Superplastic Behavior of Fine-Grained Al-Mg-Li Alloy

The superplastic behavior of fine-grained 1420 Al-Mg-Li alloy was investigated using a modern electron microscopy technique based on automatic analysis of electron backscattered diffraction patterns (EBSD analysis). The generally accepted idea that grain boundary sliding is dominant during superplastic flow suggests the preservation of an equiaxed fine-grained structure with predominantly high-angle grain boundary misorientation in the material. The present study revealed that heating prior to the onset of deformation leads to some grain growth due to static recrystallization, and superplastic deformation is accompanied by dynamic grain growth and continuous dynamic recrystallization. Continuous recrystallization has a more significant effect on microstructural changes. This mechanism involves the transverse division of pre-elongated grains into subgrains that ultimately transform into chains of nearly equiaxed small grains, resulting in a bimodal grain structure. The data obtained, including significant strain hardening, noticeable grain elongation, the formation of a well-defined dislocation structure and subboundaries within grains, as well as the development of a pronounced crystallographic texture, provide convincing evidence of the occurrence of intragranular slip during superplastic flow throughout the entire volume of the material. A comprehensive analysis of a wide range of experimental data showed that intragranular slip plays an essential role in superplastic flow, and its contribution can be much larger than previously thought. The results obtained contribute to a better fundamental understanding of the superplasticity phenomenon.