Effect of Plastic Anisotropy on Ironing Formability of 3104 Aluminum Alloy Hard Sheets

3104 aluminum alloy hard sheets are widely used for aluminum beverage can body stock (CBS) mainly because of their high ironing formability. The CBS has large anisotropy of r-value (Lankford value) and n-value (work hardening exponent), however, the effect of such anisotropy on the ironing formability remains unclear. In this study, cup and DI forming behavior was investigated using cold-rolled 3104 aluminum alloy hard sheets with different anisotropy of r and n-values. Magnitude of the anisotropy changes during drawing and ironing. Ironing fracture tests reveal that fracture occurs at angles between 10 and 20 degrees in the can circumferential direction. From the strain distribution measurement of the can wall, it is found that the axial strain of the can wall at the fracture angle is larger. A theoretical analysis method of ironing stress introducing r and n-value anisotropy is devised based on the Hill's anisotropic plasticity theory (quadratic yield function). The devised analysis reveals that as the anisotropy of r-value in the can wall becomes smaller, (1) the fracture is less likely occur, (2) the margin of stress which calculated from the ratio of the can axial tensile stress to fracture stress is larger.