Thermomechanical processing and superplastic behaviour in aluminium-based alloys produced from amorphous or nanocrystalline powders

Abstract

The Al-14wt.%Ni-14wt.%Mm (Mm ≡ misch metal) alloy and the Al-14.8wt.%Ni-6.6wt.%Mm-2.3wt.%Zr alloy have been produced by a high pressure gas atomization technique and a powder metallurgy method. Both alloys have a finely mixed structure consisting of aluminium phase and intermetallic compounds homogeneously embedded in the ultrafine-grained aluminium matrix. At room temperature, both alloys exhibit high tensile strength 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 strain 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 alloys. Both the grain size refinement of the aluminium matrix and the dispersion of intermetallic compounds are interpreted as contributing to the achievement of the ultrahigh tensile strength at room temperature and high strain rate superplasticity at high temperatures near 873 K.