ZnAlMg-Coated Metal Sheet with Improved Flexibility and Corresponding Manufacturing Process

Abstract

The present invention provides a process for the manufacture of a pre-painted sheet. The process includes supplying a steel substrate, depositing a metallic coating on at least one face by hot-dipping of the substrate in a bath including 4.4% to 5.6% by weight aluminum and 0.3% to 0.56% by weight magnesium. The rest of the bath includes exclusively zinc, unavoidable impurities resulting from the process and optionally one or more additional elements including Si, Ti, Ca, Mn, La, Ce and Bi. The content by weight of each additional element in the metallic coating is less than 0.3% and the presence of nickel is excluded. The process further includes solidifying the metallic coating, surface preparation of the metallic coating and painting of the metallic coating. The present invention further provides a pre-painted sheet.

What is claimed is: 
     
         1 - 16 . (canceled) 
     
     
         17 . A process for the manufacture of a pre-painted sheet comprising the steps of:
 supplying a steel substrate;   depositing a metallic coating on at least one face by hot-dipping the substrate in a bath including 4.4% to 5.6% by weight aluminum and 0.3% to 0.56% by weight magnesium, a remainder of the bath including zinc and unavoidable impurities resulting from the process, the presence of nickel being excluded;   solidifying the metallic coating;   surface preparation of the metallic coating; and   painting the metallic coating.   
     
     
         18 . The manufacturing process according to  claim 17 , wherein the bath comprises from 4.75 to 5.25% by weight aluminum. 
     
     
         19 . The manufacturing process according  claim 17 , wherein the bath comprises from 0.44 to 0.56% by weight magnesium. 
     
     
         20 . The manufacturing process according  claim 17 , wherein the bath further includes at least one additional element selected from the group consisting of Si, Ti, Ca, Mn, La, Ce and Bi, the content by weight of each additional element in the metallic coating being less than 0.3%. 
     
     
         21 . The manufacturing process according to  claim 17 , wherein the bath consists of aluminum, magnesium, zinc and unavoidable impurities. 
     
     
         22 . The manufacturing process according to  claim 17 , wherein the bath is at a temperature from 370° C. to 470° C. 
     
     
         23 . The manufacturing process according to  claim 17 , wherein the solidification of the metallic coating takes place at a cooling rate greater than or equal to 15° C./s between the beginning of solidification and the end of solidification of the metallic coating. 
     
     
         24 . The manufacturing process according to  claim 23 , wherein the cooling rate is between 15 and 35° C./s. 
     
     
         25 . The manufacturing process according to  claim 17 , wherein the surface preparation comprises a step selected from among rinsing, degreasing and a conversion treatment. 
     
     
         26 . The manufacturing process according to  claim 25 , wherein the degreasing is performed at a pH between 12 and 13. 
     
     
         27 . The manufacturing process according to  claim 25  wherein the conversion treatment is based on hexafluorotitanic acid. 
     
     
         28 . The manufacturing method according to  claim 17 , wherein the step of painting the metallic coating includes a paint comprising at least one polymer selected from the group consisting of melamine cross-linked polyesters, isocyanate cross-linked polyesters, polyurethanes and halogenated derivatives of vinyl polymers, with the exclusion of cataphoretic paints. 
     
     
         29 . A pre-painted sheet comprising:
 a steel substrate having at least one face;   a metallic coating coating the at least one face; the metallic coating including:
 4.4% to 5.6% by weight aluminum, 
 0.3% to 0.56% by weight magnesium, and 
 a remainder of the metallic coating including zinc and unavoidable impurities resulting from the process, the presence of nickel in the metallic coating being excluded, 
   at least one paint film covering the metallic coating.   
     
     
         30 . The pre-painted sheet according to  claim 29 , wherein the metallic coating further includes at least one additional element selected from the group consisting of Si, Ti, Ca, Mn, La, Ce and Bi, the content by weight of each additional element in the metallic coating being less than 0.3%. 
     
     
         31 . The pre-painted sheet according to  claim 29 , wherein the metal coating comprises from 4.75 to 5.25% by weight aluminum. 
     
     
         32 . The pre-painted sheet according to  claim 29 , wherein the metal coating comprises from 0.44 to 0.56% by weight magnesium. 
     
     
         33 . The pre-painted sheet according to  claim 29 , wherein the metallic coating consists of aluminum, magnesium, zinc and unavoidable impurities. 
     
     
         34 . The pre-painted sheet according to  claim 29 , wherein the at least one paint film comprises at least one polymer selected from the group consisting of melamine cross-linked polyesters, isocyanate cross-linked polyesters, polyurethanes and halogenated derivatives of vinyl polymers, with the exclusion of cataphoretic paints. 
     
     
         35 . The pre-painted sheet according to  claim 29 , further comprising a conversion layer comprising titanium at an interface between the metallic coating and the paint film.