POSITIVE EXPONENT SUPERPLASTICITY IN ADVANCED ALUMINUM-ALLOYS WITH NANO OR NEAR-NANO SCALE GRAINED STRUCTURES

Very high strain rate superplasticity was observed in near-nano scale aluminum alloys. These alloy systems include the group of mechanically alloyed IN9021, IN90211, IN9052, IN905XL alloys and SiCp/IN9021 composite, an Al-14wt.%Ni-14wt.%Mm (Mm is mischmetal) crystalline alloy consolidated from its amorphous powders and an Al-14wt.%Ni-7wt.%Mm-1wt.%Zr alloy consolidated from nanocrystalline powders, and an Al-7wt.%Cr-1wt.%Fe alloy produced by physical vapor deposition. In each of the above advanced alloy systems, large elongations of more than 500% were obtained at extremely high strain rates of more than 1 s-1 (called positive exponent superplasticity). In the mechanical alloyed IN9021 aluminum alloy with a fine grained structure 500 nm in size, a maximum elongation of 1250% was recorded at an extremely high strain rate of 50 s-1 at 823 K. In addition, a maximum elongation of 610% was obtained at a very high strain rate of 5 s-1 of 823 K in the mechanically alloyed 15vol.%SiCp/IN9021 aluminum composite. A maximum elongation of 650% was observed at a high strain rate of 1 s-1 in both Al-Ni-Mm and Al-Ni-Mm-Zr alloys consolidated from amorphous or nanocrystalline powders. Also a maximum elongation of 505% was obtained at a high strain rate of 1 s -1 in a VQ Al-Cr-Fe alloy.