Zn-Al-Mg-BASED HOT-DIP PLATED STEEL SHEET

Abstract

A Zn—Al—Mg-based hot-dip plated steel sheet includes a hot-dip plated layer formed on a surface of a steel sheet, in which the hot-dip plated layer contains, as an average composition, Al: 5 to 22 mass % and Mg: 1.0 to 10 mass %, with a remainder including Zn and impurities, and in a case where a 5 mm square cross section parallel to a surface of the hot-dip plated layer is exposed at any position of a 3t/4 position, a t/2 position, and a t/4 position from the surface with a thickness of the hot-dip plated layer represented by t, a ratio (B/A (%)) of an area fraction B of a [Zn phase] to a total area fraction A of a [Zn phase] and an [Al/MgZn 2 /Zn ternary eutectic structure] of a plating microstructure in at least one cross section is 20% or more.

1 . A Zn—Al—Mg-based hot-dip plated steel sheet, comprising a steel sheet and a hot-dip plated layer formed on a surface of the steel sheet, wherein
 the hot-dip plated layer contains, as an average composition, Al: 5 to 22 mass % and Mg: 1.0 to 10 mass %, with a remainder including Zn and impurities, and 
 in a case where a 5 mm square cross section parallel to a surface of the hot-dip plated layer is exposed at any position of a 3t/4 position, a t/2 position, and a t/4 position from the surface with a thickness of the hot-dip plated layer represented by t, a ratio (B/A (%)) of an area fraction B of a [Zn phase] to a total area fraction A of a [Zn phase] and an [Al/MgZn 2 /Zn ternary eutectic structure] of a plating microstructure in at least one of the cross sections is 20% or more. 
 
     
     
         2 . A Zn—Al—Mg-based hot-dip plated steel sheet comprising a steel sheet and a hot-dip plated layer formed on a surface of the steel sheet, wherein
 the hot-dip plated layer contains, as an average composition, Al: 5 to 22 mass % and Mg: 1.0 to 10 mass %, with a remainder including Zn and impurities, and 
 further contains one or two of group A and group B below, and 
 in a case where a 5 mm square cross section parallel to a surface of the hot-dip plated layer is exposed at any position of a 3t/4 position, a t/2 position, and a t/4 position from the surface with a thickness of the hot-dip plated layer represented by t, a ratio (B/A (%)) of an area fraction B of a [Zn phase] to a total area fraction A of a [Zn phase] and an [Al/MgZn 2 /Zn ternary eutectic structure] of a plating microstructure in at least one of the cross sections is 20% or more: 
 [group A] Si: 0.0001 to 2 mass % 
 [group B] one or more of Ni, Ti, Zr, Sr, Fe, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, Hf, and C: 0.0001 to 2 mass % in total. 
 
     
     
         3 . The Zn—Al—Mg-based hot-dip plated steel sheet according to  claim 1 , wherein the area fraction of the [Zn phase] of the plating microstructure in at least one of the cross sections is 10% or more. 
     
     
         4 . The Zn—Al—Mg-based hot-dip plated steel sheet according to  claim 1 , wherein an average grain size of the [Zn phase] of the plating microstructure in at least one of the cross sections is 2.5 to 10 μm. 
     
     
         5 . The Zn—Al—Mg-based hot-dip plated steel sheet according to  claim 3 , wherein an average grain size of the [Zn phase] of the plating microstructure in at least one of the cross sections is 2.5 to 10 μm. 
     
     
         6 . The Zn—Al—Mg-based hot-dip plated steel sheet according to  claim 2 , wherein the hot-dip plated layer has an average composition containing the group A in terms of mass %. 
     
     
         7 . The Zn—Al—Mg-based hot-dip plated steel sheet according to  claim 2 , wherein the hot-dip plated layer has an average composition containing the group B in terms of mass %. 
     
     
         8 . The Zn—Al—Mg-based hot-dip plated steel sheet according to  claim 2 , wherein the area fraction of the [Zn phase] of the plating microstructure in at least one of the cross sections is 10% or more. 
     
     
         9 . The Zn—Al—Mg-based hot-dip plated steel sheet according to  claim 8 , wherein an average grain size of the [Zn phase] of the plating microstructure in at least one of the cross sections is 2.5 to 10 μm. 
     
     
         10 . The Zn—Al—Mg-based hot-dip plated steel sheet according to  claim 2 , wherein an average grain size of the [Zn phase] of the plating microstructure in at least one of the cross sections is 2.5 to 10 μm.