Stress Softening Behavior and Microstructural Characterization of Al-Zn-Mg-Sc Alloy with High Zn Concentration Subjected to Isothermal Compression

The isothermal compression tests were conducted to study the hot compression behavior of Al-Zn-Mg-Sc alloy with high Zn concentration using a Gleeble-3500 thermal simulator in the temperature range of 300-450 degrees C and strain rate range of 0.01-5 s(-1). The stress softening behavior was analyzed, and the constitutive model was established to describe the hot compression behavior of the high Zn alloy. The microstructure evolution mechanism was clarified by optical microscopy and electron backscatter diffraction. The results indicate that the true stress rapidly increases to the peak value with the increasing accumulative true strain, and finally reaches to a steady state. As the strain rate increases and temperature decreases, the peak stress increases, and the isothermal compression behavior is regarded as a competing process of work hardening and flow softening. The softening mechanism is highly affected by the compression temperature and strain rate. The Al-Zn-Mg-Sc alloy with high Zn is characterized by the dynamic recovery at the low temperature and high strain rate. And both the dynamic recovery and dynamic recrystallization dominate at the high temperature and low strain rate. The relatively stronger (111) orientation plays a key role in developing the recrystallization grains. As the compression temperature increases and strain rate decreases, many subgrains with low-angle grain boundaries are transformed into recrystallized grains with high-angle grain boundaries. The main softening mechanism is also transformed from dynamic recovery to dynamic recrystallization.