Plated steel sheet having excellent corrosion resistance, workability and surface quality and method for manufacturing same

Abstract

Provided are a plated steel sheet and a method for manufacturing same, the plated steel sheet comprising: a base steel sheet; a Zn—Mg—Al based steel sheet plating layer provided on at least one surface of the base steel sheet; and an Fe—Al based inhibition layer provided between the base steel sheet and the Zn—Mg—Al based plating layer, wherein the plating layer comprises, in wt %: 4% or more of Mg; 2.1 times or more of Mg content and 14.2% or less of Al; 0.2% or less (including 0%) of Si; 0.1% or less (including 0%) of Sn; the remainder Zn; and unavoidable impurities.

1 . A method for manufacturing a plated steel sheet, comprising:
 an operation of dipping a base steel sheet, the base steel sheet, including by weight %: 4% or more of Mg; 2.1 times or more of a Mg content and 14.2% or less of Al; 0.2% or less (including 0%) of Si; 0.1% or less (including 0%) of Sn, with a balance of Zn and unavoidable impurities, in a plating bath maintained at a temperature 20 to 80° C. higher than a solidification start temperature in an equilibrium phase diagram and hot-dip galvanizing the same; and   an operation of cooling the steel sheet starting from a bath surface of the plating bath to a top roll section at an average cooling rate of 3 to 30° C./s using inert gas,   wherein the cooling operation controls a cooling rate to satisfy the following Relations 1-1 and 1-2,   
       
         
           
             
               
                 
                   
                     A 
                     > 
                     
                       
                         2.5 
                         / 
                         
                           
                             { 
                             
                               ln 
                               ⁡ 
                               ( 
                               
                                 t 
                                 × 
                                 2 
                                 ⁢ 
                                 0 
                               
                               ) 
                             
                             } 
                           
                           
                             1 
                             / 
                             2 
                           
                         
                       
                       × 
                       B 
                     
                   
                 
                 
                   
                     [ 
                     
                       Relation 
                       ⁢ 
                           
                       1 
                       - 
                       1 
                     
                     ] 
                   
                 
               
             
           
         
         
           
             
               
                 
                   
                     
                       0.7 
                       × 
                       C 
                     
                     ≤ 
                     B 
                     ≤ 
                     
                       1.2 
                       × 
                       C 
                     
                   
                 
                 
                   
                     [ 
                     
                       Relation 
                       ⁢ 
                           
                       1 
                       - 
                       2 
                     
                     ] 
                   
                 
               
             
           
         
         where, in Relations 1-1 and 1-2, t is a thickness of the steel sheet, A is an average cooling rate (° C./s) from a plating bath temperature to a solidification start temperature, B is an average cooling rate (° C./s) from the solidification start temperature to a solidification initiation temperature −30° C., and C is an average cooling rate (° C./s) from a solidification start temperature −30° C. to 300° C. 
       
     
     
         2 . The method of  claim 1 , after the operation of hot-dip galvanizing, an air knife treatment is performed to satisfy the following Relation 2, 
       
         
           
             
               
                   
                 
                   
                     [ 
                     
                       Relation 
                       ⁢ 
                           
                       2 
                     
                     ] 
                   
                 
               
             
           
         
         
           
             
               0.1 
               ≤ 
               
                 
                   
                     ( 
                     
                       AK 
                       ⁢ 
                           
                       interval 
                       × 
                       Thickness 
                       ⁢ 
                           
                       of 
                       ⁢ 
                           
                       steel 
                       ⁢ 
                           
                       sheet 
                     
                     ) 
                   
                   / 
                   AK 
                 
                 ⁢ 
                     
                 Pressure 
               
               ≤ 
               25 
             
           
         
         where, in the above relation 2, the AK interval represents an interval (mm) between knives, the thickness of the steel sheet represents a thickness (mm) of the steel sheet including all of the base steel sheet, the plating layer, and the inhibition layer, and the AK pressure represents air knife pressure (KPa) of a nozzle. 
       
     
     
         3 . The method of  claim 1 , wherein, before the operation of hot-dip galvanizing, further comprising:
 an operation of performing a shot blasting treatment to remove surface oxides of the base steel sheet,   wherein the shot blasting treatment is performed so that a metal ball of 300 to 3,000 kg/min collides with a surface of the steel sheet at a moving speed of 50 to 150 mpm by using a metal ball having a diameter of 0.3 to 10 μm.   
     
     
         4 . The method of  claim 1 , wherein, in the cooling operation, the cooling operation is performed such that a ratio (De/Dc) of a damper opening rate (De) of an edge portion to a damper opening rate (Dc) of a central portion is 60 to 99%.