Behaviors and modeling of thermal forming limits of AA7075 aluminum sheet

The aluminum hot stamping process has been widely studied to produce lightweight parts in automobile industry. As forming limit of aluminum sheet at elevated temperatures plays a vital role in judging stamping formability, this study aims at experimentally investigating the forming limits and establishing a constitutive model to predict them. In this study, isothermal deformation test (Nakajima test) of AA7075 was conducted to determine its forming limits at temperatures of 300–450 °C and stamping speeds of 13–40 mm/s. Based on the experimental results, a constitutive model considering continuum damage mechanics was established to predict the forming limits under different deformation conditions. It was found that the formability of the material is best at 400 °C, and a higher strain rate can improve formability slightly. The comparisons between model predictions and experimental results were evaluated; results indicated a good prediction accuracy of the model in describing forming limits of AA7075 at elevated temperatures. Moreover, comparison between different studies on the thermal forming limits of AA7075 was discussed in detail.