsing the outer surfaces of the metal coatings are dried. 
     
     
         29 . A method for producing a metal sheet, the method comprising the following series of steps:
 providing a steel substrate having two faces each coated with a metal coating obtained by dipping the substrate in a bath and cooling, each metal coating comprising zinc, between 0.1 and 20 wt % of aluminum, and between 0.1 and 10 wt % of magnesium, the substrate thus coated having been subjected to a skin-pass step;   degreasing the outer surfaces of the metal coatings;   rinsing and drying the outer surfaces of the metal coatings;   applying an acid conversion solution not containing chromium on the outer surfaces of the metal coatings, said conversion solution having a pH between 1 and 2,   drying the outer surfaces of the metal coatings;   painting the outer surfaces of the metal coatings to cover each of them with a paint film comprising at least one polymer chosen from the group consisting of melamine-cross-linking polyesters, isocyanate-cross-linking polyesters, polyurethanes and halogenated derivatives of vinyl polymers, excluding cataphoretic paints.   
     
     
         30 . The method according to  claim 29 , wherein the acid conversion solution is applied during a duration comprised between 0.2 s and 30 s on the outer surfaces of the metal coatings. 
     
     
         31 . A method for producing a metal sheet, the method comprising the following series of steps:
 providing a steel substrate having two faces each coated with a metal coating obtained by dipping the substrate in a bath and cooling, each metal coating comprising zinc, between 0.1 and 20 wt % of aluminum, and between 0.1 and 10 wt % of magnesium, the substrate thus coated having been subjected to a skin-pass step;   altering layers of magnesium oxide or magnesium hydroxide formed on the outer surfaces of the metal coatings, said altering step comprising applying mechanical forces on the outer surfaces of the metal coatings;   non-oxidizing degreasing the outer surfaces of the metal coatings;   rinsing and drying the outer surfaces of the metal coatings;   applying a conversion solution on the outer surfaces of the metal coatings;   drying the outer surfaces of the metal coatings;   painting the outer surfaces of the metal coatings to cover each of them with a paint film comprising at least one polymer chosen from the group consisting of melamine-cross-linking polyesters, isocyanate-cross-linking polyesters, polyurethanes and halogenated derivatives of vinyl polymers, excluding cataphoretic paints.   
     
     
         32 . The method according to  claim 31 , wherein the mechanical forces are applied on the outer surfaces of the metal coatings before applying the acid solution or when the acid solution is present on the outer surfaces. 
     
     
         33 . The method according to  claim 32 , wherein the mechanical forces are applied by passing through a roller leveler. 
     
     
         34 . The method according to  claim 31 , wherein the mechanical forces crack the layers of magnesium oxide or magnesium hydroxide. 
     
     
         35 . The method according to  claim 31 , wherein the altering step includes applying an acid solution on the outer surfaces of the metal coatings during the altering step. 
     
     
         36 . The method according to  claim 35 , further comprising the step of rinsing the outer surfaces of the metal coatings. 
     
     
         37 . The method according to  claim 36 , further comprising the step of drying the outer surfaces of the metal coatings. 
     
     
         38 . The method according to  claim 24 , wherein the metal coatings comprise between 0.3 and 10 wt % of magnesium. 
     
     
         39 . The method according to  claim 38 , wherein the metal coatings comprise between 0.3 and 4 wt % of magnesium. 
     
     
         40 . The method according to  claim 24 , wherein the metal coatings comprise between 0.5 and 11 wt % of aluminum. 
     
     
         41 . The method according to  claim 40 , wherein the metal coatings comprise between 0.7 and 6 wt % of aluminum. 
     
     
         42 . The method according to  claim 41 , wherein the metal coatings comprise between 1 and 6 wt % of aluminum. 
     
     
         43 . The method according to  claim 24 , wherein a weight ratio between the magnesium and the aluminum in the metal coatings is less than or equal to 1. 
     
     
         44 . A metal sheet having two faces each coated with a metal coating comprising zinc, aluminum and magnesium and by a paint film comprising at least one polymer chosen from the group consisting of melamine-cross-linking polyesters, isocyanate-cross-linking polyesters, polyurethanes and halogenated derivatives of vinyl polymers, excluding cataphoretic paints, the metal coatings comprising between 0.1 and 20 wt % of aluminum and 0.1 and 10 wt % of magnesium, the metal sheet being obtained by the method according to  claim 24 .