Effect of preform annealing on plastic anisotropy of an age-hardenable Al-Mg-Si alloy

Plastic anisotropy as characterized by the Lankford parameter (r-value), which relates to the resistance to thinning (or deep drawability) in sheet metal forming, has been investigated for an age-hardenable Al-Mg-Si alloy under different preforming and annealing conditions. Digital image correlation analysis was applied to measure r-value accurately during tensile testing as a function of effective plastic strain. X-ray diffraction techniques were used to determine the sheet texture in order to explain the changes in r-value. It was found that r-value is not constant during this two-stage forming process, but rather depends on pre-strain path and level. Rapid annealing at high temperature without pre-straining the as-received material had little influence on r-value, whereas the application of prestrain with annealing did cause significant changes in r-value that can be explained by changes in texture. Four crystal orientations were observed in the sheet texture, i.e. the cube orientation {001}〈100〉, the S orientation {123}〈634〉, the P orientation {011}〈122〉, and the C orientation {112}〈111〉; and the changes of r-value are assessed by the relative proportion of these texture components.