Study of Uniaxial Compression Process for AA7075 Aluminum Alloy

Abstract

An experimental and complementary FE modeling study was conducted to characterize the room and elevated temperature uniaxial compressive deformation behavior of AA7075-T6 and O-temper materials. The experiments consisted of testing cylindrical and cubic specimens prepared from a rolled and heat-treated plate stock of AA7075 alloy. The tests were conducted in the lower range of elevated temperatures up to 300 °C, at several different test speeds in rolling and transverse orientations, as well as under isothermal and non-isothermal test conditions. The test results were analyzed in terms of true stress-train responses of the two tempers under the above experimental conditions. The deformed test specimens were also observed for surface features and deformed microstructures in the interior of the specimen under the above experimental conditions. A suitable strain rate and temperature dependent constitutive hardening law, in the form of modified Voce-Kocks law, was developed and coded as a UMAT subroutine in ABAQUS FE code to simulate the uniaxial compression experiments and compare the experimental and model results. In general, good general agreement was obtained between experiments and model predictions. A suitable fracture criterion, in the form of Tresca fracture model, was also implemented as a VUMAT subroutine in ABAQUS FE code to simulate the uniaxial compression experiments and predict fracture mode and other characteristics. Once again, good general agreement was obtained between room temperature fracture shapes and model predictions. The experimental and model results collectively provide a broad-based understanding of the effect of temperature, strain rate, material anisotropy, temperature field on material flow and deformed shapes of cylinders and cubic specimens, the nature of deformation (predominantly shear along two intersecting shear directions) and fracture (predominantly shear). The constraints to deformation at the corners in the cubic specimen yielded rather complex curvature development in deformed cubes. The non-isothermal rapid heating of test specimens using electrical resistance heating and subsequent compression of the specimen provided results similar to the isothermal case. However, the electrical resistance method offers a cost-effective process to form smaller high quality components in forming modes such as hot upsetting.