THERMOMECHANICAL PROCESSING AND SUPERPLASTIC BEHAVIOR IN ALUMINUM-BASED ALLOYS PRODUCED FROM AMORPHOUS OR NANOCRYSTALLINE POWDERS

The Al-14wt.%Ni-14wt.%Mm (Mm = misch metal) alloy and the Al-14.8wt.%N i-6.6wt%Mn-2.3wt.%Zr alloy have been produced by a high pressure gas a tomization technique and a powder metallurgy method. Both alloys have a finely mixed structure consisting of aluminium phase and intermetall ic compounds homogeneously embedded in the ultrafine-grained aluminium matrix. At room temperature, both alloys exhibit high tensile strengt h exceeding 800 MPa and at high temperature, nearly 873 K, high strain rate superplasticity is observed. In particular, a maximum elongation of 600% is obtained at a high temperature of 873 K at a constant stra in rate of 1 s-1 in Al-Ni-Mm-Zr alloy. This strain rate is many orders of magnitude higher than those for typical commercial superplastic al loys. Both the grain size refinement of the aluminium matrix and the d ispersion of intermetallic compounds are interpreted as contributing t o the achievement of the ultrahigh tensile strength at room temperatur e and high strain rate superplasticity at high temperatures near 873 K .