Characterization and application of a constitutive model for two 7000-series aluminum alloys subjected to hot forming

Abstract

The constitutive behaviour of AA7075 and a developmental 7000-series alloy is characterized under conditions representative of hot forming. The materials were tested in a solutionized condition following a procedure in which tensile specimens were held at the solutionizing temperature after which they were quenched to the desired testing temperature (ranging from 25–400 °C) and immediately tested. Tensile tests were performed along the sheet rolling, transverse and diagonal directions. Three strain rates were considered: 0.01, 0.1 and 0.5 s−1. A novel area reduction method is proposed to measure the instantaneous cross-setcional area using in situ digital image correlation (DIC) and then calculate the true stress and strain over the cross-section. Shear tests were also performed along at 25 and 470 °C and used to calibrate the plane stress anisotropic Yld-2000 yield criterion. In the solutionized condition, both alloys exhibited Portevin–Le–Chatelier bands resulting in a negative rate sensitivity. At elevated temperatures, strong positive rate sensitivity was observed. The constitutive model and yield surface were used to model a series of hot forming, deep draw experiments. The predicted force-displacement and earing responses were in good agreement with the measured data.