Zinc alloy plated steel sheet having excellent bending workability and manufacturing method therefor

Abstract

Provided are a zinc alloy plated steel sheet and a method for manufacturing the zinc alloy plated steel sheet. The zinc alloy plated steel sheet includes a base steel sheet and a zinc alloy plating layer, wherein the zinc alloy plating layer includes a Zn single phase structure as a microstructure and a Zn—Al—Mg-based intermetallic compound, and the Zn single phase structure has a degree (f) of (0001) preferred orientation expressed by Formula 1 below within a range of 50% or greater. [Formula 1] f(%)=(I basal /I total )×100 where I total refers to the integral of all diffraction peaks of the Zn single phase structure when an X-ray diffraction pattern is measured within a range of 2 theta from 10° to 100° using a Cu-Kα source, and I basal refers to the integral of diffraction peaks of the Zn single phase relating to a basal plane.

1 . A zinc alloy plated steel sheet comprising a base steel sheet and a zinc alloy plating layer,
 wherein the zinc alloy plating layer comprises a Zn single phase structure as a microstructure and a Zn—Al—Mg-based intermetallic compound, and   the Zn single phase structure has a degree (f) of (0001) preferred orientation, expressed by Formula 1 below, within a range of 50% or greater,
     f (%)=( I   basal   /I   total )×100  [Formula 1]
 
   where I total  refers to an integral of all diffraction peaks of the Zn single phase structure when an X-ray diffraction pattern is measured within a range of 2 theta from 10° to 100° using a Cu-Kα source, and I basal  refers to an integral of diffraction peaks of the Zn single phase structure relating to a basal plane.   
     
     
         2 . The zinc alloy plated steel sheet of  claim 1 , wherein the Zn single phase structure has a degree (f) of (0001) preferred orientation, expressed by Formula 1, within a range of 60% or greater. 
     
     
         3 . The zinc alloy plated steel sheet of  claim 1 , wherein the Zn—Al—Mg-based intermetallic compound comprises at least one selected from the group consisting of a Zn/MgZn 2  binary eutectic structure, a Zn/Al binary eutectic structure, an MgZn 2  single phase structure, and a Zn/Al/MgZn 2  ternary eutectic structure. 
     
     
         4 . The zinc alloy plated steel sheet of  claim 1 , wherein an area fraction of the Zn single phase structure on a surface of the zinc alloy plating layer is 40% or less (excluding 0%). 
     
     
         5 . The zinc alloy plated steel sheet of  claim 1 , wherein a total area fraction of a Zn/MgZn 2  binary eutectic structure and a Zn/Al/MgZn 2  ternary eutectic structure is 50% or greater (excluding 100%) on a surface of the zinc alloy plating layer. 
     
     
         6 . The zinc alloy plated steel sheet of  claim 1 , wherein an area fraction of an MgZn 2  single phase structure on a surface of the zinc alloy plating layer is 10% or less (excluding 0%). 
     
     
         7 . The zinc alloy plated steel sheet of  claim 1 , wherein an average grain diameter of the Zn single phase structure observed on a cross-section of the zinc alloy plating layer taken in a sheet thickness direction is 15 μm or less (excluding 0 μm). 
     
     
         8 . The zinc alloy plated steel sheet of  claim 1 , wherein the zinc alloy plating layer comprises, by wt %, aluminum (Al): 0.5% to 3%, magnesium (Mg): 0.5% to 3%, and a balance of zinc (Zn) and inevitable impurities. 
     
     
         9 . The zinc alloy plated steel sheet of  claim 1 , wherein the zinc alloy plating layer satisfies Formula 1 below:
   1.0<[Mg]/[Al]≤4.0  [Formula 2]
   where [Mg] and [Al] refer to weight percentages (wt %) of corresponding elements, respectively.   
     
     
         10 . The zinc alloy plated steel sheet of  claim 1 , wherein a number of black spots per unit area is 0.1/cm 2  or less on a surface of the zinc alloy plated steel sheet. 
     
     
         11 . A method for manufacturing a zinc alloy plated steel sheet, the method comprising:
 preparing a zinc alloy plating bath comprising magnesium (Mg) and aluminum (Al);   obtaining a zinc alloy plated steel sheet by dipping a base steel sheet into the zinc alloy plating bath to plate the base steel sheet;   wiping the zinc alloy plated steel sheet with gas to adjust a plating weight; and   after adjusting the plating weight of the zinc alloy plated steel sheet, cooling the zinc alloy plated steel sheet by spraying droplets of water or an aqueous solution onto the zinc alloy plated steel sheet and then using air,   wherein when the droplets are sprayed, a droplet spray start temperature ranges from 405° C. to 425° C., a droplet spray stop temperature ranges from 380° C. to 400° C.   
     
     
         12 . The method of  claim 11 , wherein when the droplets are sprayed, a difference between the droplet spray start temperature and the droplet spray stop temperature is 15° C. or greater. 
     
     
         13 . The method of  claim 11 , wherein the droplets are sprayed by a charge spray method to attach the droplets by electrostatic attraction between the droplets and the zinc alloy plated steel sheet. 
     
     
         14 . The method of  claim 11 , wherein the droplets are sprayed in an amount of 50 g/m 2  to 100 g/m 2 . 
     
     
         15 . The method of  claim 11 , wherein the aqueous solution is a phosphate aqueous solution. 
     
     
         16 . The method of  claim 15 , wherein the phosphate aqueous solution comprises at least one selected from the group consisting of an aqueous solution of ammonium hydrogen phosphate ((NH 4 ) 2 HPO 4 ), an aqueous solution of sodium ammonium hydrogen phosphate (NaNH 4 HPO 4 ), an aqueous solution of zinc dihydrogen phosphate (Zn(H 2 PO 4 ) 2 ), and an aqueous solution of calcium phosphate (Ca 3 (PO 4 ) 2 ). 
     
     
         17 . The method of  claim 15 , wherein the phosphate aqueous solution has a concentration of 0.5 wt % to 5 wt %. 
     
     
         18 . The method of  claim 11 , wherein the zinc alloy plating bath comprises, by wt %, aluminum (Al): 0.5% to 3%, magnesium (Mg): 0.5% to 3%, and a balance of zinc (Zn) and inevitable impurities.