Effect of minor Sc addition on high temperature tensile behavior of Al-7Zn-2Mg-2Cu-0.2Zr alloy

Alloys of Al-7Zn-2Mg-2Cu-0.2Zr and Al-7Zn-2Mg-2Cu-0.2Zr-0.2Sc were prepared by extrusion casting. Elongation-to-failure tests and strain-rate-change tensile tests were conducted at 300, 350, 400 and 450 degrees C, and deformation mechanisms were investigated based on microstructure, stress exponent and deformation activation energy. The results show that the 0.2 wt% Sc addition improves both tensile ductility and strength by refining grains and forming second phase particles. Primary Al3(Sc, Zr) particles precipitate during solidification and refine the as-cast grains, and secondary Al3(Sc, Zr) particles precipitate and interact with moving dislocations during high temperature deformation. The Sc addition has no significant effect on high temperature deformation mechanism. The deformation of both alloys is dominated by dislocation creep strengthened by second phase particles at 300 and 350 degrees C. Such strengthening effect weakens with the increase in temperature, and the deformation transfers to solute-drag dislocation creep at 450 degrees C.