Effect of two steps annealing on the microstructure and dynamic strain aging behavior of Al-6Mg alloy

The microstructure of cold rolled Al-6Mg alloy is investigated after two steps annealing at different coupled temperatures of 250-320 degrees C and 320-400 degrees C for various times. Dynamic strain aging behavior in terms of serrated flow and strain rate sensitivity is investigated. The effect of three microstructural features, cell structure, recovered and recrystallized microstructures, on the strain rate sensitivity is elucidated. Two steps annealing process is utilized to capture the effect of recovery and precipitation phenomena on recrystallization and dy-namic strain aging behaviors. The results show that the negative strain rate sensitivity of cold rolled specimen increases to positive values in recovered specimens. Effect of precipitation on the fully recrystallized microstructure and subsequently on the strain rate sensitivity illustrates that during annealing with concurrent precipitation, dynamic strain aging is more pronounced due to increasing of dislocation waiting time in front of obstacles (precipitates). In the recrystallized microstructure without precipitates, the strain rate sensitivity is more positive, but the largest value of strain rate sensitivity is achieved in the fully recovered microstructure.