Deep drawing characteristics of automotive aluminum alloys

Limiting draw ratios (LDRs) and other axisymmetric deep drawing characteristics of AA5754-O and AA6111-T4 automotive aluminum sheet materials are investigated as a function of die profile radii by experiments and numerical predictions. A procedure for rapid determination of LDR based on a characteristic limit load of the material at fracture is developed and verified. Other deep drawing characteristics such as punch load versus displacement traces, flange draw-in, strain distribution along the cup profile, flange wrinkling, wall ironing and fracture characteristics are experimentally assessed for the two sheet materials as a function of the die profile radius. The results are compared with a recent analytical model by Schedin (Ph.D. Thesis, Royal Institute of Technology, Stockholm, Sweden, 1991). as well as axisymmetric FE models of cup draw, to analyse the sensitivity of various material and test parameters towards the maximum punch load and stresses and strains in various regions of the cup. The deep drawability of AA5754-O, as measured by cup depth at fracture and LDR, is superior to that of AA6111-T4. The differences in the deep drawing behaviour of the two materials can be explained in terms of the competition in work hardening between the material in the flange at the die profile region versus the material at the punch profile region, bendability of the two materials, and fracture characteristics. A decrease in LDR and flange draw-in is observed as a function of the die profile radius. This decrease is attributed to the increased work hardening in the die profile region resulting from additional bending, unbending, and stretching of the material as it enters the die cavity, as well as increased tendency towards fracture for AA6111-T4.