Dynamic Flow Stress Measurements of 6061-T6 Aluminum under Rapid Heating for Machining Studies
Steven P. Mates, Homar Lopez-Hawa, Wilfredo Moscoso-Kingsley, Vis Madhavan
The flow stress of aluminum alloy Al6061-T6 produced by conventional thermomechanical methods has been investigated under the application of strains up to 80 % at a strain rate of the order of 103 1/s, and temperatures ranging from ambient to near melting. The high strain and strain rate deformation was imposed using a Kolsky bar apparatus equipped with a fast pulse-heating system to reach the target temperatures at high heating rates. The flow stress was measured to provide a constitutive model under strains, strain rates, temperatures and heating rates that match thermomechanical conditions developed in the primary shear zone for specially-designed comparative machining tests. It is expected that these measurements will enable the formulation of realistic machining models for Al6061-T6. Temperature measurements were obtained using non-contact infrared (IR) full field imaging together with embedded micro-thermocouple (TC) point probing, the latter being used to estimate the emissivity of the aluminum sample via separate, in situ calibration tests. Type-K TC measurements were made using the separated junction principle by embedding the TC wires into two micromachined holes in the specimen. The temperature measurement technique is discussed in detail, and temperature uncertainties are estimated. The technique will be used going forward to study the effect of heating time on the dynamic thermal softening behavior of Al6061-T6, which has been shown to be time-sensitive under quasi-static loading when temperatures exceed 200 °C due to Mg-Si precipitate growth.
Proceeding of the Society for Experimental Mechanics 2020 Annual Meeting