On the prediction of hot deformation mechanisms and workability in Al6063/Ni_p and Al6063/steel_p composites using hyperbolic-sine constitutive equation

The present study investigates the hot deformation mechanisms and workability in novel AA6063-Ni_p and AA6063-Steel_p composites using hyperbolic-sine constitutive equation. The AA6063-Ni_p and AA6063-Steel_p composites were produced with AA 6063 as matrix, and 6 wt% Ni or 6 wt% steel particles as reinforcement for each of the composite, with the adoption of double stir casting method for the composite production. Axisymmetric compression testing was performed using Gleeble 3500 thermomechanical simulator at temperature and strain rate of 200-400 °C and 0.01-10 s^-1 respectively to a global strain of 0.5, while constitutive model was used to study the hot working characteristics of AA6063-Ni_p and AA6063-Steel_p composites. The results showed that anomalous flow stress oscillations and partial insensitivity to strain rate, characterised the flow stress patterns displayed by both composites. The activation energies (Q_HW) values derived at incremental strain, were within the range of 83.8 to 218.4 kJ/mol for AA 6063/Ni_p and 14.2 to 271.9 kJ/mol for AA 6063/Steel_p composites. The highest values of the Q_HW for AA 6063/Ni_p was 53% and for AA 6063/Steel_p was 91% higher than that for self-diffusion of Aluminium (Q_SD ~142 kJ/mol), which suggest that the deformation controlling mechanism was work hardening facilitated by dispersion strengthening. This was supported by the stress exponent values which exceeded 5 for both composites - affirming dispersion strengthening to dominate the deformation process. Also, the Q_HW of the composites was intermediate in comparison with the range of 111 - 509 kJ/mol reported for AMCs of similar reinforcement composition in literature, indicating that both composites have intermediate workability.