Formability of an Automotive Aluminum Alloy-AA5754 CC 2008-01-1094

We have studied the formability of continuous strip cast (CC) AA5754 aluminum alloy for automotive applications. Strip casting technology can considerably reduce material cost compared with conventional direct chill (DC) cast aluminum sheets. However, the CC material tends to exhibit much less post-localization deformation and lower fracture strains compared with DC sheets with similar Fe content, although both alloys show similar strains for the onset of localization. Bendability of the CC alloy is also found to be inferior. The inferior behavior (post-necking and bendability) of the CC alloy can be attributed to the higher incidence of stringer-type particle distributions in the alloy. The formability of the AA5754 alloy has also been studied using two dimensional microstructure-based finite element modeling. The microstructures are represented by grains and experimentally measured particle distributions. Uniaxial tensile tests are modeled in two stages: a plane stress unit-cell model is used to study the deformation up to localized necking, while a novel plane strain model has been developed to study the post-necking behavior. The plane stress models have shown that the influence of grain structures on strain localization prevails over that of particle structures, mainly because particles in the alloys are dilute and small compared to the matrix. The plane strain models have been able to capture the major differences of post-necking behavior between the DC and CC alloys, where the particle distribution is shown to play a major role.