<p>In this work, the hot deformation behavior of highly alloyed Al-Zn-Mg-Cu alloy prepared by electromagnetic stirring casting and conventional direct chill casting with temperature range of 300–450℃ and strain rate of 10^− 4-10&#xa0;s^− 1 is investigated by isothermal compression experiments. The processing maps of the two alloys were established based on dynamic material model, and the microstructure of the samples in the typical regions of the processing maps was characterized. The results indicate that the dynamic softening mechanism during deformation at 300℃/10^− 4 s^− 1 is dynamic recovery and discontinuous dynamic recrystallization, which changes to dynamic recovery and continuous dynamic recrystallization when deformed at 450&#xa0;°C/10^− 4 s^− 1. A comparison showed that the electromagnetic stirring casting alloys show lower flow stress than the direct chill casting alloys at 300℃, and the difference in flow stress decreases with the increase in temperature. Electromagnetic stirring casting can reduce the instability zone of hot deformation and expand the processing window. The activation energy of hot deformation was reduced from 171.6&#xa0;kJ/mol to 144.7&#xa0;kJ/mol after electromagnetic field treatment. These phenomena were explained based on grain and second phase refinement according to microstructure examination.</p> Graphical Abstract <p></p>