Precipitation kinetics of precipitates with different orientations and segregation in an ultrafine grained Al-Cu-Mg alloy

The precipitation kinetics of precipitates with different orientations and segregation in an ultrafine grained (UFG) Al-Cu-Mg alloy (AA2024) aged at 210 degrees C have been investigated using situ small angle X-ray scattering (SAXS), situ wide angle X-ray (WAXS) and Transmission Electron Microscopy (TEM). For UFG alloy, the number and size of (111) S'/S phases are larger than those of (130) S'/S phases on the whole, because spacing of slip plane near (111) S'/S phases is larger than that near (130) S'/S phases, resulting in solute atoms are easier to diffusion near (111) S'/S phases, and (111) S'/S phases are easier to grow, meanwhile, resulting in the critical shear stress for dislocation moving near (111) S'/S phases is smaller than that near (130) S'/S phases, further leading to the dislocation density near (111) S'/S phases is 1.07-1.19 times larger compared to that near (130) S'/S phases during ageing process, which provides more nucleation sites for (111) S'/S phases. After ageing for 10-40 min, the segregation degree of Cu and Mg atoms near dislocations and grain boundaries is increased in UFG alloy, while after ageing for 80 min, the segregation of Cu atoms is decreased and Mg atoms continue to increase, the segregation of Mg atoms begin to decrease after ageing for 120 min.