Effect of microstructure and texture on forming behaviour of AA-6061 aluminium alloy sheet

AA-6061 aluminium alloys are used extensively in automobile and aerospace industries owing to their excellent combination of mechanical and physical properties. This alloy exhibits prominent anisotropy in mechanical properties when produced as cold rolled sheets. In manufacturing, sheet metal anisotropy may have severe consequences for downstream processes such as stamping and deep drawing operations. In the present study, correlations among in-plane anisotropy, strain path and formability of AA-6061 sheet metal are investigated. Using limit dome height tests, forming limit diagrams (FLDs) were constructed for three different sheet directions by applying appropriate strain localization and fracture criteria. For each sheet direction and strain path, microstructure and texture evolution were also observed to identify the origin of in-plane anisotropy and formability of the AA-6061 sheet metal alloy. A detailed analysis of microstructure under different strain paths suggests the direction and texture dependent yield locus to be a significant factor for in-plane anisotropy. Intra-granular crack propagation in a particular sheet direction (transverse direction: TD) may lead to reduced formability of AA-6061. Formability, on the other hand, appears to be highly correlated to the relative fraction of specific texture components. Certain critical texture components such as Cube {001} <100> and Brass {011} <211> influence the forming behaviour of AA-6061 aluminium alloy significantly.