Hot workability and deformation mechanisms in Mg/nano-Al2O3 composite

The response of extruded Mg/nano-Al2O3 (1 vol.%) composite to hot working in the temperature range 300-500 degrees C and strain rate range 0.0003-10 s(-1) has been characterized using processing map and kinetic analysis. The hot working window for the composite occurs at strain rates >0.1 s(-1) and the optimum range of temperature is 400-450 degrees C. In this window, the behavior of the composite is similar to that of the matrix and is controlled by the grain boundary self-diffusion. At lower strain rates, however, the composite exhibits much higher apparent activation energy than that for lattice self-diffusion unlike the matrix material. The deformed microstructures revealed that the prior particle boundaries decorated by the nano-Al2O3 particles, are stable and do not slide, rotate or migrate but kink after compressive deformation and as such contribute to the high temperature strength of the composite. (C) 2009 Elsevier Ltd. All rights reserved.