Plated steel sheet having excellent corrosion resistance and weldability and method for manufacturing same

Abstract

The present invention provides a plated steel sheet excellent in corrosion resistance and excellent in at least one of weldability and phosphatability, and a manufacturing method therefor. And more specifically, the present invention provides a Zn—Mg—Al-based plated steel sheet excellent in corrosion resistance, weldability and phosphatability, and a manufacturing method therefor.

1 . A plated steel sheet, comprising:
 a base steel sheet; and   a Zn—Mg—Al-based plated layer provided on at least one surface of the base steel sheet,   wherein the plated layer satisfies relational expressions 1 and 2 as below:   
       
         
           
             
               
                 
                   
                     
                       
                         - 
                         1 
                       
                       0. 
                     
                     ≤ 
                     
                       
                         
                           [ 
                           Zn 
                           ] 
                         
                         
                           
                             1 
                             / 
                             10 
                           
                           ⁢ 
                           t 
                         
                       
                       - 
                       
                         
                           [ 
                           Zn 
                           ] 
                         
                         s 
                       
                     
                     ≤ 
                     
                       - 
                       5. 
                     
                   
                 
                 
                   
                     [ 
                     
                       Relational 
                       ⁢ 
                           
                       expression 
                       ⁢ 
                           
                       1 
                     
                     ] 
                   
                 
               
             
           
         
         (In relational expression 1, [Zn] 1/10t  represents a weight % content of Zn in a 1/10t position (t is a total thickness of the plated layer) in a thickness direction from a surface of the plated layer, and [Zn] s  represents a weight % content of Zn on a surface of the plated layer.) 
       
       
         
           
             
               
                 
                   
                     
                       + 
                       3. 
                     
                     ≤ 
                     
                       
                         
                           [ 
                           Al 
                           ] 
                         
                         
                           
                             1 
                             / 
                             10 
                           
                           ⁢ 
                           t 
                         
                       
                       - 
                       
                         
                           [ 
                           Al 
                           ] 
                         
                         s 
                       
                     
                     ≤ 
                     
                       + 
                       13. 
                     
                   
                 
                 
                   
                     [ 
                     
                       Relational 
                       ⁢ 
                           
                       expression 
                       ⁢ 
                           
                       2 
                     
                     ] 
                   
                 
               
             
           
         
         (In relational expression 2, [Al] 1/10t  represents a weight % content of Al in a 1/10t position (t is a total thickness of the plated layer) in a thickness direction from a surface of the plated layer, and [Al] s  represents a weight % content of Al on a surface of the plated layer.) 
       
     
     
         2 . The plated steel sheet of  claim 1 , further comprising:
 a Fe—Al-based inhibition layer provided between the base steel sheet and the Zn—Mg—Al-based plated layer.   
     
     
         3 . The plated steel sheet of  claim 1 , wherein the plated layer comprises, by weight %, Mg: 4.0-7.0%, Al: 8.2-19.5%, and a balance of Zn and inevitable impurities. 
     
     
         4 . The plated steel sheet of  claim 1 , wherein relational expression 3 is further satisfied: 
       
         
           
             
               
                 
                   
                     
                       - 
                       
                         1 
                         . 
                         0 
                       
                     
                     ≤ 
                     
                       
                         
                           [ 
                           Mg 
                           ] 
                         
                         
                           
                             1 
                             / 
                             1 
                           
                           ⁢ 
                           0 
                           ⁢ 
                           t 
                         
                       
                       - 
                       
                         
                           [ 
                           Mg 
                           ] 
                         
                         s 
                       
                     
                     ≤ 
                     
                       + 
                       
                         1 
                         . 
                         0 
                       
                     
                   
                 
                 
                   
                     [ 
                     
                       Relational 
                       ⁢ 
                           
                       expression 
                       ⁢ 
                           
                       3 
                     
                     ] 
                   
                 
               
             
           
         
         (In relational expression 3, [Mg] 1/10t  represents a weight % content of Mg in a 1/10t position (t is a total thickness of the plated layer) in a thickness direction from a surface of the plated layer, and [Mg] s  represents a weight % content of Mg on a surface of the plated layer.) 
       
     
     
         5 . The plated steel sheet of  claim 1 , wherein a weight % content of Mg in a 2/3t position in a thickness direction from a surface of the plated layer satisfies ±0.5 wt % based on an average weight % content of Mg in the plated layer. 
     
     
         6 . The plated steel sheet of  claim 1 , wherein an area ratio of an Al phase having a Zn solid-solution rate of 27 atomic % or more on a surface of the plated layer is 2.0 to 10.1%. 
     
     
         7 . A method of manufacturing a plated steel sheet, the method comprising:
 performing a first shot blasting treatment such that metal balls having a particle size of 0.6 to 1.0 mm are projected onto a surface of a base steel sheet at 400 to 1,200 kg/min with respect to a steel sheet processed in a shot blasting cabin in which a metal material is circulated at a rotation speed of 1200 to 2000 mpm;   performing a secondary shot blasting treatment such that metal balls having a particle size of 0.2 to 0.5 mm are projected onto a surface of the base steel sheet at 400 to 1,200 kg/min with respect to a steel sheet processed in a shot blasting cabin in which a metal material is circulated at a rotation speed of 1200 to 2000 mpm;   hot-dip galvanizing the base steel sheet, which has gone through the shot blasting treatment, by immersing the base steel sheet in a plating bath comprising, by weight %, Mg: 4.0 to 7.0%, Al: 8.2 to 19.5%, and a balance of Zn and inevitable impurities and maintained at a temperature of Ts+20° C. to Ts+80° C. based on a solidification initiation temperature (Ts) on a phase diagram; and   cooling the hot-dip galvanized steel sheet using an inert gas at an average cooling rate of 2 to 8° C./s from a solidification start temperature to a solidification end temperature.   
     
     
         8 . The method of  claim 7 , wherein the method further comprises performing pre-temper rolling on the base steel sheet, which has gone through the shot blasting treatment, by applying roll reduction of 100 to 400 tons to a surface of the steel sheet using a dull roll having surface roughness Ra of 1.8 to 2.8 μm, before performing the hot-dip galvanizing.