Effect of Sc on the recrystallization behavior and mechanical properties of Al-Zn-Mg-Cu-Zr alloys under isothermal multidirectional compression

Abstract

To better achieve grain refinement and further optimize the comprehensive mechanical properties of Al-Zn-Mg-Cu-Zr alloys, this paper investigates the effect of trace Sc on the recrystallization behavior of Al-Zn-Mg-Cu-Zr alloys under isothermal multidirectional compression (IMC) and the mechanical properties in two-stage aging state. It was discovered that the addition of Sc enhanced the tensile and yield strengths of the alloys by 3.8% and 4.3%, respectively, and simultaneously increased the elongation from 13.4% to 15.4%. The OM, EBSD and TEM techniques were used to characterize the microstructure of the alloy. The results showed that the Al3(Sc,Zr) phase produced by the addition of 0.25% Sc not only refines the grains, but also changes the recrystallization behavior of the alloy by pinning the dislocations and (sub) grain boundaries in the combination of IMC deformation. It inhibits the generation of geometric dynamic recrystallization (GDRX) grains and the nucleation of discontinuous dynamic recrystallization (DDRX) grains but promotes the formation of continuous dynamic recrystallization (CDRX) as the predominant mode of dynamic recrystallization. The alloy gains a finer grain structure by simultaneously promoting the formation and inhibiting the growth of recrystallized grains. As a result, the improvement in the overall mechanical properties of Al-Zn-Mg-Cu-Sc-Zr alloys brought about by the addition of Sc can be attributed primarily to the refinement of the initial as-cast grains, as well as fine-grain strengthening due to the inhibition of recrystallized grain growth and the Orovan strengthening of the nanoscale secondary phase Al3(Sc,Zr) itself.