High strain rate deformation behavior of 2195 Al-Li alloy: Constitutive behavior and grain fragmentation

Abstract

The high-speed forming process is a promising method for the preparation of high-performance Al-Li alloy components. However, the high-strain rate deformation behavior of the material is complex and difficult to accurately predict, which significantly restricts its development. In this paper, using the split Hopkinson pressure bar apparatus, the constitutive behavior and microstructure evolution of as-annealed and solution treated 2195 Al-Li alloy during high strain rate deformation was studied. As the strain rate increases, the flow stress first decreases and then increases for both two-state materials, showing a local strain rate softening behavior. Based on the Johnson-Cook model, a modified constitutive model is proposed, in which a correction term for the C value related to strain rate and strain is introduced. The modified Johnson-Cook model can accurately capture the abnormal strain rate sensitivity behavior observed in the experiment. In addition, it was found that the heat treatment state has a significant effect on the microstructural evolution behavior of 2195 Al-Li alloy. The as-annealed material shows the deformation behavior based on the evolution of dislocation cells. In addition to dislocation cells, there is also deformation behavior based on the evolution of submicron lath deformation bands for solution treated material. Dislocation cross slip is suppressed in the solution treated material, and its slip mode tends to be the plane slip. Through the analysis of dislocation density, mean slip distance of dislocation slip, and the interaction between solid atoms and dislocation, the mechanism of the abnormal deformation behavior of the solution treated material is revealed.