Synergistic effect of Al3(Er, Zr) precipitation and hot extrusion on the microstructural evolution of a novel Al–Mg–Si–Er–Zr alloy

Isothermal hot compression experiments of homogenized Al–Mg–Si–Er–Zr alloy were conducted at temperatures ranging from 350 to 500 °C and strain rates of 0.01–10 s−1 on a Gleeble-3500 thermal simulation tester. The hot deformation behavior and optimum processing parameters of the alloy were determined by analyzing the flow curves and processing maps. Characterization of the microstructures of the deformed specimens was done using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), and the geometrically necessary dislocation (GND) density was used based on the kernel average misorientation (KAM). The results showed that the GND density decreased with a decrease in the strain rate and with an increase in the deformation temperature. Dynamic recovery and continuous dynamic recrystallization were the main softening mechanisms during hot deformation, and dynamic recovery was dominant. It was found that the capacity for dynamic recovery was reduced, while dynamic recrystallization was prevented in the Al–Mg–Si–Er–Zr alloy. This was a result of hindered dislocations and sub-grain boundary movement caused by the pinning of dislocations and sub-grain boundaries from the Mg2Si, Al(MnFe)Si, and Al3(Er, Zr) particles. The addition of Er and Zr resulted in an increase in the activation energy, which can be attributed to the formation of Al3(Er, Zr) particles.