Microstructural evolution in cold rolled aluminum alloys during recrystallization – an in situ electron backscatter diffraction study

Understanding recrystallization processes is central to determining the properties of wrought alloys.
To characterize this process in situ electron backscatter diffraction (EBSD) was used and optimized
to measure the microstructural changes during heating at constant rates and isothermal annealing.
The number of individual measurements during recrystallization is of central importance for a sufficient evaluation of its kinetics. To this end, the acquisition parameters and evaluation strategy of
the EBSD scans have been optimized and improved, allowing heating rates of up to 10 K/min for continuous heating experiments and 90 K/min to reach the set isothermal temperature with the current
equipment. The recrystallization behavior of cold-rolled aluminum alloys was studied by the method
described. The so-called Avrami curves, the kinetic curves of recrystallization, are extracted from
the EBSD data and their dependence on heating rate, annealing temperature, deformation state and
alloy is presented. To account for potential concurrent precipitation, the precipitation state was investigated with scanning electron microscopy and energy dispersive X-ray spectroscopy before and
after the annealing treatment. In addition, the Johnson-Mehl-Avrami-Kolmogorow (JMAK) model
is used to evaluate recrystallization kinetics, and the limitations of the model are discussed. Further
evaluation analyzed the evolution of texture with special attention to the cube component during
the recrystallization process, which showed preferential nucleation at the beginning of recrystallization for one alloy. In order to compare the in situ results with more conventional methods for
determining recrystallization, a series of isothermally annealed samples were prepared and analyzed
with hardness measurements and ex situ EBSD.