Evolution of activation energy during hot deformation of Al-15% B4C composites containing Sc and Zr

Abstract

During hot deformation, the activation energy, Q, is an essential parameter that indicates the difficulty level in the hot working processing. The evolution of the activation energies of three Al-15% B4C composites (the base material, S40 with 0.4% Sc and SZ40 with 0.4% Sc and 0.2% Zr) was investigated using high-temperature flow stress data based on a revised Sellar's constitutive equation. The microstructure evolution during hot deformation was characterized using a transmission electron microscope. The calculated activation energy maps reveal that the activation energy during hot deformation was related to the microstructure change in addition to deformation conditions. For the base composite, the variation of the activation energy was small because the microstructure barely changed during deformation. For the Sc and Zr containing composites (S40 and SZ40), dynamic precipitation occurred at high deformation temperature and the activation energy map can be divided in two regions. The activation energy decreases with an increase of deformation temperature to the minimum level in the region I where the composites were in the solid solution condition. It follows by an increase with increasing temperature in the region II where dynamic precipitation occurred. Based on the combination of the activation energy map with the flow instability zone, the optimum hot workability of a composite in term of excellent processability was proposed at the domain where the less energy of hot deformation was required.