Formable aluminum alloy sheet

Abstract

The present invention provides an aluminum alloy sheet for forming which is a high-Mg-content Al—Mg alloy sheet reduced in β-phase precipitation and improved in press formability. This aluminum alloy sheet for forming comprises an Al—Mg alloy containing 6.0-15.0 mass % Mg. In each of square regions, each side of which has the dimension of the whole sheet width (W), that are set in a surface of the alloy sheet, the concentration of Mg is measured at width-direction measurement points, Px, set at given intervals a and b respectively in the sheet-width direction and the sheet-length direction, and the average of the values of Mg concentration measured at the plurality of width-direction measurement points (Px) is taken as a width-direction average Mg concentration (Co). The concentration of Mg is measured at a plurality of thickness-direction measurement points (Py) set at a given interval in the sheet-thickness direction throughout the whole sheet thickness with respect to the plurality of width-direction measurement points (Px), and the average of the values of Mg concentration measured at the plurality of thickness-direction measurement points (Py) is taken as a thickness-direction average Mg concentration (Ci). The absolute value of the degree of regional Mg segregation (X) defined by the difference (Ci−Co) between the thickness-direction average Mg concentration (Ci) and the width-direction average Mg concentration (Co) is 0.5 mass % or less at most and is 0.1 mass % or less on average.

1 . An aluminum alloy sheet, comprising Mg in a content of 6.0 percent by mass or more and 15.0 percent by mass or less and further comprising Al and an impurity, the aluminum alloy sheet having:
 a width-direction average Mg concentration of Co, wherein the width-direction average Mg concentration, Co, is an average of Mg concentrations measured at a plurality of width-direction measurement points, wherein the plurality of width-direction measurement points is arranged at predetermined spacings in a width direction and in a length direction of the sheet, respectively, in a square region set on a surface of the aluminum alloy sheet, wherein each side of the square region has a dimension of an entire sheet width;   a thickness-direction average Mg concentration, Ci, for each of the plurality of width-direction measurement points, wherein each Ci is an average of Mg concentrations measured at a plurality of thickness-direction measurement points arranged in a thickness direction of the sheet at a predetermined spacing throughout an entire sheet thickness; and   regional Mg segregation degrees of X each defined as a difference, Ci−Co, between each thickness-direction average Mg concentration, Ci, and the width-direction average Mg concentration,   wherein absolute values of the regional Mg segregation degrees, X, have a maximum of 0.5 percent by mass or less and an average of 0.1 percent by mass or less.   
     
     
         2 . The aluminum alloy sheet of  claim 1 ,
 wherein the aluminum alloy sheet has thickness-direction Mg concentrations, Ct, wherein the thickness-direction Mg concentrations are measured in a thickness direction of the sheet at a predetermined spacing throughout the entire sheet thickness for the width-direction measurement points upon determination of the regional Mg segregation degrees, X; and   thickness-direction Mg segregation degrees, Y, each defined as a difference, Ct−Ci, between each thickness-direction Mg concentration, Ct, and the thickness-direction average Mg concentration, Ci, corresponding to the respective width-direction measurement point, in which absolute values of the thickness-direction Mg segregation degrees, Y, have a maximum of 4 percent by mass or less and an average of 0.8 percent by mass or less.   
     
     
         3 . The aluminum alloy sheet of  claim 1 , wherein Mg is in a content of more than 8 percent by mass and less than or equal to 14 percent by mass. 
     
     
         4 . The aluminum alloy sheet of  claim 1 , wherein the impurity comprises at least one element selected from the group consisting of Fe in a content of 1.0 percent by mass or less, Si in a content of 0.5 percent by mass or less, Ti in a content of 0.1 percent by mass or less, B in a content of 0.05 percent by mass or less, Mn in a content of 0.3 percent by mass or less, Cr in a content of 0.3 percent by mass or less, Zr in a content of 0.3 percent by mass or less, V in a content of 0.3 percent by mass or less, Cu in a content of 1.0 percent by mass or less, and Zn in a content of 1.0 percent by mass or less. 
     
     
         5 . The aluminum alloy sheet of  claim 2 , wherein Mg is in a content of more than 8 percent by mass and less than or equal to 14 percent by mass. 
     
     
         6 . The aluminum alloy sheet of  claim 2 , wherein the impurity comprises at least one element selected from the group consisting of Fe in a content of 1.0 percent by mass or less, Si in a content of 0.5 percent by mass or less, Ti in a content of 0.1 percent by mass or less, B in a content of 0.05 percent by mass or less, Mn in a content of 0.3 percent by mass or less, Cr in a content of 0.3 percent by mass or less, Zr in a content of 0.3 percent by mass or less, V in a content of 0.3 percent by mass or less, Cu in a content of 1.0 percent by mass or less, and Zn in a content of 1.0 percent by mass or less. 
     
     
         7 . The aluminum alloy sheet of  claim 1 , comprising a fine grain. 
     
     
         8 . The aluminum alloy sheet of  claim 7 , having an average grain size of 20 μm or more and 100 μm or less on the surface. 
     
     
         9 . A method of producing the aluminum alloy sheet of  claim 1 , the method comprising:
 melt-casting by melting a high-Mg-content Al—Mg alloy to obtain a molten metal, and preparing a cast strip from the molten metal by continuous strip casting;   soaking the cast strip in a continuous heat-treating furnace at a temperature of 400° C. or above and a liquidus temperature or below;   cold rolling the cast strip to convert the cast strip into a deformation structure to obtain a cold-rolled sheet; and   final annealing the cold-rolled sheet at a temperature of 400° C. or above and below the liquidus temperature.   
     
     
         10 . The method of  claim 9 , wherein the continuous strip casting comprises a fixed graphite mold. 
     
     
         11 . The method of  claim 10 , wherein the continuous strip casting comprises:
 pouring a molten metal stored in a holding furnace through an inlet into the fixed graphite mold; and   solidifying the molten metal in the fixed graphite mold, by cooling with a water-cooling jacket.   
     
     
         12 . The method of  claim 11 , wherein the cooling is performed at a rate of 15° C./s wherein the cast strip has a thickness of from 5 to 20 mm. 
     
     
         13 . The method of  claim 12 , wherein the pouring is performed at a temperature higher than the liquidus temperature by 50° C. or more and 250° C. or less. 
     
     
         14 . The method of  claim 10 , wherein the continuous casting process is performed at an average casting rate of 100 mm/min or more and 500 mm/min or less. 
     
     
         15 . The method of  claim 10 , wherein the continuous casting comprises facing in wherein the cast strip is cut or shaved. 
     
     
         16  The method of  claim 9 , wherein the soaking is performed for a duration of one second or shorter. 
     
     
         17 . The method of  claim 9 , wherein the cold-rolling comprises cold-rolling the cast strip to a thickness of a product sheet of 0.1 mm or more and 13 mm or less. 
     
     
         18 . The method of  claim 17 , further comprising a process annealing performed midway through the cold rolling to obtain a cold rolling reduction in a final cold rolling of 60% or less. 
     
     
         19 . The method of  claim 9 , wherein the final annealing is performed at a temperature of 450° C. or above and below the liquidus temperature. 
     
     
         20 . The method of  claim 9 , further comprising cooling after final annealing at a cooling rate of 10° C./s or more at a temperature of 500° C. down to 300° C.