Plated steel material and method for manufacturing plated steel material

Abstract

Provided are: a coated steel material including a base steel and a coating layer including a Zn—Al—Mg alloy layer provided on a surface of the base steel and a Mg enrichment layer provided on a surface of the Zn—Al—Mg alloy layer in which a thickness of the Mg enrichment layer is 0.8 μm or more and (thickness of coating layer×½) or less; and a method for manufacturing the coated steel material.

1 . A coated steel material comprising a base steel and a coating layer including a Zn—Al—Mg alloy layer provided on a surface of the base steel and a Mg enrichment layer provided on a surface of the Zn—Al—Mg alloy layer,
 wherein the coating layer has a chemical composition composed of, in terms of % by mass: 
 Zn at more than 65.00%, 
 Al at more than 5.00% and less than 25.00%, 
 Mg at more than 3.00% and less than 12.50%, 
 Sn at from 0% to 3.00%, 
 Bi at from 0% to less than 5.00%, 
 In at from 0% to less than 2.00%, 
 Ca at from 0% to 3.00%, 
 Y at from 0% to 0.50%, 
 La at from 0% to less than 0.50%, 
 Ce at from 0% to less than 0.50%, 
 Si at from 0% to less than 2.5%, 
 Cr at from 0% to less than 0.25%, 
 Ti at from 0% to less than 0.25%, 
 Zr at from 0% to less than 0.25%, 
 Mo at from 0% to less than 0.25%, 
 W at from 0% to less than 0.25%, 
 Ag at from 0% to less than 0.25%, 
 P at from 0% to less than 0.25%, 
 Ni at from 0% to less than 0.25%, 
 Co at from 0% to less than 0.25% 
 V at from 0% to less than 0.25%, 
 Nb at from 0% to less than 0.25%, 
 Cu at from 0% to less than 0.25%, 
 Mn at from 0% to less than 0.25%, 
 Li at from 0% to less than 0.25%, 
 Na at from 0% to less than 0.25%, 
 K at from 0% to less than 0.25%, 
 Fe at from 0% to 5.00%, 
 Sr at from 0% to less than 0.50% 
 Sb at from 0% to less than 0.50% 
 Pb at from 0% to less than 0.50%, 
 B at from 0% to less than 0.50%, and 
 impurities, 
 in the Zn—Al—Mg alloy layer, a total area ratio of Al phase, MgZn 2  phase, and Zn/Al/MgZn 2  ternary eutectics is 90% or more, and 
 a thickness of the Mg enrichment layer is 0.8 μm or more and (thickness of coating layer×½) or less. 
 
     
     
         2 . The coated steel material according to  claim 1 , wherein the coating layer has an Al—Fe alloy layer between the base steel and the Zn—Al—Mg alloy layer. 
     
     
         3 . A method for manufacturing the coated steel material according to  claim 1 ,
 wherein a base steel is immersed in a hot-dip coating bath and pulled up from the hot-dip coating bath, and then cooled down in a temperature range of from 450° C. to 395° C. at an average cooling rate of 15° C./s or less, cooled down in a temperature range of from 395° C. to 340° C. at an average cooling rate of 3° C./s or less, and cooled down in a temperature range of from 340° C. to 280° C. at an average cooling rate of from 10 to 20° C./s or more, and   after the cooling, subjected to skin pass rolling under conditions that a surface roughness Ra of a skin pass roll is from 1 to 5 μm and a skin pass rolling force is from 100 to 500 ton.