Fig.1 Microstructure of the investigated alloy (as-delivered conditions): a, b longitudinal section, c, d transverse section of a bar

Fig.2 Stress-strain curves of AA2099 alloy obtained at different strain rates and temperatures of 450°C a and 500°C b

Fig.3 Relations between log σ and \( { \log }\;\dot{\varepsilon } \) for true strain of 0.5 a and 0.9 b

Fig.4 Changes of strain rate sensitivity exponent (m): a as a function of \( { \log }\;\left( {\dot{\varepsilon }} \right) \), for the analysed temperatures and b as a function of temperature, at constant strain of 0.9

Fig.5 Variations of J co-content as a function of temperature, strain rate and constant strain value

Fig.6 Optical a, c, e, g and SEM b, d, f, h microstructures of AA2099 alloy after deformation in isothermal conditions in uniaxial compression test, at the temperature of 500°C and strain rate of:$ a, b \( \dot{\varepsilon } = 0.00 1\,{\text{s}}^{ - 1} \), c, d \( \dot{\varepsilon } = 0. 1\,{\text{s}}^{ - 1} \), e, f \( \dot{\varepsilon } = 1\,{\text{s}}^{ - 1} \), g, h \( \dot{\varepsilon } = 10\,{\text{s}}^{ - 1} \)$, for true strain of 0.9

Fig.7 Variations of power dissipation efficiency, as a function of forging temperature and strain rate, for constant strain value of 0.5 a and 0.9 b

Fig.8 Complex map of power dissipation efficiency and flow instability parameter, for AA2099 alloy, as a function of strain rate and temperature, for true strain of 0.5 a and 0.9 b

Fig.9 Shape of the final forging of a contact tip