Revealing the Geometrically Necessary Dislocation Density Evolution during Hot Compression of AA7050

Abstract

Dislocations play a critical role in metal forming processes, and accurate values of dislocation density are important in modelling these processes. However, direct determination of the dislocation density is challenging. In this study, electron backscatter diffraction is used to estimate the evolution of geometrically necessary dislocation density as a function of plastic strain, strain rate and temperature in hot compression of AA7050 alloy. The geometrically necessary dislocation density was found to increase at a higher strain rate and lower temperature; the higher dislocation density in these samples promoted continuous dynamic recrystallisation leading to grain refinement. At lower strain rates and higher temperatures, the dislocation densities were lower and dislocations formed into walls, channels and cells. These observations agree with accepted theories of dislocation evolution and demonstrate the capability of electron backscatter diffraction to provide representative dislocation density values as well as comprehensive information linking plastic flow with microstructural evolution.Keywords: electron backscatter diffraction (EBSD), geometrically necessary dislocations (GNDs), hot deformation, AA7050