Aluminum alloy plate having excellent bake hardening responses

Abstract

One of the purposes of the present invention is to provide a 6000-series aluminum alloy plate exhibiting bake hardening (BH) properties and molding properties after aging at room temperature for a long period. In one embodiment of the present invention, in a Sn-containing 6000-series aluminum alloy plate, specific clusters that greatly contribute to the development of the BH properties, which are determined by means of a three-dimensional atom probe field ion microscope, are contained at a predetermined density or more, and the sizes of the atom clusters that meet the aforementioned requirement are uniformed to adjust the average radius of an equivalent circle diameter of each of the clusters to a value falling within a specified range and reduce the standard deviation of the radius of the equivalent circle diameter, whereby the BH properties after aging at room temperature for a long period can be improved.

1 . An aluminum alloy sheet, which is an Al—Mg—Si alloy sheet comprising, in mass %:
 Mg: 0.2% to 2.0%; 
 Si: 0.3% to 2.0%; 
 Sn: 0.005% to 0.3%; 
 Al; and 
 inevitable impurities, 
 
       comprising an aggregate of atoms when measured by a three-dimensional atom probe field ion microscope,
 wherein: 
 either or both of a Mg atom and a Si atom are contained in the aggregate of atoms by a total of 10 pieces or more and, when any atom of the Mg atom and the Si atom contained therein is used as a reference, a distance between the atom as the reference and any atom among other atoms adjacent thereto is 0.75 nm or less; 
 the aggregate of atoms satisfying these conditions is contained in the aluminum alloy sheet at an average number density of 2.5×10 23  pieces/m 3  or greater and 20.0×10 23  pieces/m 3  or less; 
 an average radius of a circle equivalent diameter of the aggregate of atoms satisfying these conditions is 1.15 nm or greater and 1.45 nm or less; and 
 a standard deviation of the radius of the circle equivalent diameter is 0.45 nm or less. 
 
     
     
         2 . The aluminum alloy sheet according to  claim 1 , further comprising at least one of, in mass %
 Mn: more than 0% and 1.0% or less,   Cu: more than 0% and 1.0% or less,   Fe: more than 0% and 1.0% or less,   Cr: more than 0% and 0.3% or less,   Zr: more than 0% and 0.3% or less,   V: more than 0% and 0.3% or less,   Ti: more than 0% and 0.1% or less,   Zn: more than 0% and 1.0% or less, and   Ag: more than 0% and 0.2% or less.   
     
     
         3 . An aluminum alloy sheet excellent in bake hardenability, which is an Al—Mg—Si alloy sheet comprising, in mass %:
 Mg: 0.2% to 2.0%; 
 Si: 0.3% to 2.0%; 
 Sn: 0.005% to 0.3%; 
 Al; and 
 inevitable impurities, 
 wherein 
 a ratio (N cluster /N total )×100 of N cluster  to N total  is 1% or greater and 15% or less; 
 N total  represents a total number of all Mg atoms and Si atoms measured by a three-dimensional atom probe field ion microscope; 
 N cluster  represents a total number of all Mg atoms and Si atoms contained in all aggregates of atoms satisfying conditions wherein an aggregate of atoms measured by the three-dimensional atom probe field ion microscope contains either or both of a Mg atom and a Si atom by a total of 10 pieces or more and, when any atom of the Mg atom and the Si atom is used as a reference, a distance between the atom as the reference and any atom among other atoms adjacent thereto is 0.75 nm or less; and 
 an average radius of a circle equivalent diameter of the aggregate of atoms is 1.20 nm or greater and 1.50 nm or less. 
 
     
     
         4 . The aluminum alloy sheet according to  claim 3 , further comprising at least one of, in mass %
 Mn: more than 0% and 1.0% or less,   Cu: more than 0% and 1.0% or less,   Fe: more than 0% and 1.0% or less,   Cr: more than 0% and 0.3% or less,   Zr: more than 0% and 0.3% or less,   V: more than 0% and 0.3% or less,   Ti: more than 0% and 0.1% or less,   Zn: more than 0% and 1.0% or less, and   Ag: more than 0% and 0.2% or less.   
     
     
         5 . An aluminum alloy sheet excellent in bake hardenability, which is an Al—Mg—Si alloy sheet comprising, in mass %:
 Mg: 0.2% to 2.0%; 
 Si: 0.3% to 2.0%; 
 Sn: 0.005% to 0.3%; 
 Al; and 
 inevitable impurities, 
 
       comprising an aggregate of atoms when measured by a three-dimensional atom probe field ion microscope,
 wherein: 
 either or both of a Mg atom and a Si atom are contained in the aggregate of atoms by a total of 10 pieces or more and, when any atom of the Mg atom and the Si atom contained therein is used as a reference, a distance between the atom as the reference and any atom among other atoms adjacent thereto is 0.75 nm or less; and 
 the aggregate of atoms satisfying these conditions has an average number density of 3.0×10 23  pieces/m 3  or greater and 25.0×10 23  pieces/m 3  or less and, among the aggregates of atoms satisfying these conditions, an average proportion of an aggregate of atoms wherein a ratio (Mg/Si) of a number of Mg atoms to a number of Si atoms is ½ or greater is 0.70 or greater. 
 
     
     
         6 . The aluminum alloy sheet according to  claim 5 , further comprising at least one of, in mass %
 Mn: more than 0% and 1.0% or less,   Cu: more than 0% and 1.0% or less,   Fe: more than 0% and 1.0% or less,   Cr: more than 0% and 0.3% or less,   Zr: more than 0% and 0.3% or less,   V: more than 0% and 0.3% or less,   Ti: more than 0% and 0.1% or less,   Zn: more than 0% and 1.0% or less, and   Ag: more than 0% and 0.2% or less.