Effect of thermo-mechanical treatment on ridging behavior and cube-oriented grain formation process in 6111 aluminum alloy

Al-Mg-Si alloys are suitable materials for automotive body application because of a good formability, a good corrosion resistance and a satisfactory strengthening. However, it is well known that when some kinds of Al-Mg-Si alloy sheets are stretched along the transverse direction, rope-like profiles (ridging/roping) parallel to the rolling direction develop on the surface. The purpose of this study is to clarify the ridging development in Al-Mg-Si alloy (6111 aluminum alloy). The effect of thermo-mechanical treatment on ridging development was investigated by 3D profile microscope and SEM/EBSD method. Rope-like profiles tended to develop remarkably in the hot-rolled and intermediate-annealed sheets. In highly ridging developed sample, there were many bands of cube-oriented grains (cube bands). Therefore, in this study, the cube-oriented grain formation process was also investigated by SEM/EBSD and TEM observation. Microstructure observations revealed that cube-oriented grains formed during the hot rolling process could remain due to rod-like precipitates in grain. And then, these cube-oriented grains were grown along the rolling direction during the intermediate annealing. Crystal orientation analysis shows the stored energy of the cube-oriented grains in the cold rolled sheet was lower than that of other-oriented grains. Therefore, we concluded that cube bands are preferentially formed during solutionized treatment.