Highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability and process for producing same

Abstract

The present invention provides a highly corrosion-resistant plated steel sheet that can achieve excellent surface smoothness and formability and, according to the process of the present invention, a hot-dip galvanized steel product excellent in surface smoothness and formability having on the steel product surface a zinc alloy plating layer composed of 4 to 22% by mass of Al, 1 to 5% by mass of Mg, 0.000001 to 0.1% by mass of Ti, 0.000001 to 0.5% by mass of Si and the balance of Zn and unavoidable impurities, the plating layer of the plated steel product having a metal structure in which an [Mg 2 Si phase], an [Al phase], a [Zn 2 Mg phase] and a [Zn phase] are present in a mixture in the matrix of an [Al/Zn/Zn 2 Mg ternary eutectic structure], and the plating layer containing a Ti—Al base intermetallic compound in the [Al phase] and/or the [Zn 2 Mg phase] and/or the [Zn phase], is produced.

1 . A highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability, comprising:
 a steel product having a surface and a zinc alloy plating layer on the surface;   the zinc alloy plating layer comprising 4 to 22% by mass of Al, 1 to 5% by mass of Mg, up to 0.1% by mass of Ti, up to 0.5% by mass of Si, and a balance of Zn and unavoidable impurities;   the plating layer of the plated steel product having a metal structure in which a Mg 2 Si phase, an Al phase, and a Zn 2 Mg phase are present in a mixture in a matrix of an Al/Zn/Zn 2 Mg ternary eutectic structure;   the plating layer containing a Ti—Al base intermetallic compound in at least one of the Al phase and Zn 2 Mg phase; wherein   the hot-dip galvanized steel product is produced in a process comprising adding a Ti—Zn base intermetallic compound to a plating bath.   
     
     
         2 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 1 , wherein the Ti—Al base intermetallic compound is TiAl 3 . 
     
     
         3 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 1 , wherein the Ti—Al base intermetallic compound is Ti(Al 1-x Si x ) 3  (wherein X=0 to 0.5). 
     
     
         4 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 1  wherein the Ti—Al base intermetallic compound contained in an Al phase in the plating layer is present in a Zn—Al eutectoid reaction structure in which Zn phases are condensed. 
     
     
         5 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 1 , wherein the size of a dendrite in an Al phase in the plating layer is up to 500 μm. 
     
     
         6 . A highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability, comprising:
 a steel product having a surface and a zinc alloy plating layer on the surface; the zinc alloy plating layer comprising 4 to 22% by mass of Al, 1 to 5% by mass of Mg, up to 0.1% by mass of Ti, up to 0.5% by mass of Si, and a balance of Zn and unavoidable impurities;   the plating layer of the plated steel product having a metal structure in which an Mg 2 Si phase, an Al phase, a Zn 2 Mg phase, and a Zn phase are present in a mixture in a matrix of an Al/Zn/Zn 2 Mg ternary eutectic structure;   the plating layer containing a Ti—Al base intermetallic compound in one of the Al phase, Zn 2 Mg phase and Zn phase; wherein   the hot-dip galvanized steel product produced by a process comprising a step of adding a Ti—Zn base intermetallic compound to a plating bath.   
     
     
         7 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 6 , wherein the Ti—Al base intermetallic compound is TiAl 3 . 
     
     
         8 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 6 , wherein the Ti—Al base intermetallic compound is Ti(Al 1-x Si x ) 3  (wherein X=0 to 0.5). 
     
     
         9 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 6  wherein the Ti—Al base intermetallic compound contained in an Al phase in the plating layer is present in a Zn—Al eutectoid reaction structure in which Zn phases are condensed. 
     
     
         10 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 6 , wherein the size of a dendrite in an Al phase in the plating layer is up to 500 μm. 
     
     
         11 . A highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability, comprising:
 a steel product having a surface and a zinc alloy plating layer on the surface;   the zinc alloy plating layer comprising 4 to 22% by mass of Al, 1 to 5% by mass of Mg, up to 0.1% by mass of Ti, up to 0.5% by mass of Si, and a balance of Zn and unavoidable impurities;   the plating layer of the plated steel product having a metal structure in which a Mg 2 Si phase, an Al phase, and a Zn phase are present in a mixture in a matrix of an Al/Zn/Zn 2 Mg ternary eutectic structure;   the plating layer containing a Ti—Al base intermetallic compound in at least one of the Al phase and Zn phase; wherein   the hot-dip galvanized steel product produced by a process comprising a step of adding a Ti—Zn base intermetallic compound to a plating bath.   
     
     
         12 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 11 , wherein the Ti—Al base intermetallic compound is TiAl 3 . 
     
     
         13 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 11 , wherein the Ti—Al base intermetallic compound is Ti(Al 1-x Si x ) 3  (wherein X=0 to 0.5). 
     
     
         14 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 11  wherein the Ti—Al base intermetallic compound contained in an Al phase in the plating layer is present in a Zn—Al eutectoid reaction structure in which Zn phases are condensed. 
     
     
         15 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 11 , wherein the size of a dendrite in an Al phase in the plating layer is up to 500 μm. 
     
     
         16 . A highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability, comprising:
 a steel product having a surface and a zinc alloy plating layer on the surface;   the zinc alloy plating layer comprising 4 to 10% by mass of Al, 1 to 5% by mass of Mg, up to 0.1% by mass of Ti, and a balance of Zn and unavoidable impurities;   the plating layer having a metal structure in which one of an Al phase, a Zn 2 Mg phase, and a Zn phase are present in a mixture in a matrix of an Al/Zn/Zn 2 Mg ternary eutectic structure;   the plating layer containing a Ti—Al base intermetallic compound in at least one of the Al phase, Zn 2 Mg phase, and Zn phase; wherein   the hot-dip galvanized steel product produced by a process comprising a step of adding a Ti—Zn base intermetallic compound to a plating bath.   
     
     
         17 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 16 , wherein the Ti—Al base intermetallic compound is TiAl 3 . 
     
     
         18 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 16 , wherein the Ti—Al base intermetallic compound is Ti(Al 1-x Si x ) 3  (wherein X=0 to 0.5). 
     
     
         19 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 16  wherein the Ti—Al base intermetallic compound contained in an Al phase in the plating layer is present in a Zn—Al eutectoid reaction structure in which Zn phases are condensed. 
     
     
         20 . The highly corrosion-resistant hot-dip galvanized steel product excellent in surface smoothness and formability according to  claim 16 , wherein the size of a dendrite in an Al phase in the plating layer is up to 500 μm.