Aluminum alloy plate having excellent moldability and bake finish hardening properties

Abstract

An aluminum alloy sheet excellent in terms of formability and bake hardenability which 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 (=4/3πr 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 accordingly 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.