Al-coated steel sheet having excellent total reflection characteristics and corrosion resistance, and method for manufacturing same

Abstract

An Al-coated steel sheet contains a base steel sheet having on a surface thereof an Al-coated layer having an average thickness of 7 mm or more with an Al—Fe—Si based alloy layer intervening therebetween, a surface layer portion of the Al-coated layer extending from the surface thereof to a depth of 3 mm having an average Si concentration of 2.0% by mass or less, and preferably 1.3% by mass or less, and an area ratio of an Al—Fe based intermetallic compound phase occupying the surface of the Al-coated layer being 10% or less. The Al-coated steel sheet is improved in total reflection characteristics, corrosion resistance, and appearance after being subjected to an anodizing treatment.

1 . An Al-coated steel sheet having excellent total reflection characteristics and corrosion resistance, comprising a base steel sheet having on a surface thereof an Al-coated layer having an average thickness of 7 μm or more with an Al—Fe—Si based alloy layer intervening therebetween, a surface layer portion of the Al-coated layer extending from the surface thereof to a depth of 3 μm having an average Si concentration of 2.0% by mass or less, and an area ratio of an Al—Fe based intermetallic compound phase occupying the surface of the Al-coated layer being 10% or less. 
     
     
         2 . An Al-coated steel sheet having excellent total reflection characteristics and corrosion resistance, comprising a base steel sheet having on a surface thereof an Al-coated layer having an average thickness of 7 μm or more with an Al—Fe—Si based alloy layer intervening therebetween, a surface layer portion of the Al-coated layer extending from the surface thereof to a depth of 3 μm having an average Si concentration of 1.3% by mass or less, and an area ratio of an Al—Fe based intermetallic compound phase occupying the surface of the Al-coated layer being 10% or less. 
     
     
         3 . The Al-coated steel sheet having excellent characteristics and corrosion resistance according to  claim 1 , wherein the Al-coated layer is obtained by modifying a hot-dip Al based alloy plated layer containing Si through a heat treatment. 
     
     
         4 . The Al-coated steel sheet having excellent total reflection characteristics and corrosion resistance according to  claim 1 , wherein the Al-coated layer is obtained by modifying a hot-dip Al based alloy plated layer formed by using a hot-dip Al based alloy plating bath having a Si content of 2.0% by mass or more and 6.0% by mass or less through a heat treatment. 
     
     
         5 . The Al-coated steel sheet having excellent total reflection characteristics and corrosion resistance according to  claim 2 , wherein the Al-coated layer is obtained by modifying a hot-dip Al based alloy plated layer formed by using a hot-dip Al based alloy plating bath having a Si content of 1.5% by mass or more and 3.0% by mass or less through a heat treatment. 
     
     
         6 . A method for manufacturing an Al-coated steel sheet having excellent total reflection characteristics and corrosion resistance, comprising:
 a step of manufacturing a hot-dip Al based alloy plated steel sheet having a plated layer having an average thickness of 7 μm or more, by using a hot-dip Al based alloy plating bath having a Si content of 2.0% by mass or more and 6.0% by mass or less; and   a step of modifying the plated layer to an Al-coated layer having a surface layer portion extending from the surface thereof to a depth of 3 μm that has an average Si concentration of 2.0% by mass or less, by heating and retaining the hot-dip Al based alloy plated steel sheet to a temperature of from 300 to 460° C. to progress diffusion of Si in the plated layer.   
     
     
         7 . A method for manufacturing an Al-coated steel sheet having excellent total reflection characteristics and corrosion resistance, comprising:
 a step of manufacturing a hot-dip Al based alloy plated steel sheet having a plated layer having an average thickness of 7 μm or more, by using a hot-dip Al based alloy plating bath having a Si content of 1.5% by mass or more and 3.0% by mass or less; and   a step of modifying the plated layer to an Al-coated layer having a surface layer portion extending from the surface thereof to a depth of 3 μm that has an average Si concentration of 1.3% by mass or less, by heating and retaining the hot-dip Al based alloy plated steel sheet to a temperature of from 300 to 460° C. to progress diffusion of Si in the plated layer.