  Superplastic behavior of ultrafine-grained (UFG) Al-6Mg-0.12Sc-0.10Zr-0.1X
alloys, where X = Yb (Alloy #1-Yb), Er (Alloy #2-Er), and Hf (Alloy #3-Hf), has
been studied. The total content of Sc, Zr, Yb, Er, Hf in the alloys was 0.32
wt.% (0.117-0.118 at.%). The alloys used for benchmarking were
Al-6Mg-0.12Sc-0.20Zr (Alloy #4-Zr) and Al-6Mg-0.22Sc-0.10Zr (Alloy #5-Sc).
Their UFG microstructure was formed with ECAP. Two different types of
deformation behavior during superplasticity were demonstrated. A simultaneous
increase in yield stress and elongation to failure during superplastic
deformation was discovered. High deformation temperatures were shown to cause a
competition between dynamic (strain-induced) grain growth and dynamic
recrystallization, leading to a finer grain microstructure. The values of
strain hardening factor (n), strain rate sensitivity factor (m), and
superplastic deformation threshold stress (Sp) were determined. The impact of
the type and concentration of alloying elements on the deformation behavior and
dynamic grain growth of Al-6%Mg alloys was investigated. It was established
that the maximum elongation to failure in Alloy #1-Yb and Alloy #2-Er is
observed at lower deformation temperatures than in Alloy #4-Zr and Alloy #5-Sc.
The superplastic properties of Alloy #3-Hf are superior to those of Alloy #4-Zr
and Alloy #5-Sc with high content of alloying elements (in at.%). Alloy #1-Yb
manifests good elongation to failure (910%) at low temperatures (400 oC). The
satisfiability of Hart's criterion for calculating uniform deformation value
under superplastic conditions was verified. It was demonstrated that cavitation
when pores are formed in large Al3X particles at high temperatures causes early
failure of aluminum alloys.
