Creep behavior of hot extruded Al-Al2O3 nanocomposite powder

A commercial gas-atomized aluminum powder was mechanically milled in a planetary ball mill under an argon atmosphere for 12 h to produce alumina dispersion strengthened aluminum powder. Transmission electron microscopy (TEM) revealed that about 2 vol.% alumina particles with an average size of 100 nm were distributed in the aluminum matrix. The nanocomposite powder was canned in an aluminum container, vacuum de-gassed, and hot extruded at 723 K at an extrusion ratio of 16:1. The creep behavior of the extruded billet in the direction of extrusion was examined at a constant applied load ranging from 10 to 40 MPa at temperatures of 648, 673 and 723 K. A threshold creep-stress was noticed which indicates that detachment of dislocations from the Al2O3 nanoparticles occurred during the high-temperature deformation process. The threshold stress was found to be temperature dependent as it decreased from 8.3 MPa at 648 K to 2.7 MPa at 723 K. The stress exponent index also decreased from 8 to 3, revealing a change in the creep mechanism by increasing the testing temperature. The creep behavior is explained according to the invariant substructure model and dislocation glide process.