Investigation of planar anisotropy evolution in aluminium alloy sheets under hot stamping conditions using digital image correlation

Hot stamping of aluminium alloy sheets is widely used for manufacturing high performance panel components across various industries. However, the anisotropic characteristics of the alloy and their evolution during deformation under hot stamping conditions, remain poorly understood, resulting in significant challenges in accurately determining its thermomechanical behaviour and developing predictive models. To address this knowledge gap, a series of uniaxial tensile tests on a 1.5°mm thick AA6082 sheet under hot deformation conditions were conducted in this study using a Gleeble simulator at temperatures ranging from 350°C to 500°C and strain rates of 0.1 s-1 and 0.5 s-1. The planar anisotropy along both the length and width directions of AA6082 samples, as well as their evolution during hot deformation was investigated by calculating the r-value (known as the Lankford coefficient) based on the full-field strain distribution within the gauge length, measured using digital image correlation (DIC). The effects of strain fields selected from different regions within the gauge area on the calculated r-value were analysed. An empirical equation for r-value was proposed, for the first time, to model the planar anisotropy evolution across various deformation temperatures and strain rates under hot stamping conditions. This equation was subsequently applied to correct the stress-strain curves obtained using the C-gauge, an alternative strain measurement method, and the corrected data were compared with curves measured by DIC. This study provides insights on accurately determining thermomechanical behaviour and developing predictive models of aluminium alloys under hot stamping conditions.