The Evolutions of Flow Stress and Microstructure of Al-Mg-Mn-Sc-Zr Alloy at Elevated Temperatures

The Al-Mg-Mn-Sc-Zr alloy is taken as the object and the tensile deformation behaviors at 298 K-673 K are studied in this research. By comparing the evolutions of flow stresses and microstructures, the research finds that the AlMg-Mn-Sc-Zr alloy softens apparently when deformed at elevated temperatures. As the temperature increases, the alloy's strength continue to decrease and the elongations continue to increase. The decrease in strength is mainly attributed to the decrease of dislocation density and the change of grain boundaries. In addition, the promotion on the movements of dislocation and softening of grain boundaries by thermal activation also reduces the strength. The increase in elongation is mainly due to the alleviation of stress concentration and the enhancement on the frequency of dislocation slip during the hot deformation process, which promotes the deforming uniformity. Furthermore, the trace addition of Sc and Zr to the Al-Mg alloy forms dispersed nano-sized Al3(Sc,Zr) particles in the matrix, which have a strong inhibition on the processes of dynamic recovery and dynamic recrystallization during hot deformation by pinning dislocations and grain boundaries. The Al3(Sc,Zr) particles show strong thermal stabilities and the particles' sizes hardly change at 573 K. However, the particles coarsen obviously and the pinning effects on dislocations weakens at 673 K, resulting in a great reduction of flow stress.