Aluminum alloy plate having excellent moldability and bake finish hardening properties

Abstract

An aluminum alloy sheet excellent in terms of formability and bake hardenability is provided. The aluminum alloy sheet contains, in terms of mass %, Mg: 0.2 to 2.0%, Si: 0.3 to 2.0% and Sn: 0.005 to 0.3%, with the remainder being Al and unavoidable impurities. A differential scanning calorimetry curve of the aluminum alloy sheet has an endothermic peak in a temperature range of 150 to 230° C. and an exothermic peak in a temperature range of 240 to 255° C. The endothermic peak corresponds to a dissolution of a Mg—Si cluster and has a peak height of 8 μW/mg or less, including 0 μW/mg. The exothermic peak corresponds to a formation of a Mg—Si cluster and has a peak height of 20 μW/mg or larger.

1 . An aluminum alloy sheet excellent in terms of formability and bake hardenability, which is an Al—Mg—Si alloy sheet comprising, in terms of mass %, Mg: 0.2 to 2.0%, Si: 0.3 to 2.0% and Sn: 0.005 to 0.3%, with the remainder being Al and unavoidable impurities, wherein a differential scanning calorimetry curve of the aluminum alloy sheet has an endothermic peak in a temperature range of 150 to 230° C., that is an endothermic peak corresponding to a dissolution of a Mg—Si cluster and that has a peak height of 8 μW/mg or less (including 0 μW/mg), and has an exothermic peak in a temperature range of 240 to 255° C., that is an exothermic peak corresponding to a formation of a Mg—Si cluster and that has a peak height of 20 μW/mg or larger. 
     
     
         2 . The aluminum alloy sheet excellent in terms of formability and bake hardenability according to  claim 1 , further comprising one kind or two or more kinds selected from the group consisting of Fe: more than 0% and 1.0% or less, Mn: 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, Cu: more than 0% and 1.0% or less, Ag: more than 0% and 0.2% or less, and Zn: more than 0% and 1.0% or less. 
     
     
         3 . An aluminum alloy sheet excellent in terms of formability and bake hardenability, which is an Al—Mg—Si alloy sheet comprising, in terms of mass %, Mg: 0.3 to 1.0%, Si: 0.5 to 1.5% and Sn: 0.005 to 0.3%, with the remainder being Al and unavoidable impurities, wherein a solid-solution amount of Mg+Si in a solution, separated by a residue extraction method with hot phenol is 1.0 mass % or more and 2.0 mass % or less, and
 wherein atom aggregates observed with a three-dimensional atom probe field ion microscope satisfy conditions that either or both of an Mg atom and an Si atom are contained therein by a total of 10 pieces or more and that, 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 regarding the atom aggregates, an average volume proportion (ΣVi/V Al )×100 is in a range of 0.3 to 1.5%, the average volume proportion (ΣVi/V Al ) being a proportion of the total volume of the atom aggregates, in terms of the total volume ΣVi obtained by summing up volumes of the individual atom aggregates Vi (=4/37πr G   3 ) calculated from a Guinier radius r G  of the individual atom aggregates each regarded as a sphere, to a volume V Al  of the aluminum alloy sheet measured with the three-dimensional atom probe field ion microscope, wherein 
 an average volume proportion (ΣVi 1.5 or more /ΣVi)×100 is 20 to 70%, the average volume proportion (ΣVi 1.5 or more /ΣVi) being a proportion of a total volume ΣVi 1.5 or more  obtained by summing up volumes V 1.5 or more  of atom aggregates each having the Guinier radius r G  of 1.5 nm or larger to a total volume of the atom aggregates ΣVi. 
 
     
     
         4 . The aluminum alloy sheet excellent in terms of formability and bake hardenability according to  claim 3 , further comprising one kind or two or more kinds selected from the group consisting of Fe: more than 0% and 1.0% or less, Mn: more than 0% and 0.4% 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, Cu: more than 0% and 0.4% or less, Ag: more than 0% and 0.2% or less, and Zn: more than 0% and 1.0% or less.