Mechanisms of Superplastic High-Rate Deformation in the Al-Mg-Zn-Fe-Ni-Zr-Sc Alloy

The microstructure and acting superplastic deformation mechanisms in the high-strength Al-7.0% Zn-2.7% Mg-1.0% Ni-0.9% Fe alloy low-doped with Sc and Zr upon deformation at a temperature of 480 degrees C and a strain rate of 1 x 10(-2) s(-1) at a stable flow stage in a true strain range of 1.1 to 1.6 have been investigated. To evaluate the contributions of superplastic deformation mechanisms to the total elongation, marker grids have been applied on the surface by ion etching, and microstructural changes of the surface have been analyzed. Grain boundary sliding and intragranular deformation play dominant roles. The contribution of each mechanism is 35-40%. The remaining 25% belongs to the diffusional creep mechanism, which is determined from the size of striated zones formed at the transverse grain boundaries on the surface of a deformed sample.