The Influence of Sc on Thermal Stability of a Nanocrystalline Al-Mg Alloy Processed by Cryogenic Ball Milling

摘要

The microstructural evolution during annealing of a ctyogenically ball-milled Al-7.5Mg-0.3Sc (in wt pet) was examined using differential scanning calorimetry and transmission electron microscopy (TEM). The as-milled alloy was a supersaturated fee solid solution with an average grain size of --25 nm and heterogeneous grain morphologies and size distributions. Calorimetric measurements at a constant heating rate of 32 K/min indicated two exothermic events in association with recovery from 100 deg C to 240 deg C and recrystallization from 300 deg C to 450 deg C. Prior to recrystallization, the precipitation of Al3Sc may occur at low annealing temperatures producing a nonuniform dispersion of approximately spherical particles with diameters of 4 to 5 nm. Recrystallization gave rise to heterogeneous microstruc-tures with bimodal grain size distributions, which may result from the heterogeneity of microstructure in the as-milled state. The heterogeneous microstructures of the recrystallized Al-Mg-Sc alloy were similar to those observed in the recrystallized Sc-free Al-Mg alloy.