Aluminum alloy sheet having high formability

Abstract

Provided is a 6xxx-series aluminum sheet having high formability for automotive body panel use, which can be produced without significant changes in conventional chemical compositions and production conditions. The 6xxx-series aluminum alloy sheet is controlled in its microstructure as follows. The average grain size of the microstructure is controlled to be small; and the average proportion of small angle grain boundaries after application of tensile deformation to the sheet is controlled at two levels in a low strain region and a high strain region according to the levels of strain imparted by the tensile deformation. This restrains heterogeneous deformation from the high strain region leading to rupture upon press forming into an automotive body panel, and allows the sheet to offer good work hardening properties and to have high formability.

1 . An aluminum alloy sheet having high formability, the aluminum alloy sheet being an Al—Mg—Si aluminum alloy sheet comprising, in mass percent:
 Si in a content of 0.30% to 2.0%; 
 Mg in a content of 0.20% to 1.5%; 
 Cu in a content of 0.05% to 1.0%; 
 Mn in a content of greater than 0% to 1.0%; and 
 Fe in a content of greater than 0% to 1.0%, 
 with the remainder consisting of Al and inevitable impurities, 
 the aluminum alloy sheet having a microstructure at a sheet thickness central position, 
 the microstructure having an average grain size of 40 μm or less, 
 the microstructure comprising small angle grain boundaries with a tilt angle of 2.0° to 15.0° in an average proportion of 12% to 30% after tensile deformation at a strain of 5% being imparted in a rolling direction of the sheet; and 
 the microstructure comprising small angle grain boundaries with a tilt angle of 2.0° to 15.0° in an average proportion of 50% to 70% after tensile deformation at a strain of 15% being imparted in the rolling direction of the sheet. 
 
       s measured by SEM/EBSD technique. 
     
     
         2 . The aluminum alloy sheet according to  claim 1 , further comprising at least one element selected from the group consisting of:
 Cr in a content of greater than 0% to 0.3%;   Zr in a content of greater than 0% to 0.3%;   V in a content of greater than 0% to 0.3%;   Ti in a content of greater than 0% to 0.1%;   Zn in a content of greater than 0% to 1.0%;   Ag in a content of greater than 0% to 0.2%; and   Sn in a content of greater than 0% to 0.15%.   
     
     
         3 . The aluminum alloy sheet according to  claim 1 ,
 wherein the aluminum alloy sheet has a 0.2% yield strength, a tensile strength and has a yield ratio of 0.56 or less, where the yield ratio is defined as a ratio of the 0.2% yield strength to the tensile strength, and   wherein the aluminum alloy sheet has a total elongation of 26% or more.