In-situ EBSD tensile revealing the evolution mechanism of high angle grain boundaries in Al-Zn-Mg alloy profile with heterogeneous structures

The evolution of grain boundary (GB) of an Al-Zn-Mg alloy profile with heterogeneous structures is studied based on in-situ EBSD tensile. This evolution is not only related to its grain boundary misorientation angle (GBMA) and slip transfer parameter (m'/(Delta b/b)) but also to the behavior of the geometrically necessary dislocation (GND) tensor in the deformation. The effect of GBMA and m'/(Delta b/b) for three types of high angle grain boundary (HAGB) on GND density and back stress has been revealed. The increase of GND density is not obvious near the HAGBs with 45 degrees-55 degrees GBMA of neighboring coarse grains or neighboring fibrous grains. The optimal grain boundary for forming back stress is the HAGBs between coarse grain and fibrous grain, which has 35 degrees-45 degrees GBMA and a low m'/(Delta b/b). The back stress is hard to form near these HAGBs with 25 degrees-35 degrees GBMA and a low m'/(Delta b/b). Combined with the neighboring grain type, slip transfer and GBMA, the new criterion is proposed to predict GND behavior near HAGBs.