Constitutive equations for hot deformation of an Al-6061/20%Al2O3 composite

The hot deformation response of an Al-6061+20%Al2O3 particulate composite was investigated by means of torsion tests. An analysis of the flow stress dependence on strain rate and temperature gave a stress exponent of n≈5.6 and an activation energy of Q≈150 kJ mol−1. This value of Q is reasonably close to the anticipated value for self-diffusion in Al. The results are in excellent agreement with other studies carried out on the hot deformation of composites but the phenomenological nature of the constitutive equation does not permit an unambiguous determination of the rate-controlling flow mechanism. Nevertheless, it is shown that an identical constitutive equation may be used to describe the creep of composites under both shear and hot torsion conditions. It is concluded that the mechanism controlling hot deformation and creep at high stresses is the climb of dislocations.